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Abstract

  1. Top of page
  2. Abstract
  3. THE INTERFERON SUPERFAMILY
  4. MECHANISMS OF CELL GROWTH INHIBITION BY IFNα: APOPTOSIS
  5. THE PROTEIN SYNTHESIS AS A TARGET OF IFNα ACTION
  6. THE MODULATION OF PROTEIN DEGRADATION
  7. ESCAPE MECHANISMS TO ANTI-PROLIFERATIVE EFFECTS OF IFNα
  8. PERSPECTIVES AND FUTURE DIRECTIONS
  9. LITERATURE CITED

Interferon-α (IFNα) is a recombinant protein widely used in the therapy of several neoplasms such as myeloma, renal cell carcinoma, epidermoid cervical and head and neck tumors, and melanoma. IFNα, the first cytokine to be produced by recombinant DNA technology, has emerged as an important regulator of cancer cell growth and differentiation, affecting cellular communication and signal transduction pathways. However, the way by which tumor cell growth is directly suppressed by IFNα is not well known. Wide evidence exists on the possibility that cancer cells undergo apoptosis after the exposure to the cytokine. Here we will review the consolidate signal transducer and activator of transcription (STAT)-dependent mechanism of action of IFNα. We will discuss data obtained by us and others on the triggering of the stress-dependent kinase pathway induced by IFNα and its correlations with the apoptotic process. The regulation of the expression of proteins involved in apoptosis occurrence will be also described. In this regard, IFNα is emerging as a post-translational controller of the intracellular levels of the apoptosis-related protein tissue transglutaminase (tTG). This new way of regulation of tTG occurs through the modulation of their proteasome-dependent degradation induced by the cytokine. Until today, inconsistent data have been obtained regarding the clinical effectiveness of IFNα in the therapy of solid tumors. In fact, the benefit of IFNα treatment is limited to some neoplasms while others are completely or partially resistant. The mechanisms of tumor resistance to IFNα have been studied in vitro. The alteration of JAK-STAT components of the IFNα-induced signaling, can be indeed a mechanism of resistance to IFN. However, we have recently described a reactive mechanism of protection of tumor cells from the apoptosis induced by IFNα dependent on the epidermal growth factor (EGF)-mediated Ras/extracellular signal regulated kinase (Erk) signaling. The involvement of the Ras[RIGHTWARDS ARROW]Erk pathway in the protection of tumor cells from the apoptosis induced by IFNα is further demonstrated by both Ras inactivation by RASN17 transfection and mitogen extracellular signal regulated kinase 1 (Mek-1) inhibition by exposure to PD098059. These data strongly suggest that the specific disruption of the latter could be a useful approach to potentiate the antitumour activity of IFNα against human tumors based on the new mechanistic insights achieved in the last years. © 2004 Wiley-Liss, Inc.


THE INTERFERON SUPERFAMILY

  1. Top of page
  2. Abstract
  3. THE INTERFERON SUPERFAMILY
  4. MECHANISMS OF CELL GROWTH INHIBITION BY IFNα: APOPTOSIS
  5. THE PROTEIN SYNTHESIS AS A TARGET OF IFNα ACTION
  6. THE MODULATION OF PROTEIN DEGRADATION
  7. ESCAPE MECHANISMS TO ANTI-PROLIFERATIVE EFFECTS OF IFNα
  8. PERSPECTIVES AND FUTURE DIRECTIONS
  9. LITERATURE CITED

The interferons (IFNs) represent proteins with antiviral activity that are secreted from cells in response to a variety of stimuli (Pestka, 1981a,b, 1986, 1987). There are at least five classes of IFN alpha, beta, gamma, tau, and omega. The interferons are divided into two groups designated type I and type II interferons. IFNγ is the only type II interferon, whereas the type I interferons consist of four major classes: IFNα, IFNβ, IFNω, and IFNτ. There is only one Hu-IFNω and one Hu-IFNβ, but a family of multiple IFNα species exists. It is unlikely that any human IFNτ exists. In general, exposure of cells to viruses and doublestranded RNAs induce the production of IFNα and IFNβ species. The classical function of these proteins is the protection against viral infections. However, soon the ability of IFN of inhibiting tumor cell proliferation emerged and, on the basis of the preclinical data, it entered the clinical practice and conquered a role in the therapy of a defined group of neoplasms. It appeared clearly, therefore, that IFN has a limited activity and several cancers are resistant to anti-proliferative action induced by this cytokine. On the other hand, the mechanisms at the basis of anti-cancer effects of IFN are not still completely clear even if the induction of programmed cell death has been recently involved. The potential role played by apoptosis and the new findings about the signal transduction elicited by this cytokine have given emphasis on the molecular pathways regulated by IFN in the view of potentiate its antitumour activity (Pestka, 2000).

Interferon alpha and signal transduction

The IFN-αR1, IFN-αR2, CRFB4, IFN-γR1, and IFN-γR2 chains are members of the cytokine type 2 receptor family as described by Bazan (1990a,b) and by Thoreau et al. (1991) who proposed that the interferon receptors as well as other receptors for cytokines and some growth factors are composed of two folding domains that comprise the ligand binding site that resides in the crevice between the folds.

The primary cytokine–receptor interaction was suggested to involve one face of the ligand while another face of the bound cytokine can interact with accessory binding components. A summary of these receptors for the interferon-related receptor components is illustrated in a recent review (Kotenko and Pestka, 2000). These homologies relate the interferon receptor components to the fibronectin type III structure, which in turn relates all these structures to the immunoglobulin superfamily.

The biochemical effects elicited by the interaction between IFNα and its receptors

One example of how intracellular tyrosines are utilized in signaling is the type I interferon (IFN) pathway. Human type I IFNs (α, β, and ω) have been shown to induce the expression of a large number of genes involved in regulating a variety of important biological responses, including antiviral, antiproliferative, and immunomodulatory activities. The mechanisms by which type I IFNs initiate such a broad spectrum of biological activities is only beginning to emerge. Type I IFN-dependent signaling requires both type I IFN receptor chains, IFNAR1 (human type I interferon receptor chain 1) and IFNAR2c (human type I interferon α receptor chain 2) (Colamonici et al., 1994a,b; Yan et al., 1996a,b). Binding of type I IFNs induces the assembly of these receptor chains, which leads to the phosphorylation of tyrosine residues located in the intracellular domain of each receptor chain. These tyrosine phosphorylation events are thought to be carried out by the Janus kinases TYK2 and JAK1, which are themselves activated by tyrosine phosphorylation (Fu, 1992; Schindler et al., 1992). The subsequent substrates of the TYK2 and JAK1 are the signal transducer and transactivator (STAT) proteins that are recruited at the phosphotyrosines located at the cytoplasmic tail of the receptor.

Signal transduction factors as substrate of type I IFN receptors
STAT family members

STAT proteins are a family of latent cytoplasmic transcription factors involved in cytokine, hormone, and growth factor signal transduction (Schindler et al., 1995; Ihle, 1996; Darnell, 1997; Imada and Leonard, 2000; Takeda and Akira, 2000; Williams, 2000; Bromberg, 2001). STAT proteins mediate broadly diverse biologic processes, including cell growth, differentiation, apoptosis, fetal development, transformation, inflammation, and immune response. Once activated, the tyrosine phosphorylated sites of the cytokine receptors become docking elements for SH2 and phosphotyrosyl-binding domain-containing proteins present in the membrane or the cytoplasmic compartment. Prominent among these are the STATs. Receptor-recruited STATs are phosphorylated on a single tyrosine residue in the carboxyl terminal portion. The modified STATs are released from the cytoplasmic region of the receptor subunits to form homodimers or heterodimers through reciprocal interaction between the phosphotyrosine of one STAT and the SH2 domain of another. Following dimerization, STATs rapidly translocate to the nucleus and interact with specific regulatory elements to induce target gene transcription. STAT proteins were originally discovered in interferon (IFN)-regulated gene transcription in the early 1990s (Sadowski et al., 1993; Shuai et al., 1993a,b; Darnell et al., 1994). Seven members of the STAT family of transcription factors have been identified in mammalian cells: STAT1, STAT2, STAT3, STAT4, STAT5a, STAT5b, and STAT6 and convincing evidence from genetic mapping studies indicates a common ancestral origin that gave rise to three chromosomal clusters of STAT genes through a series of duplication processes (Copeland et al., 1995).

STAT 1/2

IFN receptor activation classically leads to the phosphorylation and activation of STAT 1 and 2. STAT1 and STAT2 form a heterodimer that associates with a member (designated as 9) of the IFN regulatory factor (IRF) family, p48, resulting in the formation of the mature ISGF3 complex that translocates to the nucleus to initiate gene transcription by binding to interferon-stimulated response elements (ISRE) (Darnell et al., 1994; Darnell, 1997).

Stat 1:1 homodimers, Stat 3:3 homodimers, Stat 1:3 heterodimers, Stat 5:5 homodimers, and CrkL:Stat5 heterodimers are also formed during engagement of the type I IFN receptor since, as described below, also these STAT molecules can be activated by IFNα. These complexes move to the nucleus where they bind to GAS regulatory elements in the promoters of IFN-activated genes (Meinke et al., 1996; Darnell, 1997). Thus, signaling specificity via the IFNα-activated Jak/Stat pathway is established by the formation of multiple different complexes that activate distinct regulatory elements in the promoters of IFN-regulated genes.

Cross talks with other STATs and signal transducers

Additional transcription factors have been found to be activated by type I IFNs in the last decade. In fact, it has been demonstrated the IFNα-dependent activation of STAT 3 in human peripheral blood-derived T cells and the leukemic T cell line Kit225. In this experimental model, the observation that IL-2 and IFNα activate JAK1 to a comparable degree, but only IFNα activates STAT1, indicates that JAK1 activation is not the only determining factor for STAT1 activation (Beadling et al., 1994). Moreover, the data show that JAK1 stimulation is also not sufficient for STAT3 activation. It has been moreover shown that STAT3 binds to a conserved sequence in the cytoplasmic tail of the IFNAR1 chain of the receptor and undergoes interferon-dependent tyrosine phosphorylation (Constantinescu et al., 1994; Mullersman and Pfeffer, 1994).

