MicroRNAs (miRNAs) and methionine adenosyltransferase 1A (MAT1A) are dysregulated in hepatocellular carcinoma (HCC), and reduced MAT1A expression correlates with worse HCC prognosis. Expression of miR-664, miR-485-3p, and miR-495, potential regulatory miRNAs of MAT1A, is increased in HCC. Knockdown of these miRNAs individually in Hep3B and HepG2 cells induced MAT1A expression, reduced growth, and increased apoptosis, while combined knockdown exerted additional effects on all parameters. Subcutaneous and intraparenchymal injection of Hep3B cells stably overexpressing each of this trio of miRNAs promoted tumorigenesis and metastasis in mice. Treatment with miRNA-664 (miR-664), miR-485-3p, and miR-495 siRNAs reduced tumor growth, invasion, and metastasis in an orthotopic liver cancer model. Blocking MAT1A induction significantly reduced the antitumorigenic effect of miR-495 siRNA, whereas maintaining MAT1A expression prevented miRNA-mediated enhancement of growth and metastasis. Knockdown of these miRNAs increased total and nuclear level of MAT1A protein, global CpG methylation, lin-28 homolog B (Caenorhabditis elegans) (LIN28B) promoter methylation, and reduced LIN28B expression. The opposite occurred with forced expression of these miRNAs. In conclusion, upregulation of miR-664, miR-485-3p, and miR-495 contributes to lower MAT1A expression in HCC, and enhanced tumorigenesis may provide potential targets for HCC therapy.
Authors
Heping Yang, Michele E. Cho, Tony W.H. Li, Hui Peng, Kwang Suk Ko, Jose M. Mato, Shelly C. Lu
HepG2 cells were injected into the left hepatic lobe of male BALB/c nude mice and lentiviral vectors containing MAT1A siRNA (MAT1Asi), miR-495 siRNA (miR-495si), and scramble siRNA (SC), alone or together, were injected into the spleen at the time of HepG2 cell injection (n = 8 per group). Control group received only HepG2 cell injection. Two weeks later, lentiviral siRNAs were injected into the tail vein, and this was repeated every 2 weeks until sacrifice at 8 weeks. First row: arrows point to tumors at the site of injection, and tumor volumes are shown below. *P < 0.005 vs. SC+SC; †P < 0.005 vs. MAT1Asi+SC; ‡P < 0.05 vs. miR-495si+MAT1Asi. Second and third rows show metastasis to lung and pancreas (indicated by arrows) in the various treatment groups, with the incidence shown below. Original magnification, ×200.