Hepatitis C Virus Infection Upregulates CD55 Expression on the Hepatocyte Surface and Promotes Association with Virus Particles

Abstract

CD55 limits excessive complement activation on the host cell surface by accelerating the decay of C3 convertases. In this study, we observed that hepatitis C virus (HCV) infection of hepatocytes or HCV core protein expression in transfected hepatocytes upregulated CD55 expression at the mRNA and protein levels. Further analysis suggested that the HCV core protein or fulllength (FL) genome enhanced CD55 promoter activity in a luciferase-based assay, which was further augmented in the presence of interleukin-6. Mutation of the CREB or SP-1 binding site on the CD55 promoter impaired HCV core protein-mediated upregulation of CD55. HCV-infected or core protein-transfected Huh7.5 cells displayed greater viability in the presence of CD81 and CD55 antibodies and complement. Biochemical analysis revealed that CD55 was associated with cell culture-grown HCV after purification by sucrose density gradient ultracentrifugation. Consistent with this, a polyclonal antibody to CD55 captured cell culture-grown HCV. Blocking antibodies against CD55 or virus envelope glycoproteins in the presence of normal human serum as a source of complement inhibited HCV infection. The inhibition was enhanced in the presence of both the antibodies and serum complement. Collectively, these results suggest that HCV induces and associates with a negative regulator of the complement pathway, a likely mechanism for immune evasion. The complement system performs a vital effector function in the innate immune system by providing an efficient means for targeting and eliminating infected cells and invading microorganisms, including free viral particles (1-3). Activation of the complement cascade occurs primarily via the classical, alternative, or lectin pathway (2, 4). These three pathways activate C3 via cleavage to C3a and C3b by the C3 convertases. C5 convertases are generated by the association of C3b with the C3 convertases, which in turn cleaves C5 into C5a and C5b. The release of C5b initiates the nonenzymatic process of membrane-attack complex (MAC) formation that then sequentially recruits C6, C7, C8, and C9 proteins (1,3,5). The MAC forms a pore-like structure within the lipid envelope of the pathogen or the membrane of the infected cells that ultimately leads to lysis. In order to avert damage from excessive complement activation and MAC formation, host cells express membrane-bound regulatory proteins to limit these processes (6). Regulators of complement activation (RCA) are expressed on the surfaces of host cells and include CD46, CD55, and CD59 (7-9).Hepatocytes are the primary sites for synthesis of complement components in vivo. During an acute-phase (AP) response, the biosynthesis of these components is increased by the action of AP response-associated cytokines interleukin-1 (IL-1), IL-6, and tumor necrosis factor alpha (TNF-␣) (10, 11). Hepatocytes may be exposed to high local concentrations of complement components under these conditions and could promote complement-mediated damage (12)(13)(14). Decay-accelerating factor (DAF) or CD55...

CD55 is a key complement regulatory protein that counteracts complement-mediated inactivation of Newcastle Disease Virus

“…Viral infection upregulated the expression of the regulatory proteins (Fig. 2, compare lane 1 vs lane 2; lane 5 vs lane 6), which was also observed with other viruses as part of virus-induced immune regulation (Mazumdar et al, 2013). Two forms of the CD46 and CD55 molecules were detected in infected cells and the lower molecular weight versions of both CD46 and CD55 forms were enriched in infected cells and purified viruses.…”

Promotion of Cancer Stem-Like Cell Properties in Hepatitis C Virus-Infected Hepatocytes

“…c-Kit promoter activity is known to be upregulated by Sp1 (27). In previous studies, we and others have reported that HCV core enhances Sp1 promoter activity (28,29), which may be a mechanism by which c-Kit expression is enhanced in the presence of HCV.…”

Distinct CD55 Isoform Synthesis and Inhibition of Complement-Dependent Cytolysis by Hepatitis C Virus

“…We have shown that HCV core protein expression induces CD55 (15). Immortalized human hepatocytes (IHH) generated by stable transfection of HCV (genotype 1a) core genomic region into primary human hepatocytes (33) enhanced CD55 expression on cell surface.…”

“…In our previous study, we have shown that VSV G antibody induces complement dependent cytolysis (CDC) in VSV infected cells (15). Here, we used VSV infected BHK21 cells as a model to demonstrate the effect of sCD55 on CDC, as CD55 is not expressed on the cell surface of BHK21 cells (38).…”

“…CD55 accelerates the decay of preformed C3 convertases. HCV core protein upregulates CD55 expression on the cell surface and inhibits complement dependent cytolysis (15). Some tumors do not solely express a single variant of CD55, but also express different isoforms of the protein (17).…”