Reactivation of Formyl Peptide Receptors Triggers the Neutrophil NADPH-oxidase but Not a Transient Rise in Intracellular Calcium

Abstract

In neutrophils, coupling of chemoattractants to their cell surface receptor at low temperature (<15°C) leads to receptor deactivation/desensitization without any triggering of the superoxide anion-generating NADPHoxidase. We show that the deactivated formyl peptide receptors (FPRs) can be reactivated/resensitized by the cytoskeleton-disrupting drug cytochalasin B. Such cytoskeleton-dependent receptor reactivation occurs also with the closely related receptors FPR-like-1 and C5aR but not with the receptors for interleukin-8 and plateletactivating factor. The reactivation state was further characterized with FPR as a model. The signals generated by receptor reactivation induced superoxide production that was terminated in 5-8 min, after which the neutrophils entered a new state of homologous deactivation. FPR antagonists were potent inhibitors of the superoxide production induced by the reactivated receptors, suggesting that the occupied receptors turn into an actively signaling state when the cytoskeleton is disrupted. The signals generated by the reactivated receptor were pertussis toxin-sensitive, indicating involvement of a G-protein. However, no transient elevation of intracellular Ca 2؉ accompanies the NADPH-oxidase activation. This was not due to a general down-regulation of phospholipase C/Ca 2؉ signaling, and despite the fact that no intracellular Ca 2؉ transient was generated, protein kinase C still appeared to be involved in the response. Further, phosphatidylinositol 3-kinase, mitogen-activated protein kinase, and MEK all participated in the generation of second messengers from the reactivated receptors.

The Neutrophil Response Induced by an Agonist for Free Fatty Acid Receptor 2 (GPR43) Is Primed by Tumor Necrosis Factor Alpha and by Receptor Uncoupling from the Cytoskeleton but Attenuated by Tissue Recruitment

“…The formation of such a receptor-arrestin complex affects the G-protein binding interface of the receptor, which becomes sterically blocked. In contrast to most GPCRs, the actin cytoskeleton rather than ␤-arrestin seems to play an important role in physical separation of agonist-occupied FPRs from the signaling G-protein; such physical separation eventually terminates the signaling from the occupied FPRs (43,63,64). The model for how the FPRs become desensitized is very similar to this general model, except for the involvement of actin rather than arrestin.…”

“…10C). This response is triggered through FPR1, which is clear from the fact that cyclosporin H totally inhibits the activity (43). We have now determined the effect of latrunculin A as a receptor uncoupler on cells desensitized to Cmp1.…”

Vav Proteins in Neutrophils Are Required for FcγR-Mediated Signaling to Rac GTPases and Nicotinamide Adenine Dinucleotide Phosphate Oxidase Component p40(phox)

“…Thus, the dependence of Vavmediated ROS generation on the actin cytoskeleton was evaluated. It is noteworthy that activation of the NADPH oxidase following fMLP stimulation occurs even in the presence of actin depolymerizing agents and indeed is enhanced following these treatments (39). Furthermore, a recent observation suggests that the oxidative burst that takes place in the phagosome coincides with actin depolymerization (40).…”

The Lipidated Peptidomimetic Lau-((S)-Aoc)-(Lys-βNphe)6-NH2 Is a Novel Formyl Peptide Receptor 2 Agonist That Activates Both Human and Mouse Neutrophil NADPH Oxidase

“…FPR2 Desensitized with F2M2 Can Be Reactivated through Receptor Cross-talk-We have earlier shown that agonist-occupied and -desensitized FPRs can be reactivated to produce superoxide when the cytoskeleton is disrupted by latrunculin A (Lat A) (30). The molecular basis for this reactivation is an inhibition of the coupling of ligand-receptor complexes to the actin cytoskeleton, an interaction that normally terminates the response and desensitizes the receptors (30,31).…”