Abstract
A strategy for antiviral drug discovery is the elucidation and imitation of viral interference mechanisms. HIV-1 patients benefit from a coinfection with GB Virus C (GBV-C), since HIV-positive individuals with long-term GBV-C viraemia show better survival rates than HIV-1 patients without persisting GBV-C. A direct influence of GBV-C on HIV-1 replication has been shown in coinfection experiments. GBV-C is a human non-pathogenic member of the flaviviridae family that can replicate in T and B cells. Therefore, GBV-C shares partly the same ecological niche with HIV-1. In earlier work we have demonstrated that recombinant glycoprotein E2 of GBV-C and peptides derived from the E2 N-terminus interfere with HIV entry. In this study we investigated the underlying mechanism. Performing a virus-cell fusion assay and temperature-arrested HIV-infection kinetics, we provide evidence that the HIV-inhibitory E2 peptides interfere with late HIV-1 entry steps after the engagement of gp120 with CD4 receptor and coreceptor. Binding and competition experiments revealed that the N-terminal E2 peptides bind to the disulfide loop region of HIV-1 transmembrane protein gp41. In conjunction with computational analyses, we identified sequence similarities between the N-termini of GBV-C E2 and the HIV-1 glycoprotein gp120. This similarity appears to enable the GBV-C E2 N-terminus to interact with the HIV-1 gp41 disulfide loop, a crucial domain involved in the gp120-gp41 interface. Furthermore, the results of the present study provide initial proof of concept that peptides targeted to the gp41 disulfide loop are able to inhibit HIV fusion and should inspire the development of this new class of HIV-1 entry inhibitors.
Highlights
GB virus C (GBV-C) is a common human virus that can be transmitted sexually, parenterally and vertically from mother to child [1,2]
We addressed the question of whether or not the two overlapping GBV-C E2 20 mer peptides P4-7 and P6-2 have an impact on the cell surface presentation of the HIV-1 receptors CD4 and CXCR4 or CCR5, respectively
The cell surface presentation of these receptors was quantified via flow cytometry after incubation of primary peripheral blood mononuclear cells (PBMCs) and of HeLa-derived HIV indicator cells expressing CD4, CCR5 and CXCR4, designated as TZM-bl cells, with the E2 peptides P4-7 and P6-2
Summary
GB virus C (GBV-C) is a common human virus that can be transmitted sexually, parenterally and vertically from mother to child [1,2]. In contrast to HCV, in the majority of GBV-C infected individuals, the occurrence of anti-E2 antibodies is associated with clearance of the virus [12]. GBV-C RNA prevalence rates range from 20% to 30% in HCV coinfected individuals and from 15% to 40% in HIV-1 patients (reviewed in [3]). Several effects have been proposed to explain the interference with HIV-1, including induction of chemokines, CD4 receptor and coreceptor modulation, prevention of Th2 cytokine profile, reduction of T cell activation, as well as downmodulation of FAS-mediated apoptosis in GBV-C coinfected individuals [24,25,26,27,28,29,30,31]. Two overlapping 20 mer peptides (P4-7 and P6-2) presenting amino acids 37 to 56 (WDRGNVTLLCDCPNGPWVWV) and 45 to 64 (LCDCPNGPWVWVPAFCQAVG), respectively, of the GBV-C E2 protein, were shown to be most potent with IC50s between 2 and 0.2 mM in a TZM-bl-based HIV-1 replication assay
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