Selective inhibition of thrombin receptor-mediated Ca2+ entry by protein kinase C beta.
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 Ca2+ release from intracellular stores and receptor-mediated Ca2+ entry. Regulators that limit Ca2+ entry after its initiation by thrombin have not been identified. In this study, prevention of expression of a single protein kinase C isoenzyme (PKC beta) by antisense cDNA overexpressed in HEL cells, a human megakaryoblastic cell line that expresses thrombin receptors, promotes thrombin receptor-mediated Ca2+ entry without altering thrombin-induced intracellular release of Ca2+. The cytoplasmic 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 the enhancement of Ca2+ influx following thrombin. Thus, PKC beta appears to be a specific negative regulator of thrombin receptor-mediated Ca2+ entry.
Xu
Y
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Cardiovascular Division, Beth Israel Hospital, Harvard Medical School, Boston, Massachusetts 02215, USA.
Ware
J A
JA
D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D016373:DNA, Antisense / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D007700:Kinetics; D008533:Megakaryocytes; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism*; D018179:Receptors, Thrombin / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000502:physiology*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014162:Transfection
D016373:DNA, Antisense; D005456:Fluorescent Dyes; D007527:Isoenzymes; D009838:Oligodeoxyribonucleotides; D018179:Receptors, Thrombin; D011994:Recombinant Proteins; D011493:Protein Kinase C; D002118:Calcium; D016257:Fura-2