Role of type 1 and type 2A phosphatases in signal transduction of platelet-activating-factor-stimulated rabbit platelets.
Calyculin A, the potent inhibitor of type 1 (PP1) and type 2A (PP2A) phosphatases, has been employed in order to investigate the role of endogenously activated PP1/PP2A in the signal-transduction pathway of platelet-activating-factor (PAF)-stimulated platelets. Calyculin A alone caused an increase in protein phosphorylation in unstimulated platelets, with the detection of a number of newly phosphorylated proteins, whereas in PAF-stimulated platelets phosphorylation of the major substrates of protein kinase C and myosin light-chain kinase were no longer transient, but phosphorylation was sustained. PP1/PP2A appear to play a role in Ca2+ homoeostasis, as inhibition of PP1/PP2A caused an inhibition of Ca2+ mobilization and Ca2+ influx through the plasma membrane in PAF-stimulated platelets. The effect of calyculin A on Ca2+ mobilization correlated with the observed inhibition of the production of the signal molecule Ins(1,4,5)P3. The release reaction (which is a Ca(2+)-dependent event) was also inhibited by calyculin A. The results are discussed in relation to the possible role of protein kinase C in mediating the events leading to the effects observed with calyculin A.
Murphy
C T
CT
School of Pharmacy and Pharmacology, University of Bath, Avon, U.K.
Westwick
J
J
D000818:Animals; D001381:Azepines / Q000097:blood; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology; D002118:Calcium / Q000097:blood; D002413:Cations, Divalent; D007211:Indoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000097:blood / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D008301:Maleimides / Q000494:pharmacology; D008345:Manganese / Q000097:blood; D008387:Marine Toxins; D010080:Oxazoles / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000097:blood*; D010750:Phosphoproteins / Q000097:blood; D010766:Phosphorylation; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000097:blood; D011817:Rabbits; D015398:Signal Transduction; D014230:Triazoles / Q000097:blood
D001381:Azepines; D002413:Cations, Divalent; D007211:Indoles; D008301:Maleimides; D008387:Marine Toxins; D010080:Oxazoles; D010750:Phosphoproteins; D010972:Platelet Activating Factor; D014230:Triazoles; C052518:WEB 2086; D008345:Manganese; D015759:Ionomycin; C059041:calyculin A; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D002118:Calcium; C064755:Ro 31-7549