The p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3K), which activates a series of serine kinases, binds to phosphorylated STAT3, and subsequently undergoes tyrosine phosphorylation (Pfeffer et al., 1997). Thus, STAT3 acts as an adapter to couple another signaling pathway to the interferon receptor: the PI3K (Yang et al., 1998). Consequently, PI3K is activated and can transduce its signals through Akt activation which is involved in cell survival. Akt was discovered as the product of the oncogene v-akt that is able to transform lymphoid cells (Franke et al., 1995). Based on homology to the PKA and PKC family of protein kinases, Akt was also named protein kinase B and RAC-PK (Burgering and Coffer, 1995). The PI-3K/Akt pathway provides cell survival signals in response to nerve growth factor, insulin-like growth factor 1, platelet-derived growth factor, interleukin 3, and the extracellular matrix (Franke et al., 1997). Akt apparently promotes cell survival by phosphorylating multiple targets, including the Bcl-2 family member BAD (Datta et al., 1997), the apoptosis-inducing enzyme caspase-9 (Cardone et al., 1998), and the Forkhead transcription factor (FKHRL)1 that regulates Fas ligand gene expression (Brunet et al., 1999). The recent results by Yang et al. have shown in lymphoma cell models that IFN activates Akt enzymatic activity and that kinase-dead Akt blocks IFN-promoted NF-κB activation, indicating that Akt is important for IFN-promoted NF-κB activation. Moreover, a constitutively active Akt construct promotes NF-κB activation. These data suggest that the main target of the IFNα-induced Akt activation is NF-κB that in this experimental system mediates anti-apoptotic signals. It will be important to establish which possible substrates for Akt undergo IFN-dependent phosphorylation and determine their physiological significance in IFN-promoted cell survival (Yang et al., 2001). Recent data suggests a role of Akt activation induced by IFNα in the regulation of monocyte adhesion (Navarro et al., 2003).

Also STAT5 has been demonstrated to be activated by IFNα in lymphoma and tumour cells (Fish et al., 1999). A recent report has implicated STAT5 in the engagement of CrkL in IFN signaling, as shown by the requirement of STAT5 as a docking site for the SH2 domain of CrkL. CrkL, in cooperation with STAT5, binds DNA, and this complex functions as a transcription factor in IFNα/β-induced signaling (Barahmand-pour et al., 1995). Recent reports have suggested that STAT5 is involved in IFNα signaling also in myeloid cell lines and HeLa cells (Meinke et al., 1996), and its activation has been observed in response to differentiation and growth arrest signals (Eilers et al., 1994; Barahmand-pour et al., 1995; Grumbach et al., 2001).

Controversial data are, on the other hand, available, on the interaction between IFNα and the extracellular signal-regulated kinase-dependent signaling. It was, in fact, found that the serine-threonine kinase mitogen-activated protein kinase (MAPK) [specifically, the 42-kDa MAPK or 2 (erk2)], directly involved in cell growth induction, interacts with the alpha subunit of IFN-α/β receptor in vitro and in vivo. Treatment of cells with IFNβ induces tyrosine phosphorylation and activation of MAPK and caused MAPK and STAT1 alpha to coimmunoprecipitate (David et al., 1995). Furthermore, expression of dominant negative MAPK inhibits IFNβ-induced transcription. Other groups have shown that short-term treatment with IFNα can activate the mitogen extracellular signal regulated kinase (MEK)/ERK pathway (Arora et al., 1999; Lund et al., 1999) in haematological experimental models. Romerio et al. have recently demonstrated that long term exposure of leukemic and lymphoma cells to IFNα induces a decrease of the activity of MEK and ERK through a ras[RIGHTWARDS ARROW]raf-1-independent pathway. Moreover, the addition of a MEK inhibitor (and thus of MAPK activity) increases the growth inhibition induced by IFNα (Romerio et al., 2000; Romerio and Zella, 2002).

Another molecular target of type I IFN receptor is protein kinase C (PKC) δ, a member of the PKC family of proteins, that is activated during engagement of the Type I IFN receptor and, consequently, associates with STAT1. Such an activation of PKCδ appears to be critical for phosphorylation of STAT1 on serine 727, as inhibition of PKCδ activation diminishes the IFNα- or IFNβ-dependent serine phosphorylation of STAT1. In addition, treatment of cells with the PKCδ inhibitor rottlerin or the expression of a dominant-negative PKCδ mutant results in inhibition of IFNα- and IFNβ-dependent gene transcription via ISRE elements. Interestingly, PKCδ inhibition also blocks activation of the p38 MAP kinase, the function of which is required for IFNα-dependent transcriptional regulation, suggesting a dual mechanism by which this kinase participates in the generation of IFNα responses (Uddin et al., 2002). The complex signal transduction network activated by IFNα is summarized in Figure 1.

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Figure 1. Signal transduction pathways activated by IFNα. IFNα, after the interaction with its receptor, activates the tyr kinase Jak-1 and Tyk-2 that are responsible for the activation of the cytoplasmic targets of IFNα. Right part: The tyr phosphorylation of the targets causes the translocation to the nucleus of STAT1 and STAT2 hetero and homodimers, of STAT5–CrkL heterodimers that migrate to the nucleus and binds to DNA mediating the transcription of apoptotic proteins. Jak-1 and Tyk-2 can also phosphorylate and activate PKCδ that, in turn, phosphorylates STAT2 on Ser and enhances the activity of the latter. Left part: On the other hand, IFNαR can also activate PI3K via STAT5 and consequently it can stimulate Akt that, in turn, provides survival signals via FKHRL1, BAD, Caspase 9, and NF-κB. STAT1/2 dimers can also activate ERK, but the functional meaning of this interaction is still uncertain. [RIGHTWARDS ARROW] Stimulating activity. Inhibiting activity.

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MECHANISMS OF CELL GROWTH INHIBITION BY IFNα: APOPTOSIS

  1. Top of page
  2. Abstract
  3. THE INTERFERON SUPERFAMILY
  4. MECHANISMS OF CELL GROWTH INHIBITION BY IFNα: APOPTOSIS
  5. THE PROTEIN SYNTHESIS AS A TARGET OF IFNα ACTION
  6. THE MODULATION OF PROTEIN DEGRADATION
  7. ESCAPE MECHANISMS TO ANTI-PROLIFERATIVE EFFECTS OF IFNα
  8. PERSPECTIVES AND FUTURE DIRECTIONS
  9. LITERATURE CITED

The caspase and mitochondrial involvement

Apoptosis plays an important role in the control of many normal physiological processes, such as embryonic development, immune regulation, and maintenance of tissue homeostasis (Krammer, 2000). Decreased sensitivity to apoptotic stimuli is also a trait commonly shared by cancer cells. This feature provides the tumour cells with a survival advantage, facilitating the out-growth of malignant clones and may also explain a variable susceptibility to various anti-cancer drugs (Los et al., 1997; Raza, 2000). Induction of apoptosis is thus a highly attractive mechanism for IFNα's antitumoural activity, and it could also play a role in the clearing of virus-infected cells.

IFNα can indeed induce apoptosis in some transformed cell lines as well as in primary tumour cells (Sangfelt et al., 1997; Cai and Jones, 1998; Dai and Krantz, 1999; Thyrell et al., 2002). Furthermore, in myeloma, as well as in glioma cell lines, long term treatment with IFN has been suggested to sensitize the cells to Fas-induced apoptosis (Roth et al., 1998; Spets et al., 1998). Moreover, the Fas ligand (FasL)/Fas receptor (FasR) system may mediate effects of IFNα2 in basal cell carcinoma (Buechner et al., 1997). In fact, after injection of IFNα2 into basal cell carcinomas, FasR and apoptosis were induced, and tumours regressed. However, Chawla-Sarkar et al. (2001) have recently demonstrated that IFNβ is a stronger FasL/Fas and apoptosis inducer than IFNα in melanoma cells. Similar data were obtained by Sanceau et al. (2000) in sarcoma cell lines in which IFNβ induces p38 MAPK-mediated Ser 727 STAT1 phosphorylation and apoptosis more efficiently than IFNα. Despite these biological differences, the molecular basis of the diversity between IFNα and β in the induction of apoptotic events is still unknown.

The detailed molecular background to IFNα-induced apoptosis remains unclear, but it was recently shown that it involves an ordered activation of caspases and the mitochondrial pathway, for example, cytochrome c (cyt c) release, loss of mitochondrial membrane potential (DC) as well as caspase-9 activation in hematopoietic tumour cell lines (Thyrell et al., 2002). Moreover, Thyrell et al. (2002) have demonstrated, in the same experimental system, that IFNα-induced apoptosis is not inhibited by antagonistic antibodies to the Fas-receptor and, thus, it is a Fas-independent effect. Panaretakis et al. (2003) have demonstrated, in a similar experimental model, that IFNα-induced apoptopsis occurs together with the activation of the pro-apoptotic Bcl-2 related proteins Bak and Bax. In fact, they found that IFNα induces activation of the two proapoptotic Bcl-2 family members, Bak and Bax and showed that apoptotic cells always had high levels of activated Bak, and that the majority of apoptotic cells contained a high level of Bax in its active conformation suggesting their direct involvement in IFNα-induced cell death (Panaretakis et al., 2003). However, the regulation of Bak and Bax activation is distinct. In fact, Bak was activated prior to Bax, since a cell population could be found with active Bak but still negative for active caspase-3, while Bax was found only in active caspase-3-positive cells. Bak activation, moreover, occurred early in the apoptotic response, prior to the cyt c release and loss of DC, whereas Bax activation followed these events (Panaretakis et al., 2003). The same authors show a transient initial increase of Bcl-xL and Mcl-1 that could explain the late onset of the apoptosis induced by IFNα (Puthier et al., 2001). In this regard, it was reported that IFNα, similar to interleukin-6 (IL-6), extends the survival of human myeloma cells through an upregulation of the Mcl-1 anti-apoptotic molecule although it was previously reported that IFNα induces growth inhibition of other multiple myeloma cells (Matsui et al., 2003). The latter data confirm the dual effect of this cytokine on the expression and, presumably, activity of the mitochondrial bcl-related molecules. Taken together these results suggest a mitochondrial involvement in the apoptosis triggered by IFNα.

