London Regional Cancer Program, London, Ontario, Canada.
Mol Cell Biol. 2012 Mar;32(5):900-12. doi: 10.1128/MCB.06286-11. Epub 2011 Dec 19.
E2F transcription can lead to cell proliferation or apoptosis, indicating that E2Fs control opposing functions. In a similar manner, DNA double-strand breaks can signal to induce cell cycle arrest or apoptosis. Specifically, pRB is activated following DNA damage, allowing it to bind to E2Fs and block transcription at cell cycle promoters; however, E2F1 is simultaneously activated, leading to transcription at proapoptotic promoters. We examined this paradoxical control of E2F transcription by studying how E2F1's interaction with pRB is regulated following DNA damage. Our work reveals that DNA damage signals create multiple forms of E2F1 that contain mutually exclusive posttranslational modifications. Specifically, E2F1 phospho-serine 364 is found only in complex with pRB, while E2F1 phosphorylation at serine 31 and acetylation function to create a pRB-free form of E2F1. Both pRB-bound and pRB-free modifications on E2F1 are essential for the activation of TA-p73 and the maximal induction of apoptosis. Chromatin immunoprecipitation demonstrated that E2F1 phosphorylated on serine 364 is also present at proapoptotic gene promoters during the induction of apoptosis. This indicates that distinct populations of E2F1 are organized in response to DNA damage signaling. Surprisingly, these complexes act in parallel to activate transcription of proapoptotic genes. Our data suggest that DNA damage signals alter pRB and E2F1 to engage them in functions leading to apoptotic induction that are distinct from pRB-E2F regulation in cell cycle control.
E2F 转录可导致细胞增殖或凋亡，表明 E2F 控制着相反的功能。类似地，DNA 双链断裂可以发出信号诱导细胞周期停滞或凋亡。具体而言，pRB 在 DNA 损伤后被激活，使其能够与 E2F 结合并阻断细胞周期启动子处的转录；然而，E2F1 同时被激活，导致促凋亡启动子处的转录。我们通过研究 DNA 损伤后 E2F1 与 pRB 相互作用的调控方式，研究了 E2F 转录的这种矛盾控制。我们的工作揭示了 DNA 损伤信号创建了多种形式的 E2F1，它们包含相互排斥的翻译后修饰。具体而言，仅在与 pRB 形成复合物时才会发现 E2F1 的丝氨酸 364 磷酸化，而丝氨酸 31 的磷酸化和乙酰化则有助于形成无 pRB 的 E2F1 形式。E2F1 上的 pRB 结合和无 pRB 修饰对于 TA-p73 的激活和凋亡的最大诱导都是必不可少的。染色质免疫沉淀实验表明，在诱导凋亡过程中，E2F1 的丝氨酸 364 磷酸化也存在于促凋亡基因启动子处。这表明，E2F1 的不同群体是针对 DNA 损伤信号而组织起来的。令人惊讶的是，这些复合物平行作用以激活促凋亡基因的转录。我们的数据表明，DNA 损伤信号改变了 pRB 和 E2F1，使其参与到诱导凋亡的功能中，这些功能与细胞周期控制中的 pRB-E2F 调控不同。
