Critical roles and clinical perspectives of RNA methylation in cancer

Abstract RNA modification, especially RNA methylation, is a critical posttranscriptional process influencing cellular functions and disease progression, accounting for over 60% of all RNA modifications. It plays a significant role in RNA metabolism, affecting RNA processing, stability, and translation, thereby modulating gene expression and cell functions essential for proliferation, survival, and metastasis. Increasing studies have revealed the disruption in RNA metabolism mediated by RNA methylation has been implicated in various aspects of cancer progression, particularly in metabolic reprogramming and immunity. This disruption of RNA methylation has profound implications for tumor growth, metastasis, and therapy response. Herein, we elucidate the fundamental characteristics of RNA methylation and their impact on RNA metabolism and gene expression. We highlight the intricate relationship between RNA methylation, cancer metabolic reprogramming, and immunity, using the well‐characterized phenomenon of cancer metabolic reprogramming as a framework to discuss RNA methylation's specific roles and mechanisms in cancer progression. Furthermore, we explore the potential of targeting RNA methylation regulators as a novel approach for cancer therapy. By underscoring the complex mechanisms by which RNA methylation contributes to cancer progression, this review provides a foundation for developing new prognostic markers and therapeutic strategies aimed at modulating RNA methylation in cancer treatment.


INTRODUCTION
Epigenetics is the study of the mechanisms through which behavior, environment, and phenotype alter gene expression. 1,2Unlike genetic variations, epigenetic modifications are typically reversible.Epigenetic modification refers to heritable alterations in gene function that do not involve the alteration of the nucleotide sequence of a gene and that result in alterations in the genetic phenotype. 35][6] With advancements in chemistry, high-throughput sequencing, and fluorescence quantification techniques, several types of RNA modifications have been discovered.In fact, pseudouridine (Ψ), a carbon-carbon-linked ribonucleoside in ribonucleic acid, was discovered as early as 1960. 7Limited research has been conducted on RNA modification, which may be attributed to the fact that RNA, which lacks double chains in its structure, is less stable than DNA, and hence DNA, which carries genetic information, has garnered more attention from researchers.Additionally, the limited availability of suitable technology has also constrained research on RNA.At present, RNA modification, especially RNA methylation modification, is a prominent area of research. 8,9To date, more than 100 distinct varieties of RNA modifications have been identified.1][12] RNA methylation accounts for 60% of RNA modifications.Mammalian RNA methylation modifications primarily include N 6 -methyladenosine (m 6 A), N 1 -methyladenosine (m 1 A), N6,2′-O-dimethyladenosine (m 6 Am), 7-methylguanine (m 7 G), Ψ, and 5-methylcytosine (m 5 C). 13 Notably, DNA chemical modifications are named similarly, such as 5-methylcytidine (5mC) in DNA and m 5 C in RNA.An emerging mechanism research has underscored the regulatory functions of RNA methylation on various RNA metabolism, including RNA splicing, export, stability, translation, and degradation. 14,15ancer is essentially a disease caused by mutations in oncogenes or tumor suppressor genes.7][18] The basic signs of cancer are closely associated with the metabolism of cancer cells. 19Cancer metabolic reprogramming refers to the reprogramming of certain metabolic pathways in cancer cells.Metabolic reprogramming confers upon cancer cells a greater ability for survival and proliferation.As cancer progresses, cancer cells are more likely to undergo mutation, which can promote metabolic reprogramming, thereby establishing a robust positive feedback loop. 20,21Cancer metabolism was first observed by Otto Warburg.Compared with normal tissue, cancer tissues consume considerable amounts of glucose to produce lactic acid in vitro, even in the presence of oxygen.This phenomenon is referred to as aerobic glycolysis or the Warburg effect. 22,23The discovery of aerobic glycolysis in tumor cells has greatly contributed to advancements in the field of tumor metabolism.In addition to glycolysis, various metabolic processes, such as lipid metabolism, amino acid metabolism, mitochondrial metabolism, and iron metabolism, play notable roles in the development of tumors. 21The role of RNA methylation and cancer metabolism in cancer progression is apparent, and the relationship between RNA methylation and cancer progression has become a prominent area of research in recent years.5][26] RNA methylation regulators have been found to activate or inhibit metabolic signaling pathways by modulating the expression of metabolism-related genes, thereby playing a role in promoting or inhibiting cancer.RNA methylation has been observed in the abnormal metabolism of multiple types of cancer, which highlights the indispensability of the RNA methylation for cancer metabolism. 12Increasing evidence has suggested that the link of dysregulation of RNA methylation to cancer strongly supports the fruitful value of developing inhibitors targeting RNA methylation under the cancer condition.
Additionally, it is now becoming clear that cancer cells possess several distinct characteristics that endow them to proliferate uncontrollably, one of the essential hallmarks is immune escape. 27,28By escaping from immune surveillance, cancer cells usually exhibit malignant abilities to escape from immune surveillance recognized and even destroy the immune balance of the organism. 29][35][36] RNA modifications, such as m 6 A, m 5 C, m 7 G, and m 1 A, have been extensively revealed to participate in regulating tumor immunogenicity and the functions of diverse immune cells. 37,380][41][42] The exploration of RNA methylation on cancer immunity provides an excellent opportunity to exploit the RNA methylation-driven clinical use in various malignancies.
In this review, we provide a comprehensive overview of several common RNA methylation, its underlying regulatory mechanisms on RNA metabolism, and the associated expression changes of genes involved in carcinogenesis.Then, we delve into recent advancements in understanding the roles and clinical applications of RNA methylation in cancer, using well-studied cancer metabolism as an example.We highlight the challenges of identifying the predictive values of RNA methylation and developing targeted RNA modification-based tools for cancer treatment concerning the context-specific roles of RNA methylation in different types of cancer.Finally, we also briefly discuss the implications of RNA methylation with cancer immunity.We anticipate that our review will broaden the scope of research on RNA methylation in cancer and provide novel avenues for diagnosing, treating, and preventing various cancer types.

m 6 A
The most commonly observed RNA methylation modification is the m 6 A modification, accounting for 60% of all RNA methylation modifications.The m 6 A modification involves the methylation of the nitrogen-6 position of adenosine and primarily detected within the RRACH sequence, with most sites located in close proximity to stop codons and within long internal exons.The m 6 A modification is present in almost all RNA and modulates the maturation, transcription, and functional metabolism of various classes of RNA, thereby regulating various cellular processes. 45For example, m 6 A affects protein encoding and synthesis by influencing both the translation and degradation of mRNA. 46The m 6 A modification of 18S rRNA and 28S rRNA is also necessary for global translation. 47,48The m 6 A modification also facilitates the processing of microRNA (miRNA) precursors by recruiting the microprocessor complex protein DiGeorge syndrome critical region 8 (DGCR8) from the reading protein heterogeneous nuclear ribonucleoprotein A2/B1 (HNRNPA2B1). 15Furthermore, the m 6 A modification upregulates or downregulates the expression of both long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) through methylation modification, which has been observed to interfere with the progress of various diseases, including cancer.The m 6 A modification is a dynamically reversible process that is primarily accomplished through the collaborative efforts of methyltransferases ("writers"), demethylases ("erasers"), and effector proteins ("readers").To date, several methyltransferases and effector proteins have been identified; however, research on demethylases has been relatively limited.
The m 6 A methyltransferases reported to date primarily include methyltransferase-like 3 (METTL3), METTL14, METTL5, METTL16, RNA-binding motif protein 15/15B, zinc-containing finger CCCH-type 13 (ZC3H13), zinc-containing finger CCHC-type 4, Wilms tumor 1-associated protein (WTAP), and Vir-like m 6 Arelated methyltransferase (also known as KIAA1429). 49ETTL3 and METTL14 are the most widely observed m 6 A methyltransferases.METTL3 catalyzes the transfer of methyl to the N6-adenosine residue of RNA.The primary function of the latter is to stabilize the methyltransferase complex and facilitate the recognition of catalytic substrates by METTL3. 50As for the demethylases, their primary role is to reversibly remove the m 6 A modification site on RNA, thereby mitigating the effect of methylation modification to varying degrees and ultimately maintaining the dynamic equilibrium of m 6 A modifications.Two demethylases, namely FTO alpha-ketoglutarate-dependent dioxygenase (FTO) and alkylation repair homolog protein 5 (ALKBH5), have been extensively studied.Methylated reading proteins primarily recognize and bind to m 6 A-modified bases, thereby activating downstream regulatory pathways such as RNA degradation and miRNA processing pathways.Common F I G U R E 1 Overview of the mechanisms of m 6 A, m 1 A, m 6 Am, m 7 G, Ψ, and m 5 C regulation.RNA methylation is a dynamically reversible process that is modulated by methyltransferases (writers), demethylases (erasers), and recognition factors (readers).Under the regulation of these regulatory factors, RNA undergoes various RNA methylation modifications.
reading proteins primarily include YT521-B homology (YTH) domain proteins, eukaryotic initiation factor (eIF) 3, IGF2 mRNA binding protein (IGF2BP) family members, and heterogeneous ribonucleoprotein (HNRNP) protein family members.YTHDF1 and YTHDF3, which belong to the YTH family of proteins, interact with m 6 A-modified RNA to initiate RNA translation.YTHDF2 primarily regulates the degradation of m 6 A-modified RNA, whereas YTHDC1 promotes RNA splicing and export.[53][54][55]

m 1 A
The m 1 A modification refers to the methylation of the nitrogen atom located at position 1 of the adenine residue in the RNA molecule. 56,579][60] In archaea, bacteria, and eukaryotes, the m 1 A modification is often observed at positions 9, 14, 16, 22, 57, and 58 of the tRNA.9][70] In addition, researchers have found that m 1 A plays various roles and exerts diverse effects on tRNA and rRNA.2][73] Recently, the m 1 A modification has also been found to be involved in the modification of mRNA.Studies have shown that the abundance of m 1 A-modified mRNA is approximately 10-fold lower than that of m 6 A-modified mRNA. 74,757][78] The 5′ UTR, the methyl donor for which is S-adenosylmethionine, is most commonly found near the initiation codon. 74,79Functionally, the m 1 A modification may potentially alter the structural stability of mRNA. 80ethyltransferases, demethylases, and RNA-binding proteins are required to function collaboratively for the m 1 A modification to exert its effects.Researchers first discovered the tRNA m 1 A58 methyltransferase complex, a tetrameric enzyme consisting of two types of subunits (Gcd14p and Gcd10p, now designated Trm61 and Trm6), in Saccharomyces cerevisiae.2][83] The TRMT6/TRMT61A complex is the homologous form of the tetrameric enzymes in eukaryotes.TRMT6/61A recognizes a GUUCRA tRNA-like motif and promotes methylation of the m 1 A sites in mRNA.TRMT61B catalyzes the m 1 A modification of mt-mRNA transcripts.TRMT10C methylates mt tRNA Lys at positions m 1 A9 and ND5 mt-mRNA 1374. 76,77,84Regarding rRNA, Rrp8 and Bmt2 catalyze m 1 A645 and m 1 A2142 modifications of 25S rRNA, respectively. 71,85Nucleomethyl (NML) is a m 1 A-modified nucleolar factor that catalyzes m1A modifications of 28S rRNA in human and mouse cells. 86In addition, demethylase and RNA methylated reading proteins function in a similar manner as m 6 A. To summarize, the m 1 A methyltransferases (writers) in eukaryotes primarily include TRMT6, TRMT61A, TRMT61B, TRMT10C, SDR5C1, and NML.Demethylases (erasers) primarily include alpha-ketoglutarate-dependent dioxygenase ABH1 (ALKBH1), ALKBH3, ALKBH7, and FTO.Methylated reading proteins (readers) primarily include YTHDF1-3 and YTHDC1.Understanding the common sites of m 1 A modification and the types and functions of m 1 A-modified proteins will enhance our understanding of this methy-lation modification and establish a basis for identifying suitable therapeutic targets. 57,87