The stress kinase cascade involvement

In eukaryotic cells, enzymatic isoforms of MAPK, such as Jun kinase-1 (JNK1) and p38 kinase, which can mediate anti-proliferative stimuli and apoptosis, have been identified. They have large sequence homology, but are functionally different from proliferative pathway-associated erk1/2. In fact, JNK1 and p38 kinase are part of enzymatic cascades activated by anti-proliferative agents such as ionizing and ultraviolet rays and cytokines. Recently, it has been demonstrated a role of JNK1 and p38 kinase in the onset of apoptosis in several cell models. In this regard, in addition to the STAT pathway, type I IFNs activate members of the MAPK family, including erk (David et al., 1995) and the p38 MAPK (that belongs to the stress-activated kinases) (Goh et al., 1999; Uddin et al., 1999, 2000). It was recently shown that activation of p38 is required for transcriptional activation of IFN-sensitive genes (Goh et al., 1999; Uddin et al., 1999, 2000). In addition, it was demonstrated that such transcriptional regulation of IFN-sensitive genes is unrelated to effects on DNA binding of STAT complexes or serine phosphorylation of STATs (Uddin et al., 2000), apparently involving a STAT-independent nuclear mechanism. Thus, coordination of the functions of the IFN-activated STAT and p38 pathways is necessary for full transcriptional activation in response to interferons (Goh et al., 1999; Uddin et al., 1999, 2000). It was, moreover, found that p38 MAPK pathway is engaged in type I IFN signaling in primary human hematopoietic progenitors and its function is required for the generation of the suppressive effects of interferons on normal hematopoiesis. In details, p38 and its downstream effector, mitogen-activated protein kinase activated protein kinase 2 (MapKapK-2), are rapidly activated by IFNα treatment of enriched primary human progenitor cells and pharmacological inhibition of p38 MAPK activation reverses the type I IFN-dependent inhibition of hematopoietic progenitor colony formation (Verma et al., 2002). Moreover, p38 MAPK, is involved in the generation of the antileukemic effects of IFNα in break cluster region (BCR)-ABL-expressing cells of acute myeloid leukemia (Mayer et al., 2001). We have reported that IFNα increases the expression of the epidermal growth factor receptor (EGF-R) at the surface of human epidermoid carcinoma cells (Budillon et al., 1991). We have also found that IFNα enhances the activity of EGF on these cells. In fact, IFNα-treated KB cells (human epidermoid carcinoma) are sensitized to the growth promoting effects of EGF. Moreover, the EGF-induced tyrosine phosphorylation of total cellular proteins and of the EGF-R is increased in the IFNα-treated cells (Caraglia et al., 1995). On the bases of these findings, we have hypothesized that the increased expression and function of the EGF-R could represent a protective response of tumour cells (STRESS RESPONSE) to the antiproliferative effect of IFNα (Tagliaferri et al., 1994). In order to verify this hypothesis we have studied, in KB cells, the expression of heat shock proteins (HSP) which are molecules involved in the protective response of eukaryotic cells to stress. IFNα increases the expression of HSP27, HSP90, and HSP70 inducible forms while it does not change the levels of the constitutive form of HSP70. After EGF addition to IFNα-treated KB cells, the levels of the HSPs are resumed to the levels of untreated control cells (Caraglia et al., 1999). We have moreover found that IFNα induces apoptosis on human epidermoid cancer KB cells and that also this effect is antagonized by EGF. We have evaluated the effects of IFNα and EGF on the stress-induced pathway of MAPK isoenzymatic activity JNK1 and MAPKp38 in KB cells. We have found that IFNα induces an about fivefold increase of activity of these proteins while the addition of EGF to IFNα-treated cells causes a progressive reduction of the activity of the two enzymes which reaches almost basal levels after 6 h of exposure to EGF. However, EGF alone does not induce any change in the activity of JNK1 and MAPKp38 in untreated KB cells. We have evaluated the involvement of JNK1 in the triggering of IFNα-induced apoptosis by transfecting KB cells with a plasmid encoding for a wild type form of JNK1 (JNK1wt). Either the treatment of parental cells with IFNα or the overexpression of JNK1wt in transfected cells induce apoptosis and the exposure of JNK1wt-transfected cells to IFNα causes a potentiation of apoptosis. The addition of EGF to JNK1wt-transfected cells exposed to IFNα is again able to revert this effect. Therefore, the effects of EGF and IFNα on apoptosis are paralleled by changes of the activity of the stress-inducible JNK1 that appears responsible, at least in part, for the apoptotic effects of IFNα (Caraglia et al., 1999).

A tumour suppressor gene specifically activated after a genotoxic stress is p53. Takaoka et al. have recently shown that transcription of the p53 gene is induced by IFNα/β, accompanied by an increase in p53 protein level. IFNα/β signaling itself does not activate p53; rather, it contributes to boosting p53 responses to stress signals. In these experimental conditions p53 gene induction by IFNα/β contributes to tumour suppression, is activated in virally infected cells to evoke an apoptotic response and is critical for antiviral defence of the host (Takaoka et al., 2003). The role of NF-κB in the apoptosis induced by IFNα is controversial. In fact, it has been demonstrated that IFNα can activate NF-κB through STAT3 and via phosphatidyl-inositol 3 kinase (PI3K) and Akt activation in lymphoma cells and promotes survival of human primary B-lymphocytes via PI3K (Yang et al., 2001). Other studies demonstrate that IFNα sensitizes human hepatoma cells to TRAIL-induced apoptosis through DR5 upregulation and NF-κB inactivation or suppresses the antiapoptotic effect of NF-κB and sensitizes renal cell carcinoma cells in vitro to chemotherapeutic drugs (Steiner et al., 2001; Shigeno et al., 2003).

THE PROTEIN SYNTHESIS AS A TARGET OF IFNα ACTION

  1. Top of page
  2. Abstract
  3. THE INTERFERON SUPERFAMILY
  4. MECHANISMS OF CELL GROWTH INHIBITION BY IFNα: APOPTOSIS
  5. THE PROTEIN SYNTHESIS AS A TARGET OF IFNα ACTION
  6. THE MODULATION OF PROTEIN DEGRADATION
  7. ESCAPE MECHANISMS TO ANTI-PROLIFERATIVE EFFECTS OF IFNα
  8. PERSPECTIVES AND FUTURE DIRECTIONS
  9. LITERATURE CITED

In the past years, the attention of scientists has focused mainly on the study of the genetic information and alterations that regulate eukaryotic cell proliferation and that lead to neoplastic transformation. All therapeutic strategies against cancer are, to date, directed at DNA either with cytotoxic drugs or gene therapy. Little or no interest has been aroused by protein synthesis mechanisms. However, an increasing body of data is emerging about the involvement of translational processes and factors in control of cell proliferation, indicating that protein synthesis can be an additional target for anticancer strategies (for a review see Caraglia et al., 2000). One of the more studied molecular targets of IFNα is the protein kinase dependent from dsRNA, PKR. PKR activation induced by the cytokine regulates translational and transcriptional pathways (eIF-2a and NF-κB-dependent) resulting in the specific expression of selected proteins (Fas, p53, Bax, and others) that triggered cell death by engaging with the caspase pathway. Through an unknown mechanism, upon PKR activation, FADD recruits procaspase 8, activating it to its active form, caspase 8 that, in turn, activates down-stream caspases such as caspase 3, 6, 7, which cleave multiple targets triggering cell death. The role of the caspase 9 pathway in these events is unknown (Gil and Esteban, 2000).

The eukaryotic initiation factor-5A of protein synthesis (eIF-5A)

The eukaryotic initiation factor 5A (eIF-5A) is peculiar because its activity is modulated by a series of post-translational modifications that culminates in the formation of the unusual amino acid hypusine. Hypusine [Nε-(4-amino-2-hydroxybutyl)lysine] is formed by the transfer of the butylamine portion from spermidine to the ε-amino group of a specific lysine residue of eIF-5A precursor (Wolff et al., 1990) and by the subsequent hydroxylation at carbon 2 of the incoming 4-aminobutyl moiety (Abbruzzese et al., 1986; Park et al., 1993). eIF-5A probably acts in the final stage of the initiation phase of protein synthesis by promoting the formation of the first peptide bond (Hershey, 1991). Hypusine plays a key role in the regulation of eIF-5A function because its precursors, which do not contain hypusine do not have activity (Park et al., 1991). These biochemical correlates make eIF-5A peculiar. In fact, only the hypusine-containing eIF-5A form is active and, consequently, the dosage of intracellular hypusine content measures also the activity of eIF-5A since hypusine is contained only in this factor. The correlation between hypusine, and thus eIF-5A activity, and cell proliferation (Abbruzzese, 1988) suggests that activated eIF-5A might play a role in cell growth and differentiation (Shnier et al., 1991). More recently a correlation has been found between the polyamine-dependent modification of eIF-5A and the triggering of apoptosis in tumour cells (Abbruzzese et al., 1989). In fact, excess putrescine accumulation in hepatoma tissue culture DH23A/b cells induces apoptosis and suppresses the formation of hypusine-containing eIF-5A (Abbruzzese et al., 1989). Furthermore, we have evidenced an in vitro post-translational modification of eIF-5A catalyzed by tissue transglutaminase (tTG) (Beninati et al., 1998) that is involved in apoptosis regulation and if stably transfected in Balb-C 3T3 cells strongly reduces hypusine levels. These effects occurred together with a significant reduction of cell proliferation and apoptosis (Beninati et al., 1998). We have reported that IFNα induces growth inhibition and reduction of the activity of eIF-5A in human epidermoid cancer KB cells (Caraglia et al., 1997). The activity of eIF-5A was evaluated through the determination of hypusine levels since this amino acid is essential for the function of this translational factor that is involved in the regulation of cell proliferation and transformation (Caraglia et al., 1997). The cell proliferation regulatory properties of eIF-5A could be correlated by its reported mRNA chaperon functions since eIF-5A is involved in the transport of mRNAs from the nucleus to the cytoplasm (Lipowsky et al., 2000). It has been also proposed that these mRNAs could encode for proteins involved in the regulation of cell proliferation (Caraglia et al., 2000). We have, moreover, found that IFNα induces cell growth inhibition and apoptosis in human epidermoid cancer cells and these effects are antagonized by EGF. We also found that IFNα is able to induce a strong inhibition of eIF-5A activity since a reduction of hypusine synthesis is recorded with a parallel increase of eIF-5A protein expression. This finding suggests a further reduction of the active fraction of eIF-5A (hypusine-containing eIF-5A:total eIF-5A ratio). On the other hand, when EGF antagonized the apoptosis induced by IFNα a restoration of hypusine synthesis caused by the cytokine and an increase of erk activity are recorded in cancer cells. In the same experimental conditions, we have also found that PD098059, a specific inhibitor of MEK-1 and thus of erk, reduces hypusine synthesis and enhanced the decrease of intracellular hypusine content caused by IFNα (Caraglia et al., 2003a,b). Moreover, PD098059 is also able to antagonize the recovery of hypusine synthesis induced by EGF (Caraglia et al., 2003a,b). The reduction of hypusine synthesis could be even higher if tumour cells treated with IFNα did not show an antiapoptotic response based on the hyperactivation of the MEK[RIGHTWARDS ARROW]ERK pathway. Therefore, the addition of PD098059 to IFNα-pretreated cells overcome this survival pathway inducing a potentiation of both hypusine level reduction and apoptosis. On the other hand, the addition of EGF to IFNα-treated cells overstimulated this survival pathway inducing a recovery of both hypusine levels and apoptosis (Caraglia et al., 2003a,b). On the basis of these results, we have investigated if eIF-5A could be really critical for the biological effects induced by IFNα. We have used the specific deoxyhypusine synthase inhibitor N1-guanyl-1,7-diaminoheptane (GC7) that avoids hypusine formation and thus blocks eIF-5A activity (Lee and Park, 2000). We have found that this agent synergized with IFNα in inducing cell growth inhibition and apoptosis suggesting a critical role for eIF-5A in the modulation of cell proliferation induced by IFNα in human epidermoid cancer cells (Caraglia et al., 2003a,b). All these data support the hypothesis of an involvement of eIF-5A, another protein synthesis regulator, in the apoptosis induced by IFNα in human epithelial cells.

