Lang F, Friedrich F, Kahn E, Wöll E, Hammerer M, Waldegger S, Maly K, Grunicke H
Institute for Physiology, University of Innsbruck, Austria.
J Biol Chem. 1991 Mar 15;266(8):4938-42.
Products of ras genes are putative elements of growth factor signal transduction. However, the mechanism of action of these proteins in normal and malignant growth is as yet obscure. To test for functional consequences of ras oncogene expression, electrophysiological experiments were performed on NIH-3T3 fibroblasts transfected with a transforming Ha-ras MMTV-LTR construct expressing the oncogene on treatment with dexamethasone (+ras). Transfected cells in the absence of dexamethasone (-ras) and nontransfected cells in the presence of dexamethasone (oras) served as controls. In -ras and oras, bradykinin induces a single, transient hyperpolarization. In +ras, bradykinin elicits oscillations of cell membrane potential throughout the presence of the hormone by activation of calcium-sensitive K+ channels. The oscillations of cell membrane potential are abolished in the absence of extracellular calcium. As evident from fura 2 fluorescence, bradykinin leads to a transient increase of intracellular calcium both in the presence and absence of extracellular calcium. Oscillations of intracellular calcium could be observed in +ras cells, if bradykinin was applied at reduced extracellular sodium concentration possibly to impair calcium extrusion via the sodium/calcium exchange. Bradykinin induces oscillations of cell membrane potential similarly in -ras cells loaded with GTP[S], a nonhydrolyzable analogue of GTP. Thus, the altered response of ras oncogene expressing cells to bradykinin relates to the GTP binding property of the ras protein. It is concluded that in cells expressing ras oncogene but not in other fibroblasts bradykinin mimicks the effect of growth factors on the cell membrane.
ras基因的产物被认为是生长因子信号转导的元件。然而，这些蛋白质在正常生长和恶性生长中的作用机制仍不清楚。为了测试ras癌基因表达的功能后果，对用转化型Ha-ras MMTV-LTR构建体转染的NIH-3T3成纤维细胞进行了电生理实验，该构建体在用地塞米松处理时表达癌基因（+ras）。未用地塞米松处理的转染细胞（-ras）和用地塞米松处理的未转染细胞（oras）作为对照。在 -ras和oras中，缓激肽诱导单一的、短暂的超极化。在 +ras中，缓激肽通过激活钙敏感钾通道在整个激素存在期间引发细胞膜电位振荡。在没有细胞外钙的情况下，细胞膜电位振荡消失。从fura 2荧光可以明显看出，缓激肽在有或没有细胞外钙的情况下都会导致细胞内钙的短暂增加。如果在降低的细胞外钠浓度下应用缓激肽，可能会损害通过钠/钙交换的钙外排，则在 +ras细胞中可以观察到细胞内钙振荡。缓激肽在加载有GTP[S]（一种不可水解的GTP类似物）的 -ras细胞中同样诱导细胞膜电位振荡。因此，表达ras癌基因的细胞对缓激肽的反应改变与ras蛋白的GTP结合特性有关。得出的结论是，在表达ras癌基因的细胞中，而不是在其他成纤维细胞中，缓激肽模拟了生长因子对细胞膜的作用。
