HCV NS5A interacts with p53 and inhibits p53-mediated apoptosis

Abstract

Hepatitis C virus (HCV) causes a persistent infection, chronic hepatitis and hepatocellular carcinoma. HCV NS5A, one of non-structural proteins of HCV, was suggested to play a role in oncogenic transformation. Since the tumor suppressor p53 is important for preventing neoplastic transformation, we investigated the functional effects of HCV NS5A on p53. In vitro and in vivo coimmunoprecipitation and confocal microscopy were used to determine the interaction of NS5A and p53. HCV NS5A binds directly to p53 and colocalizes p53 in the perinuclear region. NS5A inhibits transcriptional transactivation by p53 in a dose-dependent manner by use of a reporter assay. Down regulation of endogenous p21/waf1 expression, which is activated by p53 in Hep3B cells, by NS5A was demonstrated by using FLAG-and FLAG-NS5A Hep3B stable cell lines. The effect of NS5A on p53-mediated apoptosis was determined by flow cytometry in both NS5A permanently and transiently transfected Hep3B cells with exogenous p53. The p53-induced apoptosis was abrogated by NS5A and the inhibition effect correlates well with the binding ability of NS5A to p53. In addition, HCV NS5A protein interacts with and colocalizes hTAF II 32, a component of TFIID and an essential coactivator of p53, in vivo. These results suggest that HCV NS5A interacts with and partially sequestrates p53 and hTAF II 32 in the cytoplasm and suppresses p53-mediated transcriptional transactivation and apoptosis during HCV infection, which may contribute to the hepatocarcinogenesis of HCV infection.

Phosphorylation Drives an Apoptotic Protein to Activate Antiapoptotic Genes

“…In contrast, during early infection, viruses protect cells from dying for their own benefit. For this, they generally initiate cell survival pathways by recruiting their encoded proteins (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Because viruses control many cellular processes utilizing a limited number of viral proteins, the function of the viral protein may depend on its localization in the cell during various stages of viral infection.…”

Dominant negative effect of wild-type NS5A on NS5A-adapted subgenomic hepatitis C virus RNA replicon

“…A second class is in NS5B (so far only one mutant has been described) which, in contrast, is resistant to the antiviral response possibly elicited by wt NS5A or, following the other hypothesis, which forms an active replication complex with wt NS5A. A number of reports have suggested various types of interaction between NS5A and cellular proteins, as well as specific interactions between NS5B and other NS proteins, including NS5A (Chung et al, 2000;Ghosh et al, 2000;He et al, 2002;Lan et al, 2002;Lin et al, 1997;Majumder et al, 2001;Tan et al, 1999;Tu et al, 1999). The two-hybrid system or immunoprecipitations are the most widely used experimental systems, with the majority of cases using the isolated NS5A polypeptide, tagged or not.…”

Modulation of p53 transcription regulatory activity and post-translational modification by hepatitis C virus core protein

“…Besides HCV core protein, other two HCV-encoded viral products, nonstructural protein 3 (NS3; Ishido and Hotta, 1998) and nonstructural protein 5A (NS5A; Majumder et al, 2001;Lan et al, 2002), have been recently demonstrated capable of interacting with the C-terminus of p53 and thereby deregulate p53 normal functions. Both NS3 and NS5 viral proteins, when being overexpressed in cells, cause the downregulation of p53-dependent transactivational activity.…”