PI3-kinase in concert with Src promotes the S-phase entry of oestradiol-stimulated MCF-7 cells

The p85-associated phosphatidylinositol (PI) 3-kinase/Akt pathway mediates the oestradiol-induced S-phase entry and cyclin D1 promoter activity in MCF-7 cells. Experiments with Src, p85α and Akt dominant-negative forms indicate that in oestradiol-treated cells these signalling effectors target the cyclin D1 promoter. Oestradiol acutely increases PI3-kinase and Akt activities in MCF-7 cells. In NIH 3T3 cells expressing ERα, a dominant-negative p85 suppresses hormone stimulation of Akt. The Src inhibitor, PP1, prevents hormone stimulation of Akt and PI3-kinase activities in MCF-7 cells. In turn, stimulation of Src activity is abolished in ERα-expressing NIH 3T3 fibroblasts by co-transfection of the dominant-negative p85α and in MCF-7 cells by the PI3-kinase inhibitor, LY294002. These findings indicate a novel reciprocal cross-talk between PI3-kinase and Src. Hormone stimulation of MCF-7 cells rapidly triggers association of ERα with Src and p85. In vitro these proteins are assembled in a ternary complex with a stronger association than that of the binary complexes composed by the same partners. The ternary complex probably favours hormone activation of Src- and PI3-kinase-dependent pathways, which converge on cell cycle progression.

与p85相关的磷脂酰肌醇(PI)3-激酶/Akt通路介导雌二醇诱导的MCF-7细胞S期进入及细胞周期蛋白D1启动子活性。采用Src、p85α及Akt显性负突变体开展的实验显示，在雌二醇处理的细胞中，这些信号效应分子靶向作用于细胞周期蛋白D1启动子。雌二醇可快速提升MCF-7细胞内PI3-激酶与Akt的活性。在表达雌激素受体α（Estrogen Receptor α, ERα）的NIH 3T3细胞中，显性负突变型p85可抑制激素对Akt的激活效应。Src抑制剂PP1能够阻断雌二醇处理的MCF-7细胞中Akt与PI3-激酶的活性激活。反之，在表达ERα的NIH 3T3成纤维细胞中，共转染显性负突变型p85α可消除Src活性的上调；而在MCF-7细胞中，PI3-激酶抑制剂LY294002同样可实现该效果。上述研究结果揭示了PI3-激酶与Src之间一种全新的相互串扰机制。雌二醇刺激MCF-7细胞可快速触发雌激素受体α与Src及p85的结合。体外实验表明，这些蛋白可组装成三元复合物，其结合强度高于由相同分子对构成的二元复合物。该三元复合物或可促进激素对Src及PI3-激酶依赖通路的激活，而这些通路最终汇聚于细胞周期进程的调控。