Han ShouWei, Khuri Fadlo R, Roman Jesse
Department of Medicine, Division of Pulmonary, Allergy and Critical Care Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Cancer Res. 2006 Jan 1;66(1):315-23. doi: 10.1158/0008-5472.CAN-05-2367.
The Akt/mammalian target of rapamycin (mTOR)/ribosomal protein S6 kinase (p70S6K) pathway is considered a central regulator of protein synthesis and of cell proliferation, differentiation, and survival. However, the role of the Akt/mTOR/p70S6K pathway in lung carcinoma remains unknown. We previously showed that fibronectin, a matrix glycoprotein highly expressed in tobacco-related lung disease, stimulates non-small cell lung carcinoma (NSCLC) cell growth and survival. Herein, we explore the role of the Akt/mTOR/p70S6K pathway in fibronectin-induced NSCLC cell growth. We found that fibronectin stimulated the phosphorylation of Akt, an upstream inducer of mTOR, and induced the phosphorylation of p70S6K1 and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), two downstream targets of mTOR in NSCLC cells (H1792 and H1838), whereas it inhibited the phosphatase and tensin homologue deleted on chromosome 10, a tumor suppressor protein that antagonizes the phosphatidylinositol 3-kinase/Akt signal. In addition, treatment with fibronectin inhibited the mRNA and protein expression of LKB1 as well as the phosphorylation of AMP-activated protein kinase (AMPKalpha), both known to down-regulate mTOR. Rapamycin, an inhibitor of mTOR, blocked the fibronectin-induced phosphorylation of p70S6K and 4E-BP1. Akt small interfering RNA (siRNA) and an antibody against the fibronectin-binding integrin alpha5beta1 also blocked the p70S6K phosphorylation in response to fibronectin. In contrast, an inhibitor of extracellular signal-regulated kinase 1/2 (PD98095) had no effect on fibronectin-induced phosphorylation of p70S6K. Moreover, the combination of rapamycin and siRNA for Akt blocked fibronectin-induced cell proliferation. Taken together, these observations suggest that fibronectin-induced stimulation of NSCLC cell proliferation requires activation of the Akt/mTOR/p70S6K pathway and is associated with inhibition of LKB1/AMPK signaling.
Akt/雷帕霉素哺乳动物靶点（mTOR）/核糖体蛋白S6激酶（p70S6K）信号通路被认为是蛋白质合成以及细胞增殖、分化和存活的核心调节因子。然而，Akt/mTOR/p70S6K信号通路在肺癌中的作用尚不清楚。我们之前发现，纤连蛋白是一种在烟草相关肺部疾病中高表达的基质糖蛋白，可刺激非小细胞肺癌（NSCLC）细胞的生长和存活。在此，我们探讨Akt/mTOR/p70S6K信号通路在纤连蛋白诱导的NSCLC细胞生长中的作用。我们发现，纤连蛋白可刺激mTOR的上游诱导因子Akt的磷酸化，并诱导p70S6K1和真核起始因子4E结合蛋白1（4E-BP1）的磷酸化，这两个都是NSCLC细胞（H1792和H1838）中mTOR的下游靶点，而它抑制了10号染色体上缺失的磷酸酶和张力蛋白同源物，这是一种拮抗磷脂酰肌醇3激酶/Akt信号的肿瘤抑制蛋白。此外，用纤连蛋白处理可抑制LKB1的mRNA和蛋白表达以及AMP活化蛋白激酶（AMPKα）的磷酸化，二者均已知可下调mTOR。雷帕霉素是一种mTOR抑制剂，可阻断纤连蛋白诱导的p70S6K和4E-BP1的磷酸化。Akt小干扰RNA（siRNA）以及抗纤连蛋白结合整合素α5β1的抗体也可阻断纤连蛋白诱导的p70S6K磷酸化。相比之下，细胞外信号调节激酶1/2抑制剂（PD98095）对纤连蛋白诱导的p70S6K磷酸化没有影响。此外，雷帕霉素和Akt的siRNA联合使用可阻断纤连蛋白诱导的细胞增殖。综上所述，这些观察结果表明，纤连蛋白诱导的NSCLC细胞增殖刺激需要激活Akt/mTOR/p70S6K信号通路，并且与LKB1/AMPK信号的抑制有关。