THE MODULATION OF PROTEIN DEGRADATION

  1. Top of page
  2. Abstract
  3. THE INTERFERON SUPERFAMILY
  4. MECHANISMS OF CELL GROWTH INHIBITION BY IFNα: APOPTOSIS
  5. THE PROTEIN SYNTHESIS AS A TARGET OF IFNα ACTION
  6. THE MODULATION OF PROTEIN DEGRADATION
  7. ESCAPE MECHANISMS TO ANTI-PROLIFERATIVE EFFECTS OF IFNα
  8. PERSPECTIVES AND FUTURE DIRECTIONS
  9. LITERATURE CITED

The proteasome is a multisubunit enzyme complex that plays a central role in the regulation of proteins that control cell-cycle progression and apoptosis, and has therefore become an important target for anticancer therapy. In fact, the expression of proteins essential for the regulation of cell growth and survival can be also controlled at post-trascriptional and post-translational levels, the latter through the regulation of protein degradation. Before a protein is degraded, it is first flagged for destruction by the ubiquitin conjugation system, which ultimately results in the attachment of a polyubiquitin chain on the target protein. The proteasome's 19S regulatory cap binds the polyubiquitin chain, denatures the protein, and feeds the protein into the proteasome's proteolytic core. The proteolytic core is composed of two inner beta rings and two outer alpha rings. The two beta rings each contain three proteolytic sites named for their trypsin-like, post-glutamyl peptide hydrolase-like (i.e., caspase-like), or chymotrypsin-like activity. Inhibition of the proteasome generally results in cell-cycle arrest and apoptosis (for a review see Adams, 2003). Since 1996 it has been demonstrated that type I IFNs (IFNτ) can regulate the expression of a 16-kDa protein that is produced by the bovine endometrium during early pregnancy and that shares epitopes with hUCRP and ubiquitin (Austin et al., 1996). These results were confirmed by a study performed with metabolic labeling and two-dimensional gel electrophoresis followed by MS and database searches to identify potentially new IFNα-induced proteins in human T cells. By this analysis, it was shown that IFNα induces the expression of ubiquitin cross-reactive protein (ISG15) and two ubiquitin-conjugating enzymes, UbcH5 and UbcH8. Northern-blot analysis showed that IFNα rapidly enhances mRNA expression of UbcH5, UbcH6, and UbcH8 in T cells. In addition, these genes were induced in macrophages in response to IFNα. Similarly, IFNs enhanced UbcH8 mRNA expression in A549 lung epithelial cells, HepG2 hepatoma cells, and NK-92 cells. Cycloheximide, a protein synthesis inhibitor, did not block IFN-induced upregulation of UbcH8 mRNA expression, suggesting that UbcH8 is the primary target gene for IFNα (Nyman et al., 2000). More recently, it was demonstrated that administration of interleukin 1β (IL-1β) in vivo attenuates IFNα-induced STAT1 tyrosine phosphorylation in the liver but not in the spleen. The inhibitory action of IL-1β in vivo is not affected by depleting hepatic Kupffer cells, suggesting that IL-1β may directly target IFNα signaling in hepatocytes. Indeed, pretreatment of human hepatocellular carcinoma HepG2 cells with IL-1β suppresses IFNα-induced antiviral activity and protein MxA mRNA expression. Furthermore, IL-1β attenuated IFNα-induced STAT1 binding and tyrosine phosphorylation without affecting the level of STAT1 protein. This inhibitory effect can be reversed by pretreatment with either proteasome inhibitors or transfection of dominant negative NF-κB inducing kinase mutants. Taken together, these findings suggest that IL-1β attenuates IFNα-induced STAT1 activation by a proteasome-dependent mechanism (Tian et al., 2000). Moreover, we have recently found that IFNα induces apoptosis through, at least in part, the increase of the expression and activity of tTGase in human epidermoid lung cancer cells (Esposito et al., 2003). The increase of the expression of tTGase was not due to the induction of its transcription, but to a decrease of its degradation via a proteasome-dependent pathway. Therefore, IFNα modulates apoptosis through the regulation of the degradation of intracellular proteins involved in the triggering of apoptotic process. Not only the target of the IFNα-dependent signaling but also the components of the pathway activated by the cytokine itself can be subjected to regulation via proteasome-dependent degradation. In fact, Mumps virus, a common infectious agent of humans, causing parotitis, meningitis, encephalitis, and orchitis, induces degradation of STAT3 mediated by its ubiquitination and subsequent proteasome-dependent degradation (Ulane et al., 2003). The latter could be a mechanism by which viruses protect themselves by the anti-viral action of IFNα. Finally, one of the modes used by SOCS to turn off the IFNα-dependent signaling is the delivery of the transductional components to the degradative proteosomal machinery (Larsen and Ropke, 2002).

ESCAPE MECHANISMS TO ANTI-PROLIFERATIVE EFFECTS OF IFNα

  1. Top of page
  2. Abstract
  3. THE INTERFERON SUPERFAMILY
  4. MECHANISMS OF CELL GROWTH INHIBITION BY IFNα: APOPTOSIS
  5. THE PROTEIN SYNTHESIS AS A TARGET OF IFNα ACTION
  6. THE MODULATION OF PROTEIN DEGRADATION
  7. ESCAPE MECHANISMS TO ANTI-PROLIFERATIVE EFFECTS OF IFNα
  8. PERSPECTIVES AND FUTURE DIRECTIONS
  9. LITERATURE CITED

Until today inconsistent data have been obtained regarding the clinical effectiveness of IFNα in the therapy of solid tumors. In fact, the benefit of IFNα treatment is limited to some neoplasms while others are completely or partially resistant. The mechanisms of tumor resistance to IFNα have been studied in deep in vitro. The alteration of JAK-STAT components of the IFNα-induced signaling, can be indeed a mechanism of resistance to IFNα. In fact, an old issue that has been associated to the resistance of tumour cells to the biological effects of IFNα is the disruption of its signal transduction pathways based on the altered expression of STAT proteins in several cancer cell types (Wong et al., 1997; Landolfo et al., 2000; Yamauchi et al., 2001; Brinckmann et al., 2002). In details, it has been shown that melanoma cell lines refractory to the antiproliferative effects of IFNs are deficient in STATs and that the expression of STATs can be restored by in vitro gene therapy (Wong et al., 1997). Analogous effects were demonstrated on myeloid leukemic and renal carcinoma cells (Yamauchi et al., 2001; Brinckmann et al., 2002).

However, recent data have demonstrated that the JAK/STAT pathway is not sufficient to sustain the antiproliferative response in an interferon-resistant human melanoma cell line. Additional studies confirm that STAT1 and STAT3 expression and IFNα induction and activation are not altered between both variants. (Jackson et al., 2003). DNA microarrays performed on two T cell lymphoma lines (resistant or sensitive to IFNα) showed that resistance to IFNα is consistently associated with changes in the expression of a set of 39 genes, involved in signal transduction, apoptosis, transcription regulation, and cell growth (Tracey et al., 2002). These results highlight the likely heterogeneity in the mechanisms leading to interferon resistance both in cell lines and tumours.

Beside these mechanisms of resistance towards the growth inhibitory and apoptotic activity of IFNα, also the triggering and/or hyperactivation of survival and proliferative pathways can be supposed in cancer cells. This hypothesis is furtherly supported by the evident disregulation of proliferative signaling in transformed cells. In this view, we have reported that IFNα increases the expression and function of the EGF-R at the surface of human epidermoid carcinoma cells (Budillon et al., 1991; Caraglia et al., 1995). On the basis of these findings, we have hypothesized that increased EGF-R expression and function could be part of an inducible survival pathway, which is activated in the tumour cells by the exposure to IFNα (Tagliaferri et al., 1994). Moreover, we have found that the addition of EGF to IFNα-treated KB cells completely antagonized apoptosis induction suggesting that the EGF-R signaling suppresses apoptosis (Caraglia et al., 1999) (Fig. 2). These results appear also in line with the recent findings demonstrating the involvement of growth factor-dependent pathways in the protection from caspase activation induced by Bad overexpression (Jan et al., 1999). Moreover, it has been demonstrated that the EGF-R-dependent pathway controls keratinocyte survival and the expression of the pro-apoptotic bcl-xL through a MEK-dependent pathway (Jan et al., 1999).

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Figure 2. Escape mechanisms to anti-tumor effects by IFNα and proposed overcoming strategies. Left: IFNα induces apoptosis likely through the activation of caspase cascade mediated by JNK-1 and/or p38MAPK activation and through the mitochondrial involvement. Right: EGF triggers a ras-dependent ERK-1/2 activation that inhibits IFNα-induced apoptosis probably counteracting on caspase cascade activation. Moreover, ERK-1/2 has also a stimulating action on the activity of eIF-5A that displays anti-apoptotic activities. The inhibition of this pathway through the use of the EGF-R-associated tyrosine kinase inhibitor ZD1839 or the dominant negative ras RASN17 or FTIs or the MEK-1 inhibitor PD098059 induces the release of this anti-apoptotic pathway with the subsequent potentiation of the apoptosis induced by IFNα. Moreover, the selective inhibition of eIF-5A with the hypusine synthesis inhibitor GC7 or with other specific inhibitors to be found could enhance the apoptotic properties of IFNα. The inhibition of the feed back mechanisms of the IFNα-dependent pathway could be an additional strategy in order to enhance anti-neoplastic effects of the cytokine. [RIGHTWARDS ARROW] Stimulating activity. equation image Inhibiting activity. Red squares show the possibilities of therapeutic interventions in order to increase the antiproliferative activity of IFNα. EGF, epidermal growth factor; EGF-R, EGF receptor; FTI, farnesyltransferase inhibitor; RASN17, dominant negative ras plasmid; TCF, ternary complex factor; Erk, extracellular signal regulated kinase; Mek, mitogen extracellular signal regulated kinase; eIF-5A, eukaryotic initiation factor of protein synthesis 5A; GC7, 1,7-diaminoheptane; JNK-1, Jun kinase-1; p38 MAPK, p38 mitogen activated protein kinase.

