Effects of protein kinase C inhibitors on thromboxane production by thrombin-stimulated platelets

The purpose of these studies was to identify a possible role for protein ki nase C in thromboxane production. The effects of four putative protein kina se C inhibitors were studied with platelet stimulation by thrombin (0.5-150 nM), Thrombin Quick I (1.5-500 nM) or a thrombin receptor (protease activa ted receptor-1) agonist peptide (TRAP) (5-120 mu M) Thromboxane production was increased by the bisindolylmaleimide derivative, 2-[1-(3-dimethylaminop ropyl)-1 H-indol-3-yl]-3-(1 H-indol-3-yl)-maleimide (GF 109203X), unchanged by the inhibitors 12-(2-cyanoethyl)-6.7,12,13-tetrahydro-13-methyl-5-oxo-5 H-indolo (2,3-a) pyrrolo (3,4-c)-carbazole (Go: 6976) and 5,21:12, 17-dimet heno-18 H-dibenzo[i, o]pyrrolo[3,4-l][1,8]diazacyclohexadecine-18,20(19H)-d ione, 8-[(dimethylamino)methyl]-6,7,8,9,10,11 -hexahydro-, monomethanesulfo nate (379196), the latter of which is protein kinase C beta-selective, and decreased by 1-[6-[(3-acetyl-2,4,6-trihydroxy-5-methylphenyl)methyl]-5,7-di hydroxy-2,2-dimethyl-2 H-1-benzopyran-8-yl]-3-phenyl-2-propen-1-one (rottle rin). an inhibitor selective for protein kinase C delta. These results indi cate complex regulation of thromboxane synthesis in human platelets includi ng a probable role for protein kinase C delta. The results taken together f urther suggest that GF 109203X may suppress negative feedback resulting fro m an unidentified kinase and that the classical protein kinase C isoforms a lpha and beta do not have a significant role in regulating thromboxane prod uction by platelets. (C) 1999 Elsevier Science B.V. All rights reserved.