Yao Xin, Pham Tri, Temple Brandi, Gray Selena, Cannon Cornita, Hardy Camry, Fletcher Kamari, Ireland Shubha Kale, Hossain Ahamed, Chen Renwei, Abdel-Mageed Asim B, Biliran Hector
Department of Biological and Public Health Sciences, Xavier University of Louisiana, New Orleans, LA 70125, USA.
Center for Bioengineering, University of California, Santa Barbara, CA 93106, USA.
Oncotarget. 2017 Jul 31;8(42):72235-72249. doi: 10.18632/oncotarget.19703. eCollection 2017 Sep 22.
The Transducin-like enhancer of split 1 (TLE1) corepressor protein is overexpressed in human lung tumors and is a putative lung-specific oncogene. However, the molecular mechanism underlying its oncogenic function remains to be delineated. Here, we report an important role of TLE1 in promoting lung tumorigenesis by a mechanism involving induction of anoikis resistance. Using the human lung adenocarcinoma A549 and immortalized bronchial epithelial BEAS-2B cell lines, we observed that TLE1 inhibits anoikis through transcriptional repression of E-cadherin gene. In support of E-cadherin as a downstream target of TLE1 to block anoikis, forced expression of E-cadherin attenuated TLE1-induced anoikis resistance while E-cadherin downregulation decreased the anoikis sensitivity of TLE1 knockdown cells. Furthermore, we determined that E-cadherin expression is transcriptionally induced upon loss of cell attachment and functions as an effector of anoikis. Loss of E-cadherin via the siRNA strategy or exogenous TLE1 expression was sufficient to attenuate anoikis in A549 and BEAS-2B cells. Importantly, we demonstrated that the ZEB1 transcriptional factor is required for TLE1-mediated E-cadherin repression and anoikis resistance. ZEB1 interacted with and recruited the TLE1 to the E-cadherin promoter to impose histone deacetylation and gene silencing. , TLE1 strongly promoted tumorigenicity of A549 cells in a ZEB1-dependent manner. Underscoring its role in anoikis insensitivity of lung cancer cells, the TLE1-mediated E-cadherin repression was negatively regulated by the tumor suppressor Bcl-2 inhibitor of transcription 1 (Bit1) to effect anoikis. These findings identify the ZEB1/TLE1/E-cadherin transcriptional mechanism as a novel pathway that promotes anoikis resistance and oncogenicity of lung cancer cells.
分裂样增强子1（TLE1）共抑制蛋白在人类肺肿瘤中过表达，是一种假定的肺特异性癌基因。然而，其致癌功能的分子机制仍有待阐明。在此，我们报告了TLE1通过诱导失巢凋亡抗性机制在促进肺癌发生中发挥的重要作用。利用人肺腺癌A549细胞系和永生化支气管上皮BEAS-2B细胞系，我们观察到TLE1通过转录抑制E-钙黏蛋白基因来抑制失巢凋亡。为支持E-钙黏蛋白作为TLE1阻断失巢凋亡的下游靶点，E-钙黏蛋白的强制表达减弱了TLE1诱导的失巢凋亡抗性，而E-钙黏蛋白的下调降低了TLE1敲低细胞的失巢凋亡敏感性。此外，我们确定E-钙黏蛋白表达在细胞附着丧失时被转录诱导，并作为失巢凋亡的效应器发挥作用。通过小干扰RNA策略使E-钙黏蛋白缺失或外源性表达TLE1足以减弱A549和BEAS-2B细胞中的失巢凋亡。重要的是，我们证明ZEB1转录因子是TLE1介导的E-钙黏蛋白抑制和失巢凋亡抗性所必需的。ZEB1与TLE1相互作用并将其募集到E-钙黏蛋白启动子上，以进行组蛋白去乙酰化和基因沉默。此外，TLE1以ZEB1依赖的方式强烈促进A549细胞的致瘤性。肿瘤抑制因子转录抑制因子1（Bit1）对TLE1介导的E-钙黏蛋白抑制进行负调控以影响失巢凋亡，这突出了其在肺癌细胞失巢凋亡不敏感中的作用。这些发现确定了ZEB1/TLE1/E-钙黏蛋白转录机制是促进肺癌细胞失巢凋亡抗性和致癌性的新途径。
