Extracellular Matrix Proteins Mediate HIV-1 gp120 Interactions with α₄β₇

Abstract

Gut-homing αβ CD4 T lymphocytes have been shown to be preferentially targeted by human immunodeficiency virus type 1 (HIV-1) and are implicated in HIV-1 pathogenesis. Previous studies demonstrated that HIV-1 envelope protein gp120 binds and signals through αβ and that this likely contributes to the infection of αβ T cells and promotes cell-to-cell virus transmission. Structures within the second variable loop (V2) of gp120, including the tripeptide motif LDV/I, are thought to mediate gp120-αβ binding. However, lack of αβ binding has been reported in gp120 proteins containing LDV/I, and the precise determinants of gp120-αβ binding are not fully defined. In this work, we report the novel finding that fibronectins mediate indirect gp120-αβ interactions. We show that Chinese hamster ovary (CHO) cells used to express recombinant gp120 produced fibronectins and other extracellular matrix proteins that copurified with gp120. CHO cell fibronectins were able to mediate the binding of a diverse panel of gp120 proteins to αβ in an cell binding assay. The V2 loop was not required for fibronectin-mediated binding of gp120 to αβ, nor did V2-specific antibodies block this interaction. Removal of fibronectin through anion-exchange chromatography abrogated V2-independent gp120-αβ binding. Additionally, we showed a recombinant human fibronectin fragment mediated gp120-αβ interactions similarly to CHO cell fibronectin. These findings provide an explanation for the apparently contradictory observations regarding the gp120-αβ interaction and offer new insights into the potential role of fibronectin and other extracellular matrix proteins in HIV-1 biology. Immune tissues within the gut are severely damaged by HIV-1, and this plays an important role in the development of AIDS. Integrin αβ plays a major role in the trafficking of lymphocytes, including CD4 T cells, into gut lymphoid tissues. Previous reports indicate that some HIV-1 gp120 envelope proteins bind to and signal through αβ, which may help explain the preferential infection of gut CD4 T cells. In this study, we demonstrate that extracellular matrix proteins can mediate interactions between gp120 and αβ This suggests that the extracellular matrix may be an important mediator of HIV-1 interaction with αβ-expressing cells. These findings provide new insight into the nature of HIV-1-αβ interactions and how these interactions may represent targets for therapeutic intervention.

Select gp120 V2 domain specific antibodies derived from HIV and SIV infection and vaccination inhibit gp120 binding to α4β7

“…The affinity of this peptide (cV2 92TH023) for α 4 β 7 ( K D (nM) 1.150) was close to that of A244 gp120 ( Fig 1E ), demonstrating that a cV2 is sufficient to mediate the high-affinity interaction shown in Fig 1B . Moreover, it indicates that this high-affinity interaction does not require the glycans that decorate the V2 of GSID A244 gp120, or any bridging protein [ 13 ]. When we replaced α 4 β 7 with α 4 β 1 affinity for cV2 92TH023 was reduced by >8000 -fold (( K D (nM) 9710) ( Fig 1F ), demonstrating binding specificity and the fact that V2, like MAdCAM, preferentially binds to α 4 β 7 .…”

“…Yet we find that V2s from three subtypes of HIV, as well as a V2 from SIV retain the capacity to bind to α 4 β 7, suggesting that this interaction is a general property across HIV subtypes. Other studies failed to detect a specific interaction between α 4 β 7 and gp120 [ 13 , 14 ]. An explanation for this discrepancy likely reflects two variables.…”

“…We and others have demonstrated that both HIV and SIV recombinant envelope proteins directly bind integrin α 4 β 7 (α 4 β 7 ), a gut homing receptor [ 9 – 12 ], while notably, some studies have failed to detect this interaction [ 13 – 15 ]. α 4 β 7 is not required for viral entry [ 15 – 17 ].…”

V2-Specific Antibodies in HIV-1 Vaccine Research and Natural Infection: Controllers or Surrogate Markers

“…The integrin α4β7 mediates homing of immune cells, including highly HIV-susceptible CD4 + T cell subsets to the gastrointestinal tract, which is one of the primary sites of HIV and SIV pathogenesis [184,185,186,187,188,189,190]. HIV Env has been shown to bind to and signal through α4β7 via a conserved tripeptide LDI/V motif in V2 (aa 179–181) (Figure 2 and Figure 3) [191], presumably complemented by secondary binding motifs (e.g., aa 170–173) and unspecific binding mechanisms [192,193,194]. Importantly, α4β7 serves as an attachment factor for HIV and not as an entry receptor, and α4β7 blocking does not neutralize HIV-1 infection [191].…”

High-level expression of the monomeric SARS-CoV-2 S protein RBD 320-537 in stably transfected CHO cells by the EEF1A1-based plasmid vector

“…Human tissue plasminogen activator signal peptide (hTPA SP, amino acid sequence MDAMKRGLCCVLLLCGAVFVSAS) is commonly used for heterologous protein expression in mammalian cells. It was successfully used for the expression of SARS-CoV S protein in the form of DNA vaccine [31] and envelope viral protein gp120 [32].…”