HIV gp41 Engages gC1qR on CD4+ T Cells to Induce the Expression of an NK Ligand through the PIP3/H2O2 Pathway

Abstract

CD4+ T cell loss is central to HIV pathogenesis. In the initial weeks post-infection, the great majority of dying cells are uninfected CD4+ T cells. We previously showed that the 3S motif of HIV-1 gp41 induces surface expression of NKp44L, a cellular ligand for an activating NK receptor, on uninfected bystander CD4+ T cells, rendering them susceptible to autologous NK killing. However, the mechanism of the 3S mediated NKp44L surface expression on CD4+ T cells remains unknown. Here, using immunoprecipitation, ELISA and blocking antibodies, we demonstrate that the 3S motif of HIV-1 gp41 binds to gC1qR on CD4+ T cells. We also show that the 3S peptide and two endogenous gC1qR ligands, C1q and HK, each trigger the translocation of pre-existing NKp44L molecules through a signaling cascade that involves sequential activation of PI3K, NADPH oxidase and p190 RhoGAP, and TC10 inactivation. The involvement of PI3K and NADPH oxidase derives from 2D PAGE experiments and the use of PIP3 and H2O2 as well as small molecule inhibitors to respectively induce and inhibit NKp44L surface expression. Using plasmid encoding wild type or mutated form of p190 RhoGAP, we show that 3S mediated NKp44L surface expression on CD4+ T cells is dependent on p190 RhoGAP. Finally, the role of TC10 in NKp44L surface induction was demonstrated by measuring Rho protein activity following 3S stimulation and using RNA interference. Thus, our results identify gC1qR as a new receptor of HIV-gp41 and demonstrate the signaling cascade it triggers. These findings identify potential mechanisms that new therapeutic strategies could use to prevent the CD4+ T cell depletion during HIV infection and provide further evidence of a detrimental role played by NK cells in CD4+ T cell depletion during HIV-1 infection.

Identification of a cellular ligand for the natural cytotoxicity receptor NKp44

“…[20][21][22]38 In these CD4 1 T cells, the cell-surface translocation of NKp44L is mediated through a signaling cascade that involves sequential activation of PI3K, and NADPH oxidase, as well as TC10 inactivation. 39 Saliently, MLL5 has been described as a nuclear protein, 28 whereas NKp44L is not found in the nucleus, consistently with data of Madrid and Ganem. 40 They also showed that during lytic Kaposi's sarcoma-associated herpes virus infection, NKp44L is instead mislocalized and concentrated in the nucleus, whereas its expression on the cell surface decreases, as previously shown in chronic HIV infection.…”

A Polysaccharide Virulence Factor of a Human Fungal Pathogen Induces Neutrophil Apoptosis via NK Cells

“…Shortening the programmed PMN lifespan by abnormally accelerating PMN apoptosis can exacerbate infections (62,63). For example, HIV-1 gp41 induces H 2 O 2 -dependent NKp44L expression on CD4 + T cells, rendering them susceptible to autologous NK killing (31). A better understanding of PMN and NK regulation has the potential to lead to novel immune-based therapies.…”

“…ROS are involved in modulating NK-ligand expression on different targets (30,31) and especially in inducing surface MIC-A/B expression on airway epithelial cells without modifying this ligand's intracellular levels (28). These data strongly suggest that ROS are key mediators in the translocation of NKG2D ligands to the surface of stressed cells that are flagged for death by NK cells.…”

NCR2 (natural cytotoxicity triggering receptor 2)

“…An envelope protein of the HIV virus, gp41 is vital for viral entry into target cells (Vieillard et al, 2005). The 3S peptide of gp41 binds to its receptor gC1qR, a receptor for the globular domain of complement component 1q, on CD4 + T cells (Fausther-Bovendo et al, 2010). Binding of the 3S motif to this receptor activates a signaling cascade involving PI3K, NADPHoxidase, Rho-A, and TC10 (Fausther-Bovendo et al, 2010).…”

“…The 3S peptide of gp41 binds to its receptor gC1qR, a receptor for the globular domain of complement component 1q, on CD4 + T cells (Fausther-Bovendo et al, 2010). Binding of the 3S motif to this receptor activates a signaling cascade involving PI3K, NADPHoxidase, Rho-A, and TC10 (Fausther-Bovendo et al, 2010). NKp44L is translocated from the cytoplasm to the plasma membrane and is expressed on the cell surface, where it can bind to NKp44 of activated NK cells.…”