Study on molecular mechanisms of hepatitis C virus infection.

尽管hCD81、LDL-R、SR-B1和DC-SIGN等几种细胞表面分子已被提出作为丙型肝炎病毒（HCV）受体的候选者，但由于缺乏强大可靠的体外细胞培养系统来繁殖HCV，尚不清楚这些分子是否能作为功能性细胞受体发挥作用。作为研究HCV感染的替代系统，基于水泡性口炎病毒（HCVpv）和逆转录病毒（HCVpp）的携带HCV包膜糖蛋白的假病毒已经被开发出来。我们之前已经证明，人成纤维细胞生长因子受体（hFGFR） 4是一种基于与患者血清中HCVpv、HCV样颗粒和真实HCV颗粒特异性结合的HCV结合受体。最近我们发现293T细胞和CHO细胞中产生的HCVpv （HCVpv/CHO）分别表现出hcd81依赖性和非依赖性感染。hFGF2可抑制HCVpv/CHO对HepG2细胞的感染，hFGF2是一种可溶性蛋白，代表hFGFR5的外域，与IgG的Fe区融合（hFGFR5/Fc），或抗hFGFR5抗体。hFGFR5在293T和Huh7细胞中的过表达增强了对HCVpv/CHO感染的易感性。相反，sirna介导的HepG2细胞中hFGFR5的敲低导致HCVpv/CHO的感染性降低。此外，hFGFR5/Fc抑制了患者血清中真实HCV颗粒与HepG2细胞的结合。最后，在CHO细胞中表达hFGFR5（而不是hFGFR4）使它们允许HCVpv/CHO感染。总之，这些结果表明hFGFR5可能以不依赖于hcd81的方式参与HCV的内化过程。

Although several cell surface molecules such as hCD81, LDL-R, SR-B1, and DC-SIGN have been proposed as candidates for hepatitis C virus (HCV) receptor, it is still unclear if any of these molecules can play a role as a functional cellular receptor, due to the lack of robust and reliable in vitro cell culture systems to propagate HCV. As a surrogate system for the study of HCV infection, pseudotype viruses bearing HCV envelope glycoproteins based on vesicular stomatitis viruses (HCVpv) and retroviruses (HCVpp) have been developed. We have previously shown that human fibroblast growth factor receptor (hFGFR) 4 is a binding receptor for HCV based on the specific binding with HCVpv, HCV-like particles and authentic HCV particles in patient sera. Recently we found that HCVpv generated in 293T cells and CHO cells (HCVpv/CHO) exhibit hCD81-dependent and -independent infection, respectively. Infection of HCVpv/CHO to HepG2 cells was inhibited by hFGF2, a soluble protein representing the ectodomain of hFGFR5 fused with the Fe region of IgG (hFGFR5/Fc), or anti-hFGFR5 antibody. Overexpression of hFGFR5 in 293T and Huh7 cells enhanced the susceptibility to HCVpv/CHO infection. In contrast, siRNA-mediated knockdown of hFGFR5 in HepG2 cells resulted in the reduction of infectivity of HCVpv/CHO. Furthermore, binding of the authentic HCV particles in patient sera to HepG2 cells was inhibited by the hFGFR5/Fc. Finally, expression of hFGFR5 (but not hFGFR4) in CHO cells rendered them permissive for HCVpv/CHO infection. Together, these results suggest the possible involvement of hFGFR5 in the internalization process of HCV in a hCD81-independent fashion.