
<ArticleTitle>Synthetic peptide MMK-1 is a highly specific chemotactic agonist for leukocyte <prot>FPRL1</prot>.</ArticleTitle>
<AbstractText>Human phagocytic leukocytes express the seven-transmembrane G-protein-coupled receptors <prot>formyl peptide receptor</prot> (<prot>FPR</prot>) and <prot>FPR-like 1</prot> (<prot>FPRL1</prot>). MMK-1, a synthetic peptide derived from a random peptide library, is reported to induce calcium mobilization specifically in human <prot>FPRL1</prot> gene-transfected cells. However, its actions on human phagocytic leukocytes remain poorly defined. We found that MMK-1 is a potent chemotactic and calcium-mobilizing agonist for human monocytes, neutrophils, and <prot>FPRL1</prot>-transfected human embryonic kidney (HEK) 293 cells but is inactive in cells transfected with <prot>FPR</prot>. MMK-1 also activated HEK 293 cells transfected with <prot>FPR2</prot>, a mouse counterpart of human <prot>FPRL1</prot>. Furthermore, MMK-1 increased pertussis toxin-sensitive production of inflammatory cytokines in human monocytes. MMK-1 signaling in human phagocytes was completely desensitized by a well-defined FPRL1 agonist, suggesting that FPRL1 is likely a receptor that mediates the action of MMK-1 in primary cells. Since MMK-1 is one of the most potent <prot>FPRL1</prot>-specific agonists identified so far, it can serve as a modulator of the host defense and a useful agent for further studying the signaling and function of <prot>FPRL1</prot>.</AbstractText>