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Furthermore, the EGF- and Ras-dependent MAPK cascade is hyperactivated in IFNα-treated cells and could be further stimulated by the addition of EGF. In these experimental conditions, an increased activity and responsiveness to EGF stimulation of Ras, Raf-1, and Erk-1 and 2 was found in KB cells exposed to IFNα (Caraglia et al., 2003a,b). These findings suggest that the EGF-R function is preserved in IFNα-treated cells. We have previously described that other anti-proliferative agents, such as cytosine arabinoside, 5aza-2′ deoxycytidine and 8-chloro-cAMP (8ClcAMP), also increase EGF-R expression on KB cells (Caraglia et al., 1993, 1994; Budillon et al., 1999). On this basis, we have hypothesized that the up-regulation of growth factor receptors is a common event in growth inhibited tumor cells and could represent a protective response towards the antiproliferative stimuli (Tagliaferri et al., 1994). Also in the case of 8ClcAMP, the EGF-induced MAPK signaling is amplified likely as a consequence of the increased expression of EGF-R (Budillon et al., 1999). However, MAPK activity is reduced in 8Cl-cAMP-treated KB cells suggesting a selective inhibition of Erks or of a still unknown upstream activator induced by the drug (Budillon et al., 1999). The involvement of the Ras[RIGHTWARDS ARROW]MAPK pathway in the protection of KB cells from the apoptosis induced by IFNα is further demonstrated by both Ras inactivation by RASN17 transfection and MEK-1 inhibition by exposure to PD098059 (Caraglia et al., 2003a,b). In fact, the transfection of RASN17 in KB cells caused apoptosis suggesting that the integrity of Ras function is necessary to produce an anti-apoptotic signal that mediates a survival response in cells exposed to IFNα via Erk-1 and 2 activation. In fact, we have demonstrated that Ras-dependent survival signaling targets Erk-1/2 since the reduction of MAPK activity by PD098059 enhanced apoptosis caused by IFNα. An additional important finding is that PD098059 specifically abrogated the recovery from apoptosis induced by EGF in IFNα-treated cells. Therefore, our results suggest that the activation of Ras[RIGHTWARDS ARROW]Raf-1[RIGHTWARDS ARROW]Mek1[RIGHTWARDS ARROW]Erk-1/2 signaling has a prominent role in the anti-apoptotic effects exerted by EGF in epidermoid cancer cells exposed to IFNα providing evidence of the potential benefits of the molecular interference with this pathway (Caraglia et al., 2003a,b) (Fig. 2). However, the occurrence of other survival pathways will warrant further investigations and we can not presently completely exclude a role of Akt pathway in the modulation of apoptosis of KB cells. We have recently found a cross-talk between ras[RIGHTWARDS ARROW]erk-dependent pathway and protein synthesis machinery. In details EGF induces increased ras and erk activity and enhanced hypusine synthesis. IFNα, on the other hand, reduces the intracellular hypusine levels and this effect is antagonized by EGF (Caraglia et al., 2003a,b). The involvement of erk in the antagonizing effect of EGF is demonstrated by the concomitant addition of the erk inhibitor PD098051 that, alone, induces apoptosis and reduces hypusine levels and when used in combination with IFNα, synergizes with the latter in inducing such biological and biochemical effects. Therefore, the regulation of eIF-5A activity and, consequently, of the efficiency and specificity of protein synthesis machinery could represent a further mechanism by which ras[RIGHTWARDS ARROW]erk-dependent pathway counteracts apoptotic and antiproliferative effects induced by IFNα in cancer cells (Caraglia et al., 2003a,b) (Fig. 2). Other mechanisms of resistance can be supposed to be based on the intrinsic properties of the IFNα-dependent signal transduction pathway and on its capacity to interact with other signal transduction pathways often involved in cell survival. In fact, as described above, IFNα can activate Akt via STAT3 and PI3K and the consequent survival signaling that leads to the activation of NFκB in lymphoma cells (Constantinescu et al., 1994; Mullersman and Pfeffer, 1994; Franke et al., 1995; Pfeffer et al., 1997; Yang et al., 1998). Moreover, a hyperactivation of the feed back mechanisms could occur in cancer cells and induce the occurrence of resistance to IFNα.

PERSPECTIVES AND FUTURE DIRECTIONS

  1. Top of page
  2. Abstract
  3. THE INTERFERON SUPERFAMILY
  4. MECHANISMS OF CELL GROWTH INHIBITION BY IFNα: APOPTOSIS
  5. THE PROTEIN SYNTHESIS AS A TARGET OF IFNα ACTION
  6. THE MODULATION OF PROTEIN DEGRADATION
  7. ESCAPE MECHANISMS TO ANTI-PROLIFERATIVE EFFECTS OF IFNα
  8. PERSPECTIVES AND FUTURE DIRECTIONS
  9. LITERATURE CITED

More germane to clinical practice is the possibility that IFNα treatment could be improved by the concomitant administration of agents known to enhance JAK-STAT responses; the use of retinoids in combination to IFNα in cancer therapy is a salient example (Harvat et al., 1997; Ransohoff, 1998). However, on the basis of our previous findings, three different therapeutic strategies are under preclinical investigation in order to increase the anti-cancer activity of IFNα. On the basis of the involvement of stress kinases in the apoptotic effects triggered by IFNα, experiments are in progress in order to construct viral vectors of JNKs to be used in combination with the cytokine in experimental preclinical models (Caraglia et al., 1999) (Fig. 2). Moreover, we have also identified in epidermoid cancer cells a specific pathway that is activated in response to apoptotic stimuli induced by IFNα. In details, we have demonstrated that the hyperactivation of ras and erk pathway dependent from tyrosine kinase activity of EGF-R is a strong antiapoptotic pathway in cancer cells exposed to IFNα (Caraglia et al., 2003a,b). Therefore, the selective inhibition of a suspected target of this pathway could be an interesting strategy in the chemoprevention of human tumor. In this view, we have preliminarily found that the specific EGF-R-associated kinase inhibitor ZD1839 (IRESSA), already used in phase II/III clinical trials in the therapy of lung epidemoid cancer, synergizes with IFNα in inducing the growth inhibition and apoptosis of several human epidermoid cancer cell lines which is coupled to complete inhibition of ras and erk activity (Budillon et al., manuscript in preparation). Moreover, the selective inhibition of ras with gene transfer therapeutic strategies based on the delivery of dominant negative forms of ras such as RASN17 or with agents that block ras farnesylation such as the farnesyl-transferase inhibitors (FTI) could be also considered in order to enhance the antiproliferative action of IFNα. MEK-1 and consequently the activation of ERK-1/2 could be also evaluated as additional target through the use of selective inhibitors such as PD098059. Finally, on the basis of the previous findings, we can also hypothesize that the selective interference on eIF-5A activity could be an additional target in order to potentiate the antitumor efficacy of IFNα. In fact, we have found that the hypusine synthesis inhibitors, and thus eIF-5A inactivator, GC7 synergizes with the cytokine in the induction of cell growth inhibition and apoptosis (Caraglia et al., 2003a,b). We have recently performed a computer-based prediction of the three dimensional structure of eIF-5A in order to define the structure of the hypusine-containing site (Facchiano et al., 2001). We are now planning a pharmacological screening of drugs with potential eIF-5A-inhibiting properties. The inhibition of eIF-5A either through the blocking of hypusine synthesis (mediated by agents similar to GC7) or the selective binding with the hypusine-containing site could represent a new scenario of intervention in anti-cancer therapy based on IFNα administration (Fig. 2).

In conclusion, the understanding of the molecular mechanisms regulating the signal transduction pathway mediated by IFNα and of the escape mechanisms activated in cancer cells could be useful in the design of new therapeutic strategies based on the use of IFNα and in order to widen the therapeutic window of this cytokine (Fig. 2).

