microRNA-199a-3p inhibits hepatic apoptosis and hepatocarcinogenesis by targeting PDCD4

Hepatic apoptosis and the initiated liver inflammation play the initial roles in inflammation-induced hepatocarcinogenesis. Molecular mechanisms underlying the regulation of hepatocyte apoptosis and their roles in hepatocarcinogenesis have attracted much attention. A set of microRNAs (miRNAs) have been determined to be dysregulated in hepatocellular carcinoma (HCC) and participated in cancer progression, however, the roles of these dysregulated miRNAs in carcinogenesis are still poorly understood. We previously analyzed the dysregulated miRNAs in HCC using high-throughput sequencing, and found that miR-199a/b-3p was abundantly expressed in human normal liver while markedly decreased in HCC, which promotes HCC progression. Whether miR-199a/b-3p participates in HCC carcinogenesis is still unknown up to now. Hence, we focused on the role and mechanism of miR-199a/b-3p in hepatocarcinogenesis in this study. Hepatic miR-199a/b-3p was determined to be expressed by miR-199a-2 gene in mice, and we constructed miR-199a-2 knockout and hepatocyte-specific miR-199a-2 knockout mice. Diethylnitrosamine (DEN)-induced hepatocarcinogenesis were markedly increased by hepatocyte-specific miR-199a-3p knockout, which is mediated by the enhanced hepatocyte apoptosis and hepatic injury by DEN administration. In acetaminophen (APAP)-induced acute hepatic injury model, hepatocyte-specific miR-199a-3p knockout also aggravated hepatic apoptosis. By proteomic screening and reporter gene validation, we identified and verified that hepatic programed cell death 4 (PDCD4), which promotes apoptosis, was directly targeted by miR-199a-3p. Furthermore, we confirmed that miR-199a-3p-suppressed hepatocyte apoptosis and hepatic injury by targeting and suppressing PDCD4. Thus, hepatic miR-199a-3p inhibits hepatocyte apoptosis and hepatocarcinogenesis, and decreased miR-199a-3p in hepatocytes may aggravate hepatic injury and HCC development.