Department of Urology, Klinikum rechts der Isar der Technischen Universität München, Munich, Germany.
PLoS One. 2011;6(11):e27509. doi: 10.1371/journal.pone.0027509. Epub 2011 Nov 15.
Aberrant activation and mutation status of proteins in the phosphatidylinositol-3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) and the mitogen activated protein kinase (MAPK) signaling pathways have been linked to tumorigenesis in various tumors including urothelial carcinoma (UC). However, anti-tumor therapy with small molecule inhibitors against mTOR turned out to be less successful than expected. We characterized the molecular mechanism of this pathway in urothelial carcinoma by interfering with different molecular components using small chemical inhibitors and siRNA technology and analyzed effects on the molecular activation status, cell growth, proliferation and apoptosis. In a majority of tested cell lines constitutive activation of the PI3K was observed. Manipulation of mTOR or Akt expression or activity only regulated phosphorylation of S6K1 but not 4E-BP1. Instead, we provide evidence for an alternative mTOR independent but PI3K dependent regulation of 4E-BP1. Only the simultaneous inhibition of both S6K1 and 4E-BP1 suppressed cell growth efficiently. Crosstalk between PI3K and the MAPK signaling pathway is mediated via PI3K and indirect by S6K1 activity. Inhibition of MEK1/2 results in activation of Akt but not mTOR/S6K1 or 4E-BP1. Our data suggest that 4E-BP1 is a potential new target molecule and stratification marker for anti cancer therapy in UC and support the consideration of a multi-targeting approach against PI3K, mTORC1/2 and MAPK.
磷脂酰肌醇-3-激酶（PI3K）/Akt/雷帕霉素靶蛋白（mTOR）和丝裂原活化蛋白激酶（MAPK）信号通路中的蛋白异常激活和突变状态与各种肿瘤的肿瘤发生有关，包括膀胱癌（UC）。然而，针对 mTOR 的小分子抑制剂的抗肿瘤治疗效果并不如预期的那样成功。我们通过使用小分子化学抑制剂和 siRNA 技术干扰不同的分子成分，对膀胱癌中的这条通路的分子机制进行了表征，并分析了对分子激活状态、细胞生长、增殖和凋亡的影响。在大多数测试的细胞系中，观察到 PI3K 的组成性激活。mTOR 或 Akt 表达或活性的操纵仅调节 S6K1 的磷酸化，但不调节 4E-BP1。相反，我们提供了替代的 mTOR 独立但 PI3K 依赖的 4E-BP1 调节的证据。只有同时抑制 S6K1 和 4E-BP1 才能有效地抑制细胞生长。PI3K 和 MAPK 信号通路之间的串扰通过 PI3K 介导，通过 S6K1 活性间接介导。MEK1/2 的抑制导致 Akt 的激活，但不导致 mTOR/S6K1 或 4E-BP1 的激活。我们的数据表明，4E-BP1 是 UC 中癌症治疗的一个潜在的新靶标分子和分层标志物，并支持考虑针对 PI3K、mTORC1/2 和 MAPK 的多靶点治疗方法。
