CLONING, IN-VITRO EXPRESSION, AND FUNCTIONAL-CHARACTERIZATION OF A NOVEL HUMAN CC CHEMOKINE OF THE MONOCYTE CHEMOTACTIC PROTEIN (MCP) FAMILY (MCP-4) THAT BINDS AND SIGNALS THROUGH THE CC CHEMOKINE RECEPTOR 2B

Here we describe the characterization of a novel human CC chemokine, t entatively named monocyte chemotactic protein (MCP-4). This chemokine was detected by random sequencing of expressed sequence tags in cDNA l ibraries. The full-length cDNA revealed an open reading frame for a 98 -amino acid residue protein, and a sequence alignment with known CC ch emokines showed high levels of similarity (59-62%) with MCP-1, MCP-3, and eotaxin. MCP-4 cDNA was cloned into Drosophila S2 cells, and the m ature protein (residues 24-98) was purified from the conditioned mediu m. Recombinant MCP-4 induced a potent chemotactic response (EC50 = 2.8 8 +/- 0.15 nM) and a transient rise in cytosolic calcium concentration in fresh human peripheral blood monocytes but not in neutrophils. Bin ding studies in monocytes showed that MCP-4 and MCP-3 were very potent in displacing high affinity binding of I-125-MCP-1 (IC50 for MCP-4, M CP-3, and unlabeled MCP-1 of 2.1 +/- 1.4, 0.85-1.6, and 0.7 +/- 0.2 nM respectively), suggesting that all three chemokines interact with the CC chemokine receptor-a (MCP-1 receptor). This was confirmed in bindi ng studies with Chinese hamster ovary cells, stably transfected with t he CC chemokine 2B receptor. Northern blot analysis in extracts of nor mal human tissues showed expression of mRNA for MCP-4 in small intesti ne, thymus, and colon, but the level of protein expression was too low to be detected in Western blot analysis. However, expression of MCP-4 protein was demonstrated by immunohistochemistry in human atheroscler otic lesion and found to be associated with endothelial cells and macr ophages.