CXCR4 engagement is required for HIV-1–induced L-selectin shedding

Abstract

IntroductionLymphocyte homing requires a sequence of critical adhesion events to allow naive lymphocytes to rapidly recirculate from the blood into lymphoid organs and is an important immune surveillance function in vivo. L-selectin (CD62L), which is constitutively expressed at high levels on naive T lymphocytes, mediates rolling and tethering of naive T lymphocytes along endothelial surfaces. 1-3 After L-selectin binds to its ligand on high endothelial venules, G protein-linked receptors activate integrins that mediate the arrest and diapedesis of naive T lymphocytes into the peripheral lymph nodes (PLNs). 4 In experiments using neutralizing anti-L-selectin monoclonal antibodies (mAbs) or mice that are genetically deficient in L-selectin, naive T lymphocytes do not home to PLNs, and primary T-cell responses to antigen are impaired. 1,5,6 L-selectin is shed from the cell surface by a proteolytic mechanism upon crosslinking by mAbs 7 or upon T-cell activation. 8,9 The signal transduction mechanisms leading to L-selectin cleavage are not yet defined.To date, little is known about homing and recirculation of lymphocytes in HIV disease. It has been shown that HIV-1 and simian immunodeficiency virus (SIV) induce preferential homing of T cells to the intestine in engrafted severe combined immunodeficiency mice. 10 A study by Zhang et al showed a significant depletion of naive CD45RA ϩ CD4 ϩ T cells, out of proportion to total CD4 ϩ T cells, in peripheral lymphoid tissue from HIV-1-infected individuals. 11 Additionally, individuals infected with HIV-1 have a 3-fold increase of soluble L-selectin in serum, 12 and recent studies show that L-selectin on lymphocytes is significantly reduced in HIV-1-infected children, compared with uninfected controls. 13 We have previously reported that ligation of CD4 by mAb or by HIV-1 NL4-3 results in the metalloproteinasedependent shedding of L-selectin from primary resting CD4 ϩ T cells. 14 We have also shown that this L-selectin shedding results in inhibition of T-cell homing to the lymph nodes. 14 In this report, using the CXC chemokine receptor 4 (CXCR4) antagonist, AMD3100, and the CXCR4 natural ligand, stromal-derived factor 1␣ (SDF-1␣), we show that engagement of CXCR4, in addition to CD4, is required for the L-selectin shedding induced by the glycoprotein (gp)120-CD4 interaction. Study design Isolation of human CD4 ؉ T cellsHuman peripheral blood mononuclear cells (PBMCs) were isolated by Ficoll-Hypaque (Amersham Pharmacia, Piscataway, NJ) density-gradient centrifugation of heparinized venous blood obtained from healthy donors. CD4 ϩ T cells were purified by negative selection with a cocktail of antibodies directed against CD8 (OKT8; American Type Culture Collection [ATCC], Rockville, MD), CD14, CD16, and CD19 (PharMingen, San Diego, CA). 14 More than 99% of cells were in the G 0 /G 1 phase of the cell cycle, and 90% to 95% of cells were CD4 ϩ . Reagents and cell linesCD62L-phycoerythrin (PE) (Leu-8) and CD4-PE (Leu3a) were purchased from Becton Dickinson (San Jose, CA). CXCR4...

HIV-1 Nef and Vpu Interfere with L-Selectin (CD62L) Cell Surface Expression To Inhibit Adhesion and Signaling in Infected CD4+T Lymphocytes

“…Moreover, studies on resting CD4 ϩ T cells exposed in vitro to HIV-1 reported transient downmodulation (18,19) or, conversely, upmodulation of CD62L (11). There- fore, the influence of HIV-1 on CD62L expression on bystander T cells clearly awaits elucidation.…”

“…Whether loss of CD62L ϩ cells and high sCD62L levels reflect the dysfunction and enhanced activation of the immune system in the infected host or are a direct effect of HIV-1 on CD62L ϩ cells is not yet clear. Finkel and colleagues reported that ligation of HIV-1 to CD4 and CXCR4 receptors is sufficient to induce MMP-mediated shedding of CD62L on CD4 ϩ T cells (18,19). Moreover, Marodon et al showed that CD62L was downmodulated on CD4 ϩ T cells infected in vitro with HIV-1, although the underlying mechanism was not analyzed (20).…”

Expanding Role of Circulating Adhesion Molecules in Assessing Prognosis and Treatment Response in Human Immunodeficiency Virus Infection

“…A possible explanation is that down-regulation of the surface L-selectin molecule might be associated with increased cleavage and/or decreased clearance, thus resulting in elevated serum sLs levels. As has recently been shown, engagement of both the CD4 molecule and the HIV coreceptor CXCR4 is required for HIV-induced L-selectin shedding on CD4-expressing T lymphocytes (86). P-selectin is stored in platelets and endothelial cells and is expressed on the cell surface upon activation (4).…”

CXCR4-Tropic HIV-1 Envelope Glycoprotein Functions as a Viral Chemokine in Unstimulated Primary CD4+ T Lymphocytes

“…Chemoattractant gradients induce the polarization of the phosphoinositide signal transduction machinery, resulting in reorganization of the actin cytoskeleton and ultimately in directed cell migration (16). Triggering of chemoreceptors by HIV-1 envelope glycoprotein was shown to induce some, though often not all, of these responses, depending on the chemoreceptor used and of the nature of target cells (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29). Previous studies showed that binding of gp120 from CXCR4-tropic (X4) HIV-1 strains to activated CD4 ϩ T cells induced the phosphorylation of kinases involved in cell adhesion and directed migration, such as Pyk-2 and PI3K (17,18).…”