Plevin R, MacNulty E E, Palmer S, Wakelam M J
Department of Biochemistry, University of Glasgow, Scotland U.K.
Biochem J. 1991 Dec 15;280 ( Pt 3)(Pt 3):609-15. doi: 10.1042/bj2800609.
Endothelin-1 (ET-1)- and lysophosphatidic acid (LPA)-stimulated PtdIns(4,5)P2 hydrolysis has been studied in Rat-1 fibroblasts. Although both agonists caused the dose-dependent accumulation of inositol phosphates, a number of differences were observed. LPA induced a transient increase in Ins(1,4,5)P3 mass which returned to basal levels within 90 s, whereas the response to ET-1 did not desensitize, with levels remaining at 3-4 times basal values for up to 15 min. Stimulated decreases in mass levels of PtdIns(4,5)P2 mirrored Ins(1,4,5)P3 formation for both agonists. Experiments with electropermeabilized cells demonstrated that the effects of both agonists are stimulated by a phospholipase C controlled by a guanine-nucleotide-binding regulatory protein; however, there are differences in the nature of these interactions. The inositol phosphate response to ET-1 is poorly potentiated by guanosine 5'-[gamma-thio]triphosphate (GTP[S]) and markedly inhibited by guanosine 5'-[beta-thio]diphosphate (GDP[S]), whereas that to LPA is potentiated by GTP[S] but is relatively insensitive to GDP[S]. In addition, LPA decreased the lag time for the onset of GTP[S]-stimulated [3H]InsP3 accumulation, whereas ET-1 was without effect. Phorbol 12-myristate 13-acetate treatment of the cells inhibited LPA-stimulated, but not ET-1-stimulated, inositol phosphate formation in both intact and permeabilized cells, suggesting that the site of protein kinase C-mediated phosphorylation may be blocked in ET-1-stimulated Rat-1 cells. The results indicate that the receptor-G-protein-phospholipase C interaction for the two agonists may not conform to the same model.
已在大鼠-1成纤维细胞中研究了内皮素-1（ET-1）和溶血磷脂酸（LPA）刺激的磷脂酰肌醇-4,5-二磷酸（PtdIns(4,5)P2）水解。尽管两种激动剂均引起磷酸肌醇的剂量依赖性积累，但观察到了一些差异。LPA诱导肌醇-1,4,5-三磷酸（Ins(1,4,5)P3）量的短暂增加，该增加在90秒内恢复到基础水平，而对ET-1的反应不会脱敏，其水平在长达15分钟内保持在基础值的3至4倍。两种激动剂刺激后PtdIns(4,5)P2量水平的降低与Ins(1,4,5)P3的形成情况相符。对电穿孔细胞进行的实验表明，两种激动剂的作用均由鸟嘌呤核苷酸结合调节蛋白控制的磷脂酶C介导；然而，这些相互作用的性质存在差异。对ET-1的磷酸肌醇反应几乎不被鸟苷5'-[γ-硫代]三磷酸（GTP[S]）增强，且被鸟苷5'-[β-硫代]二磷酸（GDP[S]）显著抑制，而对LPA的反应则被GTP[S]增强，但对GDP[S]相对不敏感。此外，LPA缩短了GTP[S]刺激的[3H]InsP3积累开始的延迟时间，而ET-1则无此作用。用佛波醇12-肉豆蔻酸酯13-乙酸酯处理细胞，在完整细胞和通透细胞中均抑制了LPA刺激的而非ET-1刺激的磷酸肌醇形成，这表明在ET-1刺激的大鼠-1细胞中，蛋白激酶C介导的磷酸化位点可能被阻断。结果表明，两种激动剂的受体-G蛋白-磷脂酶C相互作用可能不符合同一模型。
