Metformin induces miR-378 to downregulate the CDKI, leading to suppression of cell proliferation in hepatocellular carcinoma

Metformin is one of the extensively and most commonly used oral antihyperglycemic agents, but it has been shown to exert antineoplastic effects in many cancer cells. Recent studies have confirmed that metformin has an antitumor effect on hepatocellular carcinoma (HCC). However, the molecular mechanism underlying this effect needs to be further studied. Materials and methods: CDK1 and miR-378 expression was analyzed by western blotting and real-time PCR assays. We confirmed the association between miR-378 and CDK1 by dual luciferase reporter assay. The role of the miR-378/CDK1 pathway in proliferation, cell cycle and apoptosis was examined in vitro. The effect of miR-378 on HCC tumor growth was evaluated in nude xenograft mouse model. Results: Our study found that metformin significantly inhibited the HCC cell proliferation via inducing G2/M arrest. At the same time, metformin efficiently decreased CDK1 expression and elevated miR-378 level. Moreover, the upregulation of miR-378 also repressed HCC cell proliferation by causing G2/M arrest and inhibited tumor growth. Additionally, we demonstrated that miR-378 directly targeted CDK1 3'UTR and downregulated CDK1 mRNA and protein levels. Furthermore, metformin treatment could not decrease CDK1 expression, suppress HCC cell proliferation, and induce G2/M cell cycle arrest. Discussion: Metformin-suppressed HCC cell proliferation was dependent on the inhibitory effect of miR-378 on CDK1 expression. Taken together, we concluded that metformin inhibited HCC cell proliferation via modulating miR-378/CDK1 axis. Conclusion: Collectively, the current results provide the first evidence, to our knowledge, that miR-378/CDK1 axis is involved in metformin modulating the proliferation of HCC cells, which suggests a novel molecular mechanism underlying the therapeutic effect of metformin on HCC. Keywords: cell cycle, apoptosis, metformin, cancer, liver