Hepatitis C virus core protein shows a cytoplasmic localization and associates to cellular lipid storage droplets

Abstract

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...

Metabolic profiles in patients with chronic hepatitis C: a case–control study

“…In the transgenic mouse model, HCV core protein appears to interfere with the hepatic assembly and secretion of ApoB containing very low-density lipoproteins (VLDL) [41]. These effects cause TG to accumulate within hepatocytes, and contribute to decreased serum triglyceride, which may explain the association between HCV infection and lower TG levels.…”

Steatosis: Co-factor in Other Liver Diseases *

“…The virus has a direct steatogenic effect, as evidenced by the accumulation of intracellular lipids in some transgenic cell lines and animal models expressing HCV proteins. 24,25 This may be attributable to viral proteins interfering with mitochondrial function and impairing fatty acid oxidation 26 or to interference with pathways of lipid metabolism. The HCV core protein has been shown to reduce the activity of microsomal triglyceride transfer protein, interfering with the assembly and secretion of very-low-density lipoprotein.…”

Hepatitis C virus core protein binds to apolipoprotein AII and its secretion is modulated by fibrates

“…HCV core protein is predominantly a cytoplasmic protein and is in part localized around these lipid vesicles in vitro in HCV core expressing cells and in vivo in HCV infected chimpanzees. 30 In addition, our previous data showed a colocalization of full-length HCV core protein and human apolipoprotein AII (apoAII), but not apoAI, in HepG2 cells. 30 Moreover, transgenic mice expressing the HCV core protein developed steatosis, 31,32 which is a hallmark of chronic HCV infection in chimpanzees and humans.…”

“…30 In addition, our previous data showed a colocalization of full-length HCV core protein and human apolipoprotein AII (apoAII), but not apoAI, in HepG2 cells. 30 Moreover, transgenic mice expressing the HCV core protein developed steatosis, 31,32 which is a hallmark of chronic HCV infection in chimpanzees and humans. 33 The objective of the present study was to detect cellular proteins interacting specifically with the HCV core protein during HCV infection.…”