Schnabel P, Gäs H, Nohr T, Böhm M
Klinik III für Innere Medizin, Universität zu Köln, Germany.
Br J Pharmacol. 1997 Sep;122(1):31-6. doi: 10.1038/sj.bjp.0701341.
1 Phosphoinositide-specific phospholipase C (PLC) is involved in the regulation of many cellular functions. In the myocardium, PLC-generated second messengers play a role in the regulation of contractile function and in the pathophysiology of myocardial hypertrophy. 2 In the present study, the effect of mastoparan, a tetradecapeptide which is capable of activating heterotrimeric G proteins by mimicking the action of an activated receptor, on membrane-bound human myocardial PLC, was investigated in a cell-free assay with exogenous phospholipids as a substrate. 3 Mastoparan stimulated human myocardial PLC approximately two fold with a half-maximal effect at approximately 2 microM and a maximal effect at 10 microM. The peptide did not alter the dependence of PLC on free calcium ions. In order to exclude non-specific effects of mastoparan due to its amphiphilic properties, different mastoparan derivatives were used as positive and negative controls. Mas17, an inactive mastoparan analogue with physical properties very similar to mastoparan, did not induce substantial PLC stimulation in human myocardial membranes. In contrast, Mas7, the most active mastoparan derivative known, caused a more pronounced PLC activation compared with the mother compound indicating that the effect was sequence-specific. Human myocardial PLC stimulation was pertussis toxin-insensitive and could not be abolished by addition of excess alpha-subunits from purified retinal transducin or by excess GDP or GDP/beta S. In order to investigate whether mastoparan stimulate PLC via pertussis toxin-insensitive alpha q, a deletion mutant of PLC beta 2 deficient of the site of interaction with alpha q-subunits was expressed in COS-1 cells. Both wild-type and mutant PLC beta 2 were similarly sensitive to stimulation by mastoparan. It is concluded that mastoparan stimulates human myocardial PLC by a mechanism distinct from heterotrimeric G proteins.
1 磷酸肌醇特异性磷脂酶C（PLC）参与多种细胞功能的调节。在心肌中，PLC产生的第二信使在收缩功能调节及心肌肥大的病理生理学过程中发挥作用。2 在本研究中，采用以外源磷脂为底物的无细胞分析方法，研究了马斯托帕坦（一种能通过模拟活化受体的作用来激活异源三聚体G蛋白的十四肽）对膜结合型人心肌PLC的影响。3 马斯托帕坦刺激人心肌PLC的作用约为两倍，在约2微摩尔时达到半数最大效应，在10微摩尔时达到最大效应。该肽未改变PLC对游离钙离子的依赖性。为排除马斯托帕坦因其两亲性产生的非特异性效应，使用了不同的马斯托帕坦衍生物作为阳性和阴性对照。Mas17是一种物理性质与马斯托帕坦非常相似的无活性马斯托帕坦类似物，在人心肌膜中未诱导出明显的PLC刺激作用。相比之下，已知活性最强的马斯托帕坦衍生物Mas7与母体化合物相比，引起了更明显的PLC激活，表明该效应具有序列特异性。人心肌PLC刺激对百日咳毒素不敏感，加入纯化的视网膜转导蛋白的过量α亚基或过量的GDP或GDP/βS均不能消除该刺激作用。为研究马斯托帕坦是否通过百日咳毒素不敏感的αq刺激PLC，在COS-1细胞中表达了缺乏与αq亚基相互作用位点的PLCβ2缺失突变体。野生型和突变型PLCβ2对马斯托帕坦刺激的敏感性相似。结论是，马斯托帕坦通过一种不同于异源三聚体G蛋白的机制刺激人心肌PLC。
