MicroRNA-26a is a key regulon that inhibits progression and metastasis of c-Myc/EZH2 double high advanced hepatocellular carcinoma

The transcription factor c-Myc is a key driver for hepatocellular carcinomas (HCCs), while the polycombrepressive complex 2 (PRC2) subunit EZH2 is an essential biomarker of HCC. c-Myc epigenetically silences tumor suppressors by recruiting PRC2 and inducing methylation of histone H3 lysine 27. However, it remains elusive how they are regulated in HCC. We found here that microRNA-26a (miR-26a) suppresses c-Myc, a classical Wnt pathway target gene, by targeting the Wnt pathway coactivator, cyclin-dependent kinase 8 (CDK8); miR-26a also directly targets and inhibits EZH2. The expression of MIR26A2, a predominant origin of miR-26a transcripts in hepatic cells, is repressed by c-Myc/PRC2, thereby forming a c-Myc/miR-26a/CDK8 regulatory circuit in HCC. Meanwhile, miR-26a suppresses migration of HCC by targeting p21-activated kinase 2 (PAK2), a critical kinase linking Rho GTPases to cytoskeleton reorganization. Consequently, in vivo delivery of miR-26a remarkably suppressed the development of xenograft HCC and metastasis of orthotopic HCC by downregulating c-Myc, CDK8 and PAK2. These findings unraveled a novel mechanism of c-Myc and Wnt/β-catenin interplay that dictates HCC pathogenesis, and have implications for the potential applicability of miRNA delivery in targeting the newly identified signaling axis and treating metastatic HCCs.