Phosphoinositide metabolism in transmembrane signalling

许多细胞外信号引起受体连接的磷酸肌醇转换，从而诱导Ca^2+动员和蛋白激酶C激活，这是公认的。从细胞表面受体到磷脂酶C的信号传导机制尚未阐明。在这个研究项目中，我们研究了GTP结合蛋白（G蛋白）在这些跨膜信号传导机制中的作用和作用。首先，我们纯化并鉴定了突触膜磷脂酶C。我们还从包括大脑在内的几种组织中分离出Mr值约为20.000的多种G蛋白（小Mr G蛋白），纯化并表征了两种新的G蛋白，命名为smg p25 A和smg p21，以及c-Ki-ras和rho蛋白。有人建议，ras蛋白修改受体连接的磷酸肌醇营业额，我们目前正试图重建这些ras和ras相关的小G蛋白与膜磷脂酶C和细胞表面受体在无细胞系统。我们还使用几种细胞系的生长因子受体相关的磷酸肌醇营业额的特点。在NIH/3 T3细胞和培养的平滑肌细胞中，蛙皮素和血管紧张素II诱导的磷脂酰肌醇水解被蛋白激酶C通过使G蛋白与磷脂酶C解偶联而抑制。与此相反，血小板衍生生长因子诱导的反应是不敏感的蛋白激酶C在两种细胞类型。这些结果与我们早期的观察一起表明，从受体到磷脂酶C存在多种信号通路。

It is well established that many extracellular signals elicit the receptor-linked phosphoinositide turnover and thereby induce both Ca^<2+> mobilization and protein kinase C activation. The mechanisms of signalling from the cell surface receptors to the phospholipase C have not been clarified. In this research project, we have investigated the roles and actions of GTP-binding proteins (G proteins) in these transmembrane signalling mechanisms. First, we have purified and characterized the synaptic membrane phospholipase C. We have also separated multiple G proteins with Mr values of about 20.000 (small Mr G proteins) from several tissues including cerebrum, purified and characterized two novel G proteins designated as smg p25A and smg p21, in addition to c-Ki-ras and rho proteins. It has been suggested that the ras protein modifies the receptor-linked phosphoinositide turnover, we are currently attempting to reconstitute these ras and ras-related small Mr G proteins with the membrane phospholipase C and cell surface receptors in a cell-free system. We have also characterized the growth factor receptor-linked phosphoinositide turnover using several cell lines. In NIH/3T3 cells and cultured smooth muscle cells, the bombesin-and angiotensin II-induced phosphoinositide hydrolysis is inhibited by protein kinase C by uncoupling the G protein to the phospholipase C. In contrast, the platelet derived-growth factor-induced reaction is insensitive to protein kinase C in both cell types. These results together with our earlier observations suggest that there are various signalling pathways from the receptors to the phospholipase C.