CXCR4 Function Requires Membrane Cholesterol: Implications for HIV Infection

Abstract

HIV requires cholesterol and lipid rafts on target cell membranes for infection. To elucidate a possible mechanism, we determined that cholesterol extraction by hydroxypropyl-β-cyclodextrin (BCD) inhibits stromal cell-derived factor 1α (SDF-1α) binding to CXCR4 on T cell lines and PBMCs. Intracellular calcium responses to SDF-1α, as well as receptor internalization, were impaired in treated T cells. Loss in ligand binding is likely due to conformational changes in CXCR4 and not increased sensitivity to internalization. SDF-1α binding and calcium responses were effectively restored by reloading cholesterol. Immunofluorescence microscopy revealed that SDF-1α binding occurred in lipid raft microdomains that contained GM1. CXCR4 surface expression, on the other hand, only partially colocalized with GM1. HIV-1IIIB infection assays confirmed the functional loss of CXCR4 in the cell lines tested, Sup-T1 and CEM-NKR-CCR5. These data suggest that cholesterol is essential for CXCR4 conformation and function and that lipid rafts may play a regulatory role in SDF-1α signaling.