Sheng H, Shao J, DuBois R N
Department of Medicine, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Department of Veterans Affairs Medical Center, Nashville, Tennessee 37232, USA.
J Biol Chem. 2001 Apr 27;276(17):14498-504. doi: 10.1074/jbc.M010093200. Epub 2001 Feb 1.
Phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB/Akt) is thought to serve as an oncogenic signaling pathway which can be activated by Ras. The role of PI3K/Akt in Ras-mediated transformation of intestinal epithelial cells is currently not clear. Here we demonstrate that inducible expression of oncogenic Ha-Ras results in activation of PKB/Akt in rat intestinal epithelial cells (RIE-iHa-Ras), which was blocked by treatment with inhibitors of PI3K activity. The PI3K inhibitor, LY-294002, partially reversed the morphological transformation induced by Ha-Ras and resulted in a modest stimulation of apoptosis. The most pronounced phenotypic alteration following inhibition of PI3K was induction of G(1) phase cell cycle arrest. LY-294002 blocked the Ha-Ras-induced expression of cyclin D1, cyclin-dependent kinase (CDK) 2, and increased the levels of p27(kip). Both LY-294002 and wortmannin significantly reduced anchorage-independent growth of RIE-iHa-Ras cells. Forced expression of both the constitutively active forms of Raf (DeltaRaf-22W or Raf BXB) and Akt (Akt-myr) resulted in transformation of RIE cells that was not achieved by transfection with either the Raf mutant construct or Akt-myr alone. These findings delineate an important role for PI3K/Akt in Ras-mediated transformation of intestinal epithelial cells.
磷脂酰肌醇3激酶（PI3K）/蛋白激酶B（PKB/Akt）被认为是一条可被Ras激活的致癌信号通路。目前，PI3K/Akt在Ras介导的肠上皮细胞转化中的作用尚不清楚。在此我们证明，致癌性Ha-Ras的诱导表达可导致大鼠肠上皮细胞（RIE-iHa-Ras）中PKB/Akt的激活，而PI3K活性抑制剂处理可阻断这种激活。PI3K抑制剂LY-294002可部分逆转Ha-Ras诱导的形态转化，并适度刺激细胞凋亡。抑制PI3K后最明显的表型改变是诱导G(1)期细胞周期停滞。LY-294002可阻断Ha-Ras诱导的细胞周期蛋白D1、细胞周期蛋白依赖性激酶（CDK）2的表达，并增加p27(kip)的水平。LY-294002和渥曼青霉素均显著降低RIE-iHa-Ras细胞的非锚定依赖性生长。组成型活性形式的Raf（DeltaRaf-22W或Raf BXB）和Akt（Akt-myr）的强制表达均导致RIE细胞转化，而单独转染Raf突变体构建体或Akt-myr均未实现这种转化。这些发现阐明了PI3K/Akt在Ras介导的肠上皮细胞转化中的重要作用。
