Role of Scavenger Receptor Class B Type I in Hepatitis C Virus Entry: Kinetics and Molecular Determinants

Abstract

Scavenger receptor class B type I (SR-BI) is an essential receptor for hepatitis C virus (HCV) and a cellHepatitis C virus (HCV) is a global blood-borne pathogen, with 3% of the world's population chronically infected. Most infections are asymptomatic, yet 60 to 80% become persistent and lead to severe fibrosis and cirrhosis, hepatic failure, or hepatocellular carcinoma (3). Currently available therapies are limited to the administration of pegylated alpha interferon in combination with ribavirin, which are expensive and often unsuccessful, with significant side effects (23, 36). Thus, the development of novel therapeutic approaches against HCV remains a high priority (18,40,60). Targeting the early steps of HCV infection may represent one such option, and much effort is being devoted to uncovering the mechanism of viral attachment and entry.The current view is that HCV entry into target cells occurs after attachment to specific cellular receptors via its surface glycoproteins E1 and E2 (27). The molecules to which HCV initially binds might constitute a diverse collection of cellular proteins, carbohydrates, and lipids that concentrate viruses on the cell surface and determine to a large extent which cell types, tissues, and organisms HCV can infect.CD81, claudin 1 (CLDN1), occludin (OCLN), and scavenger receptor class B type I (SR-BI) were previously shown to play essential roles in HCV cell entry (15,22,26,35,42,43,50,63,64).Recent reports suggest that CD81 engagement triggers intracellular signaling responses, ultimately leading to actin remodeling and the relocalization of CD81 to tight junctions (TJ) (11). Thus, CD81 may function as a bridge between the initial interaction of the virus with receptors on the basolateral surface of the hepatocyte and the TJ where two of the HCV entry molecules, CLDN1 and OCLN, are located. CD81 acts as a postbinding factor, and the TJ proteins CLDN1 and OCLN seem to be involved in late steps of HCV entry, such as HCV glycoprotein-dependent cell fusion (9,11,22). The discovery of TJ proteins as entry factors has added complexity to the model of HCV entry, suggesting parallels with other viruses like coxsackievirus B infection, where an initial interaction of the viral particle with the primary receptor decay-accelerating factor induces the lateral movement of the virus from the luminal surface to TJ, where coxsackievirus B binds coxsackievirusadenovirus receptor and internalization takes place (17).Much less is known about the specific role of SR-BI in virus * Corresponding author. Mailing address: Okairòs, via dei Castelli Romani 22,

Characterization of the inhibition of hepatitis C virus entry byIn vitro-generated and patient-derived oxidized low-density lipoprotein

“…In a time-course experiment with synchronized infection of target cells by multiple virions and timed addition of inhibitors, oxLDL lost its effect in parallel to anti-SR-BI 34 and significantly earlier than anti-CD81 (Fig. 5).…”

“…Thus, we overexpressed murine SR-BI (mSR-BI), which has been reported to not bind sE2 yet support HCV infection, and two point mutants where individual amino acids from mSR-BI were introduced into human SR-BI. From the set of point mutants generated by Catanese et al, 34 we chose the ones with the reportedly highest (S101A) and lowest (E210A) sE2 binding. When overexpressed in Huh-7.5 cells, mSR-BI and the point mutants, but not CD36, showed enhanced HCV entry with maintained oxLDL inhibition (Fig.…”

Entry and replication of recombinant hepatitis C viruses in cell culture

“…Despite these difficulties, related viruses, easier to cultivate, for instance bovine viral diarrhoea virus, have been used as surrogate models [38]. Secondly, recombinant forms of the envelope glycoproteins were used to search for viral receptors [33,39] but also as probes for antibody screening or neutralization of binding assays [40,41], to study HCV-induced receptor signalling during entry [42], to delineate E2-receptor interacting surfaces [43,44], or to draw a theoretical model for E2 structure [45]. Most frequently a soluble form of E2 produced in mammalian or insect cells and capable of inhibiting HCV entry [46] is used.…”

“…Huh-7 Lunet, Huh-7.5 or Huh-7.5.1 cell lines) or genetically modified to encode a reporter system allowing easy infectivity assay or to permit receptor complementation studies. Importantly, the tools are now available to study individually the 4 main HCV receptors (CD81, SR-BI, Cldn1 and Ocln): cell lines expressing very low levels of one of the receptors and retroviral vectors to rescue the expression of this receptor or one of its homologs have been developed in several laboratories [44,101,102,104,106,116,165] (see Table 1). Thanks to HCVpp, it is also possible to extend these receptor-complementation studies in cell lines that poorly replicate HCV, since the readout of HCVpp infectivity is independent on HCV replication [113,116,119].…”

Impact of Intra- and Interspecies Variation of Occludin on Its Function as Coreceptor for Authentic Hepatitis C Virus Particles

“…It is a major goal of HCV research to define and overcome these restrictions in order to create a convenient smallanimal, ideally murine, model of HCV infection (25). At the cell entry stage, it has been shown that human and murine SR-BI and CLDN1 can serve as HCV (co)receptors with about equal efficiency (8,13). Conversely, CD81 and OCLN have been reported to confer species restriction since the murine homologues of these entry factors are significantly less efficient than their human counterparts (16,29,31).…”