Hepatocyte Nuclear Factor 4α and Downstream Secreted Phospholipase A2 GXIIB Regulate Production of Infectious Hepatitis C Virus

Hepatitis C virus (HCV) is a major cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma in humans. The life cycle of HCV is closely associated with the metabolism of lipids, especially very-low-density lipoprotein (VLDL) in hepatocytes. Hepatocyte nuclear factor 4 alpha (HNF4 alpha), the most abundant transcription factor in the liver, regulates the VLDL secretory pathway. However, the effects of HNF4 alpha on the HCV life cycle are unclear. In this study, we investigated the regulatory effects of HNF4 alpha on HCV assembly and secretion. HCV in HNF4 alpha-deficient hepatocytes showed reduced assembly and secretion but unchanged entry and RNA replication. Bezafibrate, a chemical inhibitor of HNF4 alpha, suppressed HCV assembly and secretion. HNF4 alpha downregulation resulted in rearrangement of cytosolic lipid droplets (LDs), as evidenced by the aggregation of large LDs and distorted cytosolic distribution. Phospholipase A(2) GXIIB (PLA(2)GXIIB), an HNF4 alpha-regulated factor involved in VLDL secretion, was found to be crucial in HCV secretion. PLA(2)GXIIB expression was upregulated in hepatocytes harboring HCV sub-genomic replicons or in HCV-infected hepatocytes. This upregulation was transcriptionally controlled in an HNF4 alpha-dependent manner after HCV infection. Furthermore, PLA(2)GXIIB combined with microsomal triglyceride transfer protein was found to be responsible for the regulation of HNF4 alpha-induced HCV infectivity. These results suggest that HNF4 alpha and its downstream PLA(2)GXIIB are important factors affecting the late stage of the HCV life cycle and may serve as potential drug targets for the treatment of HCV infection. IMPORTANCE The assembly and secretion of hepatitis C virus (HCV) are closely correlated with the very-low-density lipoprotein (VLDL) secretory pathway. However, the molecular mechanism by which HCV cooperates with VLDL to facilitate assembly and release is unclear. In this study, we report the function of hepatocyte nuclear factor 4 alpha (HNF4 alpha), the most abundant liver-enriched transcription factor, in HCV assembly and release. HNF4 alpha is crucial in VLDL-mediated lipid transport. We found that HNF4 alpha abundance was increased upon HCV infection and that HNF4 alpha downregulation impaired the assembly and secretion of HCV. We also determined that PLA(2)GXIIB, a direct target factor of HNF4 alpha involved in VLDL secretion, was upregulated upon HCV infection. These results suggest that PLA(2)GXIIB is required in the late stage of the HCV life cycle and that the VLDL secretory pathway is important for HCV assembly and secretion. This study provides insights into the mechanism by which HCV cooperates with HNF4 alpha to be assembled into and released together with VLDL particles.