Heterologously expressed formyl peptide receptor 2 (FPR2/ALX) does not respond to lipoxin A4

Lipoxin A4 (LXA4) has been described as an anti-inflammatory mediator, which exerts its effects through the formyl peptide receptor FPR2, also known as ALX. However, there has been a controversy whether or not cells expressing FPR2/ALX, such as neutrophils, respond to LXA4. We, therefore, systematically examined the ability of the human and murine forms of the receptor to respond to LXA4. We show that both receptor orthologues responded to the FPR2/ALX peptide agonist WKYMVM when expressed heterologously. In contrast, LXA4 from different sources neither increased [Ca2+]i and extracellular-signal-regulated kinase (ERK) phosphorylation, nor did it induce a decrease in cAMP levels or a translocation of v-arrestin. Also, several LXA4 analogs were found to be unable to signal through FPR2/ALX. We conclude that FPR2/ALX is not activated by LXA4 and that the molecular mechanism by which LXA4 functions still needs to be identified.