beta-chemokine receptor CCR5 signals through SHP1, SHP2, and Syk

The beta-chemokine receptor CCR5 has been shown to modulate cell migration, proliferation, and immune functions and to serve as a co-receptor for the human immunodeficiency virus. We and others have shown that CCR5 activates related adhesion focal tyrosine kinase (RAFTK)/Pyk2/CAK-beta. In this study , we further characterize the signaling molecules activated by CCR5 upon bi nding to its cognate ligand, macrophage inflammatory protein-1 beta (MIP1 b eta). We observed enhanced tyrosine phosphorylation of the phosphatases SHP 1 and SHP2 upon MIP1 beta stimulation of CCR5 L1.2 transfectants and T-cell s derived from peripheral blood mononuclear cells. Furthermore, we observed that SHP1 associated with RAFTK. However, using a dominant-negative phosph atase-binding mutant of RAFTK (RAFTK(m906)), we found that RAFTK does not m ediate SHP1 or SHP2 phosphorylation. SHP1 and SHP2 also associated with the adaptor protein Grb2 and the Src-related kinase Syk. Pretreatment of CCR5 L1.2 transfectants or T-cells with the phosphatase inhibitor orthovanadate markedly abolished MIP1 beta-induced chemotaxis. Syk was also activated upo n MIP1 beta stimulation of CCR5 L1.2 transfectants or T-cells and associate d with RAFTK. Overexpression of a dominant-negative Src-binding mutant of R AFTK (RAFTK(m402)) significantly attenuated Syk activation, whereas overexp ression of wild-type RAFTK enhanced Syk activity, indicating that RAFTK act s upstream of CCR5-mediated Syk activation. Taken together, these results s uggest that MIP1 beta stimulation mediated by CCR5 induces the formation of a signaling complex consisting of RAFTK, Syk, SHP1, and Grb2.