CD81 is an entry coreceptor for hepatitis C virus

Abstract

Hepatitis C virus (HCV) envelope glycoproteins E1͞E2 can pseudotype retroviral particles and efficiently mediate entry into target cells. Using this experimental system, we determined HCV tropism for different cell types. Only primary hepatocytes and one hepatoma cell line were susceptible to HCV pseudovirus entry, which could be inhibited by sera from HCV-infected individuals. Furthermore, expression of the putative HCV receptor CD81 on nonpermissive human hepatic but not murine cells enabled HCV pseudovirus entry. Importantly, inhibition of viral entry by an anti-CD81 mAb occurred at a step following HCV attachment to target cells. Our results indicate that CD81 functions as a postattachment entry coreceptor and that other cellular factors act in concert with CD81 to mediate HCV binding and entry into hepatocytes.I t is estimated that 170 million people worldwide are infected with the hepatitis C virus (HCV) and are at risk of developing chronic hepatitis or cirrhosis, the latter often leading to hepatocellular carcinoma (1, 2). In the past, difficulties with culturing the virus and expressing fusogenic envelope glycoproteins limited studies of HCV tropism and entry. RT-PCR-and electron microscopy-based approaches were relied on to demonstrate the presence of HCV RNA and proteins in primary hepatocytes and certain hepatoma cell lines (3-8). Furthermore, the existence of extrahepatic HCV reservoirs was suggested by the detection of viral RNA in serum and peripheral blood mononuclear cells (PBMC) (9-11). Recently, a major technical advance in the field has been the discovery that unmodified HCV envelope glycoproteins can pseudotype retroviral particles and mediate entry into target cells (12)(13)(14)(15). This model seems to authentically replicate the early steps of the HCV life cycle, enabling detailed studies of HCV tropism and entry into target cells.The cellular tropism of enveloped viruses is largely determined by selective interactions of viral envelope glycoproteins with specific cell-surface receptors. Entry generally proceeds by a cascade of coordinated events wherein virus binding to a host molecule triggers exposure of cryptic envelope glycoprotein domains that mediate downstream interactions and functions. We and others recently demonstrated that DC-SIGN (dendritic cell-specific ICAM-3 grabbing nonintegrin; CD209) and L-SIGN (DC-SIGNR, liver and lymph node specific; CD209L) function as HCV capture receptors but do not mediate viral entry into target cells (16,17). Candidate HCV entry receptors include CD81, scavenger receptor class B type 1, low density lipoprotein receptor, and glycosaminoglycans (18)(19)(20). CD81 is the most extensively characterized putative HCV receptor. A number of groups have demonstrated that the soluble ectodomain of HCV envelope glycoprotein E2 binds specifically and with relatively high affinity (K d Ϸ10 Ϫ8 M) to human and chimpanzee CD81 (21-24). However, CD81 is widely expressed on human cells and therefore cannot account for the restricted tropism of HCV to hepatocytes...

Centrifugal enhancement of hepatitis C virus infection of human hepatocytes

“…Thus, the impact of centrifugation on the known cellular factors that modulate HCV infection of human hepatocytes was examined. In addition to determine the effect of centrifugation on the expression of CD81 and claudin-1, the two recognized receptors used by HCV to entry into hepatocyts (Cormier et al, 2004;Evans et al, 2007), whether centrifugation inhibit the expression of IFN-α, a potent anti-HCV cytokine , was also investigated.…”

“…In order to explore the mechanism(s) involved in the centrifugal enhancement of HCV infectivity, the effect of centrifugation on the expression of CD81 or claudin-1, two recognized receptors for HCV entry into human hepatocytes (Cormier et al, 2004;Evans et al, 2007), was investigated. The centrifugation had little effect on CD81 or claudin-1 expression in Huh7.5.1 cells at both RNA and protein levels ( Fig.…”

Identification of Conserved Residues in the E2 Envelope Glycoprotein of the Hepatitis C Virus That Are Critical for CD81 Binding

“…Several other cell surface molecules have been reported to bind to native HCV particles or recombinant E2, including the low-density lipoprotein receptor (1,51), dendritic-cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) and liver/lymph nodespecific intercellular adhesion molecule 3-grabbing integrin (L-SIGN or DC-SIGNR) (20,32,42), glycosaminoglycans (4), and scavenger receptor class B type I (SR-B1) (6,44). Despite early doubts about the function of CD81 in HCV entry, data using recently developed assays of retroviral pseudoparticles (HCVpp) and in vitro infectious clones support a central role for CD81 in mediating infection (6,11,29,31).…”

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

“…It is thought that the viral envelope glycoproteins E1 and E2 interact with these four (co)receptors sequentially and that these interactions are orchestrated by cell signaling processes (6,14,28). SR-BI may act early and the tight junction components may act later in this process (11,13,21,24,42). The exact mechanisms and sequence of the interactions remain to be determined, but the result is known to be the uptake of the virion or a virion-coreceptor complex into an endosomal compartment.…”