Cyclic AMP-elevating agents block chemoattractant activation of diradylglycerol generation by inhibiting phospholipase D activation.
Agents which elevate cellular cAMP (prostaglandin E2, theophylline, and forskolin) or mimic cAMP action (dibutyryl cAMP) are known to inhibit human neutrophil activation (superoxide generation and secretion) by receptor-linked agonists such as formyl-methionyl-leucyl-phenylalanine (fMLP). Herein, we show that these agents also markedly inhibit fMLP-stimulated diradylglycerol generation (assayed by mass methods). The magnitude of inhibition correlated with the ability of a given agent or combination of agents to elevate cAMP. Both 1,2-diacylglycerol and 1-O-alkyl,2-acyl glycerol generation were affected. Effects on the latter species, as well as a lack of effect on fMLP-stimulated inositol phosphate release, implied that cAMP affected diradylglycerol generation from a source other than phospholipase C-dependent phosphoinositide hydrolysis, since phosphatidylinositols do not contain appreciable quantities of the 1-O-alkyl linkage. In cells in which the phosphatidylcholine pool was prelabeled using 1-O-[3H]octadecyl-2-lyso-sn-glycero-3-phosphocholine, prostaglandin E2 plus theophylline inhibited the fMLP-activated rapid generation of [3H]phosphatidic acid and its subsequent conversion to [3H]diradylglycerol, implying an effect at the level of phospholipase D. In the presence of ethanol, the fMLP-activated transphosphatidylation of [3H]phosphatidylcholine to generate [3H]phosphatidylethanol (a phospholipase D-dependent reaction) was also markedly inhibited. In contrast, when phorbol 12-myristate 13-acetate was used to activate cells, cAMP-related agents had no effect on phospholipase D activity, diradylglycerol generation, or superoxide generation. The data indicate an inhibitory effect of cyclic AMP on receptor-mediated phospholipase D activation at a site proximal to phospholipase D (e.g., the receptor or G protein). These studies provide a new example of "cross-talk" among signal transduction systems.
Tyagi
S R
SR
Department of Biochemistry, Emory University Medical School, Atlanta, Georgia 30322.
Olson
S C
SC
Burnham
D N
DN
Lambeth
J D
JD
D002630:Chemotactic Factors / Q000494:pharmacology*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004075:Diglycerides / Q000096:biosynthesis*; D015232:Dinoprostone / Q000494:pharmacology; D004789:Enzyme Activation; D006801:Humans; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000201:enzymology; D010739:Phospholipase D / Q000037:antagonists & inhibitors*; D013268:Stimulation, Chemical; D013481:Superoxides; D013806:Theophylline / Q000494:pharmacology
D002630:Chemotactic Factors; D004075:Diglycerides; D013481:Superoxides; D005576:Colforsin; D009240:N-Formylmethionine Leucyl-Phenylalanine; C035561:diarachidonyl diglyceride; D013806:Theophylline; D000242:Cyclic AMP; D010739:Phospholipase D; D015232:Dinoprostone