Interaction of Glycoprotein H of Human Herpesvirus 6 with the Cellular Receptor CD46

Abstract

Human herpesvirus 6 (HHV-6) employs the complement regulator CD46 (membrane cofactor protein) as a receptor for fusion and entry into target cells. Like other known herpesviruses, HHV-6 encodes multiple glycoproteins, several of which have been implicated in the entry process. In this report, we present evidence that glycoprotein H (gH) is the viral component responsible for binding to CD46. Antibodies to CD46 co-immunoprecipitated an ϳ110-kDa protein band specifically associated with HHV-6-infected cells. This protein was identified as gH by selective depletion with an anti-gH monoclonal antibody, as well as by immunoblot analysis with a rabbit hyperimmune serum directed against a gH synthetic peptide. In reciprocal experiments, a monoclonal antibody against HHV-6 gH was found to co-immunoprecipitate CD46. Studies using monoclonal antibodies directed against specific CD46 domains, as well as engineered constructs lacking defined CD46 regions, demonstrated a close correspondence between the CD46 domains involved in the interaction with gH and those previously shown to be critical for HHV-6 fusion (i.e. short consensus repeats 2 and 3).Human herpesvirus 6 (HHV-6) 1 is a member of the ␤-herpesvirus subfamily (reviewed in Ref. 1). Two major HHV-6 variants, A and B, have been defined that form two segregated clusters with unique genetic, biologic, and immunologic characteristics. Primary infection with HHV-6 B occurs almost universally in early childhood and has been etiologically linked to exanthema subitum. In adult life, HHV-6 infection and/or reactivation have been associated with a wide range of diseases, including multiple sclerosis, but most of these associations have yet to be substantiated by rigorous epidemiological studies. In immunocompromised people, including those infected with human immunodeficiency virus, HHV-6 B has been implicated as an opportunistic agent that may cause life-threatening respiratory tract and central nervous system infections, as well as bone marrow or organ graft failure. Moreover, HHV-6 may act as a cofactor to accelerate progression of human immunodeficiency virus disease.The best studied members of the herpesvirus family enter cells by direct fusion with the plasma membrane in a process involving binding of viral glycoproteins to specific protein receptors on the target cell (reviewed in Ref.2). Fusion is also facilitated by virus interactions with cell surface glycosaminoglycans. Recently, we identified CD46 (membrane cofactor protein) as a cellular receptor mediating fusion and entry for both HHV-6 variants (3). This glycoprotein also serves as a cellular receptor mediating critical events in the infectious process of other human pathogens, including binding/fusion/ entry of measles virus, pilus binding of different pathogenic Neisseriae, and adhesion of group A Streptococci (reviewed in Ref. 4). CD46 is a member of the regulators of complement activation (RCA) protein family. It is a type I transmembrane glycoprotein of 45-67 kDa, expressed on most or all human nucleated ce...

Variant-Specific Tropism of Human Herpesvirus 6 in Human Astrocytes

“…Evidence has been presented in this report that underlines the crucial relevance of the SCR-2 domain of CD46 in HHV-6A binding to HPDA. In contrast, it has been reported that the SCR-2 and SCR-3 domains of CD46 were involved in HHV-6A binding to lymphocytes (18,30). Ongoing experiments are exploring mechanisms of HHV-6B in HPDA.…”

Cell-surface expression of a mutated Epstein–Barr virus glycoprotein B allows fusion independent of other viral proteins

“…Recently, soluble gH͞gL was found to bind to both AGS and SVKCR2 cell lines, but not EBV-negative Akata cells, suggesting a specific receptor for gH͞gL (gHgLR) is present on epithelial cells (18). Despite the conservation of gH and gL, the only binding partner of this complex identified thus far is the binding of human herpesvirus (HHV)-6 to CD46 (19), but this does not appear to be functionally significant.…”

Intracellular Processing of Human Herpesvirus 6 Glycoproteins Q1 and Q2 into Tetrameric Complexes Expressed on the Viral Envelope

“…At 72 h postinfection, for pulse-chase labeling, the cells were incubated in methionine-free RPMI 1640 for 1 h and then pulse-labeled with Redivue Pro-mix L- 35 S in vitro cell labeling mix (400 Ci/ml; Amersham Pharmacia Biotech) for 30 min. The pulse-labeled cells were chased for 1, 2, and 4 h. At 72 h postinfection, for metabolic labeling, the cells were incubated in methionine-free RPMI 1640 for 1 h and then radiolabeled with Redivue Pro-mix L- 35 S in vitro cell labeling mix (20 Ci/ml) for 16 h. The cells were recovered and lysed in radioimmunoprecipitation (RIPA) buffer (0.01 M Tris-HCl [pH 7.4], 0.15 M NaCl, 1% sodium deoxycholate, 1% Nonidet P-40, 0.1% sodium dodecyl sulfate [SDS], 1 mM EDTA, 1 mM phenylmethylsulfonyl fluoride) for 30 min on ice. After centrifugation at 200,000 ϫ g for 1 h, the supernatants were incubated with MAb AgQ-119-or AgQ-182-protein G-Sepharose (Amersham Pharmacia Biotech) complex at 4°C for 4 h. Immunocomplexes were washed with RIPA buffer to remove unbound proteins.…”

“…Furthermore, the gH-gL-gQ-80K complex of HHV-6A was identified as a viral ligand for human CD46 (27), which is a cellular receptor of . gH has been reported to be the viral component responsible for binding to CD46 (35).In this study, we focused our attention on the analysis of this novel glycoprotein, gQ, which is unique to To further analyze HHV-6 gQ, we performed Northern blotting and found in the gQ gene region another small transcript which encodes a protein of 214 amino acids. MAbs against the predicted protein recognized 37-kDa (gQ-37K) and 34-kDa (gQ-34K) forms in HHV-6A-infected cells.…”

“…Furthermore, the gH-gL-gQ-80K complex of HHV-6A was identified as a viral ligand for human CD46 (27), which is a cellular receptor of . gH has been reported to be the viral component responsible for binding to CD46 (35).…”