HIV-1 GP120 INDUCES AN ASSOCIATION BETWEEN CD4 AND THE CHEMOKINE RECEPTOR CXCR4

For efficient entry into target cells, certain T cell-tropic HIV-1 iso lates require both CD4 and the coreceptor CXCR4. However, the molecula r interactions among CD4, CXCR4, and the HIV-1 envelope glycoproteins are only now being elucidated. Here we show that the binding of solubl e gp120 from one macrophage-tropic and four T cell-tropic viruses to a CD4(+), but not to a CD4(-), T cell line, decreased the binding of an mAb specific for CXCR4 to its epitope, implying an interaction among gp120, CD4, and CXCR4. To confirm such an interaction, we conducted do uble-and triple-color confocal laser scanning microscopy on CD4(+)/CXC R4(+) cells and determined the extent of CD4 and CXCR4 colocalization by a semiquantitative analysis. In the absence of gp120, a low level o f constitutive colocalization between CD4 and CXCR4 was observed. Trea tment with T cell-tropic-derived gp120 and, to a lesser extent, macrop hage-tropic-derived gp120, increased the colocalization of CD4 with CX CR4 and triple staining indicated that gp120 was associated with the C D4-CXCR4 complexes. Cocapping of the gp120-CD4-CXCR4 complexes at 37 d egrees C resulted in the cointernalization of a proportion of the gp12 0-CXCR4 complexes into intracellular vesicles. These data demonstrate that the binding of gp120 to CD4(+) T cells induces the formation of a trimolecular complex consisting of gp120, CD4, and the HIV-1 corecept or molecule CXCR4.