Monocyte chemotactic protein-4: tissue-specific expression and signaling through CC chemokine receptor-2

Chemokines constitute a family of low-molecular-weight proteins that attract or activate a variety of cell types, including leukocytes, endothelial cells, and fibroblasts. An electronic search of the GenBank Expressed Sequence Tags database uncovered a partial cDNA sequence with homology to the chemokine monocyte chemotactic protein-1 (MCP-1). Isolation of the full-length clone revealed that it encodes the chemokine MCP-4, an eosinophil chemoattractant recently described by Uguccioni et al. [J. Exp. Med. 183, 2379-2384]. Recombinant MCP-4 was expressed in mammalian cells and purified by heparin-Sepharose chromatography. Sequencing the amino terminus of this protein corroborated the reported sequence of recombinant MCP-4 produced in insect cells. As shown by calcium flux assays, MCP-4 activated the cloned G protein-coupled receptor CCR-2, which also recognizes MCP-1 and MCP-3. Northern hybridization indicated that MCP-4 is constitutively expressed at high levels in the small intestine, colon, and lung. This expression profile is consistent with its role as a chemoattractant for eosinophils, which can be rapidly mobilized to the lung or intestine in response to invading pathogens. In marked contrast to MCP-1, MCP-4 was not induced in cell lines treated with pro-inflammatory stimuli such as lipopolysaccharide or tumor necrosis factor alpha.