There is now abundant evidence to substantiate an important role of hepatitis C virus (HCV) core protein in cellular gene expression as well as in the viral cycle. Thus the subcellular localization of this protein has important implications. However, several studies have shown controversial results: the HCV core has been, indeed, described as cytoplasmic or nuclear depending on the size of the protein or on the genotype analyzed. We have studied the localization of the HCV core protein in two different cell lines, one nonhepatic (CHO) and the other hepatic (HepG2). Double immunof luorescence staining using a nuclear membrane marker and confocal analysis showed the core protein pattern to be cytoplasmic and globular. This pattern is not cell cycleregulated. Electron microscopy analysis revealed the nature of the globular staining observed in immunof luorescence. The HCV core protein accumulated at the surface of lipid droplets that were also the unique morphological feature of nonhepatic core transfected cells. The lipid droplets were isolated by sequential ultracentrifugation on the basis of their density; biochemical analysis revealed a prevalence of triglycerides. In addition the core protein colocalized with apolipoprotein AII at the surface of the lipid droplets as revealed by confocal microscopy. Moreover analysis of liver biopsies from chronically HCV-infected chimpanzees revealed that HCV core is cytoplasmic and localized on the endoplasmic reticulum and on lipid droplets. These results clearly define the subcellular localization of the HCV core protein and suggest a relationship between the expression of the HCV core protein and cellular lipid metabolism.The hepatitis C virus (HCV), the major causative agent of non-A͞non-B hepatitis (1), is a positive-stranded RNA virus of about 10 kb evolutionary related to pestivirus and flavivirus (2, 3). The HCV ORF is flanked by a 341-bp long 5Ј untranslated region and a 3Ј untranslated region with a poly(U) or a poly(A) tail (3, 4) and encodes for a precursor polyprotein of about 3000 aa that is then cleaved into structural and nonstructural proteins (5, 6).A major characteristic of HCV infection is the extremely high (up to 80%) risk of chronicity; in addition, chronic infection can lead to liver cirrhosis and liver cancer (7,8). An important issue regarding the pathogenesis of HCV-associated liver lesions is to determine whether or not HCV proteins might have a direct effect on cellular phenotype as suggested by some recent works (9, 10). In this view, a regulative effect by HCV core protein, one of the structural proteins of the virus, has been shown by transfection both on hepatitis B viral genome expression and replication (11) and on expression of different cellular genes such as c-myc oncogene (12) or genes encoding for interferon ␤ in a human cell line (13).The observations reported above would suggest that the HCV core protein could have not only a packaging function in the cytoplasm, but also a regulatory role on cell functions. Precise informatio...

No abstract

No abstract