m 6 Am
As a result of the methylation of 2-O-methyladenosine, m 6 Am is a modification of the first nucleotide proximal to the 7-methylguanosine cap. 88,89This modification was first discovered in viral mRNA and animal cells in the 1970s. 90,91lthough the formation of m 6 Am and m 6 A is similar, there are a few obvious differences between the two.First, the m 6 A modification sites are often situated in the 3′ UTR, whereas the m 6 Am modification is often detected in the 5′ m7G cap structure.Second, m 6 A exhibits various methyltransferases, including METTL3 and METTL14.Phosphorylated CTD interaction factor 1 (PCIF1) was traditionally considered the only m 6 Am methyltransferase.3][94] However, studies in recent years have revealed that apart from PCIF1, METTL14 can also function as a m 6 Am "writer."METTL4 catalyzes the methylation of the m 6 Am modification site in U2 small nuclear RNA (snRNA) and regulates pre-mRNA splicing. 95,96Third, while m 6 A can be demethylated by both ALKBH5 and FTO, m 6 Am is only preferentially and specifically demethylated by FTO. 97,98t present, no regulatory protein for m 6 Am has been reported, and additional investigations are needed to delve into this unexplored area of research in the future.In general, m 6 Am is also a crucial RNA methylation modification in eukaryotes.100][101]

m 7 G
The m 7 G modification refers to the addition of a methyl group at the N7 position of ribonucleoside, existing at internal positions in both tRNA and rRNA. 102Extensive research has revealed that levels of m 7 G modification are similar to those of m 1 A modification, that is, approximately 0.04% of all guanosine residues are modified. 103he m 7 G modification is predominantly observed in the 5′ cap region, or the internal region of mRNA, in eukaryotes.][106][107][108] In mammals, the most common and well-studied m 7 G methyltransferase is METTTL1, which binds to WD repeat domain 4 (WDR4) and participates in the regulation of the m 7 G modification of various RNAs, including tRNA and mRNA.METTL1, located at 12q13, 26 is widely expressed in many types of tissues.0][111] Located at 21q22.3,3][114] The action sites of the METTL1/WDR4 complex are primarily located at the internal site of the mRNA, the G46 site of the tRNA, and the G-quadruplex structure of the miRNA. 108,115,116Knocking out WDR4 significantly reduces the expression of METTL1.In addition, the Williams-Beuren syndrome chromosomal region 22 (WBSCR22) and tRNA methyltransferase activator subunits 11−2 have been demonstrated to be responsible for the m 7 G modification of target rRNA. 116,117The WBSCR22/TRMT112 complex primarily regulates the m 7 G modification of 18s rRNA to promote the maturation of 18s rRNA.The two methylase complexes are homologues of the Trm8p/Trm82p heterodimer complex and Bud23/Trm112 in yeast, respectively.In addition, RNA guanine-7 methyltransferase (RNMT) and its cofactor, RNMT-activated small protein (RAM), are also common m 7 G methyltransferases. 118This complex is primarily involved in the m 7 G modification at the 5′ cap of mRNA, thereby mediating the nuclear output of mRNA and translation.RAM, which consists of an N-terminal RNMT activation domain and a C-terminal RNA binding domain, increases the affinity of RNMT for RNA, thereby indirectly participating in the maintenance of mRNA levels and mRNA translation. 119To date, no definitive studies have reported m 7 G demethylases.As for "readers," the m 7 G cap has been reported to be recognized by eIF4E and the cap-binding complex consisting of CBP80 and CBP20, thereby affecting RNA maturation, nuclear output, and translation. 45,120Zhao et al. 121 elucidated that Quaking recognizes and binds to m 7 G-modified mRNA.

Ψ
Ψ refers to a compound in which the C-5 atom of the heterocycle is linked to the C-1′ atom of pentose, unlike normal pyrimidine nucleosides in which the C-1′ atom of pentose is linked to the N-1 atom of the heterocycle to form a glycosidic bond. 122Ψ is the earliest identified modified nucleoside in RNA and exhibits the highest abundance.It is called the "fifth nucleoside" in RNA.To date, 13 writers of Ψ have been identified in humans, one of which is Dyskerin pseudouridine synthase 1 (DKC1) with an RNAdependent mechanism.DKC1 is the catalytic subunit of the H/ACA snoRNP complex and catalyzes the formation of Ψ in rRNA. 123,124The other methylases in humans are primarily members of the PUS family, including PUS1-4, PUS6, PUS7, PUS7L, PUS9, PUS10, and RPUSD1-4. 125,126o date, there have been no reports of Ψ erasers or readers.The lack of erasers may be owing to the inert C─C bond formed between a ribose and a base, leading to an irreversible pseudourification process.One of the key directions of future research will be to identify Ψ erasers and readers.In addition, given that Ψ is excreted directly through urine, it may serve as a promising biomarker for the diagnosis and treatment of cancer.It is worth mentioning that Ψ has been used to produce an effective COVID-19 mRNA vaccine; therefore, it has notable research value. 127

m 5 C
The m 5 C modification refers to the methylation of carbon located at position 5 in the cytosine residue of the RNA molecule. 128The m 5 C modification is widely observed in phenotypic transcriptomes, including RNA, such as mRNA, tRNA, rRNA, and enhancer RNA.m 5 C modification is most prevalent in tRNA and rRNA in eukaryotes. 129he m 5 C modification is relatively conserved in tRNA and rRNA and is primarily enriched in the 5′ UTR, CDS, and 3′ UTR in mRNA. 130,131m 5 C methyltransferases primarily include DNA methyltransferase 2 (DNMT2) and members of the NOP2/SUN (NSUN) RNA methyltransferase family.The NSUN family has been most extensively studied for NSUN2, which modulates the m 5 C modification in diverse RNA transcripts, including tRNA, mRNA, rRNA, mitochondrial tRNA (mt-tRNA), and vault-derived small RNA. 13For instance, NSUN1 primarily regulates the m 5 C modification at position 4447 in human 28S rRNA and position 2870 in yeast 25S rRNA. 132NSUN3 initiates the biogenesis of m 5 C in mt-tRNA (Met) in humans. 133Furthermore, NSUN4 and NSUN5 are associated with the m 5 C modification at position 911 in human 12S RNA and position 3782 in human 28S RNA, respectively. 134,135NSUN6 primarily facilitates the m 5 C modification of tRNA (Cys) and tRNA (Thr) at cytosine C72. 136,137DNMT2 (also known as TRMDT1) not only catalyzes tRNA methylation but also mRNA methylation. 138Erasers that have been identified thus far include the 10−11 translocation (Tet) family (Tet 1−3) and ALKBH1.The members of the Tet family successively oxidize 5mC to 5-hydroxymethyl cytidine, 5formyl cytidine (5frC), and then to 5-carboxy cytidine in RNA. 139,140The m 5 C modification may undergo additional oxidation by ALKBH1/ABH1, resulting in the production of 5frC at the same position. 141The methylated reading proteins of m 5 C primarily include Aly/REF derivation factor (ALYREF, also known as THOC4) and Y-box binding protein 1. 45 More recently, Lan et al. elucidated a novel m 5 C interpreter, namely fragile x messenger ribonucleoprotein 1. 142 This interpreter is recruited by DNMT2 to sites of DNA damage and facilitates the demethylation of Tet 1-mediated m 5 C-modified RNA in DNA:RNA hybrids.

Regulation of RNA methylation on RNA metabolism
][145] In terms of RNA splicing, previous studies have highlighted the role of m 6 A as a splicing regulator, facilitating the production of mature mRNAs by removing introns from precursor mRNA. 146Additionally, mRNAs generated through alternative splicing have been observed to possess more RNA methylation sites. 147FTO has been found to inversely control m 6 A levels around splice sites of Runt-related transcription factor 1 (RUNX1) in an m 6 A demethylation manner, thereby restoring adipogenesis. 148urthermore, HNRNPC has been shown to bind to the altered local structure in mRNA and lncRNA caused by m 6 A, thereby influencing alternative splicing and the abundance of target RNAs. 149,150Research has also shown that m 1 A is observed in nascent polycistronic mitochondrial RNA and involves the processing of mitochondrial polycistronic RNAs. 57,151Additionally, m 1 A induces the proper folding of tRNA, contributing to early tRNA maturation events. 66,82Regarding RNA export, the protein ALKBH5 plays a significant role in mRNA export and the assembly of mRNA processing factors by colocalizing with nuclear speckles. 152,153In addition, recent studies have reported that ALYREF specifically recognizes m 5 C modifications catalyzed by NSUN2, enhancing mRNA export. 130,154In the case of RNA translation, YTHDF1 typically binds to m 6 A sites around stop codons in mRNA, recruiting translation initiation factors such as eukaryotic translation initiation factor 3 (eIF3), eukaryotic translation initiation factor 4E (eIF4E), eukaryotic translation initiation factor 4G (eIF4G), and the 40S ribosomal subunit to increase the translation efficiency of the target RNAs. 155n some cases, cap-independent translation has also been observed near the 5′ UTR of RNA. 156Emerging studies suggest that mRNAs modified by m 6 A in their 5′ UTR can directly initiate translation by interacting with eIF3 and recruiting the 43S complex. 157Moreover, m 7 G methyltransferase METTL1/WDR4 complex also exerts essential effects on the process of mRNA translation, particularly for regulating cell cycle genes and brain abnormality-related genes. 110It has also been indicated that m 1 A participates in the translation initiation and elongation process of tRNA, mRNA and rRNA. 62,158As a m 1 A demethylase, ALKBH1 reversibly attenuates translation initiation and usage of tRNAs in protein synthesis by catalyzing the demethylation of the target tRNAs. 158In course of RNA degradation, YTHDF2 reduces the stability of target transcripts by recognizing m 6 A modification and eventually transporting RNA to the processing body (P-body). 52,147,159Furthermore, m 1 A RNA-binding protein HRSP12 has been identified as an adaptor that facilitates the connection between YTHDF2 and RNase P/MRP (endoribonucleases), thereby involving in the acceleration of mRNA degradation. 14,160,161t has also been indicated that METTL1 are responsible for the base triple interaction of tRNA variable loop, which influences the stability of tRNA. 162,163

