Joyce-Brady M, Rubins J B, Panchenko M P, Bernardo J, Steele M P, Kolm L, Simons E R, Dickey B F
Pulmonary Center, Boston University School of Medicine, Massachusetts 02118.
J Biol Chem. 1991 Apr 15;266(11):6859-65.
Mastoparan, a tetradecapeptide component of wasp venom, is a potent activator of secretion in a variety of cell types, and has been shown to activate purified G-proteins reconstituted into phospholipid vesicles with a preferential activation of Gi over Gs (Higashijima, T., Uzu, S., Nakajima, T., and Ross, E. R. (1988) J. Biol. Chem. 263, 6491-6494). To identify the biochemical activities of mastoparan in a cellular system, we characterized the effects of mastoparan on signal transduction pathways in rat pulmonary alveolar type 2 epithelial cells, which synthesize and secrete pulmonary surfactant. Mastoparan inhibited adenylylcyclase activity in a manner that was dose-dependent (IC50 = 30 microM), but sensitive to neither guanine nucleotide nor pertussis toxin (PT). Mastoparan induced a PT-sensitive increase in cellular inositol trisphosphate and a rapid rise in cytosolic calcium released from intracellular stores; the time to onset of the calcium rise, but neither the rate nor the amplitude of the rise, were PT-sensitive. Mastoparan also caused a dose- (EC50 = 16 microM) and time-dependent activation of arachidonic acid release that was completely insensitive to pretreatment with PT. Secretion of pulmonary surfactant was increased by mastoparan approximately 8-fold over constitutive levels at 1 h with an EC50 = 20 microM, and mastoparan-stimulated secretion was partially sensitive to PT at late time points and to inhibitors of arachidonic acid metabolism, but not to the protein kinase C inhibitor H7. These findings are consistent with the activation of Gi proteins in type 2 cells by mastoparan, although the lack of predicted triphosphoguanine nucleotide and PT sensitivity for some activities indicates that mastoparan does not act in a manner strictly analogous to liganded receptors or that some activities are not mediated by activation of Gi. While mastoparan is a potent secretagogue in several cell types, its secretory activity appears to have only a limited dependence on the activation of Gi proteins in type 2 cells.
蜂毒明肽是黄蜂毒液中的一种十四肽成分，是多种细胞类型中分泌的强效激活剂，并且已被证明能激活重构到磷脂囊泡中的纯化G蛋白，对Gi的激活优先于Gs（东岛，T.，宇津，S.，中岛，T.，和罗斯，E.R.（1988年）《生物化学杂志》263，6491 - 6494）。为了确定蜂毒明肽在细胞系统中的生化活性，我们表征了蜂毒明肽对大鼠肺泡II型上皮细胞信号转导途径的影响，该细胞合成并分泌肺表面活性物质。蜂毒明肽以剂量依赖性方式抑制腺苷酸环化酶活性（IC50 = 30微摩尔），但对鸟嘌呤核苷酸和百日咳毒素（PT）均不敏感。蜂毒明肽诱导细胞内三磷酸肌醇的PT敏感性增加以及从细胞内储存释放的胞质钙快速升高；钙升高开始的时间，但不是升高的速率或幅度，对PT敏感。蜂毒明肽还引起花生四烯酸释放的剂量依赖性（EC50 = 16微摩尔）和时间依赖性激活，这对PT预处理完全不敏感。蜂毒明肽在1小时时使肺表面活性物质的分泌比基础水平增加约8倍，EC50 = 20微摩尔，并且蜂毒明肽刺激的分泌在后期对PT以及花生四烯酸代谢抑制剂部分敏感，但对蛋白激酶C抑制剂H7不敏感。这些发现与蜂毒明肽在II型细胞中激活Gi蛋白一致，尽管某些活性缺乏预测的三磷酸鸟嘌呤核苷酸和PT敏感性表明蜂毒明肽的作用方式与配体结合受体并不严格类似，或者某些活性不是由Gi的激活介导的。虽然蜂毒明肽在几种细胞类型中是一种强效促分泌剂，但其分泌活性似乎仅在有限程度上依赖于II型细胞中Gi蛋白的激活。
