HIV-1 infection triggers lateral membrane diffusion following interaction of the viral envelope with cell surface receptors. We show that these membrane changes are necessary for infection, as initial gp120-CD4 engagement leads to redistribution and clustering of membrane microdomains, enabling subsequent interaction of this complex with HIV-1 co-receptors. Disruption of cell membrane rafts by cholesterol depletion before viral exposure inhibits entry by both X4 and R5 strains of HIV-1, although viral replication in infected cells is unaffected by this treatment. This inhibitory effect is fully reversed by cholesterol replenishment of the cell membrane. These results indicate a general mechanism for HIV-1 envelope glycoprotein-mediated fusion by reorganization of membrane microdomains in the target cell, and offer new strategies for preventing HIV-1 infection.

Human immunodeficiency virus (HIV)-1 infectivity requires actin-dependent clustering of host lipid raft–associated receptors, a process that might be linked to Rho guanosine triphosphatase (GTPase) activation. Rho GTPase activity can be negatively regulated by statins, a family of drugs used to treat hypercholesterolemia in man. Statins mediate inhibition of Rho GTPases by impeding prenylation of small G proteins through blockade of 3-hydroxy-3-methylglutaryl coenzyme A reductase. We show that statins decreased viral load and increased CD4+ cell counts in acute infection models and in chronically HIV-1–infected patients. Viral entry and exit was reduced in statin-treated cells, and inhibition was blocked by the addition of l-mevalonate or of geranylgeranylpyrophosphate, but not by cholesterol. Cell treatment with a geranylgeranyl transferase inhibitor, but not a farnesyl transferase inhibitor, specifically inhibited entry of HIV-1–pseudotyped viruses. Statins blocked Rho-A activation induced by HIV-1 binding to target cells, and expression of the dominant negative mutant RhoN19 inhibited HIV-1 envelope fusion with target cell membranes, reducing cell infection rates. We suggest that statins have direct anti–HIV-1 effects by targeting Rho.

The CXCR4 chemokine receptor and the delta opioid receptor (DOR) are pertussis toxinsensitive G protein-coupled receptors (GPCR). Both are widely distributed in brain tissues and immune cells, and have key roles in inflammation processes and in pain sensation on proximal nerve endings. We show that in immune cells expressing CXCR4 and DOR, simultaneous addition of their ligands CXCL12 and [D-Pen2, DPen5]enkephalin does not trigger receptor function. This treatment does not affect ligand binding or receptor expression, nor does it promote heterologous desensitization. Our data indicate that CXCR4 and DOR form heterodimeric complexes that are dynamically regulated by the ligands. This is compatible with a model in which GPCR oligomerization leads to suppression of signaling, promoting a dominant negative effect. Knockdown of CXCR4 and DOR signaling by heterodimerization might have repercussions on physiological and pathological processes such as inflammation, pain sensation and HIV-1 infection.Supporting Information for this article is available at http://www.wiley-vch.de/contents/jc_2040/2008/37630_s.pdf See accompanying article: http://dx.doi.org/10.1002/eji200738101 IntroductionThe G protein-coupled receptors (GPCR) represent the largest, most diverse family of transmembrane receptors expressed in the body. They act through G proteins to regulate intracellular processes including cell adhesion, migration and proliferation [1]. Studies show that the GPCR can function as oligomers [2,3]. Perhaps their most striking feature is that GPCR form not only functional homo-oligomers, but can also associate with other GPCR to form hetero-oligomers. Homo-and hetero-oligomers differ in their pharmacological pro- files, ligand binding affinity, and/or internalization pathways [4][5][6]. GPCR hetero-oligomerization would thus enable generation of new types of signaling units. Opioid and chemokine receptors are members of the Ga i protein-linked GPCR. These receptors and their ligands are expressed in neurons and glial cells, and in immune system cells such as lymphocytes, monocytes and neutrophils [7]. They share the same microenvironment in many physiological situations and are essential for inflammation processes. Chemokine receptors promote immune cell migration to and adhesion at the inflammation site, whereas opioid receptors reduce pain sensation on proximal nerve endings. Opioid receptors can also regulate the immune response, as they alter antibody responses, cell-mediated immunity, phagocytic activity, adhesion and chemotaxis [8][9][10][11]. Opioids also prevent leukocyte movement toward chemokine gradients [12], and cross-desensitization is described between opioid and chemokine receptors [8,10]. The CCR5 chemokine receptor can form heterodimers with each of the three opioid receptor subtypes (l, d, and j) [8,10].CXCR4, the most widely expressed chemokine receptor [13], is crucial for correct lymphocyte trafficking [14], hematopoiesis, and development [15][16][17]. It is also a coreceptor for T-tropic HIV strains [1...

A current challenge in cell motility studies is to understand the molecular and physical mechanisms that govern chemokine receptor nanoscale organization at the cell membrane, and their influence on cell response. Using single-particle tracking and super-resolution microscopy, we found that the chemokine receptor CXCR4 forms basal nanoclusters in resting T cells, whose extent, dynamics, and signaling strength are modulated by the orchestrated action of the actin cytoskeleton, the co-receptor CD4, and its ligand CXCL12. We identified three CXCR4 structural residues that are crucial for nanoclustering and generated an oligomerization-defective mutant that dimerized but did not form nanoclusters in response to CXCL12, which severely impaired signaling. Overall, our data provide new insights to the field of chemokine biology by showing that receptor dimerization in the absence of nanoclustering is unable to fully support CXCL12-mediated responses, including signaling and cell function in vivo.