Hepatitis C Virus Core Protein Blocks Interferon Signaling by Interaction with the STAT1 SH2 Domain

Abstract

Emerging data have indicated that hepatitis C virus (HCV) subverts the host antiviral response to ensure its persistence. We previously demonstrated that HCV protein expression suppresses type I interferon (IFN) signaling by leading to the reduction of phosphorylated STAT1 (P-STAT1). We also demonstrated that HCV core protein directly bound to STAT1. However, the detailed mechanisms by which HCV core protein impacts IFN signaling components have not been fully clarified. In this report, we show that the STAT1 interaction domain resides in the N-terminal portion of HCV core (amino acids [aa] 1 to 23). This domain is also required to produce P-STAT1 reduction and inhibit IFN signaling transduction. Conversely, the C-terminal region of STAT1, specifically the SH2 domain (aa 577 to 684), is required for the interaction of HCV core with STAT1. The STAT1 SH2 domain is critical for STAT1 hetero-or homodimerization. We propose a model by which the binding of HCV core to STAT1 results in decreased P-STAT, blocked STAT1 heterodimerization to STAT2, and, therefore, reduced IFN-stimulated gene factor-3 binding to DNA and disrupted IFN-stimulated gene transcription. Hepatitis C virus (HCV)is an enveloped, single-stranded RNA virus member of the family Flaviviridae. Its 9.6-kb genome includes a 5Ј untranslated region that acts as an internal ribosome entry site (IRES). The IRES directs the translation of a single open reading frame encoding the 3,010-amino-acid polyprotein, which is posttranslationally cleaved by host and virus-encoded protease into mature structural and nonstructural proteins (1, 14). The structural proteins include core, which forms the HCV viral nucleocapsid, and two envelope glycoproteins, E1 and E2 (31). The HCV structural proteins are cleaved and further processed to generate the mature and stable form of p21 HCV core (amino acids 1 to 191) (43). The nonstructural proteins NS2 through NS5 support viral RNA replication. For example, the NS3/4A protease catalyzes the posttranslational processing of nonstructural proteins from the viral polyprotein. NS5B encodes the HCV-encoded RNA-dependent RNA polymerase that is critical for HCV RNA replication. The HCV core protein has been found to be primarily located within the membranes of cytoplasmic organelles. The C terminus of HCV core is hydrophobic, while the N-terminal domain of HCV core is basic (33).HCV infection causes the development of chronic hepatitis and progression to liver cirrhosis and hepatocellular carcinoma. More than 170 million people are infected with HCV worldwide. Alpha interferon (IFN-␣) alone or in combination with ribavirin is the only currently approved treatment for HCV infection (9). Unfortunately, in many genotype 1 HCVinfected patients, HCV is refractory to the action of interferon (15). The precise mechanisms for HCV persistence are still not fully understood (21); thus, a more detailed understanding of virus-host interactions is critical.Viral infection stimulates the host type I IFN pathway. Following binding of secreted IFN to t...

Interferons and viruses: an interplay between induction, signalling, antiviral responses and virus countermeasures

“…Amongst the reported ways that HCV blocks IFN signalling (see also below), the core protein interacts with STAT1 to inhibit its phosphorylation and interaction with STAT2 (Lin et al, 2006c). However, whether this mechanism also operates in vivo is not clear, because treatment of HCV-infected or HCV-transfected cell cultures with IFN potently reduces HCV RNA replication (Frese et al, 2001;Windisch et al, 2005;Kim et al, 2007).…”

Mechanisms of action of interferon and ribavirin in chronic hepatitis C: Summary of a workshop

“…The HCV core protein interferes with STAT signaling and may contribute to resistance to both endogenous and exogenous IFN. 15 The NS5A protein binds to the catalytic site of PKR, blocking its ability to phosphorylate eukaryotic initiation factor 2 alpha and thereby inhibiting dsRNA-induced shutdown of host cell protein translation.16…”

“…The HCV core protein interferes with STAT signaling and may contribute to resistance to both endogenous and exogenous IFN. 15 The NS5A protein binds to the catalytic site of PKR, blocking its ability to phosphorylate eukaryotic initiation factor 2 alpha and thereby inhibiting dsRNA-induced shutdown of host cell protein translation.16A number of important questions remain concerning the clinical importance of these in vitro observations, particularly as related to the disruption of IRF-3 signaling by the NS3/4A protease. For example, is it possible that genotype-specific differences in the ability of NS3/4A to cleave IPS-1 or TRIF might explain different rates of long-term viral persistence or different rates of response to IFN-α-based therapies?…”

Toll Like Receptors in Chronic Viral Hepatitis – Friend and Foe

“…In addition, also HCV core protein effects JAK-STAT signaling. The core protein induces STAT1 degradation, inhibits STAT1 activation/phosphorylation and increases the induction of suppressor of cytokine signaling (SOCS) proteins (Bode et al 2003;Lin et al 2005;Lin et al 2006). Furthermore, the core protein suppresses the binding capacity of ISGF3 to the ISRE, resulting in decreased expression of anti-HCV effective ISG (de Lucas et al 2005).…”