Association of RNA methylation with abnormal RNA metabolism in cancer
][170][171] Numerous studies have established that multiple m 6 A regulators disturb cancer-associated gene expression by influencing RNA splicing, translation, and stability, thereby performing oncogenic activities in cancer progression. 172Previous studies have reported that METTL3 methylates pri-miR221/222, leading to enhanced recognition and combination by microprocessor protein DGCR8 of modified pri-miR221/222.This process promotes the processing and maturation of pri-miR221/222 in bladder cancer and highlights the oncogenic role of METTL3.Specifically, matured miR221/222 mediated by METTL3 inhibits the expression of phosphatase and tensin homolog (PTEN), contributing to the development and progression of bladder cancer. 173Recent evidence has shed light on the role of YTHDF2 in accelerating the mRNA degradation of phospholysine phosphohistidine inorganic pyrophosphate phosphatase (LHPP) and the prostate-specific homeobox gene NKX3−1 and the consequent activation of Akt This acceleration occurs via METTL3-mediated m 6 A-dependent mechanisms and significantly enhances tumor growth and metastasis in prostate cancer (PCa).YTHDF2 has also been shown to induce METTL3-mediated suppressor of cytokine signaling 2 (SOCS2) mRNA degradation in hepatocellular carcinoma (HCC), therefore driving HCC cell proliferation, migration, and colony formation. 174While ALKBH5 is indicated to perform vital inhibitory effects in HCC tumorigenesis.Through mediating demethylation on LY6/PLAUR Domain Containing 1 (LYPD1) mRNA to enhance its degradation, ALKBH5 attenuates the proliferation and invasion capabilities of HCC cells. 175As the most common and fatal types of hematopoietic malignancies, acute myeloid leukemia (AML) is recently reported to aberrantly upregulate FTO expression, especially in AML cases with t(11q23)/MLL-rearranged chromosomal abnormalities.Elevated FTO level in AML cells suppresses the m 6 A abundance and stability of ankyrin repeat and SOCS box-containing 2 (ASB2) and retinoic acid receptor alpha (RARA) mRNA.This suppression leads to cell transformation and leukemogenesis.It has also been reported that METTL14 increases stability and translational efficiency of MYB and MYC mRNAs in an RNA methylation-dependent manner, thereby contributing to self-renewal and proliferation of AML cells during malignant hematopoiesis. 176rowing evidence also suggests that abnormal m 5 C modification affects the expression of downstream cancerassociated genes by altering related RNA metabolism processes.In cervical cancer (CC), NSUN2 and YBX1 were also observed to mediate m 5 C modification and strengthen the mRNA stability of LRRC8A, a core component of the volume-regulated anion channel.Then, upregulated LRRC8A further activated PI3K/AKT signaling to exert its tumor-promoting role in CC. 177 In bladder cancer, m 5 C reader YBX1 recognized NSUN2-induced m5C modification in 3′ UTR of hepatoma-derived growth factor (HDGF) mRNA and further maintained its stability, therefore driving the oncogenic molecular mechanism of HDGF in bladder cancer. 178Research has also revealed the involvement of m 5 C in regulating RNA stability and ferroptosis during cancer progression.In endometrial cancer (EC), NSUN2 enhances the m 5 C modification of SLC7A11 mRNA, increasing its stability and expression levels.This leads to reduced susceptibility to ferroptosis and enhanced proliferation of EC cells. 1797][188][189] Recent studies have highlighted the role of the METTL1/WDR4 complex in elevated mRNA translation and enhanced tRNA stability, which contributes to the development of several cancers.Notably, the upregulated expression of the METTL1/WDR4 complex has been found to drive translational regulation of specific oncogenic mRNAs in HCC through m 7 G tRNA modificationdependent mechanisms, thereby fueling hepatocarcinogenesis.This dysregulation is accompanied by increased HCC cell growth, migration, and invasion. 190,191In AML, the METTL1/WDR4 complex has been shown to positively control global translation efficiency, underscoring its role in leukemogenesis. 192Additionally, in the progression of head and neck squamous cell carcinoma (HNSCC), the upregulation of the METTL1/WDR4 complex enhances the translation of oncogenic transcripts associated with the PI3K/AKT/mTOR signaling pathway, leading to alterations in the immune landscape and subsequent malignant development of HNSCC. 193ecently, m 1 A methylation has also emerged as a novel layer of epigenetic regulation implicated in human carcinogenesis. 194,195One example is the interaction between ribosomal RNA methyltransferase NSUN4 and mitochondrial transcription termination factor 4 (MTERF4) to form a stable complex.This complex is essential for the generation of functional ribosomes and translation in mammalian mitochondria. 196Moreover, tRNA methyltransferase TRM6/61 plays a role in stabilizing and accumulating charged initiator methionyl-tRNA (tRNAi Met ) by methylating its adenosine 58, therefore contributing to the increased translation of mRNA that are frequently deregulated in gliomas. 197Additionally, it has been confirmed that protein kinase C α (PKCα) is confirmed to restrain TRM61 activity and TRM61-induced cancer-promoting effects on anchorage-independent growth and sphere-forming ability of glioma C6 cells. 198oreover, the knockdown of ALKBH3 in HEK293T cells has been observed to reduce the expression of epidermal growth factor receptor 2 (ErbB2) and AKT1 substrate 1 (AKT1S1), a potential role for ALKBH3 in the progression or regulation of gastrointestinal cancer. 199It has also demonstrated that ALKBH3 exerts the oncogenic role in the survival, angiogenesis, and invasion of urothelial carcinoma cells.Upregulated ALKBH3 has been found to significantly elevate the expression of downstream molecules, including NAD(P)H oxidase-2 (NOX-2) and TNF-like weak inducer of apoptosis (Tweak), in urothelial carcinoma UMUC2 and UMUC3 cells, thereby inducing the accelerated cell cycle and angiogenesis in the development of urothelial carcinoma. 200hese findings consistently emphasize the intricate associations between RNA methylation, RNA metabolism, and cancer development in different cellular contexts.Disruption of these processes contribute to the initiation and advancement of cancer.Gaining a deeper understanding of the mechanisms that underlie these connections could offer valuable insights into the development of innovative therapeutic approaches for cancer treatment. 201

RNA METHYLATION AND CANCER METABOLISM
This section utilizes the extensively studied phenomenon of cancer metabolic reprogramming as a focal point to dissect the specific roles and mechanisms through which RNA methylation influences cancer biology.This exploration not only sheds light on the direct impact of RNA methylation on the metabolic pathways pivotal for cancer cell survival and proliferation but also emphasizes the translational potential for clinical applications of these findings.By understanding the intricacies of how RNA methylation regulates key metabolic processes in cancer, we pave the way for the development of RNA methylationtargeted prognostic markers and therapeutic tools.The focus on tumor metabolism driven by RNA methylation underscores the potential of targeting RNA methylation as an innovative strategy in the clinical setting to improve cancer management and patient outcomes.

Cancer metabolism
Energy metabolism is essential for all living organisms to sustain basal biological processes. 202In a broad sense, energy metabolism primarily encompasses the metabolism of carbohydrates, proteins, lipids, nucleic acids, and other substances.The interplay and influence of diverse metabolic substances, which undergo a series of biochemical reactions, involve various enzymes and substrates, thereby establishing an intricately interconnected metabolic network that drives various vital physiological processes throughout an organism's lifespan. 203,204nlike normal cells, cancer cells exhibit increased nutrient requirements, such as those for glucose, glutamine (Gln), and fatty acids (FAs), to generate ATP and meet high energy demands (Figure 2). 205,206The concept of the "Warburg effect" was first proposed by Nobel laureate Otto Warburg in the 1920s and has since contributed to notable advancements in research on cancer metabolism. 207,208Metabolic reprogramming exhibited by cancer cells has been recognized as one of the fundamental characteristics of cancer. 19,20Interestingly, a metabolic trait observed in nearly all cancer cells is their ability to acquire nutrients from a nutrient-deficient environment and utilize the nutrients to sustain their hyperproliferative capacity and biomass synthesis. 209,210Cancer cells typically exhibit unique metabolic adaptations that switch different metabolic patterns to maximize the generation of energy and biomass.2][213][214] Studies have demonstrated that these biosynthetic processes involve the regulation of signaling pathways associated with cell growth.These signaling pathways (commonly PI3K/AKT/mTOR signaling) are activated as a result of tumorigenic mutations in the cancer cells. 209Metabolic reprogramming is accompanied by cancer initiation and development, with the enhancement of diverse neoplastic processes, including cell proliferation, survival, invasion, metastasis, and resistance to treatment.The progression of cancer is characterized by the acquisition of additional oncogenic mutations, which further enhance metabolic reprogramming and subsequently accelerate cancer growth. 215Notably, metabolic reprogramming is influenced by genetic alterations, the surrounding microenvironment, and their interactions. 216To address depleted supplies of precursors for macromolecule biosynthesis and cell survival, a few cancer-related genes acquire specific mutations to drive metabolic reprogramming. 217][220] While nutrient availability and complex noncancer components in the TME influence the metabolic state of cancer cells and consequently lead to epigenetic alterations in these cells, [221][222][223][224][225] the interactions between oncogenic mutations and the TME jointly endow cancer cells with advantageous metabolic traits. 226,227Several studies have shown that the uptake of both glucose and Gln is notably higher than that of other nutrients in cancer cell.The increased uptake of glucose and Gln in cancer underscores the importance of energy and biosynthesis in cancer. 228lucose and Gln metabolism are interconnected in various ways. 2291][232][233][234] Therefore, we focus on the major metabolic processes associated with glucose, amino acids, lipids, and the mitochondria in cancer cells and summarize the mechanisms underlying classical and common metabolic pathways, taking into account the influence of both genetic and microenvironmental factors.
F I G U R E 2 Metabolic reprogramming plays an indispensable role in tumorigenesis.Cancer cells often exhibit fiendishly complicated metabolic patterns and initiate the most suitable metabolic pathways to address the requirements of cell proliferation and survival in a hostile microenvironment.In contrast to normal cells, cancer cells predominantly rely on the enhanced glycolytic pathway to efficiently generate ATP at a rapid rate to meet the high energy demands associated with cancer growth.Cancer cells also exhibit increased uptake and metabolism of many other nutrients, including glutamine and FAs, thereby facilitating their proliferation and invasion.Additionally, cancer cells exhibit altered mitochondrial metabolism to meet the changeable need of energy generation and biosynthetic processes.FA, fatty acid; FASN, FA synthase; HK, hexokinase; GPI, glucose-6-phosphate isomerase; PFK1, phosphofructokinase 1; GPT, glutamic pyruvate transaminase; PSAT, phosphoserine aminotransferase; GLS, glutaminase; GLUD, glutamate dehydrogenase; TPO1, transporter protein 1; PGK, phosphoglycerate kinase; LDH, lactate dehydrogenase; GOT1, glutamic-oxaloacetic transaminase 1; ACLY, ATP citrate lyase.

