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 pathwa ys of a recently cloned receptor for monocyte chemoattractant protein- 1 (MCP-1). In human 293 cells stably transfected with the MCP-1 recept or, MCP-1 bound specifically with high affinity (K-d = 260 pM) and ind uced a rapid mobilization of calcium from intracellular stores, The cl osely 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 cycl ase with an IC50 = 90 pM. Activation of the MIP-1 alpha/RANTES recepto r also mediated inhibition of adenylyl cyclase activity but with a dif ferent pharmacological profile: MIP-1 alpha (110 pM, IC50), RANTES (14 0 pM), MIP-1 beta (10 nM), and MCP-1 (820 nM). Mobilization of intrace llular calcium and inhibition of adenylyl cyclase were blocked by pert ussis 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 ma nner. Signaling was manifested as mobilization of intracellular calciu m and inhibition of adenylyl cyclase and was mediated by a pertussis t oxin-sensitive G-protein(s).