Differential regulation of G-protein-mediated signaling by chemokine receptors

Abstract

Monocyte chemoattractant protein-1 (MCP-1) is a member of a family of chemotactic cytoklnes that induce directed migration of leukocytes via activation of seven-transmembrane domain receptors. To identify G-proteins that couple to the two forms of the MCP-1 receptor, as well as to related chemokine receptors, we have performed cotransfection experiments in mammalian cells. In COS-7 cells, the type A and type B MCP-1 receptors coupled to Gα(i), Gα(q), and Gα16, whereas the macrophage inflammatory protein-1α/RANTES (regulated on activation, normal T cell-expressed and secreted) receptor (C-CR1) coupled to Gα(i) and Gα(q) but failed to couple to Gα16. In HEK-293 cells, however, the MCP-1 receptors and C-CR1 coupled to Gα(q) but failed to couple to Gα16. In contrast, the interleukin-8 and C5a receptors did not couple to Gα(q) in either COS-7 or HEK-293 cells but did couple to Gα16. Exchange of intracellular loops between the MCP-1 and interleukin-8 receptors to create chimeric receptors revealed that the third loop of the MCP-1 receptor accounted for virtually all of the coupling to Gα(q). We conclude that the MCP-1 and related chemokine receptors couple to multiple G-proteins, that coupling is cell type.specific, and that the third intracellular loop of the C-C type receptors mediates Gα(q) coupling.