Hepatitis C virus activates interleukin-1ß via caspase-1-inflammasome complex.

Interleukin-1ß (IL-1ß) is a potent pro-inflammatory cytokine involved in the pathogenesis of HCV, but the sensors and underlying mechanisms that facilitate HCV-induced IL-1ß proteolytic activation and secretion remains unclear. In this study, we have identified a signalling pathway leading to IL-1ß activation and secretion in response to HCV infection. Previous studies have shown the induction and secretion of IL-1ß through the inflammasome complex in macrophages/monocytes. Here, we report for the first time the induction and assembly of the NALP3-inflammasome complex in human hepatoma cells infected with HCV (JFH-1). We demonstrate that activation of IL-1ß in HCV-infected cells involves the proteolytic processing of pro-caspase-1 into mature caspase-1 in a multiprotein inflammasome complex. Next, we demonstrate that HCV is sensed by NALP3 protein, which recruits the adaptor protein ASC for the assembly of the inflammasome complex. Using a small interfering RNA approach, we further show that components of the inflammasome complex are involved in the activation of IL-1ß in HCV-infected cells. Our study also demonstrates the role of reactive oxygen species in HCV-induced IL-1ß secretion. Collectively, these observations provide an insight into the mechanism of IL-1ß processing and secretion, which is likely to provide novel strategies for targeting the viral or cellular determinants to arrest the progression of liver disease associated with chronic HCV infection.

Hepatitis C virus-induced furin and thrombospondin-1 activate TGF-ß1: role of TGF-ß1 in HCV replication.

In this study, we demonstrated the molecular mechanisms of TGF-ß1 induction as well as proteolytic activation in HCV (JFH-1)-infected cells. Our studies showed the synthesis and secretion of TGF-ß1 in HCV-infected cells which was reduced in the presence of Ca(2+) chelators, an inhibitor of mitochondrial Ca(2+) uptake, and antioxidants. We also showed that the expression of HCV NS proteins NS3/4A, and NS5A can induce TGF-ß1 by cell-based luciferase assay. Furthermore, mutational analysis revealed that the functionally active protease domain of NS3 and N-terminus domain of NS5A are required for TGF-ß1 activity. Using siRNA approach we demonstrated that HCV-induced furin and thrombospondin-1 (TSP-1) are involved in the proteolytic activation of TGF-ß1. Our results also suggest that TGF-ß1 positively regulates HCV RNA replication. Collectively, these observations provide insight into the mechanism of TGF-ß1 activation, which likely manifest in liver fibrosis associated with hepatitis C infection.