MONOCYTE CHEMOATTRACTANT PROTEIN-1 - RECEPTOR INTERACTIONS AND CALCIUM SIGNALING MECHANISMS

Monocyte chemoattractant protein-1 (MCP-1) is a member of the Cys-Cys chemokine family, Two related MCP-1 receptors have been identified (CC -CKR2A and CC-CKR2B), although the precise kinetics of ligand binding and calcium signaling of these receptors has yet to be investigated, T o examine this more closely, the human MCP-1 receptors were cloned and expressed in Chinese hamster ovary (CHO) cells, Membranes prepared fr om cells expressing CC-CKR2B bind MCP-1 selectively and with high affi nity (K-d = 120 pM), MCP-1 stimulation of recombinant CHO cells expres sing CC-CKR2B induces a rapid increase in intracellular Ca2+ through b oth receptor-operated Ca2+ channels and mobilization of Ca2+ from intr acellular stores, and leads to a rapid temperature-dependent internali zation of the ligand/receptor complexes, In contrast, recombinant CHO cells expressing CC-CKR2A, and membranes prepared from these cells, fa il to bind detectable levels of MCP-1, However, MCP-1 stimulation of c ells expressing CC-CKR2A induces a small but significant increase in i ntracellular Ca2+, Repeated stimulation of these cells with MCP-1 lead s to a potentiation of the response to a level comparable to that seen in cells expressing CC-CKR2B, These observations suggest that the lev els of cell surface CC-CKR2A are controlled by novel mechanisms.