Functional Role of COP1 Gene in Hepatocellular Carcinoma Lipid Metabolism and Stemness.

We have previously defined the constitutive photomorphogenic protein 1 (COP1) gene as a therapeutic target in hepatocellular carcinoma (HCC). A recent study demonstrated that COP1 induces non-alcoholic fatty liver disease (NAFLD), a precursor to HCC, in normal hepatocytes and that reducing COP1 expression significantly improves high-fat diet-induced hepatic steatosis. Thus, in this study, we investigated if the function of COP1 was associated with HCC metabolism and evolution. Silencing of COP1 expression by a target siRNA significantly suppressed long-term colony formation in Huh7, HepG2, Huh1, and PLC/PRF/5 HCC cell lines. RNA sequencing of COP1-silenced Huh7 and HepG2 cells revealed the same directional regulation of 24 (14 up- and 10 down-regulated) genes. Notable molecular alterations were upregulation of AKR1D1 and downregulation of TMEM65, which involves negative regulation of lipid metabolism and promotion of metastasis, respectively. Correlation analysis using GEPIA2 supported inverse relationship between COP1 and AKR1D1 expression and positive relationship between COP1 and TMEM65 expression in HCC clinical samples. Targeting of COP1 reduced fat accumulation and metastatic potential in both HCC parental cells and CD133(+) liver cancer stem cells. Overexpression of COP1 reversed the phenotypic changes. Collectively, our findings indicate that the COP1 is functionally correlated with HCC lipid metabolism and stemness.