Glucose metabolism
9][240] Glucose plays a central role in biosynthetic processes by serving as carbon skeletons (accounting for over 90%) and a source of reducing power. 213Glycolysis is the virtually ubiquitous metabolic pathway for glucose once it is transported into cells via glucose transporters (GLUTs). 241The OXPHOS pathway is another major pathway for glucose, where ATP is produced across the mitochondrial inner membrane with the consumption of oxygen. 242The dysregulation of glucose metabolism is a key characteristic of metabolic reprogramming during tumorigenesis.Aerobic glycolysis, which is widely recognized as the predominant metabolic pathway in cancer cells, has been extensively investigated to determine the association between metabolism and tumorigenesis, thereby providing insights into cancer metabolic reprogramming. 243During the early twentieth century, Otto Warburg demonstrated that in a large proportion of cancers, cancer cells exhibit increased glucose uptake and convert a considerable proportion of glucose into lactate, regardless of the availability of oxygen, in comparison with normal cells. 207Although decades of research have been devoted to determining the causes and mechanisms of upregulated aerobic glycolysis, the precise mechanism remains incompletely understood. 244Several widely recognized potential reasons for the upregulation of aerobic glycolysis in cancer cells include mitochondrial dysfunction, high-efficiency ATP generation, the upregulation of oncogenes and glycolytic enzymes, and hypoxia. 245Warburg has postulated that the occurrence of aerobic glycolysis can be attributed, at least in part, to mitochondrial dysfunction leading to compromised aerobic respiration. 208,246Multiple studies have demonstrated the frequent occurrence of mitochondrial impairment in various cancers. 243,247,248However, aerobic glycolysis is also observed in well-functioning mitochondria in cancer cells in the presence of oxygen.][251] Cancer cells exhibit alterations in the genes associated with glucose metabolism, including well-characterized mutations in RAS and MYC oncogenes, dysregulation of PI3K/AKT/mTOR and LKB1/AMPK signaling pathways, and the deletion of the tumor suppressor p53. 252,253merging evidence has revealed that alterations in HIF-1α, oncogenes, and tumor suppressor genes lead to upregu-lated expression of GLUTs and key metabolic enzymes of glucose metabolism, thereby increasing the rate of glucose metabolism in various cancer types, including lung, breast, liver, and oral cancer. 254,2557][258] The tumor suppressor p53, which holds prominence, has also been demonstrated to upregulate the glycolytic pathway and disrupt the equilibrium between anabolism and redox interactions. 2591][262] Multiple studies have reported GLUT1 upregulation owing to mutations in HIF-1α, RAS, p53, and the PI3K/AKT signaling pathway in breast cancer (BC), esophageal cancer (EC), pancreatic cancer, and colorectal cancer (CRC).Moreover, the activity of the three critical enzymes of glycolysis, namely HK2, phosphofructokinase 1, and pyruvate kinases type M2 (PKM2), has also been found to be increased as a result of the activation of AMPK, HIF-1α, MYC, and the PI3K/AKT signaling pathway. 263,2646][267][268][269] Certain metabolites, including acetyl-coenzyme A (acetyl-CoA) and α-ketoglutarate (α-KG) also participate in the epigenetic reprogramming of glucose metabolism. 213,270,271More importantly, the cooccurrence of excessively activated mTOR signaling pathways and microenvironmental stimuli has been observed to lead to a novel glycolytic phenotype in hematological malignancies. 272

Gln metabolism
Besides increased glucose metabolism, cancer cells also exhibit substantial uptake of amino acids to sustained proliferation and the biosynthesis of biological macromolecules. 273Gln serves as not only a carbon substrate that enters the TCA cycle to fuse with biosynthetic precursors, including acetyl-CoA and oxaloacetate, and as a bioenergetic source for NADH and FADH2, but also a nitrogen substrate that is metabolized to address the rapidly increasing demand for the synthesis of nucleotides, glucosamine-6-phosphate, asparagine, and even NAD in cancer cells. 274In 1935, Hans Krebs, the individual credited for discovering the TCA cycle, demonstrated the significance of Gln metabolism in the maintenance of organismal homeostasis using animal models, thereby sparking an interest among researchers to investigate the role of Gln in cell growth. 275In the 1950s, the American physiologist Harry Eagle was the first to propose that proliferating cancer cells exhibit an increased requirement for Gln based on the observation that human carcinoma cells (HeLA strain) exhibit higher uptake of Gln than other amino acids. 2768][279] On the one hand, amino acids are metabolized to meet the increased requirements for protein synthesis in proliferating cancer cells.On the other hand, the requirement for the catabolism of amino acids, especially Gln, for energy generation and biomass synthesis surpasses that for protein synthesis in cancer cells. 280,281Indeed, cancer cells are profoundly dependent on Gln metabolism, a phenomenon commonly referred to as Gln addiction. 282Cancer cells inevitably experience a deficit of nutrients and energy; therefore, they frequently exhibit aberrant activation of certain genes and signaling pathways to address the increased demands for nutrients and energy. 283The expression of key enzymes involved in Gln metabolism has been found to be upregulated owing to onco-genotypes and the TME.5][286][287][288] Recent research has shown that MYC upregulates the expression of the Gln transporters alanine-serine-cysteine transporter 2 (ASCT2), [289][290][291] which facilitates the uptake of Gln, and glutaminase (GLS), which facilitates the transformation of Gln to glutamate and subsequently α-KG, thereby promoting the TCA cycle. 292,293The loss of the tumor suppressor Rb also leads to increased Gln uptake by upregulating the expression of ASCT2 and GLS1.Moreover, MYC increases the expression of the enzymes involved in nucleotide biosynthesis, such as carbamoyl phosphate synthetase II (CAD), phosphoribosyl pyrophosphate synthetase 2, thymidylate synthase, and inosine monophosphate dehydrogenase. 280,294Additionally, mutant RAS drives micropinocytosis to degrade extracellular proteins by remodeling the actin cytoskeleton for the supplement of amino acids, including Gln. [295][296][297] KAS facilitates the crucial metabolism of the Gln carbon skeleton by upregulating aspartate transaminase (GOT) expression and thus maintains equilibrium between redox balance and the increasing growth demand of PDAC cells. 298ln metabolism is regulated by the mTOR pathway, which induces glutamate dehydrogenase expression to convert glutamate to α-KG. 286,299Moreover, mTOR also upregulates CAD, thereby facilitating Gln to participate in nucleotide synthesis. 300,301Interestingly enough, the products of Gln metabolism, such as glutamate, α-KG, and aspartate, and even Gln itself have been observed to influence Gln metabolism. 275,302,303Furthermore, Gln metabolism in cancer cells has been observed to be also affected by conditions in the TME, especially hypoxia. 304 unique Gln metabolic phenotype is observed in lung cancer and liver cancer, which underscores the importance of the TME in cancer metabolic reprogramming. 2306][307] Increased levels of reactive oxygen species (ROS) in the TME upregulate HIF-1α expression, and glutathione generated from Gln downregulates HIF-1α expression. 308,309These insights into Gln metabolism have led to ongoing research efforts aimed at understanding how targeting Gln utilization in cancer cells could potentially yield therapeutic benefits.

Lipid metabolism
Studies have indicated that lipids supply energy and biomass via FA oxidation (FAO), contribute to the formation of cell membranes, maintain cell barrier function and fluidity, and participate in intercellular communication and various biological processes during growth and development. 310,311Multiple studies have demonstrated substantial alterations in lipid metabolism, particularly FA synthesis, across various cancer types. 312,313ancer cells commonly exhibit elevated de novo lipogenesis or lipid uptake to sustain rapid proliferation, adapt to changes in the surrounding environment, and produce signaling molecules. 3146][317] It is well established that multiple oncogenic signaling pathways and transcription factors lead to the overexpression of key enzymes in FA synthesis. 318In cancer cells, constitutively activated AKT has been found to downregulate the level of sterol regulatory element binding protein (SREBP) under the synergy of mTORC1 and subsequently enhance de novo lipogenesis. 319,320High MYC expression in cancer cells also upregulates the transcriptional activator MondoA, thereby promoting lipid biosynthesis. 321Additionally, numerous studies have validated that lipid metabolism is susceptible to the changes in TME.Under conditions of hypoxia, reduced FA synthesis leads cancer cells to increase exoge-nous lipid uptake, modify cellular lipids, and scavenge lysophospholipids. 322

Other metabolisms
Despite the typical increase in glycolytic rates in cancer cells, most cancer cells generate the majority of ATP through mitochondrial function.Mitochondria, as cellular energy factories, mediate metabolism, bioenergetics, redox homeostasis, and ROS in cells through OXPHOS. 3238][329][330] For example, SDH type B (SDHB)-mutated pheochromocytomas/paragangliomas tend to exhibit more invasive phenotypes. 331Gain-of-function mutations in IDH1/2 generate excess oncometabolite D-2-hydroxyglutarate, which leads to metabolic changes in chromatin structure and contributes to tumorigenesis. 332,333Moreover, the accumulation of certain mitochondrial metabolites in the TME has been found to contribute to cancer progression. 3346][337] Mounting evidence suggests that succinate accumulation directly induces oncogenic effects in diverse cancer types, primarily through epigenetic modifications and the activation of hypoxic signaling. 338Notably, mitochondrial metabolic reprogramming is a dynamic process accompanied by energy requirements of cell growth during various stages of cancer development, suggesting that mitochondrial metabolism is a double-edged sword in tumorigenesis. 339,340For example, ROS produced as a result of mitochondrial metabolism has dual functions within cells.Elevated levels of ROS lead to oxidative damage of cellular proteins, lipids, and nucleic acids, and even cell death.A chronic increase in ROS levels below a certain threshold enhances malignant behavior of cancer cells. 323,341[344]

