Autophagy has been shown to facilitate replication of hepatitis C virus (HCV); however, the mechanism by which HCV induces autophagy has not been fully established. NS5A, a nonstructural protein expressed by HCV, regulates numerous cellular pathways, including autophagy, by up-regulating Beclin 1; however, the underlying mechanism remains unclear. To obtain new insights into HCV-regulated autophagy, NS5ATP9 was overexpressed in HepG2 and L02 cells, resulting in up-regulation of endogenous Beclin 1 mRNA and protein levels, respectively. The luciferase-reporter assay results showed that both NS5A and NS5ATP9 could transactivate Beclin 1 promoter activity, but that NS5A could not transactivate the Beclin 1 promoter in NS5ATP9-silenced HepG2 and L02 cells. Up-regulation of Beclin 1 mRNA and protein expression by NS5A could also be attenuated by NS5ATP9 knock-down. Furthermore, the HepG2 and L02 cells that transiently overexpressed NS5ATP9 had enhanced accumulation of vacuoles carrying the autophagy marker LC3, consistent with the conversion of endogenous LC3-I to LC3-II. In contrast, the conversion of endogenous LC3-I to LC3-II could not be enhanced by NS5A in NS5ATP9-silenced HepG2 cells. These results highlight an important potential role for NS5ATP9 in HCV NS5A-induced hepatocyte autophagy.

Hepatitis C virus (HCV) core protein stimulates many signaling pathways related to apoptosis inhibition resulting in hepatocellular carcinoma (HCC). It has been reported that sirt1 is involved in regulating apoptosis; therefore, we investigated the influence of HCV core protein on sirt1 expression and apoptosis in human HepG2 cells. Our study showed that HCV core protein inhibited apoptosis of HepG2 cells as well as caspase-3 expression and activity (P < 0.05). At the same time, sirt1 expression was increased at both the mRNA (P < 0.05) and protein (P < 0.05) levels. Furthermore, apoptosis inhibition was reversed when sirt1 was knocked down (P < 0.05). Our study provides further evidence that the sirt1-p53-Bax signaling pathway plays an important role in regulating the suppression of cell apoptosis induced by HCV core protein.

HCV core protein disturbs the cholesterol homeostasis in HepG2 cells via the SREBP2 pathway; miR-185-5p is involved in the regulation of SREBP2 by the core protein.