LITERATURE CITED

  1. Top of page
  2. Abstract
  3. THE INTERFERON SUPERFAMILY
  4. MECHANISMS OF CELL GROWTH INHIBITION BY IFNα: APOPTOSIS
  5. THE PROTEIN SYNTHESIS AS A TARGET OF IFNα ACTION
  6. THE MODULATION OF PROTEIN DEGRADATION
  7. ESCAPE MECHANISMS TO ANTI-PROLIFERATIVE EFFECTS OF IFNα
  8. PERSPECTIVES AND FUTURE DIRECTIONS
  9. LITERATURE CITED
  • Abbruzzese A. 1988. Developmental pattern for deoxyhypusine hydroxylase in rat brain. J Neurochem 50: 695699.
  • Abbruzzese A, Park MH, Folk JE. 1986. Deoxyhypusine hydroxylase from rat testis. Partial purification and characterization. J Biol Chem 261: 30853089.
  • Abbruzzese A, Park MH, Beninati S, Folk JE. 1989. Inhibition of deoxyhypusine hydroxylase by polyamines and by a deoxyhypusine peptide. Biochem Biophys Acta 997: 248255.
  • Adams J. 2003. The proteasome: Structure, function, and role in the cell. Cancer Treat Rev 29: 39.
  • Arora T, Floyd-Smith G, Espy MJ, Jelinek DF. 1999. Dissociation between IFN-alpha-induced anti-viral and growth signalling pathways. J Immunol 162: 32893297.
  • Austin KJ, Ward SK, Teixeira MG, Dean VC, Moore DW, Hansen TR. 1996. Ubiquitin cross-reactive protein is released by the bovine uterus in response to interferon during early pregnancy. Biol Reprod 54: 600606.
  • Barahmand-pour F, Meinke A, Eilers A, Gouilleux F, Groner B, Decker T. 1995. Colony-stimulating factors and interferon-gamma activate a protein related to MGF-Stat 5 to cause formation of the differentiation-induced factor in myeloid cells. FEBS Lett 360: 2933.
  • Bazan JF. 1990a. Shared architecture of hormone binding domains in type I and II interferon receptors. Cell 61: 753754.
  • Bazan JF. 1990b. Structural design and molecular evolution of a cytokine receptor superfamily. Proc Natl Acad Sci USA 87: 69346938.
  • Beadling C, Guschin D, Witthuhn BA, Ziemiecki A, Ihle JN, Kerr IM, Cantrell DA. 1994. Activation of JAK kinases and STAT proteins by interleukin-2 and interferon alpha, but not the T cell antigen receptor, in human T lymphocytes. EMBO J 13: 56055615.
  • Beninati S, Gentile V, Caraglia M, Lentini A, Tagliaferri P, Abbruzzese A. 1998. Tissue transglutaminase expression affects hypusine metabolism in BALB/c 3T3 cells. FEBS Lett 437: 3438.
  • Brinckmann A, Axer S, Jakschies D, Dallmann I, Grosse J, Patzelt T, Bernier T, Emmendoerffer A, Atzpodien J. 2002. Interferon-alpha resistance in renal carcinoma cells is associated with defective induction of signal transducer and activator of transcription 1 which can be restored by a supernatant of phorbol 12-myristate 13-acetate stimulated peripheral blood mononuclear cells. Br J Cancer 86: 449455.
  • Bromberg JF. 2001. Activation of STAT proteins and growth control. Bioassays 23: 161169.
  • Bromberg JF, Horvath CM, Besser D, Lathem WW, Darnell JE Jr. 1998. Stat3 activation is required for cellular transformation by v-src. Mol Cell Biol 18: 25532558.
  • Brunet A, Bonni A, Zigmond MJ, Lin MZ, Juo P, Hu LS, Anderson MJ, Arden KC, Blenis J, Greenberg ME. 1999. Akt promotes cell survival by phosphorylating and inhibiting a forkhead transcription factor. Cell 96: 857868.
  • Budillon A, Tagliaferri P, Caraglia M, Torrisi MR, Normanno N, Iacobelli S, Palmieri G, Stoppelli MP, Frati L, Bianco AR. 1991. Upregulation of epidermal growth factor receptor induced by alpha-interferon in human epidermoid cancer cells. Cancer Res 51: 12941299.
  • Budillon A, Di Gennaro E, Caraglia M, Barbarulo D, Abbruzzese A, Tagliaferri P. 1999. 8-Cl-cAMP antagonizes mitogen-activated protein kinase activation and cell growth stimulation induced by epidermal growth factor. Br J Cancer 81: 11341141.
  • Buechner SA, Wernli M, Harr T, Hahn S, Itin P, Erb P. 1997. Regression of basal cell carcinoma by intralesional interferon-alpha treatment is mediated by CD95 (Apo-1/Fas)-CD95 ligand-induced suicide. J Clin Investig 100: 26912696.
  • Burgering BMT, Coffer PJ. 1995. Protein kinase B (c-Akt) in phosphatidylinositol-3-OH kinase signal transduction. Nature 376: 599602.
  • Cai J, Jones DP. 1998. Superoxide in apoptosis. Mitochondrial generation triggered by cytochrome c loss. J Biol Chem 273: 1140111404.
  • Caraglia M, Tagliaferri P, Correale P, Genua G, Pepe S, Pinto A, Del Vecchio S, Esposito G, Bianco AR. 1993. Cytosine arabinoside increases the binding of 125I-labelled epidermal growth factor and 125I-transferrin and enhances the in vitro targeting of human tumour cells with anti-(growth factor receptor) mAb. Cancer Immunol Immunother 37: 150156.
  • Caraglia M, Pinto A, Correale P, Zagonel V, Genua G, Leardi A, Pepe S, Bianco AR, Tagliaferri P. 1994. 5-Aza-2′-deoxycytidine induces growth inhibition and upregulation of epidermal growth factor receptor on human epithelial cancer cells. Ann Oncol 5: 269276.
  • Caraglia M, Leardi A, Corradino S, Ciardiello F, Budillon A, Guarrasi R, Bianco AR, Tagliaferri P. 1995. alpha-interferon potentiates epidermal growth factor receptor-mediated effects on human epidermoid carcinoma KB cells. Int J Cancer 61: 342347.
  • Caraglia M, Passeggio A, Beninati S, Leardi A, Nicolini L, Improta S, Pinto A, Bianco AR, Tagliaferri P, Abbruzzese A. 1997. Interferon alpha2 recombinant and epidermal growth factor modulate proliferation and hypusine synthesis in human epidermoid cancer KB cells. Biochem J 324: 737741.
  • Caraglia M, Abbruzzese A, Leardi A, Pepe S, Budillon A, Baldassarre G, Selleri C, De Lorenzo S, Fabbrocini A, Giuberti G, Vitale G, Lupoli G, Bianco AR, Tagliaferri P. 1999. Interferon-alpha induces apoptosis in human KB cells through a stress-dependent mitogen activated protein kinase pathway that is antagonized by epidermal growth factor. Cell Death Differ 6: 773780.
  • Caraglia M, Budillon A, Vitale G, Lupoli G, Tagliaferri P, Abbruzzese A. 2000. Modulation of molecular mechanisms involved in protein synthesis machinery as a new tool for the control of cell proliferation. Eur J Biochem 267: 39193936.
  • Caraglia M, Marra M, Giuberti G, D'Alessandro AM, Tassone P, Venuta S, Tagliaferri P, Abbruzzese A. 2003a. The eukaryotic initiation factor 5A is involved in the regulation of proliferation and apoptosis induced by interferon-alpha and EGF in human cancer cells. J Biochem 133: 757765.
  • Caraglia M, Tagliaferri P, Marra M, Giuberti G, Budillon A, Di Gennaro E, Pepe S, Vitale G, Improta S, Tassone PF, Venuta S, Bianco AR, Abbruzzese A. 2003b. EGF activates an inducible survival response via the RAS[RIGHTWARDS ARROW]Erk-1/2 pathway to counteract interferon-alpha-mediated apoptosis in epidermoid cancer cells. Cell Death Differ 10: 218229.
  • Cardone MH, Roy N, Stennicke HR, Salvesen GS, Franke TF, Stanbridge E, Frisch S, Reed JC. 1998. Regulation of cell death protease caspase-9 by phosphorylation. Science 282: 13181321.
  • Chawla-Sarkar M, Leaman DW, Borden EC. 2001. Preferential induction of apoptosis by interferon (IFN)-beta compared with IFN-alpha2: Correlation with TRAIL/Apo2L induction in melanoma cell lines. Clin Cancer Res 7: 18211831.
  • Colamonici OR, Uyttendaele H, Domanski P, Yan H, Krolewski JJ. 1994a. p135tyk2, an interferon-alpha-activated tyrosine kinase, is physically associated with an interferon-alpha receptor. J Biol Chem 269: 35183522.
  • Colamonici OR, Yan H, Domanski P, Handa R, Smalley D, Mullersman J, Witte M, Krishnan K, Krolewski JJ. 1994b. Direct binding to and tyrosine phosphorylation of the alpha subunit of the type I interferon receptor by p135tyk2 tyrosine kinase. Mol Cell Biol 14: 81338142.
  • Constantinescu SN, Croze E, Wang C, Murti A, Basu L, Mullersman JE, Pfeffer LM. 1994. Role of interferon alpha/beta receptor chain 1 in the structure and transmembrane signaling of the interferon alpha/beta receptor complex. Proc Natl Acad Sci USA 91: 96029606.
  • Copeland NG, Gilbert DJ, Schindler C, Zhong Z, Wen Z, Darnell JE Jr, Mui AL, Miyajima A, Quelle FW, Ihle JN. 1995. Distribution of the mammalian Stat gene family in mouse chromosomes. Genomics 29: 225228.
  • Dai C, Krantz SB. 1999. Interferon gamma induces upregulation and activation of caspases 1, 3, and 8 to produce apoptosis in human erythroid progenitor cells. Blood 93: 33093316.
  • Darnell JE Jr. 1997. STATs and gene regulation. Science 277: 16301635.
  • Darnell JE, Kerr IM, Stark GR. 1994. Jak-STAT pathways and transcriptional activation in response to IFNs and other extracellular signaling proteins. Science 264: 14151421.
  • Datta SR, Dudek H, Tao X, Masters S, Fu H, Gotoh Y, Greenberg ME. 1997. Akt phosphorylation of BAD couples survival signals to the cell-intrinsic death machinery. Cell 91: 231241.
  • David M, Petricoin E 3rd, Benjamin C, Pine R, Weber MJ, Larner AC. 1995. Requirement for MAP kinase (ERK2) activity in interferon alpha- and interferon beta-stimulated gene expression through STAT proteins. Science 269: 17211723.
  • Duncan SA, Zhong Z, Wen Z, Darnell JE. 1997. STAT signaling is active during early mammalian development. Dev Dyn 208: 190198.
  • Durbin JE, Hackenmiller R, Simon MC, Levy DE. 1996. Targeted disruption of the mouse Stat1 gene results in compromised innate immunity to viral disease. Cell 84: 443450.
  • Eilers A, Baccarini M, Hipskind RA, Schindler C, Decker T. 1994. A factor induced by differentiation signals in cells of the macrophage lineage binds to the gamma interferon activation site. Mol Cell Biol 14: 13641373.
  • Esposito C, Marra M, Giuberti G, D'Alessandro AM, Porta R, Cozzolino A, Caraglia M, Abbruzzese A. 2003. Ubiquitination of tissue transglutaminase is modulated by interferon alpha in human lung cancer cells. Biochem J 370: 205212.