Association of RNA methylation with abnormal cancer metabolism
A growing body of evidence suggests that RNA methylation is broadly dysregulated in human cancer and has been implicated in the regulation of cancer metabolic reprogramming. 345The dysregulation of glucose, lipid, and Gln metabolism is closely associated with malignant bioprocesses, including cell proliferation, invasion, and drug resistance.Cancer metabolic reprogramming involves alterations in the expression of various metabolismassociated proteins and downstream signaling pathways.Recent studies have demonstrated that RNA methylation is closely associated with the metabolic reprogramming of cancer cells.In cancer, the specific functions of RNA methylation primarily depend on the category of targeted genes (oncogenic or tumor-suppressive effect), the activity of writers and erasers, and the regulation of readers.In addition, distinct metabolic pathways are likely regulated by the same signaling pathways and methylation-modified RNA. 26Most notably, RNA modification plays a paradoxical role in cancer, wherein certain genes, upon methylation, promote cancer development, whereas others impede cancer progression. 346In the subsequent sections, we emphatically discuss the recent discoveries concerning the effect of commonly observed RNA methylation modifications on cancer metabolism, including glucose, amino acid, and FA metabolism.We also summarize the mechanisms underlying RNA methylation concerning cancer metabolic reprogramming (Table 1).
IGF2BP2/3-dependent pattern during CRC tumorigenesis, respectively. 352Additionally, H3K18 lactylation induced by lactate accumulation upregulates METTL3 expression and subsequently mediates m 6 A modification of JAK1, thereby enhancing the immunosuppressive roles of CRC tumor-infiltrating myeloid cells. 353,354Studies have also elucidated that LINRIS inhibits IGF2BP2 degradation in CRC HCT116 cells by inhibiting K139 ubiquitination, thereby promoting downstream MYC-mediated glycolysis and tumor proliferation.In vivo experiment on the BALB/c nude mice injected HCT116 cells with or without LINRIS knockdown observes that LINRIS knockdown suppresses the growth of CRC tumors and glycolysis mediated by IGF2BP2-MYC axis. 355Emerging evidence indicates that the m 6 A methyltransferase KIAA1429 promotes aerobic glycolysis by upregulating HK2 expression. 356Moreover, the m 6 A writer YTHDF2 degrades circ_0003215 to suppress signaling via the miR-663b/discs large MAGUK scaffold protein 4 (DLG4)/G6PD axis and subsequently upregulate PPP and enhance the malignant phenotypes of CRC. 357And IGF2BP2 also enhances lncRNA ZFAS1 expression to elevate the activity of Obg-like ATPase 1 (OLA1) and ultimately accelerates glycolysis and CRC progression. 358Remarkably, Lactoferrin was recently found to alleviate the effect of the m 6 A writer WTAP on 5′-nucleotidase domain-containing protein 3 (NT5DC3) and Hexokinase domain component 1 (HKDC1) expression to suppress CRC progression under conditions of hyperglycemia. 359In HCC, upregulated METTL3 expression is correlated with poor outcomes and has been validated to upregulate glycolysis by promoting mTOR activity. 360Hepatitis B virus X-interacting protein (HBXIP) positively modulates METTL3 level to interfere with the m 6 A methylation of HIF-1α, thereby regulating the rate of aerobic glycolysis and the malignant behavior of HCC cells. 361In clinical samples of HCC samples and HCC cells, METTL3 and IGF2BP2 have been shown to induce the m 6 A modification of WW domain-containing protein 2 (WWP2), thereby upregulating WWP2 expression, activating AKT signaling, and enhancing glycolysis and doxorubicin resistance. 362Moreover, the circRNA circRHBDD1 upregulates YTHDF1 expression, thereby inducing PIK3R1 translation and attenuating the response to anti-PD-1 therapy. 363YTHDF1 also promotes PDK4 expression under the involvement of IGF2BP3 to enhance glycolysis and ATP generation in HCC. 364The m 6 A reader YTHDF3 suppresses the degradation of the phosphofructokinase (PFKL) and establishes a positive functional loop with PFKL to promote HCC progression through glucose metabolism. 365The lncRNA mir4458hG, along with IGF2BP2, upregulates HK2 and GLUT1 expression to upregulate glucose metabolism in HCC. 366In contrast, the m 6 A methyltransferase ZC3H13 impairs PKM2 mRNA stability, thereby attenuating glycolysis and improving the susceptibility of HCC cells to cisplatin. 367nd investigation of clinical human samples has revealed that the m 6 A demethylase ALKBH5 upregulates the expression of ubiquitin protein ligase E3 component N-recognin 7 (UBR7), which is a negative regulator of glycolysis, and activates the kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2)/BTB domain and CNC homolog 1(Bach1)/HK2 pathway, thereby attenuating aerobic glycolysis in HCC. 368ETTL14 has also been reported to upregulate the expression of the ubiquitin-specific peptidase 48 (USP48) and the histone deacetylase sirtuins (SIRT6), thereby performing a suppressive function in the metabolic reprogramming of HCC cells. 369Gastric cancer (GC) exhibits increased levels of m 6 A-modified RNA, which shows a strong association with poor clinical outcomes in patients.Stimulation of METTL3 by P300-mediated H3K27 acetylation and its subsequent cooperation with IGF2BP3 upregulates HDGF, whereas its collaboration with IGF2BP1 upregulates NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 4 (NDUFA4) expression, which is associated with the upregulation of glycolysis in GC. 370,371 LIN28B collaborates with IGF2BP3 to recognize and stabilize c-MYC transcription and promotes aerobic glycolysis in the presence of LOC101929709. 372In vitro assays have revealed that IGF2BP1 directly interacts with c-MYC to upregulate aerobic glycolysis in GC cells. 373FTO regulates the m 6 A modification of AMPK catalytic subunit α1 (PRKAA1) and enhances the ability of PRKAA1 to promote glycolysis in GC. 374 The lncRNA LINC00958 is modified by the m 6 A methyltransferase KIAA1429 and interacts with GLUT1 to induce aerobic glycolysis in GC. 375 Functional experiments have shown that WTAP bound to the 3′-UTR m 6 A site of HK2 enhances the glycolytic capacity of GC cells. 376dditionally, METTL14 increases the mRNA stability of the acetylated protein LHPP, thereby attenuating glycogen synthase kinase-3β (GSK-3β) phosphorylation and the Wnt signaling pathway to suppress aerobic glycolysis in GC cells. 377In PDAC, YTHDC1 augments miR-30d expression to attenuate aerobic glycolysis by suppressing the activity of the transcription factor RUNX1 along with the promoters of SLC2A1 and HK1. 378Furthermore, the upregulation of IGF2BP2 has been reported to directly increase GLUT1 expression, thereby promoting aerobic glycolysis, which results in a poor prognosis for patients with PDAC. 379imilarly, RNA methylation is also involved in BC progression.METTL3 induces a high degree of m 6 A methylation of the tumor suppressor LATS1, which is further stabilized by YTHDF2, and attenuates the antitumor activity of the Hippo pathway, thereby promoting glycolysis and tumorigenesis. 380C5aR1-positive neutrophils, a novel neutrophil subset, promote extracellular signal-regulated kinase 1/2 (ERK1/2) signaling and stabilize WTAP to upregulate enolase 1 (ENO1) expression through the secretion of IL-1β and TNF-α, thereby promoting glycolysis in BC. 381 The upregulated YTHDF1 has been observed to inhibit miR-16-5p expression under hypoxic conditions, thereby upregulating PKM2 expression to enhance glycolysis in BC cells. 382Furthermore, the m 6 A demethylase ALKBH5 upregulates GLUT4 expression in a YTHDF2dependent manner to promote glycolysis and resistance to HER2-targeted therapy in BC cells. 383METTL3 is also upregulated in CC tissues and cells and is closely associated with the poor prognosis of patients.Functional analysis has shown that METTL3 pronounces the Warburg effect in CC cells by mobilizing YTHDF1 to stabilize HK2 expression. 384The upregulated expression of human papillomavirus (HPV) E6/E7 drives aerobic glycolysis in CC by directing IGF2BP2 to actively regulate MYC methylation or upregulate serine/threonine kinase GSK-3β expression and by degrading m 6 A demethylase FTO to increase HK2 expression. 385,386In renal cell carcinoma (RCC), METTL14 downregulates the expression of bromodomain PHD finger transcription factor (BPTF) to attenuate the oncogenic transcriptome, glycolytic reprogramming, and distal lung metastasis. 387In bladder cancer, the m 6 A demethylase ALKBH5 downregulates the expression of casein kinase 2α (CK2α) and glycolysis-associated proteins to inhibit glycolysis and increase sensitivity of cancer cells to cisplatin. 388n PCa, METTL3 stabilizes the lncRNA SNHG7 to promote glycolysis via the serine/arginine-rich splicing factor 1 (SRSF1)/c-MYC axis. 389In leukemia, FTO and YTHDF2 are found to upregulate phosphofructokinase PFKP and LDHB levels to facilitate aerobic glycolysis, which process can be damped by a metabolite of mutant isocitrate dehydrogenases R-2-hydroxyglutarate (R-2HG). 390n papillary thyroid cancer, FTO decreases the stability of apolipoprotein E mRNA through IGF2BP2-induced m 6 A modification to abrogate glycolysis. 391In esophageal squamous cell carcinoma (ESCC), METTL3 and YTHDF collaborate to downregulate adenomatous polyposis coli (APC) expression, thereby activating the Wnt/β-catenin signaling pathway and promoting aerobic glycolysis. 392n lung adenocarcinoma, Wnt/β-catenin signaling, along with YTHDF1, inhibits FTO expression and subsequently enhances c-MYC expression, thereby promoting aerobic glycolysis and malignant behavior in cancer cells. 393In glioblastoma multiforme (GBM), increased levels of the lncRNA that is proximal to X-inactive (JPX) positively modulate the level of a limiting enzyme of glycolysis, namely PDK1, in an FTO-dependent manner, thereby contributing to temozolomide chemoresistance. 394esides the pathogenesis of the m 6 A modification in relation to glucose metabolism reprogramming in can-cer, the m 5 C modification also affects glucose metabolism, thereby contributing to cancer development.Little is known about the specific biological function and roles of m 5 C methylation in cancer metabolism.A previous study revealed that the m 5 C modification plays a role in the carcinogenesis of bladder cancer by stabilizing oncogenic mRNAs, recovering the underlying mechanism of RNA m5C-mediated oncogene activation. 178Furthermore, the m 5 C reader ALYREF has been reported to extend the half-life of PKM2 mRNA, that is, stabilize PKM2 mRNA, by binding to the 3′-UTR of the mRNA.HIF-1α also indirectly upregulates PKM2 by cooperating with ALYREF to enhance glucose utilization, lactate production, and ATP generation, thereby increasing cell proliferation.These findings suggest that ALYREF significantly upregulates glycolysis and cell proliferation by stabilizing PKM2 mRNA in bladder cancer. 395In general, the function of m 1 A methylation in cancer development and cancer metabolic reprogramming has been largely unexplored.Emerging evidence demonstrates that the m 1 A methylation of RNA plays a role in the regulation of metabolic processes in cancer cells. 396A study revealed that the m 1 A eraser ALKBH3 targets exon 1 of ATP5D (the δ subunit of ATP synthase) mRNA and inhibits its transcription and translation through the YTHDF1/eRF3 axis.ALKBH3 knockdown has been shown to repress cell growth, migration, and invasion and decrease overall glycolytic flux.Furthermore, ATP5D overexpression upregulates glycolysis and ATP generation in cancer cells. 397The m 1 A eraser ALKBH1 notably induces the demethylation of targeted tRNAs, such as tRNA Glu (CUC) , tRNA Lys (yUU) , and tRNA Gln (CUG) , thereby rapidly responding to conditions of glucose deprivation. 158As considerable progress has been made in understanding the effects of RNA methylation on glucose metabolism in cancer circumstances, the regulatory mechanisms involved in their interaction can be exploited for clinical applications.

