Formyl peptide receptors and the regulation of ACTH secretion: targets for annexin A1, lipoxins, and bacterial peptides

ABSTRACT The N ‐formyl peptide receptors (FPRs) are a family of G‐protein coupled receptors that re‐spond to proinflammatory N ‐formylated bacterial peptides (e.g. , formyl‐Met‐Leu‐Phe, fMLF) and, thus, contribute to the host response to bacterial infection. Paradoxically, a growing body of evidence suggests that some members of this receptor family may also be targets for certain anti‐inflammatory molecules, including annexin Al (ANXA1), which is an important mediator of glucocorticoid (GC) action. To explore further the potential role of FPRs in mediating ANXA1 actions, we have focused on the pituitary gland, where ANXA1 has a well‐defined role as a cell‐cell mediator of the inhibitory effects of GCs on the secretion of cortico‐trophin (ACTH), and used molecular, genetic, and pharmacological approaches to address the question in well‐established rodent models. Reverse transcriptase‐polymerase chain reaction (RT‐PCR) analysis identified mRNAs for four FPR family members in the mouse anterior pituitary gland, Fpr‐rsl, Fpr‐rs2, Fpr‐rs6, and Fpr‐rs7. Functional studies confirmed that, like dexa‐methasone, ANXA1 and two ANXAl‐derived peptides (ANXA1 1 _ 188 and ANXA1 Ac2 _ 26 ) inhibit the evoked release of ACTH from rodent anterior pituitary tissue in vitro. Fpr1 gene deletion failed to modify the pituitary responses to dexamethasone or ANXA1 Ac2_26 . However, lipoxin A4 (LXA4, 0.02–2μM, a lipid mediator with high affinity for Fpr‐rs1) mimicked the inhibitory effects of ANXA1 on ACTH release as also did fMLF in high (1–100 μM) but not lower (10–100 nM) concentrations. Additionally, a nonselective FPR antagonist (Boc1, 100 μM) overcame the effects of dexametha‐sone, ANXA1 1 _ 188 , ANXA1 Ac2 _ 26 , fMLF, and LXA4 on ACTH release, although at a lower concentration (50 μM), it was without effect. Together, the results suggest that the actions of ANXA1 in the pituitary gland are independent of Fpr1 but may involve other FPR family members, in particular, Fpr‐rs1 or a closely related receptor. They thus provide the first evidence for a role of the FPR family in the regulation of neuroendocrine function.—John, C. D., Sahni, V., Mehet, D., Morris, J. F., Christian, H. C., Perretti, M., Flower, R. J., Solito E., Buckingham J. C. Formyl peptide receptors and the regulation of ACTH secretion: targets for annexin A1, lipoxins, and bacterial peptides. FASEB J. 21, 1037–1046 (2007)