Identification of New Regions in HIV-1 gp120 Variable 2 and 3 Loops that Bind to [alpha]4[beta]7 Integrin Receptor

• Published in: PloS one 2015-12, Vol.10 (12), p.e0143895
• Main Authors: Peachman, Kristina K, Karasavvas, Nicos, Chenine, Agnes-Laurence, McLinden, Robert, Rerks-Ngarm, Supachai, Jaranit, Kaewkungwal, Nitayaphan, Sorachai, Pitisuttithum, Punnee, Tovanabutra, Sodsai, Zolla-Pazner, Susan, Michael, Nelson L, Kim, Jerome H, Alving, Carl R, Rao, Mangala
• Format: Article
• Language: English
• Subjects: Analysis; Cell adhesion; HIV; Integrins; Protein binding
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0143895

The gut mucosal homing integrin receptor [alpha]4[beta]7 present on activated CD4.sup.+ T cells interacts with the HIV-1 gp120 second variable loop (V2). Case control analysis of the RV144 phase III vaccine trial demonstrated that plasma IgG binding antibodies specific to scaffolded proteins expressing the first and second variable regions (V1V2) of HIV envelope protein gp120 containing the [alpha]4[beta]7 binding motif correlated inversely with risk of infection. Subsequently antibodies to the V3 region were also shown to correlate with protection. The integrin receptor [alpha]4[beta]7 was shown to interact with the LDI/V motif on V2 loop but recent studies suggest that additional regions of V2 loop could interact with the [alpha]4[beta]7. Thus, there may be several regions on the V2 and possibly V3 loops that may be involved in this binding. Using a cell line, that constitutively expressed [alpha]4[beta]7 receptors but lacked CD4, we examined the contribution of V2 and V3 loops and the ability of V2 peptide-, V2 integrin-, V3-specific monoclonal antibodies (mAbs), and purified IgG from RV144 vaccinees to block the V2/V3-[alpha]4[beta]7 interaction. We demonstrate that [alpha]4[beta]7 on RPMI8866 cells bound specifically to its natural ligand mucosal addressin cell adhesion molecule-1 (MAdCAM-1) as well as to cyclic-V2 and cyclic-V3 peptides. This binding was inhibited by anti-[alpha]4[beta]7-specific monoclonal antibody (mAb) ACT-1, mAbs specific to either V2 or V3 loops, and by purified primary virions or infectious molecular clones expressing envelopes from acute or chronic subtypes A, C, and CRF01_AE viruses. Plasma from HIV-1 infected Thai individuals as well as purified IgG from uninfected RV144 vaccinees inhibited (0-50%) the binding of V2 and V3 peptides to [alpha]4[beta]7. Our results indicate that in addition to the tripeptide LDI/V motif, other regions of the V2 and V3 loops of gp120 were involved in binding to [alpha]4[beta]7 receptors and this interaction was blocked by anti-V2 peptide, anti-V2 integrin, and anti-V3 antibodies. The ability of purified IgG from some of the uninfected RV144 vaccinees to inhibit [alpha]4[beta]7 raises the hypothesis that anti-V2 and anti-V3 antibodies may play a role in blocking the gp120-[alpha]4[beta]7 interaction after vaccination and thus prevent HIV-1 acquisition.