Gln metabolism and RNA methylation in caner
Besides glucose metabolism, RNA methylation also possesses vital roles in Gln metabolism of multiple cancers.Recent studies showed that IGF2BP2 enhances the expression of MYC, glutamic pyruvate transaminase 2 (GPT2), and solute carrier family 1 member 5 (SLC1A5), thus promoting Gln metabolism in AML. 398Elevated levels of YTHDF1 in CRC have been validated to promote GLS1 activity, leading to increased Gln uptake and cisplatin chemoresistance.The role of YTHDF1 in mediating cisplatin resistance through enhanced Gln consumption has been further validated in a xenograft mouse model.The in vivo experimental data support that YTHDF1 silencing combined with cisplatin treatment demonstrates a reduction in cisplatin resistance by attenuating YTHDF1mediated Gln metabolism. 399Furthermore, the upregulation of activating transcription factor 4 (ATF4) by YTHDF2 results in an increase in the transcript levels of DNA damage-inducible transcript 4 (DDIT4), an mTOR inhibitor, thereby facilitating prosurvival autophagy during glutaminolysis inhibition in CRC. 400In clear cell RCC (ccRCC) with VHL deletion or mutation, upregulated FTO targets the Gln transporter SLC1A5 to increase the Gln consumption rate and the sustain growth and survival of ccRCC cells. 401However, it should be noted that METTL14 participates in the regulation of mRNA involved in glutamate metabolism, including glutamic-oxaloacetic transaminase 2 (GOT2), cysteine sulfinic acid decarboxylase (CSAD), and SOCS2, to suppress HCC progression (Figure 4). 402Overall, these findings showcase the crucial roles of RNA methylation in orchestrating Gln metabolism in cancer cells through various mechanisms.The intricate interplay between RNA methylation and aberrant Gln metabolism in cancer cells holds therapeutic potential across different types of cancers.

Lipid metabolism and RNA methylation in cancer
The liver is the principal lipid-metabolizing organ in the body.In HCC, owing to increased modification of METTL3/14, the expression of ATP citrate lyase (ACLY) and stearoyl-CoA desaturase 1 (SCD1) is upregulated, which contributes to increased lipid production and the accumulation of lipid droplets (Figure 5). 403The upregulation of METTL5 and TRMT112 expression in HCC samples is positively correlated with poor prognosis and mediates 18S rRNA m 6 A modification, thereby facilitating de novo lipogenesis via the overexpression of the acyl-CoA synthetase long-chain family (ACSL) in HCC cells. 404It has also validated that stomatin-like protein 2 (SLP2), which is upregulated by METTL3 and YTHDF1, binds to the C-terminal of c-Jun N-terminal Kinase 2 (JNK2) to increase JNK2 levels and subsequently enhance SREBP1 activity, thereby facilitating de novo lipogenesis in HCC.The SLP2 overexpression HCC animal model further confirmed the enhanced METTL3-induced lipid metabolism and its carcinogenic functions. 405Functional experiments have revealed that METTL3 upregulates INC00958, which then interacts with miR-3619-5p to elevate the levels of HDGF, thereby promoting lipogenesis and cancer progression in HCC. 406][409] Additionally, METTL3 overexpression is associated with increased estrogen receptor-related receptor γ (ERRγ) levels in chemo-resistant HCC and BC cells.ERRγ binds to p65 to upregulate ATP binding cassette subfamily B member 1 (ABCB1) and the rate-limiting FAO enzyme carnitine palmitoyltransferase 1B (CPT1B), thereby enhancing FAO and drug resistance in cancer cells. 410In CRC, the overexpression of DEGS2, a key ceramide-synthesizing enzyme, results in the inhibition of ceramide synthesis and the proliferation and migration of CRC cells through reduced m 6 A modification of METTL3 and YTHDF2. 411In EC, FTO, along with YTHDF1 upregulates the expression of 17betahydroxysteroid dehydrogenase 11 (HSD17B11), thereby promoting the formation of lipid droplets in EC cells and cancer development, which is associated with a poor prognosis for patients with EC. 412 Moreover, increased HNRNPA2B1 levels upregulate the expression of the FA synthetic enzymes ACLY and acetyl-CoA carboxylase 1 (ACC1) and subsequently contribute to lipid accumulation in EC. 413 In AML, IGF2BP2 stabilizes protein arginine methyltransferase 6 (PRMT6) and subsequently downregulates the expression of the lipid transporter major facilitator superfamily domain containing 2A (MFSD2A), thereby maintaining the function of leukemia stem cells. 414In CC, depleted levels of the demethylase ALKBH5 indicate an unfavorable prognosis, and ALKBH5 functionally suppresses the expression of silent mating type information regulation 2 homologue 3 and ACC1 in an IGF2BP1dependent manner, ultimately inhibiting FA synthesis. 415n bladder cancer, METTL14 induces lncDBET overexpression, and along with FA binding protein 5 (FABP5), it promotes lipid metabolism and the malignant progression of bladder cancer. 416In GBM, constitutively activated EGFR/SRC/ERK pathway results in YTHDF2 overexpression and subsequently downregulate LXRA and HIVEP2 expression, thereby disrupting cholesterol homeostasis and sustaining GBM tumorigenesis. 417he m 5 C modification was recently found to regulate diverse biological processes involved in lipid metabolism.Studies have revealed that the m 5 C methyltransferase NSUN2 inhibits adipogenesis by accelerating the cell cycle of preadipocytes during the early stage of differentiation. 418The m 5 C reader ALYREF has also been found to repress adipogenesis and lipid accumulation by downregulating the expression of adipogenic differentiation marker genes. 419These findings are expected to shed light on the role of the m 5 C modification in cancer lipid metabolic reprogramming.In recent years, a study concerning osteosarcoma has shown that upregulated NSUN2 positively mediates lipid metabolism and cell proliferation F I G U R E 4 RNA methylation regulates the reprogramming of amino acid metabolism in multiple cancers.As the most abundant amino acid in the circulation, glutamine undertakes a versatile role in cell metabolism, participating in the supplementation of tricarboxylic acid (TCA) cycle and the biosynthesis of nucleotides, glutathione, and other nonessential amino acids.Given the energy-generating and biosynthetic roles of glutamine in growing cells, cancer cells manipulate oncogenic alterations of glutamine metabolism through the regulation of RNA methylation to address the increased requirements for growth and proliferation.In acute myeloid leukemia, IGF2BP2 enhances the expression of glutamic pyruvate transaminase 2 (GPT2), and solute carrier family 1 member 5 (SLC1A5), thus driving glutamine metabolism.In colorectal cancer, YTHDF1 promote glutaminase 1 (GLS1) activity and increase glutamine uptake, while YTHDF2 elevates activating transcription factor 4 (ATF4) and DNA damage-inducible transcript 4 (DDIT4) during the glutaminolysis inhibition.In clear cell renal cell carcinoma, FTO targets the glutamine transporter SLC1A5 to increase the glutamine consumption.Moreover, METTL14 participates in the regulation of glutamic-oxaloacetic transaminase 2 (GOT2), and cysteine sulfinic acid decarboxylase (CSAD) during the progression of hepatocellular carcinoma.

F I G U R E 5
In liver cancer, RNA methylation is involved in the regulation of lipid metabolism to boost cancer development.The liver is the principal metabolizing organ.Liver cancer cells exhibit increased uptake of lipids, de novo fatty acid synthesis, lipid storage, and even fatty acid oxidation to meet the high demands of substrate and energy for cell proliferation and to adapt to a nutrient-deficient microenvironment.In liver cancer, RNA modification plays a critical role in the modulation of lipid metabolism and triggers cancer progression.The m 6 A reader YTHDF1 and m 6 A writers (including METTL3, METTL5, and METTL14), upregulate the expression of RNA associated with lipid metabolism and result in enhanced lipogenesis.The m 6 A eraser FTO also upregulates lipid metabolism and contributes to cancer progression by modifying targets associated with the process of lipogenesis.FA, fatty acid; ACSL, acyl-CoA synthetase long chain family member, CPT1, carnitine palmitoyltransferase 1; LDLR, low density lipoprotein receptor; FASPs, fatty acid synthesis proteins; ACLY, ATP citrate lyase; SCD1, stearoyl-CoA desaturase 1; ERRγ, estrogen receptor-related receptor γ; ABCB1, ATP binding cassette subfamily B member 1; CPT1B, carnitine palmitoyltransferase 1B; SLP2, stomatin-like protein 2; JNK2, c-Jun N-terminal kinase 2; SREBP1, sterol regulatory element binding protein-1; FASN, FA synthase; CIDEC, cell death-inducing DFFA-like effector C. of osteosarcoma cells through the overexpression of FABP5. 420Moreover, the m 1 A methyltransferase complexes TRMT6 and TRMT61A have been demonstrated to increase the m 1 A methylation of tRNA, thereby triggering PPARδ and Hedgehog signaling, which in turn promote cholesterol synthesis and self-renewal of liver cancer stem cells. 421In general, these discoveries underscore the essential functions of RNA methylation in coordinating lipid metabolism to fulfill the increased energy demands of cancer cells through a variety of mechanisms.The regulatory mechanisms of RNA methylation on altered lipid metabolism in cancer cells presents a promising avenue for advancing cancer treatment.

4.2.4
Other metabolic processes and RNA methylation in cancer In addition to the regulation of the metabolism of three major nutrients during carcinogenesis, emerging evidence demonstrates that RNA methylation actively modulates other types of metabolism, such as mitochondrial metabolism and iron metabolism.Regarding mitochondrial metabolism, the RNA-binding protein RALY upregulates a set of miRNAs, including miR-676, miR-483, and miR-877, as a result of modification by METTL3, and downregulates the expression of electron transport chain genes, such as ATP5G3, ATP5I, ATP5G1, and CYC1, which are involved in the ROS-related stress signal of mitochondrial metabolism in CRC. 422In GC, FTO increases the rate of degradation of the complete membrane protein caveolin-1, thereby modulating mitochondrial fission/fusion and metabolism. 423METTL3 has been suggested to cooperate with IGF2BP1 to upregulate NDUFA4 expression and promote mitochondrial fission in GC. 371 In RCC, the mitochondrial enzyme MTHFD2 modulates m 6 A methylation of HIF-2α mRNA, thereby contributing to the metabolic reprograming of RCC. 424FTO downregulation is also associated with poor survival of patients with ccRCC and upregulates the expression of a central regulator of mitochondrial function, namely PPARδ coactivators-1α (PGC-1α), to induce oxidative stress and suppress ccRCC growth. 425In BC, METTL3 increases adenylate kinase 4 (AK4) expression to elevate ROS and p38 activity and augment tamoxifen resistance in cancer cells. 426Recently, a study reported that the m 1 A eraser ALKBH7 reduces the steady-state levels of mt-RNAs to enhance mitochondrial activity and upregulate OXPHOS. 151Additionally, recent evidence suggests a close association between m 6 A modification and iron metabolism during tumorigenesis. 427n hypopharyngeal squamous cell carcinoma, YTHDF1, upregulates TFRC expression to increase iron uptake and is positively correlated with ferritin levels and intracellular iron concentrations. 427The m 6 A demethylase ALKBH5 has been reported as a favorable prognostic marker for PDAC and to upregulate FBXL5 to degrade iron regulatory protein 2 and reduce intracellular iron levels. 428

