Institut National de la Santé et de la Recherche Médicale UMR866, Dijon, F-21079, France.
J Biol Chem. 2011 Jul 29;286(30):26406-17. doi: 10.1074/jbc.M110.191239. Epub 2011 Jun 8.
The inhibitor of apoptosis protein cIAP1 (cellular inhibitor of apoptosis protein-1) is a potent regulator of the tumor necrosis factor (TNF) receptor family and NF-κB signaling pathways in the cytoplasm. However, in some primary cells and tumor cell lines, cIAP1 is expressed in the nucleus, and its nuclear function remains poorly understood. Here, we show that the N-terminal part of cIAP1 directly interacts with the DNA binding domain of the E2F1 transcription factor. cIAP1 dramatically increases the transcriptional activity of E2F1 on synthetic and CCNE promoters. This function is not conserved for cIAP2 and XIAP, which are cytoplasmic proteins. Chromatin immunoprecipitation experiments demonstrate that cIAP1 is recruited on E2F binding sites of the CCNE and CCNA promoters in a cell cycle- and differentiation-dependent manner. cIAP1 silencing inhibits E2F1 DNA binding and E2F1-mediated transcriptional activation of the CCNE gene. In cells that express a nuclear cIAP1 such as HeLa, THP1 cells and primary human mammary epithelial cells, down-regulation of cIAP1 inhibits cyclin E and A expression and cell proliferation. We conclude that one of the functions of cIAP1 when localized in the nucleus is to regulate E2F1 transcriptional activity.
凋亡蛋白抑制因子 cIAP1（细胞凋亡抑制蛋白-1）是细胞质中肿瘤坏死因子（TNF）受体家族和 NF-κB 信号通路的强效调节剂。然而，在一些原代细胞和肿瘤细胞系中，cIAP1 表达于细胞核内，但其核功能仍知之甚少。本文中，我们发现 cIAP1 的 N 端部分可直接与 E2F1 转录因子的 DNA 结合域相互作用。cIAP1 可显著增加 E2F1 在合成和 CCNE 启动子上的转录活性。该功能在细胞质蛋白 cIAP2 和 XIAP 中并不保守。染色质免疫沉淀实验表明，cIAP1 以细胞周期和分化依赖的方式被募集到 CCNE 和 CCNA 启动子的 E2F 结合位点上。cIAP1 沉默抑制 E2F1 的 DNA 结合和 E2F1 介导的 CCNE 基因转录激活。在表达核内 cIAP1 的细胞（如 HeLa、THP1 细胞和原代人乳腺上皮细胞）中，下调 cIAP1 可抑制 cyclin E 和 A 的表达和细胞增殖。综上，cIAP1 定位于核内的功能之一是调节 E2F1 的转录活性。
