Hepatitis C virus core protein upregulates the expression of vascular endothelial growth factor via the nuclear factor-κB/hypoxia-inducible factor-1α axis under hypoxic conditions

Aim: Hepatitis C virus (HCV) core protein critically contributes to hepatocarcinogenesis, which is often observed in liver cirrhosis. Since the liver cirrhosis microenvironment is affected by hypoxia, we focused on the possible driving force of HCV core protein on signal relay from hypoxia-inducible factor (HIF)-1a to vascular endothelial growth factor (VEGF). Methods: Human hepatocellular carcinoma cells stably overexpressing HCV core (Core cells) and NS5A (NS5A cells) were established; empty vector-transfected (EV) cells were used as controls. Hypoxia was induced by oxygen deprivation or by using cobalt chloride (CoCl2). YC-1 was used to inhibit HIF-1a expression. Protein analyses for cultured cells and liver tissues obtained from CoCl2-treated HCV core-transgenic (Core-Tg) mice were performed by western blot and/or immunocytochemistry. Cellular mRNA levels were evaluated by quantitative real-time reverse transcription-polymerase chain reaction. Results: Under hypoxia, the sustained expression of HIF-1a, but not HIF-2a, was profoundly observed in Core cells but, was faint in EV and NS5A cells. Immunocytochemistry revealed increased HIF-1a in the nucleus. HIF-1a mRNA levels were significantly higher in Core cells than in EV cells under both normoxia and hypoxia. The HIF-1a-targeted VEGF and Bcl-xL expressions were increased in Core cells under hypoxia and abolished by YC-1 treatment. Hypoxic liver samples of Core-Tg mice indicated significant increases in both HIF-1a and VEGF expression compared with the wild type. Conclusions: Hepatitis C virus core protein has the distinct potential to transcriptionally upregulate and sustain HIF-1a expression under hypoxia, thereby contributing to increased VEGF expression, a key regulator in the hypoxic milieu of liver cirrhosis.