Grove, J., T. Huby, Z. Stamataki, T. Vanwolleghem, P. Meuleman, M. Farquhar, A. Schwarz, M. Moreau, J. S. Owen, G. Leroux-Roels, P. Balfe, and J. A. McKeating. J Virol 81:3162-9. 2007
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In this study we demonstrated that human SR-BI and SR-BII confer sE2 binding to CHO cells and, when over-expressed in Huh-7.5 cells, increase susceptibility to HCV infection. Antibodies specific for SR-BI could inhibit the infectivity of cell culture and plasma derived HCV, suggesting a critical role for the receptors in the HCV lifecycle. Over-expression of SR-BI and II in Huh-7.5 cells significantly increased their susceptibility to cell culture and plasma derived HCV, suggesting that SR-BI/II density plays an important role in HCV infection. Similar observations have been reported for CD4 and chemokine receptor expression levels influencing HIV-cell entry. Over-expression of SR-BI/II enhanced JFH infectivity to a much greater extent than J6/JFH; 18 fold and 3 fold, respectively, suggesting strain specific variation within genotypic clades. Since J6/JFH and JFH differ in their Core-NS2 region, it is possible that the observed differences may be due to altered affinity of the envelope proteins for SR-BI/II.
Hepatitis C virus (HCV) enters cells via a pH- and clathrin-dependent endocytic pathway. Scavenger receptor BI (SR-BI) and CD81 are important entry factors for HCV internalization into target cells. The SR-BI gene gives rise to at least two mRNA splice variants, SR-BI and SR-BII, which differ in their C termini. SR-BI internalization remains poorly understood, but SR-BII is reported to endocytose via a clathrin-dependent pathway, making it an attractive target for HCV internalization. We demonstrate that HCV soluble E2 can interact with human SR-BI and SR-BII. Increased expression of SR-BI and SR-BII in the Huh-7.5 hepatoma cell line enhanced HCV strain J6/JFH and JFH infectivity, suggesting that endogenous levels of these receptors limit infection. Elevated expression of SR-BI, but not SR-BII, increased the rate of J6/JFH infection, which may reflect altered intracellular trafficking of the splice variants. In human plasma, HCV particles have been reported to be complexed with lipoproteins, suggesting an indirect interaction of the virus with SR-BI and other lipoprotein receptors. Plasma from J6/JFH-infected uPA-SCID mice transplanted with human hepatocytes demonstrates an increased infectivity for SR-BI/II-overexpressing Huh-7.5 cells. Plasma-derived J6/JFH infectivity was inhibited by an anti-E2 monoclonal antibody, suggesting that plasma virus interaction with SR-BI was glycoprotein dependent. Finally, anti-SR-BI antibodies inhibited the infectivity of cell culture- and plasma-derived J6/JFH, suggesting a critical role for SR-BI/II in HCV infection.
Expression of SR-BII in CHO cells confers sE2 binding. (A) Anti-SR-BI serum reactivity for CHO (closed symbol) and CHO-SR-BI (open symbol). (B) sE2 reactivity for CHO (closed symbol) and CHO-SR-BI (open symbol). Bound E2 antigen was detected with rat anti-E2 monoclonal antibody 9/75 and alexa fluor 488 anti-rat Ig. Data is expressed as the mean fluorescence intensity (MFI). CHO were transduced with TRIP lentiviral vectors expressing human SR-BI or SR-BII and assessed for their reactivity with anti-SR-BI (1:400 dilution) (C) and sE2 (30ug/ml) (D). Each panel displays parental CHO (filled), CHO SR-BI (solid line) and CHO SR-BII (dashed line)
Over-expression of SR-BI and SR-BII in Huh-7.5 cells increases infected foci size. Parental and Huh-7.5 cells over expressing human CD9, SR-BI or SR-BII were infected with JFHcc for 1 h and the infection allowed to proceed for 72h. Infected cells were visualised by staining for NS5A (green) and the nuclei counterstained with DAPI. The images were taken at 100x magnification. The bar chart in the lower panel shows the relative infection of the transduced cell lines by JFH-1 compared to the original Huh-7.5 cells.