title: Hepatitis C virus core protein decreases lipid droplet turnover: a mechanism for core-induced steatosis.
abstract: Steatosis is a frequent complication of hepatitis C virus infection. In mice, this condition is recapitulated by the expression of a single viral protein, the nucleocapsid core. Core localizes to the surface of lipid droplets (LDs) in infected liver cells through a process dependent on host diacylglycerol acyltransferase 1 (DGAT1), an enzyme that synthesizes triglycerides in the endoplasmic reticulum. Whether DGAT1 also plays a role in core-induced steatosis is uncertain. Here, we show that mouse embryonic fibroblasts isolated from DGAT1(-/-) mice are protected from core-induced steatosis, as are livers of DGAT1(-/-) mice expressing core, demonstrating that the steatosis is DGAT1-dependent. Surprisingly, core expression did not increase DGAT1 activity or triglyceride synthesis, thus excluding the possibility that core activates DGAT1 to cause steatosis. Instead, we find that DGAT1-dependent localization of core to LDs is a prerequisite for the steatogenic properties of the core. Using biochemical and immunofluorescence microscopy techniques, we show that the turnover of lipids in core-coated droplets is decreased, providing a physiological mechanism for core-induced steatosis. Our results support a bipartite model in which core first requires DGAT1 to gain access to LDs, and then LD-localized core interferes with triglyceride turnover, thus stabilizing lipid droplets and leading to steatosis.
authors: Gladstone Institute of Cardiovascular Disease, University of California, San Francisco, California 94158; Liver Center, University of California, San Francisco, California 94158; Department of Medicine, University of California, San Francisco, California 94158.
authors: Charles
authors: C
authors: Harris
authors: Liver Center, University of California, San Francisco, California 94158; Department of Medicine, University of California, San Francisco, California 94158; Gladstone Institute of Virology and Immunology, University of California, San Francisco, California 94158.
authors: Eva
authors: E
authors: Herker
authors: Gladstone Institute of Cardiovascular Disease, University of California, San Francisco, California 94158; Liver Center, University of California, San Francisco, California 94158; Department of Medicine, University of California, San Francisco, California 94158; Department of Biochemistry and Biophysics, University of California, San Francisco, California 94158. Electronic address: bfarese@gladstone.ucsf.edu.
authors: Robert V
authors: RV
authors: Farese
authors: Liver Center, University of California, San Francisco, California 94158; Department of Medicine, University of California, San Francisco, California 94158; Gladstone Institute of Virology and Immunology, University of California, San Francisco, California 94158. Electronic address: mott@gladstone.ucsf.edu.
authors: Melanie
authors: M
authors: Ott
mesh_terms: D000818:Animals; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D051048:Diacylglycerol O-Acyltransferase / Q000378:metabolism; D005234:Fatty Liver / Q000473:pathology*; D005347:Fibroblasts / Q000378:metabolism / Q000821:virology; D016174:Hepacivirus / Q000378:metabolism*; D006801:Humans; D016086:Lentivirus / Q000378:metabolism; D008055:Lipids / Q000737:chemistry*; D008066:Lipolysis; D051379:Mice; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence / Q000379:methods; D010957:Plasmids / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism; D014758:Viral Core Proteins / Q000737:chemistry / Q000502:physiology*
chemical_list: D008055:Lipids; D014280:Triglycerides; D014758:Viral Core Proteins; C069130:nucleocapsid protein, Hepatitis C virus; C494882:Dgat1 protein, mouse; D051048:Diacylglycerol O-Acyltransferase