PROTEIN-KINASE-A DOWN-REGULATES THE PHOSPHORYLATION OF P47 PHOX IN HUMAN NEUTROPHILS - A POSSIBLE PATHWAY FOR INHIBITION OF THE RESPIRATORYBURST

Cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) is considered to be a physiologic modulator of superoxide generation by stimulated neutrophils. Mechanisms of the inhibitory action of PKA are poorly understood. In this study, we investigated effects of cAMP- elevating agents on the phosphorylation of p47 phox in human neutrophi ls stimulated with the chemotactic peptide fMet-Leu-Phe (fMLP). We obs erved that the fMLP-induced phosphorylation of p47 phox, an essential component of neutrophil NADPH oxidase, was significantly attenuated in the presence of dibutyryl-cAMP or of receptor agonists of adenylate c yclase. This attenuation was reversed in the presence of 0.4 mu M KT 5 720, a selective inhibitor of PKA. The effects of cAMP agonists and of KT 5720 on the phosphorylation of p47 phox were paralleled by similar effects on superoxide generation. In neutrophils stimulated with phor bol myristate acetate (PMA), which directly activates protein kinase C (PKC), neither cAMP agonists nor dibutyryl cAMP exerted any effects o n p47 phox phosphorylation or superoxide generation. These results ind icated that the PKA-dependent downregulation of fMLP-induced p47 phox phosphorylation apparently involves step(s) in the fMLP-signaling path way that are upstream of PKC. The inhibition demonstrated here of p47 phox phosphorylation by cAMP agonists may underlie a physiologically s ignificant mechanism whereby cAMP modulates the receptor-mediated resp iratory burst in neutrophils.