Non-structural protein 4A of Hepatitis C virus accumulates on mitochondria and renders the cells prone to undergoing mitochondria-mediated apoptosis.
ABSTRACT Non-structural protein 4A (NS4A) of Hepatitis C virus (HCV) functions as a cofactor for NS3 by forming a complex with it to augment its enzymic activities. NS4A also forms a complex with other HCV proteins, such as NS4B/NS5A, to facilitate the formation of the viral RNA replication complex on the endoplasmic reticulum (ER) membrane. In addition to its essential role in HCV replication, NS4A is thought to be involved in viral pathogenesis by affecting cellular functions. In this study, it was demonstrated that NS4A was localized not only on the ER, but also on mitochondria when expressed either alone or together with NS3 in the form of the NS3/4A polyprotein and in the context of HCV RNA replication in Huh7 cells harbouring an HCV RNA replicon. Moreover, NS4A expression altered the intracellular distribution of mitochondria significantly and caused mitochondrial damage, as evidenced by the collapsed mitochondrial transmembrane potential and release of cytochrome c into the cytoplasm, which led ultimately to induction of apoptosis through activation of caspase-3, but not caspase-8. Consistently, Huh7 cells expressing NS3/4A and those harbouring an HCV RNA replicon were shown to be more prone to undergoing actinomycin D-induced, mitochondria-mediated apoptosis, compared with the control Huh7 cells. Taken together, these results suggest the possibility that HCV exerts cytopathic effect (CPE) on the infected cells under certain conditions and that NS4A is responsible, at least in part, for the conditional CPE in HCV-infected cells.
Article: Apoptotic effects of a chimeric plant virus carrying a mimotope of the hepatitis C virus hypervariable region 1: role of caspases and endoplasmic reticulum-stress.[show abstract] [hide abstract]
ABSTRACT: The role of apoptosis in the persistence of hepatitis C virus (HCV) infection is controversial. Moreover, conflicting data on the modulation of this process by HCV proteins have been provided. We evaluated the susceptibility of peripheral lymphocytes from patients with chronic hepatitis C to apoptosis both spontaneous and after incubation with a chimeric Cucumber mosaic virus (CMV) carrying 180 copies of the synthetic R9 mimotope obtained from more than 200 hypervariable region-1 sequences of HCV. Resting T lymphocytes were found to be sensitized to apoptosis as a result of chronic HCV infection. The plant virus-derived vector R9-CMV displayed a strong pro-apoptotic effect associated with activation of both caspase-8 and -9, indicating the involvement of both extrinsic and intrinsic apoptotic pathways. A parallel R9-CMV-mediated activation of endoplasmic reticulum-stress was suggested by the significant induction of BiP/GRP78, GADD153 and caspase-12. These data contribute to define the complex HCV/host interaction, and open new prospects for developing a plant-derived antigen-presenting system to strengthen host defences against persistent pathogens.Journal of Clinical Immunology 03/2012; 32(4):866-76. · 3.08 Impact Factor
Article: Enhanced apoptosis in post-liver transplant hepatitis C: effects of virus and immunosuppressants.[show abstract] [hide abstract]
ABSTRACT: Hepatitis C (HCV)-infected patients have a poorer survival post-liver transplantation compared to patients transplanted for other indications, since HCV recurrence post-transplant is universal and commonly follows an aggressive course. There is increasing evidence that in the non-transplant setting, induction of hepatocyte apoptosis is one of the main mechanisms by which HCV drives liver inflammation and fibrosis, and that HCV proteins directly promote apoptosis. Recent studies have shown that post-liver transplant, there is a link between high levels of HCV replication, enhanced hepatocyte apoptosis and the subsequent development of rapidly progressive liver fibrosis. Although the responsible mechanisms remain unclear, it is likely that immunosuppressive drugs play an important role. It is well known that immunosuppressants impair immune control of HCV, thereby allowing increased viral replication. However there is also evidence that immunosuppressants may directly induce apoptosis and this may be facilitated by the presence of high levels of HCV replication. Thus HCV and immunosuppressants may synergistically interact to further enhance apoptosis and drive more rapid fibrosis. These findings suggest that modulation of apoptosis within the liver either by changing immunosuppressive therapy or the use of apoptosis inhibitors may help prevent fibrosis progression in patients with post-transplant HCV disease.World Journal of Gastroenterology 05/2012; 18(18):2172-9. · 2.47 Impact Factor
Article: Enterovirus 71 Protease 2A(pro) Targets MAVS to Inhibit Anti-Viral Type I Interferon Responses.[show abstract] [hide abstract]
ABSTRACT: Enterovirus 71 (EV71) is the major causative pathogen of hand, foot, and mouth disease (HFMD). Its pathogenicity is not fully understood, but innate immune evasion is likely a key factor. Strategies to circumvent the initiation and effector phases of anti-viral innate immunity are well known; less well known is whether EV71 evades the signal transduction phase regulated by a sophisticated interplay of cellular and viral proteins. Here, we show that EV71 inhibits anti-viral type I interferon (IFN) responses by targeting the mitochondrial anti-viral signaling (MAVS) protein-a unique adaptor molecule activated upon retinoic acid induced gene-I (RIG-I) and melanoma differentiation associated gene (MDA-5) viral recognition receptor signaling-upstream of type I interferon production. MAVS was cleaved and released from mitochondria during EV71 infection. An in vitro cleavage assay demonstrated that the viral 2A protease (2A(pro)), but not the mutant 2A(pro) (2A(pro)-110) containing an inactivated catalytic site, cleaved MAVS. The Protease-Glo assay revealed that MAVS was cleaved at 3 residues between the proline-rich and transmembrane domains, and the resulting fragmentation effectively inactivated downstream signaling. In addition to MAVS cleavage, we found that EV71 infection also induced morphologic and functional changes to the mitochondria. The EV71 structural protein VP1 was detected on purified mitochondria, suggesting not only a novel role for mitochondria in the EV71 replication cycle but also an explanation of how EV71-derived 2A(pro) could approach MAVS. Taken together, our findings reveal a novel strategy employed by EV71 to escape host anti-viral innate immunity that complements the known EV71-mediated immune-evasion mechanisms.PLoS Pathogens 03/2013; 9(3):e1003231. · 9.13 Impact Factor