MONOCYTE CHEMOTACTIC PROTEIN-2 (MCP-2) USES CCR1 AND CCR2B AS ITS FUNCTIONAL RECEPTORS

Monocyte chemotactic protein (MCP)-2 is a member of the C-C chemokine subfamily, which shares more than 60% sequence homology with MCP-1 and MCP-8 and about 30% homology with macrophage inflammatory protein (MI P)-1 alpha, regulated on activation of normal T cell expressed (RANTES ), and MIP-1 beta. Despite this considerable sequence homology to othe r C-C chemokines, MCP-2 appears to have unique functional properties i n comparison with other C-C chemokines such as MCP-1 and MCP-3. Althou gh evidence obtained from studies on leukocytes suggested that MCP-2 m ay share the receptors with these C-C chemokines, the actual functiona l receptors for MCP-2 have not yet been identified. In this study, by using radioiodinated MCP-2, we identified high affinity binding sites for MCP-2 on human peripheral blood monocytes. The MCP-2 binding was c ompeted for by MCP-1 and MCP-3, but less well by MIP-1 alpha or RANTES . In experiments using cells transfected with C-C chemokine receptors, I-125-MCP-2 bound to human embryonic kidney 293 cells transfected wit h CCR1 or CCR2B, known to also bind MIP-1 alpha/RANTES and MCP-1, resp ectively, but both shared by MCP-3. The binding of I-125-MCP-2 to thes e receptor-transfected cells was displaced completely by chemokines th at bind to these receptors. Both CCR1- and CCR2B-transfected 293 cells showed significant migration in response to MCP-2, in addition to res ponding to other specific chemokines. These results clearly demonstrat e that MCP-2, unlike MCP-1, uses both CCR1 as well as CCR2B as its fun ctional receptors, and this accounts for the unique activities of MCP- 2.