MONOCYTE CHEMOTACTIC PROTEIN-4 (MCP-4), A NOVEL STRUCTURAL AND FUNCTIONAL ANALOG OF MCP-3 AND EOTAXIN

A novel human CC chemokine complementary DNA was identified in a libra ry constructed from human fetal RNA, cloned into a baculovirus vector, and expressed in Sf9 insect cells. The mature recombinant protein tha t was released had the NH2-terminal sequence pyro-QPDALNVPSTC...and co nsisted of 75 amino acids. Minor amounts of two variants of 77 and 82 residues (NH2 termini: LAQPDA...and FNPQGLAQPDA...) were released as w ell. The novel chemokine was designated monocyte chemotactic protein 4 (MCP-4) and the variants were designated (LA)MCP-4 and (FNPQGLA)MCP-4 . MCP-4 shares the pyroglutamic acid-proline NH2-terminal motif and 56 -61% sequence identity with the three known monocyte chemotactic prote ins and is 60% identical to eotaxin. It has marked functional similari ties to MCP-3 and eotaxin. Like MCP-3, MCP-4 is a chemoattractant of h igh efficacy for monocytes and T lymphocytes. On these cells, it binds to receptors that recognize MCP-1, MCP-3, and RANTES. On eosinophils, MCP-4 has similar efficacy and potency as MCP-3, RANTES, and eotaxin. It shares receptors with eotaxin and shows full cross-desensitization with this eosinophil-selective chemokine. Of the two variants, only ( LA)MCP-4 could be purified in sufficient quantities for testing and wa s found to be at least 30-fold less potent than MCP-1 itself This sugg ests that the 75-residue form with the characteristic NH2 terminus of an MCP is the biologically relevant species.