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      Hepatitis C Virus and Cellular Stress Response: Implications to Molecular Pathogenesis of Liver Diseases

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          Abstract

          Infection with hepatitis C virus (HCV) is a leading risk factor for chronic liver disease progression, including steatosis, cirrhosis, and hepatocellular carcinoma. With approximately 3% of the human population infected worldwide, HCV infection remains a global public health challenge. The efficacy of current therapy is still limited in many patients infected with HCV, thus a greater understanding of pathogenesis in HCV infection is desperately needed. Emerging lines of evidence indicate that HCV triggers a wide range of cellular stress responses, including cell cycle arrest, apoptosis, endoplasmic reticulum (ER) stress/ unfolded protein response (UPR), and autophagy. Also, recent studies suggest that these HCV-induced cellular responses may contribute to chronic liver diseases by modulating cell proliferation, altering lipid metabolism, and potentiating oncogenic pathways. However, the molecular mechanism underlying HCV infection in the pathogenesis of chronic liver diseases still remains to be determined. Here, we review the known stress response activation in HCV infection in vitro and in vivo, and also explore the possible relationship of a variety of cellular responses with the pathogenicity of HCV-associated diseases. Comprehensive knowledge of HCV-mediated disease progression shall shed new insights into the discovery of novel therapeutic targets and the development of new intervention strategy.

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          Most cited references134

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          Autophagosome formation from membrane compartments enriched in phosphatidylinositol 3-phosphate and dynamically connected to the endoplasmic reticulum

          Autophagy is the engulfment of cytosol and organelles by double-membrane vesicles termed autophagosomes. Autophagosome formation is known to require phosphatidylinositol 3-phosphate (PI(3)P) and occurs near the endoplasmic reticulum (ER), but the exact mechanisms are unknown. We show that double FYVE domain–containing protein 1, a PI(3)P-binding protein with unusual localization on ER and Golgi membranes, translocates in response to amino acid starvation to a punctate compartment partially colocalized with autophagosomal proteins. Translocation is dependent on Vps34 and beclin function. Other PI(3)P-binding probes targeted to the ER show the same starvation-induced translocation that is dependent on PI(3)P formation and recognition. Live imaging experiments show that this punctate compartment forms near Vps34-containing vesicles, is in dynamic equilibrium with the ER, and provides a membrane platform for accumulation of autophagosomal proteins, expansion of autophagosomal membranes, and emergence of fully formed autophagosomes. This PI(3)P-enriched compartment may be involved in autophagosome biogenesis. Its dynamic relationship with the ER is consistent with the idea that the ER may provide important components for autophagosome formation.
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            Autophagy is activated for cell survival after endoplasmic reticulum stress.

            Eukaryotic cells deal with accumulation of unfolded proteins in the endoplasmic reticulum (ER) by the unfolded protein response, involving the induction of molecular chaperones, translational attenuation, and ER-associated degradation, to prevent cell death. Here, we found that the autophagy system is activated as a novel signaling pathway in response to ER stress. Treatment of SK-N-SH neuroblastoma cells with ER stressors markedly induced the formation of autophagosomes, which were recognized at the ultrastructural level. The formation of green fluorescent protein (GFP)-LC3-labeled structures (GFP-LC3 "dots"), representing autophagosomes, was extensively induced in cells exposed to ER stress with conversion from LC3-I to LC3-II. In IRE1-deficient cells or cells treated with c-Jun N-terminal kinase (JNK) inhibitor, the autophagy induced by ER stress was inhibited, indicating that the IRE1-JNK pathway is required for autophagy activation after ER stress. In contrast, PERK-deficient cells and ATF6 knockdown cells showed that autophagy was induced after ER stress in a manner similar to the wild-type cells. Disturbance of autophagy rendered cells vulnerable to ER stress, suggesting that autophagy plays important roles in cell survival after ER stress.
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              Beclin 1, an autophagy gene essential for early embryonic development, is a haploinsufficient tumor suppressor.

              The biochemical properties of beclin 1 suggest a role in two fundamentally important cell biological pathways: autophagy and apoptosis. We show here that beclin 1-/- mutant mice die early in embryogenesis and beclin 1+/- mutant mice suffer from a high incidence of spontaneous tumors. These tumors continue to express wild-type beclin 1 mRNA and protein, establishing that beclin 1 is a haploinsufficient tumor suppressor gene. Beclin 1-/- embryonic stem cells have a severely altered autophagic response, whereas their apoptotic response to serum withdrawal or UV light is normal. These results demonstrate that beclin 1 is a critical component of mammalian autophagy and establish a role for autophagy in tumor suppression. They both provide a biological explanation for recent evidence implicating beclin 1 in human cancer and suggest that mutations in other genes operating in this pathway may contribute to tumor formation through deregulation of autophagy.
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                Author and article information

                Journal
                Viruses
                Viruses
                viruses
                Viruses
                MDPI
                1999-4915
                19 October 2012
                October 2012
                : 4
                : 10
                : 2251-2290
                Affiliations
                [1 ]Department of Biochemistry and Molecular Biology, College of Medicine, Chang Gung University, Taoyuan 33371, Taiwan, Republic of China; Email: pyke0324@ 123456ibms.sinica.edu.tw (P.-Y.K.);
                [2 ]Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan, Republic of China
                Author notes
                [* ] Author to whom correspondence should be addressed; Email: schen@ 123456ibms.sinica.edu.tw (S.-L.C.); Tel.: +886-2-2652-3933, Fax: +886-2-2652-3073.
                Article
                viruses-04-02251
                10.3390/v4102251
                3497051
                23202463
                ffc60307-2f96-4ac4-aef7-ace3dacd5430
                © 2012 by the authors; licensee MDPI, Basel, Switzerland.

                This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/3.0/).

                History
                : 31 August 2012
                : 07 October 2012
                : 09 October 2012
                Categories
                Review

                Microbiology & Virology
                liver diseases,cell cycle arrest,autophagy,hcv,er stress,unfolded protein response,host factor,apoptosis,cellular response,dna damage

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