HIV-1 infection through the CCR5 receptor is blocked by receptor dimerization

Abstract

The identification of the chemokine receptors as receptors for HIV-1 has boosted interest in these molecules, raising expectations for the development of new strategies to prevent HIV-1 infection. The discovery that chemokines block HIV-1 replication has focused attention on identifying their mechanism of action. Previous studies concluded that this inhibitory effect may be mediated by steric hindrance or by receptor down-regulation. We have identified a CCR5 receptor-specific mAb that neither competes with the chemokine for binding nor triggers signaling, as measured by Ca 2+ influx or chemotaxis. The antibody neither triggers receptor down-regulation nor interferes with the R5 JRFL viral strain gp120 binding to CCR5, but blocks HIV-1 replication in both in vitro assays using peripheral blood mononuclear cells as HIV-1 targets, as well as in vivo using human peripheral blood mononuclear cell-reconstituted SCID (severe combined immunodeficient) mice. Our evidence shows that the anti-CCR5 mAb efficiently prevents HIV-1 infection by inducing receptor dimerization. Chemokine receptor dimerization also is induced by chemokines and is required for their anti-HIV-1 activity. In addition to providing a molecular mechanism through which chemokines block HIV-1 infection, these results illustrate the prospects for developing new tools that possess HIV-1 suppressor activity, but lack the undesired inflammatory side effects of the chemokines.

Rescue of HIV-1 Receptor Function through Cooperation between Different Forms of the CCR5 Chemokine Receptor

“…The finding that complexes of defective CCR5 mutants mediate HIV-1 infection can appear to be contradictory with conclusions of a study linking the antiviral activity of an anti-CCR5 mAb (designated CCR5-02) to the dimerization of CCR5 that it apparently induced (36). Because the CCR5-02 mAb did not interfere with the surface expression and chemokine receptor activity of CCR5, the authors inferred that its conformation in the context of dimers does not permit a functional interaction with HIV-1.…”

“…This process was apparently constitutive and proposed to play a role in the routing of CCR5 to the cell surface. However, in other studies, dimers of the CCR2, CCR5, or CXCR4 were detected only if cells were treated with the cognate chemokine ligands (35)(36)(37) or with a monoclonal antibody in the case of CCR5 (36). In these different studies, dimers of …”

“…Conflicting results have been obtained in the case of chemokine receptors. In a series of studies, the formation of CCR5, CCR2, or CXCR4 homodimers as well as CCR5/CCR2 heterodimers was found to occur upon treatment of cells with the cognate chemokine ligands (35)(36)(37)(38). On the contrary, Benkirane et al found that wild-type CCR5 could be trapped in the endoplasmic reticulum of cells expressing the truncated form of CCR5 (residues 1-187) encoded by the ⌬32 allele and proposed that formation of dimers was a constitutive process necessary for efficient processing of the receptor to the cell surface (39).…”

Reduced Cell Surface Expression of CCR5 in CCR5Δ32 Heterozygotes Is Mediated by Gene Dosage, Rather Than by Receptor Sequestration

“…Among human CKRs, both CCR2 and CCR5 have been shown to form dimers upon ligand binding (43,49), and CCR5 dimerization has been presumed to modulate HIV entry (49) and T cell activation through the Jak signaling pathway (50). Ligandor antibody-induced CCR5 dimerization (49) and heterodimerization of CCR5 or CXCR4 with a natural CCR2 mutant allele, CCR2-V64I (51), have been proposed to hinder HIV infection. Using a yeast two-hybrid system, Benkirane et al (20) demonstrated that CCR5 formed dimers through sequence spanning the N terminus and the first TM domain.…”

“…Heterodimerization between related subunits of GPCRs may alter or expand ligand specificity (45), and some may function as oligomers in vivo (48). Among human CKRs, both CCR2 and CCR5 have been shown to form dimers upon ligand binding (43,49), and CCR5 dimerization has been presumed to modulate HIV entry (49) and T cell activation through the Jak signaling pathway (50). Ligandor antibody-induced CCR5 dimerization (49) and heterodimerization of CCR5 or CXCR4 with a natural CCR2 mutant allele, CCR2-V64I (51), have been proposed to hinder HIV infection.…”