374-1회 Hepatitis C virus pathogenesis: implications of nonstructural p…

374회

연사 :  황 순 봉, 한림대학교 일송생명과학연구소

제목:  Hepatitis C virus pathogenesis: implications of nonstructural proteins in immune modulation and hepatocellular carcinoma

Abstract

  The most prominent feature of hepatitis C virus (HCV) is its ability to persist in virus-infected patients. If HCV could modulate the cellular responses to immune stimulatory cytokines, it could be advantageous for the virus to maintain persistent infection in the host. To investigate the molecular mechanism underlying HCV pathogenesis, we have explored the potential involvement of HCV nonstructural (NS) 5A and 5B proteins in TNF-asignaling pathways. The HCV NS5A is a multifunctional phosphoprotein that leads to pleiotropic responses, in part by regulating cell growth and cellular signaling pathways. We have previously shown that NS5A inhibits TNF-a-induced NF-kB activation and this inhibition is mediated by interaction with TRAF2. We have further demonstrated that NS5A protein synergistically activated both TNF-a- and TRAF2-medidated JNK in HEK 293T cells. Since NS5A is physically associated with NS5B and both NS5A and NS5B are the essential components of the HCV replication complex, we then examined whether NS5B could modulate TNF-induced NF-kB and JNK activation. HCV NS5B protein is a membrane-associated phosphoprotein that possesses an RNA-dependent RNA polymerase (RdRp) activity. In this study, we have demonstrated that TNF-a-induced NF-kB activation is also inhibited by NS5B protein in a dose-dependent manner in 293 cells. Furthermore, NS5B protein inhibits both TRAF2- and IKKb-induced NF-kB activation. Using coimmunoprecipitation and confocal assays, we show that NS5B interacts with IKKa  and IKKb. Using in vitro kinase assay, we have further found that NS5B protein synergistically activated TNF-a-mediated JNK activity in HEK293 cells.

HCV is the major etiologic agent of chronic hepatitis and hepatocellular carcinoma (HCC).

However, the mechanism of hepatocarcinogenesis by HCV infection is not well understood. Both core and NS5A proteins of HCV are multifunctional phosphoproteins that are involved in modulation of transcriptional activation of cellular genes, cell proliferation and cell death. In the present study, we have investigated the role of HCV core and NS5A proteins in the development of HCC using transgenic mice. Transgenic animals harboring core gene did not develop HCC. However, three independent lines of mice harboring NS5A gene developed HCC at 15 months of age. These mice developed progressive histopathological changes in the liver at 10 months of age with multifocal areas of altered hepatocytes and developed hepatic tumors containing prominent steatosis thereafter. This work provides a good animal model to study molecular and pathological events during the development of HCC. Taken together, both NS5A and NS5B proteins modulate TNF signaling pathways of the host cells and NS5A may play a major role in the development of HCC.