The chemokine monocyte chemoattractant protein-1 induces functional responses through dimerization of its receptor CCR2

Cytokines interact with hematopoietin superfamily receptors and stimulate r eceptor dimerization. We demonstrate that chemoattractant cytokines (chemok ines) also trigger biological responses through receptor dimerization. Func tional responses are induced after pairwise crosslinking of chemokine recep tors by bivalent agonistic antichemokine receptor mAb, but not by their Fab fragments. Monocyte chemoattractant protein (MCP)-1-triggered receptor dim erization was studied in human embryonic kidney (HEK)-293 cells cotransfect ed with genes coding for the CCR2b receptor tagged with YSK or Myc sequence s. After MCP-1 stimulation, immunoprecipitation with Myc-specific antibodie s revealed YSK-tagged receptors in immunoblotting. Receptor dimerization al so was validated by chemical crosslinking in both HEK-293 cells and the hum an monocytic cell line Mono Mac 1. Finally, we constructed a loss-of-functi on CCR2bY139F mutant that acted as a dominant negative, blocking signaling through the CCR2 wild-type receptor. This study provides functional support for a model in which the MCP-1 receptor is activated by ligand-induced hom odimerization, allowing discussion of the similarities between bacterial an d leukocyte chemotaxis.