Gao Ning, Flynn Daniel C, Zhang Zhuo, Zhong Xiao-Song, Walker Valerie, Liu Ke Jian, Shi Xianglin, Jiang Bing-Hua
1820 MBR Cancer Center and Dept. of Microbiology, Immunology and Cell Biology, West Virginia University, Morgantown, WV 26506-9300, USA.
Am J Physiol Cell Physiol. 2004 Aug;287(2):C281-91. doi: 10.1152/ajpcell.00422.2003. Epub 2004 Mar 17.
Ovarian cancer is one of the most common cancers among women. Recent studies demonstrated that the gene encoding the p110alpha catalytic subunit of phosphatidylinositol 3-kinase (PI3K) is frequently amplified in ovarian cancer cells. PI3K is involved in multiple cellular functions, including proliferation, differentiation, antiapoptosis, tumorigenesis, and angiogenesis. In this study, we demonstrate that the inhibition of PI3K activity by LY-294002 inhibited ovarian cancer cell proliferation and induced G(1) cell cycle arrest. This effect was accompanied by the decreased expression of G(1)-associated proteins, including cyclin D1, cyclin-dependent kinase (CDK) 4, CDC25A, and retinoblastoma phosphorylation at Ser(780), Ser(795), and Ser(807/811). Expression of CDK6 and beta-actin was not affected by LY-294002. Expression of the cyclin kinase inhibitor p16(INK4a) was induced by the PI3K inhibitor, whereas steady-state levels of p21(CIP1/WAF1) were decreased in the same experiment. The inhibition of PI3K activity also inhibited the phosphorylation of AKT and p70S6K1, but not extracellular regulated kinase 1/2. The G(1) cell cycle arrest induced by LY-294002 was restored by the expression of active forms of AKT and p70S6K1 in the cells. Our study shows that PI3K transmits a mitogenic signal through AKT and mammalian target of rapamycin (mTOR) to p70S6K1. The mTOR inhibitor rapamycin had similar inhibitory effects on G(1) cell cycle progression and on the expression of cyclin D1, CDK4, CDC25A, and retinoblastoma phosphorylation. These results indicate that PI3K mediates G(1) progression and cyclin expression through activation of an AKT/mTOR/p70S6K1 signaling pathway in the ovarian cancer cells.
卵巢癌是女性中最常见的癌症之一。最近的研究表明，编码磷脂酰肌醇3激酶（PI3K）的p110α催化亚基的基因在卵巢癌细胞中经常扩增。PI3K参与多种细胞功能，包括增殖、分化、抗凋亡、肿瘤发生和血管生成。在本研究中，我们证明LY-294002抑制PI3K活性可抑制卵巢癌细胞增殖并诱导G(1)期细胞周期停滞。这种效应伴随着与G(1)相关蛋白表达的降低，包括细胞周期蛋白D1、细胞周期蛋白依赖性激酶（CDK）4、细胞周期蛋白磷酸酶25A（CDC25A）以及视网膜母细胞瘤蛋白在Ser(780)、Ser(795)和Ser(807/811)位点的磷酸化。CDK6和β-肌动蛋白的表达不受LY-294002影响。细胞周期蛋白激酶抑制剂p16(INK4a)的表达由PI3K抑制剂诱导，而在同一实验中p21(CIP1/WAF1)的稳态水平降低。PI3K活性的抑制也抑制了AKT和p70S6K1的磷酸化，但不影响细胞外调节激酶1/2。细胞中表达活性形式的AKT和p70S6K1可恢复LY-294002诱导的G(1)期细胞周期停滞。我们的研究表明，PI3K通过AKT和雷帕霉素哺乳动物靶蛋白（mTOR）向p70S6K1传递有丝分裂信号。mTOR抑制剂雷帕霉素对G(1)期细胞周期进程以及细胞周期蛋白D1、CDK4、CDC25A的表达和视网膜母细胞瘤蛋白磷酸化具有类似的抑制作用。这些结果表明，PI3K通过激活卵巢癌细胞中的AKT/mTOR/p70S6K1信号通路介导G(1)期进程和细胞周期蛋白表达。