  • Facchiano AM, Stiuso P, Chiusano ML, Caraglia M, Giuberti G, Marra M, Abbruzzese A, Colonna G. 2001. Homology modelling of the human eukaryotic initiation factor 5A (eIF-5A). Protein Eng 14: 881890.
  • Feldman GM, Rosenthal LA, Liu X, Hayes MP, Wynshaw-Boris A, Leonard WJ, Hennighausen L, Finbloom DS. 1997. STAT5A-deficient mice demonstrate a defect in granulocyte-macrophage colony-stimulating factor-induced proliferation and gene expression. Blood 90: 17681776.
  • Fish EN, Uddin S, Korkmaz M, Majchrzak B, Druker BJ, Platanias LC. 1999. Activation of a CrkL-stat5 signaling complex by type I interferons. J Biol Chem 274: 571573.
  • Franke TF, Yang S-I, Chan TO, Datta K, Kazlaukas A, Morrison DK, Kaplan DR, Tsichlis PN. 1995. The protein kinase encoded by the Akt proto-oncogene is a target of the PDGF-activated phosphatidylinositol 3-kinase. Cell 81: 727736.
  • Franke TF, Kaplan DR, Cantley LC. 1997. PI3K: Downstream AKTion blocks apoptosis. Cell 88: 435437.
  • Fu XY. 1992. A transcription factor with SH2 and SH3 domains is directly activated by an interferon alpha-induced cytoplasmic protein tyrosine kinase(s). Cell 70: 323335.
  • Gil J, Esteban M. 2000. Induction of apoptosis by the dsRNA-dependent protein kinase (PKR): Mechanism of action. Apoptosis 5: 107114.
  • Goh KC, Haque SJ, Williams BRG. 1999. p38 MAP kinase is required for STAT1 serine phosphorylation and transcriptional activation induced by interferons. EMBO J 18: 56015609.
  • Grumbach IM, Mayer IA, Uddin S, Lekmine F, Majchrzak B, Yamauchi H, Fujita S, Druker B, Fish EN, Platanias LC. 2001. Engagement of the CrkL adaptor in interferon alpha signalling in BCR-ABL-expressing cells. Br J Haematol 112: 327336.
  • Gupta S, Yan H, Wong LH, Ralph S, Krolewski J, Schindler C. 1996. The SH2 domains of Stat1 and Stat2 mediate multiple interactions in the transduction of IFN-alpha signals. EMBO J 15: 10751084.
  • Haan S, Hemmann U, Hassiepen U, Schaper F, Schneider-Mergener J, Wollmer A, Heinrich PC, Grotzinger J. 1999. Characterization and binding specificity of the monomeric STAT3-SH2 domain. J Biol Chem 274: 13421348.
  • Harvat BL, Jetten AM, Seth P. 1997. The role of p27Kip1 in gamma interferon-mediated growth arrest of mammary epithelial cells and related defects in mammary carcinoma cells. Oncogene 14: 21112122.
  • Heim MH, Kerr IM, Stark GR, Darnell JE Jr. 1995. Contribution of STAT SH2 groups to specific interferon signaling by the Jak-STAT pathway. Science 267: 13471349.
  • Hershey JWB. 1991. Translational control in mammalian cells. Annu Rev Biochem 61: 717755.
  • Hoey T, Schindler U. 1998. STAT structure and function in signaling. Curr Opin Genet Dev 8: 582587.
  • Horvath CM, Darnell JE. 1997. The state of the STATs: Recent developments in the study of signal transduction to the nucleus. Curr Opin Cell Biol 9: 233239.
  • Horvath CM, Wen Z, Darnell JE. 1995. A STAT protein domain that determines DNA sequence recognition suggests a novel DNA-binding domain. Genes Dev 9: 984994.
  • Ihle JN. 1996. STATs: Signal transducers and activators of transcription. Cell 84: 331334.
  • Imada K, Leonard WJ. 2000. The Jak-STAT pathway. Mol Immunol 37: 111.
  • Jackson DP, Watling D, Rogers NC, Banks RE, Kerr IM, Selby PJ, Patel PM. 2003. The JAK/STAT pathway is not sufficient to sustain the antiproliferative response in an interferon-resistant human melanoma cell line. Melanoma Res 13: 219229.
  • Jan MS, Liu HS, Lin YS. 1999. Bad overexpression sensitizes NIH/3T3 cells to undergo apoptosis which involves caspase activation and ERK inactivation. Biochem Biophys Res Commun 264: 724729.
  • Kaplan MH, Schindler U, Smiley ST, Gruspy MJ. 1996. Stat6 is required for mediating responses to IL-4 and for development of Th2 cells. Immunity 4: 313319.
  • Kaplan MH, Sun Y-L, Hoey T, Grusby MJ. 1996. Impaired IL-12 responses and enhanced development of Th2 cells in Stat4-deficient mice. Nature 382: 174177.
  • Kim H, Baumann H. 1997. The carboxyl-terminal region of STAT3 controls gene induction by the mouse haptoglobin promoter. J Biol Chem 272: 1457114579.
  • Kotenko SV, Pestka S. 2000. Jak-Stat signal transduction pathway through the eyes of cytokine class II receptor complexes. Oncogene 19: 25572565.
  • Krammer PH. 2000. CD95's deadly mission in the immune system. Nature 407: 789795.
  • Landolfo S, Guarini A, Riera L, Gariglio M, Gribaudo G, Cignetti A, Cordone I, Montefusco E, Mandelli F, Foa R. 2000. Chronic myeloid leukemia cells resistant to interferon-alpha lack STAT1 expression. Hematol J 1: 714.
  • Larsen L, Ropke C. 2002. Suppressors of cytokine signalling: SOCS. APMIS 110: 833844.
  • Lee CH, Park MH. 2000. Human deoxyhypusine synthase: Interrelationship between binding of NAD and substrates. Biochem J 352: 851857.
  • Leonard WJ, O'Shea JJ. 1998. Jaks and STATs: Biological implications. Annu Rev Immunol 16: 293322.
  • Levy DE. 1999. Physiological significance of STAT proteins: Investigations through gene disruption in vivo. Cell Mol Life Sci 55: 15591567.
  • Lipowsky G, Bischoff FR, Schwarzmaier P, Kraft R, Kostka S, Hartmann E, Kutay U, Gorlich D. 2000. Exportin 4: A mediator of a novel nuclear export pathway in higher eukaryotes. EMBO J 19: 43624371.
  • Liu X, Robinson GW, Wagner KU, Garrett L, Wynshaw-Boris A, Hennighausen L. 1997. Stat5a is mandatory for adult mammary gland development and lactogenesis. Genes Dev 11: 179186.
  • Los M, Herr I, Friesen C, Fulda S, Schulze-Osthoff K, Debatin KM. 1997. Cross-resistance of CD95- and drug-induced apoptosis as a consequence of deficient activation of caspases (ICE/Ced-3 proteases). Blood 90: 31183129.
  • Lund TC, Medveczky MM, Medveczky PG. 1999. Interferon-alpha induction of STATs1, -3 DNA binding and growth arrest is independent of Lck and active mitogen-activated kinase in T cells. Cell Immunol 192: 133139.
  • Matsui W, Huff CA, Vala M, Barber J, Smith BD, Jones RJ. 2003. Anti-tumour activity of interferon-alpha in multiple myeloma: Role of interleukin 6 and tumor cell differentiation. Br J Haematol 121: 251258.
  • Mayer IA, Verma A, Grumbach IM, Uddin S, Lekmine F, Ravandi F, Majchrzak B, Fujita S, Fish EN, Platanias LC. 2001. The p38 MAPK pathway mediates the growth inhibitory effects of interferon-alpha in BCR-ABL-expressing cells. J Biol Chem 276: 2857028577.
  • Meinke A, Barahmand-Pour F, Wohrl S, Stoiber D, Decker T. 1996. Activation of different Stat5 isoforms contributes to cell-type-restricted signaling in response to interferons. Mol Cell Biol 16: 69376945.
  • Meraz MA, White JM, Sheehan KC, Bach EA, Rodig SJ, Dighe AS, Kaplan DH, Riley JK, Greenlund AC, Campbell D, Carver-Moore K, DuBois RN, Clark R, Aguet M, Schreiber RD. 1996. Targeted disruption of the Stat1 gene in mice reveals unexpected physiologic specificity in the JAK-STAT signaling pathway. Cell 84: 431442.
  • Moriggl R, Berchtold S, Friedrich K, Standke GJ, Kammer W, Heim M, Wissler M, Stocklin E, Gouilleux F, Groner B. 1997. Comparison of the transactivation domains of Stat5 and Stat6 in lymphoid cells and mammary epithelial cells. Mol Cell Biol 17: 36633678.
  • Mullersman JE, Pfeffer LM. 1994. Role of interferon alpha/beta receptor chain 1 in the structure and transmembrane signaling of the interferon alpha/beta receptor complex. Trends Biochem Sci 20: 5556.
  • Navarro A, Anand-Apte B, Tanabe Y, Feldman G, Larner AC. 2003. A PI-3 kinase-dependent, Stat1-independent signaling pathway regulates interferon-stimulated monocyte adhesion. J Leukoc Biol 73: 540545.
  • Nyman TA, Matikainen S, Sareneva T, Julkunen I, Kalkkinen N. 2000. Proteome analysis reveals ubiquitin-conjugating enzymes to be a new family of interferon-alpha-regulated genes. Eur J Biochem 267: 40114019.
  • Panaretakis T, Pokrovskaja K, Shoshan MC, Grandèr D. 2003. Interferon-alpha-induced apoptosis in U266 cells is associated with activation of the proapoptotic Bcl-2 family members Bak and Bax. Oncogene 22: 45434556.
  • Park MH, Wolff EC, Smit-McBride Z, Hershey JWB, Folk JE. 1991. Comparison of the activities of variant forms of eIF-4D. The requirement for hypusine or deoxyhypusine. J Biol Chem 266: 79887994.
  • Park MH, Wolff EC, Folk JE. 1993. Hypusine: Its post-translational formation in eukaryotic initiation factor 5A and its potential role in cellular regulation. BioFactors 4: 95104.
  • Pestka S. 1981a. Cloning of the human interferons. Methods Enzymol 78: 1632.
  • Pestka S. 1981b. Interferons. Part B. Introduction. Methods Enzymol 79: 1677.
  • Pestka S. 1986. Interferon from 1981 to 1986. Methods Enzymol 119: 1845.
  • Pestka S. 2000. The human interferon alpha species and receptors. Biopolymers (Peptide Sci) 55: 254287.
  • Pestka S, Langer JA, Zoon KC, Samuel CE. 1987. Interferons and their actions. Ann Rev Biochem 56: 727777.
  • Pfeffer LM, Mullersman JE, Pfeffer SR, Murti A, Shi W, Yang CH. 1997. STAT3 as an adapter to couple phosphatidylinositol 3-kinase to the IFNAR1 chain of the type I interferon receptor. Science 276: 14181420.
  • Puthier D, Thabard W, Rapp M, Etrillard M, Harousseau J, Bataille R, Amiot M. 2001. Interferon alpha extends the survival of human myeloma cells through an upregulation of the Mcl-1 anti-apoptotic molecule. Br J Haematol 112: 358363.
  • Ransohoff RM. 1998. Cellular responses to interferons and other cytokines: The JAK-STAT paradigm. N Engl J Med 338: 616618.
  • Raza A. 2000. Consilience across evolving dysplasias affecting myeloid, cervical, esophageal, gastric, and liver cells: Common themes and emerging patterns. Leuk Res 24: 6372.
  • Romerio F, Zella D. 2002. MEK and ERK inhibitors enhance the anti-proliferative effect of interferon-alpha2b. FASEB J 16: 16801682.
