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 kinase C in thromboxane production. The effects of four putative protein kinase 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 activated receptor-1) agonist peptide (TRAP) (5-120 microM). Thromboxane production was increased by the bisindolylmaleimide derivative, 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimi de (GF 109203X), unchanged by the inhibitors 12-(2-cyanoethyl)-6,7, 12,13-tetrahydro-13-methyl-5-oxo-5H-indolo (2,3-a) pyrrolo (3, 4-c)-carbazole (Gö 6976) and 5,21:12,17-dimetheno-18H-dibenzo[i, o]pyrrolo[3,4-l][1,8]diazacyclohexadecine-18,20(19H)-dione, 8-[(dimethylamino)methyl]-6,7,8,9,10,11-hexahydro-, monomethanesulfonate (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-dihydroxy-2, 2-dimethyl-2H-1-benzopyran-8-yl]-3-phenyl-2-propen-1-one (rottlerin), an inhibitor selective for protein kinase C delta. These results indicate complex regulation of thromboxane synthesis in human platelets including a probable role for protein kinase C delta. The results taken together further suggest that GF 109203X may suppress negative feedback resulting from an unidentified kinase and that the classical protein kinase C isoforms alpha and beta do not have a significant role in regulating thromboxane production by platelets.