PKC AND THE SECRETION AND BIOSYNTHESIS OF NEUROPEPTIDES IN ATT-20 CELLS

蛋白磷酸化增强是细胞内事件之一， 总是在膜受体激活之后。 最近发现 蛋白激酶C（也称为钙和磷脂依赖性蛋白 激酶）是磷酸化特定蛋白质的独特酶，所述蛋白质 职能有待确定。 蛋白激酶C（PKC）需要一个 磷脂和二酰基甘油（DAG）的混合物以获得最大活性。 DAG是 膜聚磷酸肌醇分解水解产物， 在膜受体占据之后，并且是细胞内的初始事件之一。 信号转导 在PI周转期间释放DAG， 刺激PKC活性超过在静止细胞中观察到的。 已知 辅助致癌物或肿瘤促进剂TPA特异性地增加膜PKC 活动 与这种增加的膜PKC活性相关的是 胞浆PKC活性的降低，这表明 蛋白激酶C（PKC）的合成是一个重要的细胞内事件。 使用同质的细胞群体（小鼠来源的，前 垂体瘤细胞系[AtT-20 s]），其对多种膜 和细胞内激活剂通过释放POMC衍生肽，我们有 通过监测细胞内蛋白激酶C的表达， 释放β-内啡肽（BE）以及膜和胞浆PKC 活动 TPA治疗导致BE呈剂量相关性增加 PKC从胞质分泌和转运到膜 分数 TPA增强膜的最大刺激浓度 PKC活性在1分钟内增加2倍，在3分钟内增加5倍。 它 PKC的激活（易位）似乎会导致增强的 通过不涉及腺苷酸的途径释放激素 环化酶/cAMP系统。

Enhanced protein phosphorylation is one of the intracellular events which invariably follow membrane receptor activation. Recently identified protein kinase C (also termed calcium- and phospholipid-dependent protein kinase) is a unique enzyme that phosphorylates specific proteins whose functions remain to be determined. Protein kinase C (PKC) requires a phospholipid and a diacylglycerol (DAG) for maximal activity. DAG is the hydrolytic product of membrane polyphosphoinositide breakdown, which occurs following membrane receptor occupancy, and is one of the initial events in signal transduction. The release of DAG during PI turnover substantially stimulates PKC activity over that observed in quiescent cells. The known co-carcinogen or tumor promotor TPA specifically increases membrane PKC activity. Associated with this increased membrane PKC activity is a reduction of cytosolic PKC activity, which suggests that the translocation of PKC is an important intracellular event. Using a homogeneous population of cells (a mouse-derived, anterior pituitary tumor cell line [AtT-20s]) that respond to a variety of membrane and intracellular activators by releasing POMC-derived peptides, we have explored the involvement of PKC in hormone secretion by monitoring the release of beta-endorphin (BE) as well as membrane and cytosolic PKC activity. TPA treatment resulted in a dose-related increase in BE secretion and translocation of PKC from the cytosolic to the membrane fraction. A maximally stimulating concentration of TPA enhanced membrane PKC activity twofold within 1 minute and fivefold within 3 minutes. It would appear that activation (translocation) of PKC results in enhanced hormone release through a pathway that does not involve the adenylate cyclase/cAMP system.