The synthetic peptide Trp-Lys-Tyr-Met-Val-Met-NH2 specifically activates neutrophils through FPRL1/lipoxin A(4) receptors and is an agonist for the orphan monocyte-expressed chemoattractant receptor FPRL2

Neutrophils express the G protein-coupled N-formyl peptide receptor (FPR) a nd its homologue FPRL1, whereas monocytes express FPR, FPRL1, and FPRL2, an orphan receptor sharing 83% amino acid identity with FPRL1, FPRL1 is a pro miscuous receptor activated by serum amyloid A and by different synthetic p eptides, including the hexapeptide Trp-Lys-Tyr-Met-Val-D-Met-NH2 (WKYMVm), By measuring calcium flux in HL-60 cells transfected with FPR, FPRL1, or FP RL2, we show that WKYMVm activated all three receptors, whereas the L-confo rmer WKYMVM activated exclusively FPRL1 and FPRL2, The functionality of FPR L2 was further assessed by the ability of HL-60-FPRL2 cells to migrate towa rd nanomolar concentrations of hexapeptides. The half-maximal effective con centrations of WKYMVM for calcium mobilization in HL-60-FPRL1 and HL-60-FPR L2 cells were 2 and 80 nM, respectively. Those of WKYMVm were 75 pM and 3 n M, The tritiated peptide WK[3,5-H-3(2)]YMVM bound to FPRL1 (K-D similar to 160 nM), but not to FPR, The two conformers similarly inhibited binding of I-125-labeled WKYMVm to FPRL2-expressing cells (IC50 similar to 2.5-3 muM). Metabolic labeling with orthophosphoric acid revealed that FPRL1 was diffe rentially phosphorylated upon addition of the L- or D-conformer, indicating that it induced different conformational changes. In contrast to FPRL1, FP RL2 was already phosphorylated in the absence of agonist and not evenly dis tributed in the plasma membrane of unstimulated cells. However, both recept ors were internalized upon addition of either of the two conformers. Taken together, the results indicate that neutrophils are activated by WKYMVM thr ough FPRL1 and that FPRL2 is a chemotactic receptor transducing signals in myeloid cells.