SELECTIVE-INHIBITION OF THROMBIN RECEPTOR-MEDIATED CA2-KINASE-C-BETA(ENTRY BY PROTEIN)

Thrombin initiates many physiological processes in platelets and other megakaryocyte-lineage cells by interacting with surface receptors and generating rises in cytoplasmic Ca2+; these rises result from both Ca 2+ release from intracellular stores and receptor-mediated Ca2+ entry. Regulators that limit Ca2+ entry after its initiation by thrombin hav e not been identified, In this study, prevention of expression of a si ngle protein kinase C isoenzyme (PKC beta) by antisense cDNA overexpre ssed in HEL cells, a human megakaryoblastic cell line that expresses t hrombin receptors, promotes thrombin receptor-mediated Ca2+ entry with out altering thrombin-induced intracellular release of Ca2+, The cytop lasmic Ca2+ rise initiated by endoperoxide analogs was not affected by inhibiting PKC beta. Overexpression of a cDNA encoding wild-type PKC beta mutated to prevent recognition by the antisense cDNA abolished th e enhancement of Ca2+ influx following thrombin, Thus, PKC beta appear s to be a specific negative regulator of thrombin receptor-mediated Ca 2+ entry.