  • Romerio F, Riva A, Zella D. 2000. Interferon-alpha2b reduces phosphorylation and activity of MEK and ERK through a Ras/Raf-independent mechanism. Br J Cancer 83: 532538.
  • Roth W, Wagenknecht B, Dichgans J, Weller M. 1998. Interferon-alpha enhances CD95L-induced apoptosis of human malignant glioma cells. J Neuroimmunol 87: 121129.
  • Sadowski HB, Shuai K, Darnell JE Jr, Gilman MZ. 1993. A common nuclear signal transduction pathway activated by growth factor and cytokine receptors. Science 261: 17391744.
  • Sanceau J, Hiscott J, Delattre O, Wietzerbin J. 2000. IFN-beta induces serine phosphorylation of Stat-1 in Ewing's sarcoma cells and mediates apoptosis via induction of IRF-1 and activation of caspase-7. Oncogene 19: 33723383.
  • Sangfelt O, Erickson S, Castro J, Heiden T, Einhorn S, Grander D. 1997. Induction of apoptosis and inhibition of cell growth are independent responses to interferon-alpha in hematopoietic cell lines. Cell Growth Differ 8: 343352.
  • Schindler C, Darnell JE Jr. 1995. Transcriptional responses to polypeptide ligands: The JAK-STAT pathway. Annu Rev Biochem 64: 621651.
  • Schindler CW, Shuai K, Prezioso VR, Darnell JE Jr. 1992. Interferon-dependent tyrosine phosphorylation of a latent cytoplasmic transcription factor. Science 257: 809813.
  • Schindler U, Wu P, Rothe M, Brasseur M, Mc-Knight SL. 1995. Components of a Stat recognition code: Evidence for two layers of molecular selectivity. Immunity 2: 689697.
  • Shigeno M, Nakao K, Ichikawa T, Suzuki K, Kawakami A, Abiru S, Miyazoe S, Nakagawa Y, Ishikawa H, Hamasaki H, Nakata K, Ishii N, Eguchi K. 2003. Interferon-alpha sensitizes human hepatoma cells to TRAIL-induced apoptosis through DR5 upregulation and NF-kappa B inactivation. Oncogene 22: 16531662.
  • Shimoda K, van Deursen J, Sangster MY, Sarawar SR, Carson RT, Tripp RA, Chu C, Quelle FW, Nosaka T, Vignali DA, Doherty PC, Grosveld G, Paul WE, Ihle JN. 1996. Lack of IL-4-induced Th2 response and IgE class switching in mice with disrupted Stat6 gene. Nature 380: 630633.
  • Shnier J, Schwelberger H, Smit-McBride Z, Kang HA, Hershey JWB. 1991. Translation initiation factor 5A and its hypusine modification are essential for cell viability in the yeast Saccharomyces cerevisiae. Mol Cell Biol 11: 31053114.
  • Shuai K, Stark GR, Kerr IM, Darnell JE Jr. 1993a A single phosphotyrosine residue of Stat91 required for gene activation by interferon-gamma. Science 261: 17441746.
  • Shuai K, Ziemiecki A, Wilks AF, Harpur AG, Sadowski HB, Gilman MZ, Darnell JE. 1993b. Polypeptide signalling to the nucleus through tyrosine phosphorylation of Jak and Stat proteins. Nature 366: 580583.
  • Shuai K, Horvath CM, Huang LHT, Qureshi SA, Cowburn D, Darnell JE Jr. 1994. Interferon activation of the transcription factor Stat91 involves dimerization through SH2-phosphotyrosyl peptide interactions. Cell 76: 821828.
  • Spets H, Georgii-Hemming P, Siljason J, Nilsson K, Jernberg-Wiklund H. 1998. Fas/APO-1 (CD95)-mediated apoptosis is activated by interferon-gamma and interferon- in interleukin-6 (IL-6)-dependent and IL-6-independent multiple myeloma cell lines. Blood 92: 29142923.
  • Steiner T, Junker U, Henzgen B, Nuske K, Durum SK, Schubert J. 2001. Interferon-alpha suppresses the antiapoptotic effect of NF-κB and sensitizes renal cell carcinoma cells in vitro to chemotherapeutic drugs. Eur Urol 39: 478483.
  • Tagliaferri P, Caraglia M, Muraro R, Budillon A, Pinto A, Bianco AR. 1994. Pharmacological modulation of peptide growth factor receptor expression on tumor cells as a basis for cancer therapy. Anti-Cancer Drugs 5: 379393.
  • Takaoka A, Hayakawa S, Yanai H, Stoiber D, Negishi H, Kikuchi H, Sasaki S, Imai K, Shibue T, Honda K, Taniguchi T. 2003. Integration of interferon-alpha/beta signalling to p53 responses in tumour suppression and antiviral defence. Nature 424: 516523.
  • Takeda K, Akira S. 2000. STAT family of transcription factors in cytokine-mediated biological responses. Cytokine Growth Factor Rev 11: 199207.
  • Takeda K, Noguchi K, Shi W, Tanaka T, Matsumoto M, Yoshida N, Kishimoto T, Akira S. 1997. Targeted disruption of the mouse Stat3 gene leads to early embryonic lethality. Proc Natl Acad Sci USA 94: 38013804.
  • Thierfelder WE, van Deursen JM, Yamamoto K, Tripp RA, Sarawar SR, Carson RT, Sangster MY, Vignali DA, Doherty PC, Grosveld GC, Ihle JN. 1996. Requirement for Stat4 in interleukin-12-mediated responses of natural killer and T cells. Nature 382: 171174.
  • Thoreau E, Petridou B, Kelly PA, Djiane J, Mornon JB. 1991. Structural symmetry of the extracellular domain of the cytokine/growth hormone/prolactin receptor family and interferon receptors revealed by hydrophobic cluster analysis. FEBS Lett 282: 2631.
  • Thyrell L, Erickson S, Zhivotovsky B, Pokrovskaja K, Sangfelt O, Castro J, Einhorn S, Grander D. 2002. Mechanisms of interferon-alpha induced apoptosis in malignant cells. Oncogene 21: 12511262.
  • Tian Z, Shen X, Feng H, Gao B. 2000. IL-1 beta attenuates IFN-alpha beta-induced antiviral activity and STAT1 activation in the liver: Involvement of proteasome-dependent pathway. J Immunol 165: 39593965.
  • Tracey L, Villuendas R, Ortiz P, Dopazo A, Spiteri I, Lombardia L, Rodriguez-Peralto JL, Fernandez-Herrera J, Hernandez A, Fraga J, Dominguez O, Herrero J, Alonso MA, Dopazo J, Piris MA. 2002. Identification of genes involved in resistance to interferon-alpha in cutaneous T-cell lymphoma. Am J Pathol 161: 18251837.
  • Turkson J, Bowman T, Adnane J, Zhang Y, Djeu JY, Sekharam M, Frank DA, Holzman LB, Wu J, Sebti S, Jove R. 1999. Requirement for Ras/Rac1-mediated p38 and c-Jun N-terminal kinase signaling in Stat3 transcriptional activity induced by the Src oncoprotein. Mol Cell Biol 19: 75197528.
  • Uddin S, Majchrzak B, Woodson J, Arunkumar P, Alsayed Y, Pine R, Young PR, Fish EN, Platanias LC. 1999. Activation of the p38 mitogen-activated protein kinase by type I interferons. J Biol Chem 274: 3012730131.
  • Uddin S, Lekmine F, Sharma N, Majchrzak B, Mayer I, Young PR, Bokoch GM, Fish EN, Platanias LC. 2000. The Rac1/p38 mitogen-activated protein kinase pathway is required for interferon alpha-dependent transcriptional activation but not serine phosphorylation of Stat proteins. J Biol Chem 275: 2763427640.
  • Uddin S, Sassano A, Deb DK, Verma A, Majchrzak B, Rahman A, Malik AB, Fish EN, Platanias LC. 2002. Protein kinase C-delta (PKC-delta) is activated by type I interferons and mediates phosphorylation of Stat1 on serine 727. J Biol Chem 277: 1440814416.
  • Udy GB, Towers RP, Snell RG, Wilkins RJ, Park SH, Ram PA, Waxman DJ, Davey HW. 1997. Requirement of STAT5b for sexual dimorphism of body growth rates and liver gene expression. Proc Natl Acad Sci USA 94: 72397244.
  • Ulane CM, Rodriguez JJ, Parisien JP, Horvath CM. 2003. STAT3 ubiquitylation and degradation by mumps virus suppress cytokine and oncogene signaling. J Virol 77: 63856393.
  • Verma A, Deb DK, Sassano A, Uddin S, Varga G, Wickrema A, Platanias LC. 2002. Activation of the p38 mitogen-activated protein kinase mediates the suppressive effects of type I interferons and transforming growth factor-beta on normal hematopoiesis. J Biol Chem 277: 77267735.
  • Vinkemeier U, Cohen SL, Moarefi I, Chait BT, Kuriyan J, Darnell JE Jr. 1996. DNA binding of in vitro activated Stat1 alpha, Stat1 beta, and truncated Stat1: Interaction between NH2-terminal domains stabilizes binding of two dimers to tandem DNA sites. EMBO J 15: 56165626.
  • Wen Z, Zhong Z, Darnell JE Jr. 1995. Maximal activation of transcription by Stat1 and Stat3 requires both tyrosine and serine phosphorylation. Cell 82: 241250.
  • Williams JG. 2000. STAT signalling in cell proliferation and in development. Curr Opin Genet Dev 10: 503507.
  • Wolff EC, Park MH, Folk JE. 1990. Cleavage of spermidine as the first step in deoxyhypusine synthesis. The role of NAD. J Biol Chem 265: 47934799.
  • Wong LH, Krauer KG, Hatzinisiriou I, Estcourt MJ, Hersey P, Tam ND, Edmondson S, Devenish RJ, Ralph SJ. 1997. Interferon-resistant human melanoma cells are deficient in ISGF3 components, STAT1, STAT2, and p48-ISGF3gamma. J Biol Chem 272: 2877928785.
  • Xu X, Sun YL, Hoey T. 1996. Cooperative DNA binding and sequence-selective recognition conferred by the STAT amino-terminal domain. Science 273: 794797.
  • Yamauchi H, Sakai I, Narumi H, Takeuchi K, Soga S, Fujita S. 2001. Development of interferon-alpha resistant subline from human chronic myelogenous leukemia cell line KT-1. Intern Med 40: 607612.
  • Yan H, Krishnan K, Lim JTE, Contillo LG, Krolewski JJ. 1996a. Molecular characterization of an alpha interferon receptor 1 subunit (IFNαR1) domain required for TYK2 binding and signal transduction. Mol Cell Biol 16: 20742082.
  • Yan H, Krishnan K, Greenlund AC, Gupta S, Lim JTE, Schreiber RD, Schindler CW, Krolewski JJ. 1996b. Phosphorylated interferon-alpha receptor 1 subunit (IFNαR1) acts as a docking site for the latent form of the 113 kDa STAT2 protein. EMBO J 15: 10641074.
  • Yang CH, Murti A, Pfeffer LM. 1998. STAT3 complements defects in an interferon-resistant cell line: Evidence for an essential role for STAT3 in interferon signaling and biological activities. Proc Natl Acad Sci USA 95: 55685572.
  • Yang CH, Murti A, Pfeffer SR, Kim JG, Donner DB, Pfeffer LM. 2001. Interferon alpha /beta promotes cell survival by activating nuclear factor kappa B through phosphatidylinositol 3-kinase and Akt. J Biol Chem 17: 1375613761.
  • Zhang X, Blenis J, Li HC, Schindler C, Chen-Kiang S. 1995. Requirement of serine phosphorylation for formation of STAT-promoter complexes. Science 267: 19901994.