The V3 domain of the HIV–1 gp120 envelope glycoprotein is critical for chemokine–mediated blockade of infection

Abstract

The ability of CD8 T cells derived from human immunodeficiency virus (HIV)-infected patients to produce soluble HIV-suppressive factor(s) (HIV-SF) has been suggested as an important mechanism of control of HIV infection in vivo. The C-C chemokines RANTES, MIP-1 alpha and MIP-1 beta were recently identified as the major components of the HIV-SF produced by both immortalized and primary patient CD8 T cells. Whereas they potently inhibit infection by primary and macrophage-tropic HIV-1 isolates, T-cell line-adapted viral strains tend to be insensitive to their suppressive effects. Consistent with this discrepancy, two distinct chemokine receptors, namely, CXCR4 (ref. 7) and CCR5 (ref. 8), were recently identified as potential co-receptors for T-cell line-adapted and macrophage-tropic HIV-1 isolates, respectively. Here, we demonstrate that the third hypervariable domain of the gp 120 envelope glycoprotein is a critical determinant of the susceptibility of HIV-1 to chemokines. Moreover, we show that RANTES, MIP-1 alpha and MIP-1 beta block the entry of HIV-1 into cells and that their antiviral activity is independent of pertussis toxin-sensitive signal transduction pathways mediated by chemokine receptors. The ability of the chemokines to block the early steps of HIV infection could be exploited to develop novel therapeutic approaches for AIDS.

Identification of Residues of CXCR4 Critical for Human Immunodeficiency Virus Coreceptor and Chemokine Receptor Activities

“…In general, HIV-1 infection mediated by CXCR4 mutants with amino acid substitutions in the extracellular domains was efficiently blocked by SDF-1 (Ͼ50% of WT), suggesting that ligand binding was relatively conserved. This was in particular the case for mutations at residues Glu 14 -Glu 15 and Tyr 21 , previously found to be important for interaction with SDF-1 in the mAb competition assay. By contrast, markedly lower antiviral effect of SDF-1, suggesting inefficient binding to CXCR4, was observed for the D187A mutant (40% of WT), and for the D97N and E288Q mutants (Ͻ10% of WT in both cases).…”

“…1. Besides charged residues, mutations in NT addressed the role of Tyr 7 , Tyr 12 , and Tyr 21 , which are potential sites of sulfation (50), and of the potential N-glycosylation site Asn 11 , mutated alone or with Asn 176 in ECL2. The cell surface expression of wild-type (WT) and mutant CXCR4 was monitored in simian COS cells by flow cytometry.…”

Impact of Mutations in the Coreceptor Binding Site on Human Immunodeficiency Virus Type 1 Fusion, Infection, and Entry Inhibitor Sensitivity

“…The V3 loop of gp120 is primarily responsible for mediating coreceptor specificity, determining whether CCR5, CXCR4, or both coreceptors can be used by a given virus strain (12,13,52,56). Recent modeling data suggest that the V3 loop of gp120 mimics a region of the chemokine ligands for CCR5 or CXCR4 (50) and interacts with the extracellular loops of the coreceptor.…”

“…CD4 binding by the gp120 subunit of Env induces conformational changes that enable subsequent binding to a coreceptor (6,19). These changes include the exposure of a conserved region in gp120 that, in conjunction with the V3 loop of gp120, mediates coreceptor binding (12,13,30,48,52,56). Mutations in the coreceptor-binding site of gp120 have been shown to modulate the affinity of gp120 for CCR5 and CXCR4 (5,47,48), although the effects of these mutations on membrane fusion activity have not been investigated in detail (42,53).…”

Use of G-Protein-Coupled and -Uncoupled CCR5 Receptors by CCR5 Inhibitor-Resistant and -Sensitive Human Immunodeficiency Virus Type 1 Variants

“…There have been no definitive answers, not least because various studies have used multiple different cell types that differ in their activation state and therefore yield inconsistent or contradictory outcomes (reviewed by Wu and Yoder [16]). Early studies in which G␣ i -mediated CCR5 signaling was inhibited with PTX or that used CCR5 mutants with an impaired ability to couple to G proteins (e.g., CCR5-R126N) demonstrated that signaling via CCR5 is dispensable for HIV-1 replication in cell lines or activated T cells (17)(18)(19). More recently, Env was found to trigger actin rearrangement through G␣ i -mediated CXCR4 signaling or G␣ q -mediated CCR5 signaling.…”