S‐Adenosylmethionine Regulates Ubiquitin‐Conjugating Enzyme 9 Protein Level and Sumoylation

BACKGROUND&AIMS Ubiquitin‐conjugating enzyme 9 (Ubc9) catalyzes the conjugation of SUMO (small ubiquitin‐related modifier) to proteins that regulate growth, differentiation and apoptosis. Ubc9 is overexpressed in several cancers but its expression in hepatocellular carcinoma (HCC) is unknown. Methionine adenosyltransferase 1a knockout ( Mat1a KO) mice have hepatic S‐adenosylmethionine (SAMe) deficiency and develop HCC. Ethanol feeding also deplete hepatic SAMe. Our aim was to examine whether SAMe regulates Ubc9 expression. METHODS Real‐time PCR and Western blotting measured Ubc9 expression in Mat1a KO and ethanol‐fed mice livers, HCC specimens, HepG2 and Huh‐7 cells. RESULTS Ubc9 mRNA and protein levels increased in livers of Mat1a KO and ethanol‐fed mice, and in human HCC. Mat1a KO mice exhibit increased protein sumoylation and SAMe treatment normalized Ubc9 protein levels and reduced sumoylation. SAMe and its metabolite methylthioadenosine (MTA) treatment reduced Bcl‐2 expression, lowered Ubc9 protein but not mRNA levels in HepG2 and Huh‐7 cells. SAMe and MTA are pro‐apoptotic in liver cancer cells and Ubc9 knockdown promoted apoptosis and reduced Bcl‐2 expression. CONCLUSIONS Ubc9 expression increases when hepatic SAMe level fall and in human HCC. SAMe treatment decreases Ubc9 protein level and sumoylation. Inhibiting Ubc9 expression can contribute to SAMe and MTA's pro‐apoptotic effects. Supported by National Institutes of Health Grants FAA020150A (to M. L. Tomasi) and DK51719 (to S. C. Lu)