Hepatitis C Virus Nonstructural Proteins Inhibit Apolipoprotein B100 Secretion

Abstract

Host genes involved in lipid metabolism are differentially regulated during the early stages of hepatitis C virus (HCV) infection. The majority of lipids synthesized in the liver are exported to other tissues in the form of lipoproteins. The formation of these lipoproteins is dependent upon the association of triglycerides with apolipoprotein B100. Using the HCV subgenomic replicon expression system, we show that secretion of apoB100 is significantly reduced. Inhibition of apoB100 degradation by ALLN did not improve secretion. Triglyceride levels as well as microsomal triglyceride transfer protein mRNA and activity levels were reduced in replicon-expressing cells, indicating potential reasons for the observed decrease. Further evidence is presented for the interaction between the HCV nonstructural protein 5A and apoB100. These results provide further insight into the alteration of lipid metabolism by HCV. Hepatitis C virus (HCV)3 infection is a major health problem worldwide. HCV infection causes chronic hepatitis in up to 60 -80% of infected adults (1) and is associated with steatosis, cirrhosis, and hepatocellular carcinoma (2). The HCV viral genome consists of a positive sense single-stranded RNA 9.6 kb in length and encodes a polyprotein precursor of ϳ3000 amino acids (3). The resulting polyprotein is cleaved into at least three structural proteins (the core protein and the envelope proteins E1 and E2) and a variety of nonstructural proteins (p7 through NS5A/B) (3, 4). Many of the nonstructural proteins are essential for productive viral replication (5).The development of selectable subgenomic HCV RNA replicons has led to important advances in the field of HCV. Recently, several groups have reported the full-length infectious tissue culture system (6 -8), which is likely to further our understanding of the infectious process. The subgenomic replicons are bicistronic constructs composed of the HCV internal ribosomal entry site (IRES), the neomycin phosphotransferase (neo) gene, and the encephalomyocarditis IRES, which mediates the translation of the HCV nonstructural proteins NS3 through NS5, followed by the 3Ј-noncoding region (9).Chronic HCV is characterized by several histological features of the liver such as bile duct damage, lymphoid follicles, low serum cholesterol levels, and, in ϳ50 -60% of the cases, steatosis (10, 11). Recently, genomic analysis conducted on the livers of HCV-infected chimpanzees revealed that the transcript levels of genes involved in lipid metabolism and homeostasis are altered (12, 13).The liver is a major site of lipid synthesis. Many of the synthesized lipids are exported from the liver in the form of apolipoprotein-containing particles known as very low density lipoproteins (VLDLs), precursors of low-density lipoproteins. The VLDLs are composed of a nonpolar core of triglycerides and cholesteryl esters surrounded by a monolayer amphipathic coating of protein, phospholipids, and cholesterol (14, 15). VLDLs are formed in the luminal space within the endoplasmic reticulum (ER), ...

Hepatitis C virus production by human hepatocytes dependent on assembly and secretion of very low-density lipoproteins

“…These vesicular structures were not prominent when we stained control Huh7 cells with anti-apoB, suggesting that these structures may be induced by the viral NS proteins as reported (28). Diversion of nascent VLDL to these structures might explain the previous reports that HCV infection decreases the rate of VLDL secretion in patient (29) and Huh7 cells (30). The vesicles containing the HCV replication complex appears to be derived from the ER because apoB in the vesicles is endo H-sensitive (SI Fig.…”

Regulatory effects of arachidonate 5-lipoxygenase on hepatic microsomal TG transfer protein activity and VLDL-triglyceride and apoB secretion in obese mice

“…The principal role of MTP is to facilitate the transfer of lipids to the nascent apoB-containing lipoprotein particle, which is then converted to VLDL by the addition of lipid droplets (26)(27)(28)(29). Although MTP is capable of transferring the four major lipid classes (free cholesterol, phospholipids, TG, and cholesteryl esters), this transfer protein strongly prefers TG and cholesteryl esters (30). Previous studies have shown that a defective mutation in MTP causes a b lipoproteinemia characterized by the absence of apoB lipoproteins accompanied by fatty liver disease (31).…”

Investigation of Plasma Biomarkers in HIV-1/HCV Mono- and Coinfected Individuals by Multiplex iTRAQ Quantitative Proteomics

“…APOB is a protein that is part of the lipoprotein family and one that largely moves cholesterol around the body. A study found that proteins involved in the virus' progression inhibit the secretion of the APOB protein; the significance of the finding is that it provides evidence that HCV alters the lipid structure throughout the body (Domitrovich et al, 2005). The complement system, a group of proteins with a role in the immune system, naturally is important to both HIV/HCV pathogenesis and treatment.…”