Downward J, de Gunzburg J, Riehl R, Weinberg R A
Whitehead Institute for Biomedical Research, Cambridge, MA 02142.
Proc Natl Acad Sci U S A. 1988 Aug;85(16):5774-8. doi: 10.1073/pnas.85.16.5774.
Proteins encoded by ras genes have recently been reported to couple certain growth factor receptors to phospholipase C, the enzyme catalyzing phosphatidylinositol breakdown. To investigate this hypothesis, the normal and the transforming Ha-, Ki-, and N-ras genes were each transfected into Rat-1 fibroblasts under the control of strong promoters. Several cell lines, both normal and transformed, were selected that expressed high levels of p21ras. Phosphatidylinositol turnover was measured in these cells in response to a wide variety of peptide factors; bradykinin was found to have a greatly enhanced effect on the p21ras overexpressors relative to the parental and control cells. Bradykinin receptor numbers were measured in these lines and found to be up to 40-fold higher in the p21ras overexpressors than in the parental cells. This was found to be the case for both normal and transforming forms of all three varieties of ras genes. Receptor number correlated well with the bradykinin-dependent phosphatidylinositol turnover response in all cases. These data indicate that the effects of p21ras on cellular responses to the peptide hormone bradykinin are due to changes in receptor number rather than to direct coupling by p21ras between the receptor and phospholipase C.
最近有报道称，ras基因编码的蛋白质可将某些生长因子受体与磷脂酶C偶联，磷脂酶C是催化磷脂酰肌醇分解的酶。为了验证这一假说，将正常的以及具有转化活性的Ha-、Ki-和N-ras基因分别在强启动子的控制下转染到大鼠-1成纤维细胞中。筛选出了几个正常和转化的细胞系，这些细胞系均高表达p21ras。检测了这些细胞对多种肽类因子的磷脂酰肌醇周转率；结果发现，相对于亲代细胞和对照细胞，缓激肽对p21ras过表达细胞的作用大大增强。检测了这些细胞系中的缓激肽受体数量，发现p21ras过表达细胞中的受体数量比亲代细胞高40倍。所有三种ras基因的正常形式和具有转化活性的形式均是如此。在所有情况下，受体数量与缓激肽依赖性磷脂酰肌醇周转反应均密切相关。这些数据表明，p21ras对细胞对肽类激素缓激肽反应的影响是由于受体数量的变化，而不是p21ras在受体与磷脂酶C之间的直接偶联。
