Protein kinase C inhibitors enhance G-protein induced phospholipase A2 activation in intact human platelets.
Washed intact human platelets were prelabelled with [3H]arachidonic acid ([3H]AA) and stimulated with thrombin or with AlF4-, a known unspecific activator of G-proteins. Both stimuli induced the liberation of [3H]AA, the release of beta-thromboglobulin (beta-TG) and platelet aggregation. PMA did not induce liberation of [3H]AA although it induced beta-TG release and aggregation; preincubation with PMA did not modify significantly the amounts of [3H]AA and beta-TG released by thrombin or AlF4-. Different inhibitors of PKC (staurosporine, H-7 and calphostin C) increased the release of [3H]AA and inhibited beta-TG release and aggregation induced by AlF4- but they had no effect when platelets were stimulated with thrombin (0.5 U/ml). Calphostin C was able to release [3H]AA by itself without inducing aggregation of beta-TG release. Okadaic acid (a serine/threonine phosphoprotein phosphatase inhibitor) greatly inhibited the release of [3H]AA, beta-TG and aggregation in AlF4--stimulated platelets. These results indicate the presence of a G-protein mediated mechanism for the activation of a platelet phospholipase A2 which is negatively affected by a protein kinase, sensible to putative inhibitors of protein kinase C, and it is activated by a protein phosphatase, sensible to okadaic acid.
Iorio
P
P
Institute of Medical Biochemistry, University of Perugia, Italy.
Gresele
P
P
Stasi
M
M
Nucciarelli
F
F
Vezza
R
R
Nenci
G G
GG
Goracci
G
G
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000470:Alkaloids / Q000494:pharmacology; D017607:Aluminum Compounds / Q000494:pharmacology; D016718:Arachidonic Acid / Q000097:blood; D001792:Blood Platelets / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004988:Ethers, Cyclic / Q000494:pharmacology; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D009281:Naphthalenes / Q000494:pharmacology; D019319:Okadaic Acid; D010741:Phospholipases A / Q000097:blood*; D054467:Phospholipases A2; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010879:Piperazines / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D001620:beta-Thromboglobulin / Q000096:biosynthesis
D000470:Alkaloids; D017607:Aluminum Compounds; D004791:Enzyme Inhibitors; D004988:Ethers, Cyclic; D007546:Isoquinolines; D009281:Naphthalenes; D010879:Piperazines; D001620:beta-Thromboglobulin; D019319:Okadaic Acid; C050992:tetrafluoroaluminate; D016718:Arachidonic Acid; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011493:Protein Kinase C; D010741:Phospholipases A; D054467:Phospholipases A2; D010749:Phosphoprotein Phosphatases; D013917:Thrombin; D019204:GTP-Binding Proteins; D019311:Staurosporine; C058819:calphostin C; D013755:Tetradecanoylphorbol Acetate; D005459:Fluorides