Clinical significance of metabolism-focused RNA methylation in cancer
Research has provided strong evidence for the vital influence of RNA methylation on cancer cell metabolism, influencing processes such as glycolysis, glutaminolysis, lipid metabolism, and other key metabolic pathways.Dysregulation of RNA methylation in cancer cells impacts critical metabolic pathways, contributing to tumor progression, therapy resistance, and patient prognosis. 4280][431][432][433] The different expression patterns of RNA modification regulators between cancers and para-cancerous tissues enable researchers to accurately make a differential diagnosis of benign and malignant diseases. 434,435][438][439] Additionally, in the era of precision medicine, the clinical significance of metabolism-focused RNA methylation extends to the potential development of personalized treatment strategies.Although current research is still in early stages and primarily focuses on basic investigations, numerous in vitro and in vivo assays have shown exhibited results for therapeutic approaches targeting RNA methylation in overcoming drug resistance in several cancer treatments. 440Exploring the mechanism by which RNA methylation affects tumor metabolism is beneficial for the development of targeted RNA methylation for tumor treatment.RNA methylation is regarded as important carcinogenic factors of clinical and functional significance.Several key molecules involved in RNA modification pathways have been identified as potential therapeutic targets in diverse cancers, including CRC, HCC, GC, BC, AML, CC, and PC.This section summarizes the progress made in research aimed at targeting RNA methylation to disrupt metabolic reprogramming and achieve the regulation of cancer progression.Additionally, we provide an overview of the performance of RNA methylation as a prognosis predictor and treatment target in several cancer types (Table 2).and CNC homolog 1, HK2, hexokinase 2; ACSL, acyl-CoA synthetase long-chain family; HDGF, heparin binding growth factor; ENO2, enolase 2; APC, adenomatous polyposis coli; PKM2, pyruvate kinases type M2; HSD17B11, 17beta-hydroxysteroid dehydrogenase 11; ACLY, ATP citrate lyase; ACC1, acetyl-CoA carboxylase 1; BPTF, bromodomain PHD finger transcription factor; PGC-1α, PPARδ coactivators-1α; ATP5D, the δ subunit of ATP synthase; E2F1, E2F transcription factor 1; LXRα, liver X receptor alpha; HIVEP2, human immunodeficiency virus type I enhancer binding protein 2; GPT2, glutamic pyruvate transaminase 2; SLC1A5, solute carrier family 1 member 5; FABP5, FA binding protein 5.

Clinical significance of m6A modification in CRC
One such molecule is METTL3, increased METTL3 levels indicate poor prognosis in patients with CRC, including shorter disease-free intervals, and undesirable clinicopathological factors such as pathological differentiation, AJCC stage, and disease recurrence. 349,353,441Currently, 5-FU is the most prevalent chemotherapeutic agent employed in CRC therapy.Several in vitro and in vivo experiments have indicated that 5-FU-resistant CRC cells exhibit METTL3 upregulation and aberrant activation of glycolysis.Inhibiting the METTL3/LDHA axis has been validated to effectively resensitize 5-FU-resistant CRC cells to 5-FU.This finding presents a potential strategy to restore 5-FU efficacy in CRC. 350Targeting METTL3 also decreases glucose uptake, impairs cell proliferation, and inhibits cancer growth, providing novel perspectives for CRC therapeutic strategies. 352Another molecule of interest is METTL16, which is highly expressed in CRC tissues and cell lines.Elevated METTL16 expression is positively related to deleterious clinicopathological parameters, such as tumor size, lymph node metastasis, and distant metastasis of patients with CRC.Further analysis applying multivariate Cox regression also validates the independent performance of METTLE16 for prognosis prediction in CRC. 442Another study conducted at the Sun Yat-sen University Cancer Center has reported a negative correlation between the expression of LINRIS and IGF2BP2 and prognosis of patients with CRC.Two patientderived xenograft models of type 2 diabetes (T2D) with xenografted colon tumors under high glucose concentrations, including the C57BL/6 and the BALB/c nude mouse model, have provided further evidence that inhibiting the LINRIS/IGF2BP2/MYC axis effectively suppresses cancer growth without notable side effects, indicating a potential treatment approach for CRC. 355Lactoferrin suppresses the m 6 A modification of NT5DC3 mediated by WTAP, leading to the inhibition of CRC progression in both two types of mouse models.Moreover, analysis of clinical blood samples also suggests that NT5DC3 levels could be used as a predictive marker for CRC occurrence in patients with T2D. 359In addition, the overexpression of YTHDF1 notably enhances cisplatin resistance in cisplatin-resistant CRC cells (LoVo CDDP R) and in vivo xenograft mouse models by upregulating GLS1-induced Gln metabolism.Several experiments have validated that the inhibition of YTHDF1 and cisplatin synergistically perform tumor-suppressive functions. 399These findings underscore the importance of RNA modifications, such as m 6 A methylation, in CRC development and progression.Targeted therapies against specific molecules involved in RNA modification pathways hold promise for the development of innovative treatment approaches for CRC.

4.3.2
Clinical significance of m6A modification in HCC Moreover, METTL3 has been found to upregulate LINC00958 and promote lipogenesis in HCC.In HCC mouse models, a nanoplatform based on si-LINC00958 for HCC systemic delivery has exhibited superior efficacy and safety as a systemic delivery option for HCC treatment.This approach shows promise in effectively targeting the aberrant lipogenesis pathway to inhibit tumor growth and progression in HCC. 406Likewise, YTHDF1 upregulates SLP2 expression in a METTL3/m 6 A-dependent manner, which is correlated with the overall and disease-free survival in patients with HCC.Overexpression of SLP2 enhances lipid synthesis in HCC cells by regulating JNK2, thereby promoting cancer proliferation and metastasis.
The aforementioned findings highlight the potential of targeting the expression pattern of SLP2 as a viable strategy for HCC treatment. 405Moreover, an established m 1 A-related scoring system based on the metabolic characteristics of HCC was validated as a reliable tool for evaluating drug sensitivity of patients and facilitating risk stratification. 396These recent discoveries not only shed light on the role of RNA modifications and their impact on HCC development and treatment but also present potential avenues for targeted therapies and precision medicine approaches in managing this challenging disease.

4.3.3
][445] Recent research has revealed that METTL14 regulates LHPP through m 6 A modification, leading to the inhibition of GSK-3β acetylation.This, in turn, suppresses the HIF-1α-induced aerobic glycolysis, as well as the subsequent proliferation and invasion of GC HGC-27 cells. 377he observed tumor suppression effects demonstrated by METTL14 and LHPP highlight the potential of m 6 A methylation as a viable therapeutic approach for GC treatment.Additionally, increased expression of IGF2BP1 in GC tissues has been associated with enhanced aerobic glycolysis, aggressive behaviors of GC cells, and poor prognosis in GC patients.In vivo experiments have shown that knockdown of IGF2BP1 suppresses GC carcinogenesis, offering a promising target for GC treatment.These findings provide important insights into potential therapeutic interventions for GC. 373Furthermore, it has been found that METTL3 induces the upregulation of RPRD1B, which enhances FA uptake and synthesis, as well as lymph node metastasis of GC, through the c-Jun/c-Fos/SREBP1 axis.The disruption of this functional circuitry is observed to achieve the impairment of FA metabolism and lymph node metastasis. 446The association between METTL3 and FA metabolism presents a new therapeutic target for GC.][454][455] Additionally, the curcumin analog WZ35 induces multiple metabolic remodeling processes that suppress GC cell metastasis and growth.Mechanistically, WZ35 increases the m 6 A levels in GLS2 levels to deplete intracellular glutathione through upregulating YAP, AXL, and ALKBH5 expression. 456The involvement of ALKBH5 expression in WZ35-induced glutathione depletion uncovers new potential targets for GC treatment.Moreover, integrative proteomics analysis of METTL3 overexpressing GC BGC-823 cells has revealed an association between METTL3 and proteins involved in mitochondria-related OXPHOS.Notably, METTL3 upregulates AVEN and DNAJB1 levels, contributing to a poorer clinicopathological grade and stage in GC patients.These findings suggest that METTL3 influences GC cell metabolism, particularly OXPHOS, and hold promise for developing novel therapeutic targets and predictive markers in GC. 457 Additionally, the upregulation of IGF2BP1 in GC tissues is associated with enhanced aerobic glycolysis and malignant behaviors of GC cells and with a poor prognosis in patients with GC.In vivo experiments have shown that IGF2BP1 knockdown suppresses the carcinogenesis of GC.This finding provides critical insights into therapeutic interventions for GC. 373hese findings offer valuable insights into the interplay between RNA methylation and cancer metabolism, providing potential avenues for therapeutic interventions and prognostic predictions in GC.

4.3.4
Clinical significance of m6A modification in CC Moreover, in CC, upregulated IGF2BP2 expression in CC tissues is positively associated with the tumor stage.
HPV 16/18 E6/E7 activates IGF2BP2 and regulates MYC methylation to facilitate aerobic glycolysis and cancer progression in CC.The correlation between HPV E6/E7 and aerobic glycolysis may serve as a potential avenue for CC treatment. 385Furthermore, the Kaplan-Meier survival curves based on TCGA datasets indicate that patients with CC who exhibit ALKBH3 upregulation show poorer overall survival, suggesting its implication in prognosis prediction. 397Thus, strategies such as genetic knockout, pharmacological inhibition, or interference with these molecules significantly reverse drug resistance and improve the treatment outcomes for refractory BC.Moreover, understanding the role of HPV E6/E7 and IGF2BP2 in regulating aerobic glycolysis opens up new possibilities for targeted therapies in CC.The upregulation of ALKBH3 in CC also indicates its potential as a prognostic biomarker that could aid in predicting overall survival.
Moreover, CWI1-2, a small-molecule compound, was recently identified to suppress IGF2BP2 and its functional targets (MYC, GPT2, and SLC1A5) and disrupt the Gln pathway, thereby attenuating the colony-forming and self-renewal abilities of AML cells, delaying the onset of leukemia, and prolonging the survival of mice with MA9-induced leukemia.Given the high significance of AML to Gln metabolism, CWI1-2, which inhibits IGF2BP2, is an effective compound for AML treatment. 398Mutant IDH1/2 enzymes were previously reported to upregulate R-2HG production, accompanying by the suppression of the FTO/m 6 A/MYC/CEBPA signaling axis.These changes cause the antileukemic effects including the inhibition of fat mass and leukemia cell viability, which provides a novel theoretical direction for leukemic therapy. 458otably, patients with BC who exhibit ALKBH5 or GLUT4 overexpression typically show a poor prognosis and resistance to HER2-targeted therapy.The significant reversal of resistance in BC cells to trastuzumab and lapatinib has been achieved through genetic knockout and pharmacological inhibition of GLUT4, as well as interfering with ALKBH5 to suppress GLUT4 expression.This effect provides a new breakthrough for improving the treatment of drug-resistant BC. 383 In addition, increased expression of ALKBH5 has been observed in PC tissues as well as in PANC-1 and MIA PaCa-2 cells exposed to hypoxia.Through the combined application of MeRIPseq and RNA-seq technologies, it has been revealed that the m 6 A reader YTHDF2 enhances the stability of histone deacetylase type 4 (HDAC4), thus promoting glycolytic metabolism and migration of PC cells under hypoxic conditions.This forms a positive feedback loop comprising ALKBH5, HDAC4, and HIF-1α, which mutually accelerates glycolytic metabolism to adapt to hypoxic conditions.Based on these findings, the blockade of the ALKBH5/HDAC4/HIF-1α feedback loop represents a potentially novel approach for targeted treatment of hypoxia-driven PC. 459 These findings shed light on novel therapeutic approaches and prognostic markers by targeting m 6 A modification and m 6 A regulators for female reproductive system cancers, offering new avenues for improving treatment efficacy and patient outcomes.

