MONOCYTE CHEMOTACTIC PROTEIN-3 (MCP3) INTERACTS WITH MULTIPLE LEUKOCYTE RECEPTORS - C-C-CKR1, A RECEPTOR FOR MACROPHAGE INFLAMMATORY PROTEIN-1-ALPHA, RANTES, IS ALSO A FUNCTIONAL RECEPTOR FOR MCP3

Monocyte chemotactic protein-3 (MCP3) is a recently identified and mol ecularly cloned C-C chemokine that is chemotactic for and activates a great variety of inflammatory cell types. MCP3 has been reported to in teract with several C-C chemokine receptors, which can be simultaneous ly or selectively expressed on leukocyte subpopulations. In order to i solate receptor(s) for MCP3, a cDNA library was constructed using mRNA from a human Mt-like cell line, YT. These cells showed high affinity binding sites for I-125-MCP3 and migrated in response to MCP3. A chemo kine receptor cDNA clone, designated YT4, was sequenced and found to b e identical to the known C-C CKR1 or macrophage inflammatory protein-1 alpha (MIP1 alpha)/Rantes receptor. YT4 cDNA was subcloned into a mam malian expression vector, and stable transfectants were prepared using the embryonic kidney cell line 293. The transfectants (YT4/293) showe d high affinity binding for I-125-MCP3 in addition to specifically bin ding I-125-MIP1 alpha and I-125-Rantes. All three C-C chemokines were able to cross compete for binding sites on YT4/293 cells and induced d irectional migration of YT4/293 cells in vitro, with MCP3 being the mo st potent chemoattractant. MCP3, MTP1 alpha, and Rantes were equally a ble to cross-attenuate the migratory response of YT4/293 cells to one another. In contrast, MCP1 and MIP1 beta had very limited capacity to compete for MCP3 binding on YT4/293 cells and had only a minor attenua ting effect on MCP3-induced migration. Since MCP3 has been reported to use MCP1 receptor(s), our results with transfected 293 cells expressi ng only C-C CKR1 clearly establish that C-C CKR1 is also a functional receptor for MCP3.