Signal Transduction and Ligand Specificity of the Human Monocyte Chemoattractant Protein-1 Receptor in Transfected Embryonic Kidney Cells

We have examined the ligand specificity and signal transduction pathways of a recently cloned receptor for monocyte chemoattractant protein-1 (MCP-1). In human 293 cells stably transfected with the MCP-1 receptor, MCP-1 bound specifically with high affinity (Kd = 260 pM) and induced a rapid mobilization of calcium from intracellular stores. The closely related chemokines MIP-1 alpha, MIP-1 beta, RANTES, interleukin 8 (IL-8), and Gro-alpha were inactive at concentrations as high as 300 nM. Activation of the MCP-1 receptor potently inhibited adenylyl cyclase with an IC50 = 90 pM. Activation of the MIP-1 alpha/RANTES receptor also mediated inhibition of adenylyl cyclase activity but with a different pharmacological profile: MIP-1 alpha (110 pM, IC50), RANTES (140 pM), MIP-1 beta (10 nM), and MCP-1 (820 nM). Mobilization of intracellular calcium and inhibition of adenylyl cyclase were blocked by pertussis toxin, suggesting that the MCP-1 receptor coupled to G alpha i. These results demonstrate that the MCP-1 receptor binds and signals in response to picomolar concentrations of MCP-1 in a highly specific manner. Signaling was manifested as mobilization of intracellular calcium and inhibition of adenylyl cyclase and was mediated by a pertussis toxin-sensitive G-protein(s).