S-adenosyl methionine regulates ubiquitin-conjugating enzyme 9 protein expression and sumoylation in murine liver and human cancers

Authors

  • Maria Lauda Tomasi,

    1. Division of Gastroenterology and Liver Diseases, Keck School of Medicine of University of Southern California, Los Angeles, CA
    2. University of Southern California Research Center for Liver Diseases, Keck School of Medicine of University of Southern California, Los Angeles, CA
    3. The Southern California Research Center for ALPD & Cirrhosis, Keck School of Medicine of University of Southern California, Los Angeles, CA
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  • Ivan Tomasi,

    1. Department of Colorectal Surgery, Whipps Cross University Hospital, London, United Kingdom
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  • Komal Ramani,

    1. Division of Gastroenterology and Liver Diseases, Keck School of Medicine of University of Southern California, Los Angeles, CA
    2. University of Southern California Research Center for Liver Diseases, Keck School of Medicine of University of Southern California, Los Angeles, CA
    3. The Southern California Research Center for ALPD & Cirrhosis, Keck School of Medicine of University of Southern California, Los Angeles, CA
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  • Rosa Maria Pascale,

    1. Division of Experimental Pathology and Oncology, University of Sassari, Sassari, Italy
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  • Jun Xu,

    1. The Southern California Research Center for ALPD & Cirrhosis, Keck School of Medicine of University of Southern California, Los Angeles, CA
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  • Pasquale Giordano,

    1. Department of Colorectal Surgery, Whipps Cross University Hospital, London, United Kingdom
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  • José M. Mato,

    1. CIC bioGUNE, CIBERehd, Technology Park of Bizkaia, Bizkaia, Spain
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  • Shelly C. Lu

    Corresponding author
    1. Division of Gastroenterology and Liver Diseases, Keck School of Medicine of University of Southern California, Los Angeles, CA
    2. University of Southern California Research Center for Liver Diseases, Keck School of Medicine of University of Southern California, Los Angeles, CA
    3. The Southern California Research Center for ALPD & Cirrhosis, Keck School of Medicine of University of Southern California, Los Angeles, CA
    • Division of Gastrointestinal and Liver Diseases, Department of Medicine, Keck School of Medicine, University of Southern California, 2011 Zonal Avenue, Los Angeles, CA 90033===

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    • fax: 323-442-3234


  • Potential conflict of interest: Nothing to report.

Abstract

Ubiquitin-conjugating enzyme 9 (Ubc9) is required for sumoylation and is overexpressed in several malignancies, but its expression in hepatocellular carcinoma (HCC) is unknown. Hepatic S-adenosyl methionine (SAMe) levels decrease in methionine adenosyltransferase 1A (Mat1a) knockout (KO) mice, which develop HCC, and in ethanol-fed mice. We examined the regulation of Ubc9 by SAMe in murine liver and human HCC, breast, and colon carcinoma cell lines and specimens. Real-time polymerase chain reaction and western blotting measured gene and protein expression, respectively. Immunoprecipitation followed by western blotting examined protein-protein interactions. Ubc9 expression increased in HCC and when hepatic SAMe levels decreased. SAMe treatment in Mat1a KO mice reduced Ubc9 protein, but not messenger RNA (mRNA) levels, and lowered sumoylation. Similarly, treatment of liver cancer cell lines HepG2 and Huh7, colon cancer cell line RKO, and breast cancer cell line MCF-7 with SAMe or its metabolite 5′-methylthioadenosine (MTA) reduced only Ubc9 protein level. Ubc9 posttranslational regulation is unknown. Ubc9 sequence predicted a possible phosphorylation site by cell division cycle 2 (Cdc2), which directly phosphorylated recombinant Ubc9. Mat1a KO mice had higher phosphorylated (phospho)-Ubc9 levels, which normalized after SAMe treatment. SAMe and MTA treatment lowered Cdc2 mRNA and protein levels, as well as phospho-Ubc9 and protein sumoylation in liver, colon, and breast cancer cells. Serine 71 of Ubc9 was required for phosphorylation, interaction with Cdc2, and protein stability. Cdc2, Ubc9, and phospho-Ubc9 levels increased in human liver, breast, and colon cancers. Conclusion: Cdc2 expression is increased and Ubc9 is hyperphosphorylated in several cancers, and this represents a novel mechanism to maintain high Ubc9 protein expression that can be inhibited by SAMe and MTA. (HEPATOLOGY 2012;56:982–993)

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