Murayama T, Kajiyama Y, Takahashi A, Nomura Y
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Arch Biochem Biophys. 1990 Jan;276(1):146-52. doi: 10.1016/0003-9861(90)90021-p.
The tumor-promoting phorbol ester 4 beta-phorbol 12-myristate 13-acetate (PMA) inhibited thrombin-stimulated arachidonic acid (AA) release in rabbit and human platelets. PMA was effective over the same concentration range that activates protein kinase C in intact rabbit platelets: IC50 vs thrombin = 0.5 nM, greater than 90% inhibition at 10 nM. Suppression of thrombin-stimulated AA release was evident within 5 min of pretreatment with 1 nM PMA. A non-tumor-promoting phorbol ester, 4-O-methyl PMA, showed a very weak ability to inhibit AA release. Thrombin-stimulated serotonin secretion was progressively inhibited by PMA pretreatment in platelets, while PMA was a stimulus for secretion at higher concentrations. 1-(5-Isoquinolinylsulfonyl)-2-methyl-piperazine (H-7), a selective inhibitor of protein kinase C, blocked PMA-induced inhibition of AA release. Furthermore, H-7 enhanced the effect of thrombin on AA release. PMA pretreatment reduced the inhibitory effect of thrombin on forskolin-stimulated cAMP accumulation, but had no effect on nonstimulated cAMP metabolism in the presence of thrombin. PMA did not inhibit AA release caused by A23187 or melittin. In digitonin-permeabilized platelets, thrombin plus guanosine 5'-(3-O-thio)triphosphate (GTP gamma S)-stimulated AA release, but not GTP gamma S- and AIF4(-)-stimulated AA release, was abolished by PMA pretreatment. These results suggest that activation of protein kinase C may exert negative feedback on the receptor-mediated activation of phospholipase A2. A possible uncoupling of thrombin receptor to GTP-binding protein leading to activation of phospholipase A2 by PMA pretreatment is discussed.
促肿瘤佛波酯4β-佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）可抑制凝血酶刺激的兔和人血小板中花生四烯酸（AA）的释放。PMA在激活完整兔血小板中蛋白激酶C的相同浓度范围内有效：对凝血酶的IC50 = 0.5 nM，在10 nM时抑制率大于90%。用1 nM PMA预处理5分钟内，凝血酶刺激的AA释放明显受到抑制。一种非促肿瘤佛波酯4-O-甲基PMA抑制AA释放的能力非常弱。PMA预处理可逐渐抑制血小板中凝血酶刺激的5-羟色胺分泌，而PMA在较高浓度时是分泌的刺激物。蛋白激酶C的选择性抑制剂1-(5-异喹啉磺酰基)-2-甲基哌嗪（H-7）可阻断PMA诱导的AA释放抑制作用。此外，H-7增强了凝血酶对AA释放的作用。PMA预处理降低了凝血酶对福斯高林刺激的环磷酸腺苷（cAMP）积累的抑制作用，但在有凝血酶存在时对非刺激状态下的cAMP代谢没有影响。PMA不抑制由A23187或蜂毒肽引起的AA释放。在洋地黄皂苷通透的血小板中，PMA预处理可消除凝血酶加鸟苷5'-(3-O-硫代)三磷酸（GTPγS）刺激的AA释放，但不影响GTPγS和氟化铝（AIF4(-)）刺激的AA释放。这些结果表明，蛋白激酶C的激活可能对受体介导的磷脂酶A2激活产生负反馈。文中讨论了PMA预处理导致凝血酶受体与GTP结合蛋白解偶联从而激活磷脂酶A2的可能性。
