Anti-oncogenic effects of SOX2 silencing on hepatocellular carcinoma achieved by upregulating miR-222-5p-dependent CYLD via the long noncoding RNA CCAT1

In this study, we determined the involvement of SOX2 and its downstream signaling molecules in hepatocellular carcinoma (HCC) progression. We carried out lentiviral transfection in HepG2 cells to determine the roles of SOX2, CCAT1, EGFR, miR-222-5p, and CYLD in HepG2 cells. We first determined the interaction between SOX2 and CCAT1 and that between miR-222-5p and CYLD and their effect on tumor growth in vivo was analyzed in HCC-xenograft bearing nude mice xenografts. SOX2 and CCAT1 were highly expressed in HCC tissues and HepG2 cells. SOX2 bound to the regulatory site of CCAT1. Silencing of SOX2 or CCAT1 inhibited HepG2 cell proliferation, migration, and invasion as well as decreased the expression of CCAT1 and EGFR. CCAT1 silencing reduced EGFR expression, but EGFR expression was increased in HCC tissues and HepG2 cells, which promoted proliferation, migration, and invasion in vitro. EGFR upregulated miR-222-5p, leading to downregulation of CYLD. miR-222-5p inhibition or CYLD overexpression repressed cell functions in HepG2 cells. SOX2 silencing decreased CCAT1, EGFR, and miR-222-5p expression but increased CYLD expression. Loss of SOX2 also reduced the growth rate of tumor xenografts. In summary, SOX2-mediated HCC progression through an axis involving CCAT1, EGFR, and miR-222-5p upregulation and CYLD downregulation.