PHOSPHORYLATION BY A G-PROTEIN-COUPLED KINASE INHIBITS SIGNALING AND PROMOTES INTERNALIZATION OF THE MONOCYTE CHEMOATTRACTANT PROTEIN-1 RECEPTOR - CRITICAL ROLE OF CARBOXYL-TAIL SERINES THREONINES IN RECEPTOR FUNCTION/

Monocyte chemoattractant protein-1 (MCP-1) is a member of the chemokin e family of chemotactic cytokines and signals via activation of a C pr otein-coupled seven-transmembrane domain receptor to mediate chemotaxi s. Monocyte activation is limited by desensitization and internalizati on of the MCP-1R, but these mechanisms are not well understood, In thi s study, we show that the type B MCP-1R (MCP-1RB/CCR2B) is rapidly pho sphorylated and internalized in response to nanomolar concentrations o f MCP-1, Co-expression of CCR2B in Xenopus oocytes with beta-adrenergi c receptor kinase 2 (beta ark2), but not beta ark1 or rhodopsin kinase , specifically blocked receptor activation by MCP-1, Mutation of serin e (Ser) and threonine (Thr) residues in the terminal carboxyl-tail of the receptor, which are potential targets of park-mediated phosphoryla tion, prevented inhibition of receptor activation by beta ark2 in micr oinjected oocytes, Finally, a construct in which multiple Ser and Thr residues in the carboxyl-tail were changed to alanine significantly pr olonged the agonist-dependent intracellular calcium flux and inhibited receptor internalization in transfected human embryonic kidney (HEK)- 293 cells, These studies demonstrate that phosphorylation of Ser and T hr residues in the carboxyl-tail of CCR2B mediates receptor desensitiz ation and internalization and may serve to limit the chemotactic respo nse of leukocytes to MCP-1 and related chemokines.