4.3.5
Clinical significance of other types of RNA modifications in cancer The overexpression of the m 5 C reader ALYREF also exerts carcinogenic effects to promote glycolysis, which is implicated in the poor overall and recurrence-free survival of patients with bladder cancer. 395Moreover, the increased expression of the m 5 C eraser NSUN2 is correlated with an unfavorable prognosis in patients with osteosarcoma.The FAO inhibitor etomoxir and FABP5 deficiency have proven effective in counterbalancing the impact of NSUN2 upregulation on FA metabolism and the proliferation, migration, and invasion of osteosarcoma 143b cells.Animal models have validated that the inhibition of the NSUN2/FABP5 axis attenuates the prooncogenic effects of m 5 C modification in osteosarcoma, thus presenting novel avenues for osteosarcoma treatment. 420Overall, these findings also underscore the importance of addressing m 5 C modifications in multiple types of cancer therapy.It is worth noting that the findings discussed in this section are based on current research and metabolism-focused RNA methylation in cancer has substantial clinical significance, with the potential to impact cancer diagnosis, treatment, and patient outcomes.However, further investigations are necessary to fully elucidate the therapeutic potential of targeted RNA methylation and its application in disrupting cancer metabolic reprogramming.

ASSOCIATION OF RNA METHYLATION WITH CANCER IMMUNITY
In addition to cancer metabolism reprogramming, RNA methylations have been shown to influence tumor immune response in tumor progression.Growing evidence has shown the correlation between m 6 A methylation and immune landscape in diverse types of cancer. 460An increasing number of studies suggest that METTL3 plays a pivotal role in maintaining the homeostasis of immune cells. 460,4613][464][465] For instance, METTL3 mediates the modification of circIGF2BP3 in combination with YTHDC1, and elevated circIGF2BP3 sponges miR-328-3p and miR-3173-5p to upregulate plakophilin 3 (PKP3) expression.Subsequently, PKP3 stabilizes only the deubiquitinating enzyme otubain-1 (OTUB1) mRNA to inhibit the ubiquitination of PD-L1, contributing to reduced CD8+ T cell infiltration in non-small cell lung cancer. 466Multiple m 6 A methylation regulators have also been found to be highly expressed in ESCC tissues, along with high PD-L1 expression.Moreover, copy number alterations of m 6 A regulators have been observed to significantly disrupt immune cell infiltration in the ESCC immune microenvironment, affecting B cells, CD4+T cells, CD8+T cells, neutrophils, and dendritic cells. 467dditionally, m 6 A has been implicated in the association between methionine metabolism and tumor immunity in tumor progression.YTHDF1 and methionine metabolism mediate the m 6 A modification of PD-L1 and V-domain Ig suppressor of T cell activation, therefore contributing to reduced CD8+T cell infiltration, immune surveillance escape, and antitumor immunity resistance. 468High WTAP expression also causes the suppressed infiltration of T lymphocytes in gastric cancer, especially T regulatory (Treg) and CD4 memory-activated T cells. 469And m 6 A methylation has been found to involve in innate immunity evasion through the modification of circRNAs. 470vidence has revealed that YTHDF2 attenuates the immunogenicity of circRNAs and induces the evasion of circRNAs away from innate immune response by acting with m 6 A modification. 471It has also demonstrated that loss of YTHDF1 in classical dendritic cells enhances the cross-presentation of tumor antigens and CD8+T cell antitumor response through the recognition of methylated transcripts encoding lysosomal proteases. 51Furthermore, the deletion of ALKBH5 has been shown to hamper the accumulation of immunosuppressive Treg and myeloidderived suppressor cells in melanoma via the inhibition of monocarboxylate transporter 4 expression. 472And pharmacological inhibition of ALKBH5 has shown to prolong the survival of mice and enhance the effectiveness of anti-PD-1 immunotherapy. 473imilar to m 6 A modification, m 5 C RNA methylation is also required for the regulation of the immune microenvironment in diverse cancer types.5][476][477] In triple-negative BC, NSUN2 has been found to be expressed in monocytes/macrophages and NSUN6, on the other hand, is expressed in Treg cells. 478Additionally, NSUN6 expression has been shown to correlate strongly with multiple immune cells, particularly CD4+ T cells, suggesting a broader role in modulating immune responses. 479It has been also reported that NSUN2 triggers the translation of intercellular adhesion molecule 1 mRNA and further strengthens the adhesion of leukocytes to endothelial cells. 480Notably, NSUN2 expression level has been found to have an essential implication with T-cell activation and patient survival in the development of HNSCC.Patients with high T-cell activation status have worse overall survival when NSUN2 expression is low, suggesting that NSUN2 expression plays a crucial role in influencing T-cell activation and subsequent antitumor immune responses in HNSCC. 481Emerging studies have also highlighted the influence of m 7 G methylation for the maturation and functions of immune cells and tumor immunity. 474he established m 7 G-related risk score model has exhibited a strong association with immune cell infiltration, immune checkpoints and immune-related signaling pathways in uterine corpus endometrial carcinoma. 482Moreover, recent research has also uncovered the negative association between m 1 A levels and CD8+ T effector cell proliferation in colon cancer. 195The m 1 A Score system based on the expression of the 71 m 1 A-related genes offers an efficient insight for the identification of immune cell infiltration in TME and the development of antitumor immunotherapy strategies.
In summary, RNA modifications have been shown to affect various biological properties of immune cells, including differentiation, activation, and development, thus participating in the immune responses in diverse cancers.The intricate interaction between different patterns of RNA methylations and various immune cell types also profoundly influences the efficacy of antitumor immunotherapy targeting the PD-L1 checkpoint.However, while the mechanism presented primarily focuses on m 6 A methylation in the tumor immune microenvironment, there is a need for more in-depth understanding of the interaction network of other RNA methylation patterns on specific immune cells in cancer.Further research is essential for improved insight into this important aspect of cancer immunology.

CONCLUSION AND FUTURE PERSPECTIVES
RNA modification is a rapidly developing field within the context of epigenetic modifications in oncology.Accumulating evidence has validated that the aberrant expression of RNA modification regulators is closely associated with prognosis especially in cancer metabolism, suggesting that these regulators can serve as crucial indicators of prognosis in clinical settings. 483These alterations in cancer cell metabolism affects tumor growth, metastasis, and response to therapy.Therefore, understanding the clini-cal significance of metabolism-focused RNA methylation is essential for developing targeted therapeutic strategies and improving patient outcomes.The current mechanistic findings of RNA methylation on cancer development provide a theoretical foundation and insights for treating diseases using inhibitors of RNA methylation.The role of RNA methylation in cancer metabolism and therapy resistance has been increasingly recognized, making it a potential target for precise cancer treatment. 441,484ecent in vitro and in vivo assays have indicated encouraging outcomes for therapeutic strategies aimed at targeting RNA methylation. 472,485,486However, it is important to note that current research efforts pertaining to the role of RNA methylation in cancer metabolic reprogramming have primarily concentrated on basic research.Clinical trials of small-molecule inhibitors of RNA methylation in cancer metabolic reprogramming are still in the early stages and have yet to reach the clinical application stage. 487In addition, the same writer, eraser, and reader proteins of RNA methylation display diverse biological functions and regulatory mechanisms that vary not only across different types of cancers but also within the same cancer type. 488This phenomenon is likely attributed to factors such as cancer heterogeneity, variations in sample size, differences in experimental approaches, and disparities in the cancer microenvironment.To advance our understanding, future studies should strive to unravel the precise mechanisms underlying the effects of RNA methylation on cancer metabolic reprogramming, taking into account these varying factors.Another important consideration is the cell or tissue specificity of RNA methylation.The development of cell-or tissue-specific small-molecule inhibitors targeting RNA methylation would be highly desirable.It is anticipated that preclinical findings related to targeted RNA methylation in cancer metabolism will eventually translate into clinical applications. 26Furthermore, the integration of artificial intelligence technology and chemosynthesis holds potential for the development of anticancer agents targeting RNA methylation in cancer metabolic reprogramming. 489This interdisciplinary approach could provide innovative solutions and contribute to the advancement of precision medicine in oncology.Overall, the rapidly evolving exploration of RNA modification in oncology has shown promising prospects for improving cancer prognosis and treatment.Through

C O N F L I C T O F I N T E R E S T S TAT E M E N T
There are no conflict of interest to declare.

TA B L E 1
Role of RNA methylation in cancer metabolism reprogramming.2; GLUT1, glutamate dehydrogenase 1; OLA1, Obg-like ATPase 1; PTTG3P, pituitary tumor-transforming gene 3 pseudogene; LDHA, lactate dehydrogenase A; DLG4, discs large MAGUK scaffold protein 4; G6PD, glucose-6-phosphate dehydrogenase; NT5DC3, 5′-nucleotidase domain-containing protein 3; HKdc1, hexokinase domain component 1; HBXIP, Hepatitis B virus X-interacting protein; PDK4, pyruvate dehydrogenase kinase isozyme4; PFKL, phosphofructokinase, liver type; WWP2, WW domain-containing protein 2;UBR7, ubiquitin protein ligase E3 component N-recognin 7; Keap1, kelch-like ECH-associated protein 1; further research efforts, a deeper understanding of the underlying mechanisms and the development of targeted interventions can be achieved, leading to improved clinical outcomes in the future.A U T H O R C O N T R I B U T I O N S W. Z. designed the study, and reviewed and edited the manuscript.G. L., Q. Y., and P. L. participated in original draft preparation.H. Z., Y. L., S. L., Z. L., and Y. S. collected the references and help with reviewing the manuscript.All authors have read and approved the article.A C K N O W L E D G M E N T SThis study was supported by the National Natural Science Foundation of China (82171311, 82271339, and 82201466), Shanghai Excellent Academic Leader Program (21XD1400600), Clinical Research Plan of SHDC (SHDC2020CR2034B), and Shanghai Sailing Program (23Y1404500).Portions of the figure included in this manuscript were generated with the help of BioRender.