Reciprocal regulation of microRNA-122 and c-Myc in hepatocellular cancer: Role of E2F1 and transcription factor dimerization partner 2

Authors

  • Bo Wang,

    1. Department of Molecular and Cellular Biochemistry, Ohio State University, Columbus, OH
    2. Molecular, Cellular and Developmental Biology Program, Ohio State University, Columbus, OH
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  • Shu-hao Hsu,

    1. Department of Molecular and Cellular Biochemistry, Ohio State University, Columbus, OH
    2. Molecular, Cellular and Developmental Biology Program, Ohio State University, Columbus, OH
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  • Xinmei Wang,

    1. Comprehensive Cancer Center, Ohio State University, Columbus, OH
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  • Huban Kutay,

    1. Comprehensive Cancer Center, Ohio State University, Columbus, OH
    2. Wexner Medical Center, Ohio State University, Columbus, OH
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  • Hemant Kumar Bid,

    1. Center for Childhood Cancer, Nationwide Children's Hospital, Columbus, OH
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  • Jianhua Yu,

    1. Comprehensive Cancer Center, Ohio State University, Columbus, OH
    2. Wexner Medical Center, Ohio State University, Columbus, OH
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  • Ramesh K. Ganju,

    1. Comprehensive Cancer Center, Ohio State University, Columbus, OH
    2. Wexner Medical Center, Ohio State University, Columbus, OH
    3. Department of Pathology, Ohio State University, Columbus, OH
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  • Samson T. Jacob,

    1. Department of Molecular and Cellular Biochemistry, Ohio State University, Columbus, OH
    2. Comprehensive Cancer Center, Ohio State University, Columbus, OH
    3. Wexner Medical Center, Ohio State University, Columbus, OH
    4. Experimental Therapeutics Program, College of Medicine, Ohio State University, Columbus, OH
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  • Mariia Yuneva,

    1. University of California, San Francisco, San Francisco, CA
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  • Kalpana Ghoshal

    Corresponding author
    1. Department of Molecular and Cellular Biochemistry, Ohio State University, Columbus, OH
    2. Comprehensive Cancer Center, Ohio State University, Columbus, OH
    3. Wexner Medical Center, Ohio State University, Columbus, OH
    4. Department of Pathology, Ohio State University, Columbus, OH
    5. Experimental Therapeutics Program, College of Medicine, Ohio State University, Columbus, OH
    6. Center for Childhood Cancer, Nationwide Children's Hospital, Columbus, OH
    • Address reprint requests to: Kalpana Ghoshal, Ph.D., 646C MRF Bldg., 420 W. 12th Ave., Columbus, OH 43210. E-mail: Kalpana.ghoshal@osumc.edu; fax: 614-688-5600.

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  • Potential conflict of interest: Nothing to report.

  • Supported in part by NIH grants DK088076 and CA086978.

Abstract

c-Myc is a well-known oncogene frequently up-regulated in different malignancies, whereas liver-specific microRNA (miR)-122, a bona fide tumor suppressor, is down-regulated in hepatocellular cancer (HCC). Here we explored the underlying mechanism of reciprocal regulation of these two genes. Real-time reverse-transcription polymerase chain reaction (RT-PCR) and northern blot analysis demonstrated reduced expression of the primary, precursor, and mature miR-122 in c-MYC-induced HCCs compared to the benign livers, indicating transcriptional suppression of miR-122 upon MYC overexpression. Indeed, chromatin immunoprecipitation (ChIP) assay showed significantly reduced association of RNA polymerase II and histone H3K9Ac, markers of active chromatin, with the miR-122 promoter in tumors relative to the c-MYC-uninduced livers, indicating transcriptional repression of miR-122 in c-MYC-overexpressing tumors. The ChIP assay also demonstrated a significant increase in c-Myc association with the miR-122 promoter region that harbors a conserved noncanonical c-Myc binding site in tumors compared to the livers. Ectopic expression and knockdown studies showed that c-Myc indeed suppresses expression of primary and mature miR-122 in hepatic cells. Additionally, Hnf-3β, a liver enriched transcription factor that activates miR-122 gene, was suppressed in c-MYC-induced tumors. Notably, miR-122 also repressed c-Myc transcription by targeting transcriptional activator E2f1 and coactivator Tfdp2, as evident from ectopic expression and knockdown studies and luciferase reporter assays in mouse and human hepatic cells. Conclusion: c-Myc represses miR-122 gene expression by associating with its promoter and by down-regulating Hnf-3β expression, whereas miR-122 indirectly inhibits c-Myc transcription by targeting Tfdp2 and E2f1. In essence, these results suggest a double-negative feedback loop between a tumor suppressor (miR-122) and an oncogene (c-Myc). (Hepatology 2014;59:555–566)

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