Entry of HIV-1 into target cells requires cell-surface CD4 and additional host cell cofactors. A cofactor required for infection with virus adapted for growth in transformed T-cell lines was recently identified and named fusin. However, fusin does not promote entry of macrophage-tropic viruses, which are believed to be the key pathogenic strains in vivo. The principal cofactor for entry mediated by the envelope glycoproteins of primary macrophage-tropic strains of HIV-1 is CC-CKR-5, a receptor for the beta-chemokines RANTES, MIP-1alpha and MIP-1beta.

Infection with HIV-1 requires expression of CD4 and the chemokine receptors CXCR4 or CCR5 at the target cell surface. Engagement of these receptors by the HIV-1 envelope glycoprotein is essential for membrane fusion, but may additionally activate intracellular signaling pathways. In this study, we demonstrate that chemokines and HIV-1 envelope glycoproteins from both T-tropic and macrophage-tropic strains rapidly induce tyrosine phosphorylation of the protein tyrosine kinase Pyk2. The response requires CXCR4 and CCR5 to be accessible on the cell surface. The results presented here provide the first evidence for activation of an intracellular signaling event that can initiate multiple signaling pathways as a consequence of contact between HIV-1 and chemokine receptors.