Monocyte chemotactic protein-3 (MCP3) interacts with multiple leukocyte receptors: C-C CKR1, a receptor for macrophage inflammatory protein-1α/rantes, is also a functional receptor for MCP3

Monocyte chemotactic protein-3 (MCP3) is a recently identified and molecularly cloned C-C chemokine that is chemotactic for and activates a great variety of inflammatory cell types. MCP3 has been reported to interact with several C-C chemokine receptors, which can be simultaneously or selectively expressed on leukocyte subpopulations. In order to isolate receptor(s) for MCP3, a cDNA library was constructed using mRNA from a human NK-like cell line, YT. These cells showed high affinity binding sites for ¹²⁵I-MCP3 and migrated in response to MCP3. A chemokine receptor cDNA clone, designated YT4, was sequenced and found to be identical to the known C-C CKR1 or macrophage inflammatory protein-1α (MIP1α)/Rantes receptor. YT4 cDNA was subcloned into a mammalian expression vector, and stable transfectants were prepared using the embryonic kidney cell line 293. The transfectants (YT4/293) showed high affinity binding for ¹²⁵I-MCP3 in addition to specifically binding ¹²⁵I-MIP1α and ¹²⁵I-Rantes. All three C-C chemokines were able to cross-compete for binding sites on YT4/293 cells and induced directional migration of YT4/293 cells in vitro, with MCP3 being the most potent chemoattractant. MCP3, MIP1α, and Rantes were equally able to cross-attenuate the migratory response of YT4/293 cells to one another. In contrast, MCP1 and MIP1β had very limited capacity to compete for MCP3 binding on YT4/293 cells and had only a minor attenuating effect on MCP3-induced migration. Since MCP3 has been reported to use MCP1 receptor(s), our results with transfected 293 cells expressing only C-C CKR1 clearly establish that C-C CKR1 is also a functional receptor for MCP3.