Gomez-Manzano C, Mitlianga P, Fueyo J, Lee H Y, Hu M, Spurgers K B, Glass T L, Koul D, Liu T J, McDonnell T J, Yung W K
Department of Neuro-Oncology, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030, USA.
Cancer Res. 2001 Sep 15;61(18):6693-7.
Strong evidence exists to support the tenet that activation of E2F transcription factors, via alterations in the p16-cyclin D-Rb pathway, is a key event in the malignant progression of most human malignant gliomas. The oncogenic ability of E2F has been related to the E2F-mediated up-regulation of several proteins that positively regulate cell proliferation. However, E2F may indirectly enhance proliferation by activating antiapoptotic molecules. In this work, we sought to ascertain whether E2F-1-mediated events involve the up-regulation of the antiapoptotic molecule Bcl-2. Western blot analyses showed up-regulation of Bcl-2 but not of Bcl-x(L) by 24 h after the transfer of E2F-1. Northern blot studies showed that transfer of E2F-1 also up-regulated Bcl-2 RNA. In support of these findings and the concept that E2F-1 has a direct effect in the induction of Bcl-2, we found a putative E2F binding site within the Bcl-2 sequence. Subsequent gel-mobility shift and supershift experiments involving the CTCCGCGC site in the bcl-2 promoter showed that E2F-1 bound Bcl-2. Transactivation experiments consistently showed that ectopic E2F-1 activated responsive elements located in the -1448/-1441 region in the P1 promoter region of the bcl-2 gene. As expected, other members of the E2F family of transcription factors such as E2F-2 and E2F-4 also transactivated the bcl-2 promoter. Our results demonstrate that E2F-1 modulates the expression of the antiapoptotic molecule Bcl-2 and suggest that up-regulation of Bcl-2 may favor the oncogenic role of E2F-1 and other members of the E2F family of transcription factors.
通过p16 - 细胞周期蛋白D - Rb途径的改变激活E2F转录因子是大多数人类恶性胶质瘤恶性进展中的关键事件。E2F的致癌能力与E2F介导的几种正向调节细胞增殖的蛋白质上调有关。然而，E2F可能通过激活抗凋亡分子间接增强增殖。在这项研究中，我们试图确定E2F - 1介导的事件是否涉及抗凋亡分子Bcl - 2的上调。蛋白质免疫印迹分析显示，E2F - 1转染24小时后，Bcl - 2上调，但Bcl - x(L)未上调。Northern印迹研究表明，E2F - 1转染也上调了Bcl - 2 RNA。为支持这些发现以及E2F - 1对Bcl - 2诱导有直接作用这一概念，我们在Bcl - 2序列中发现了一个推定的E2F结合位点。随后涉及bcl - 2启动子中CTCCGCGC位点的凝胶迁移率变动和超迁移实验表明，E2F - 1与Bcl - 2结合。反式激活实验一致显示，异位表达的E2F - 1激活了位于bcl - 2基因P1启动子区域 - 1448 / - 1441区域的反应元件。正如预期的那样，E2F转录因子家族的其他成员，如E2F - 2和E2F - 4也反式激活了bcl - 2启动子。我们的结果表明，E2F - 1调节抗凋亡分子Bcl - 2的表达，并提示Bcl - 2的上调可能有利于E2F - 1和E2F转录因子家族其他成员的致癌作用。
