Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
Cell Death Dis. 2012 Jul 26;3(7):e359. doi: 10.1038/cddis.2012.76.
H2AX, a histone H2A variant, has a key role in the cellular response to DNA double-strand breaks (DSBs). H2AX senses DSBs through rapid serine 139 phosphorylation, concurrently leading to the formation of phospho-(γ)H2AX foci with various proteins. However, in the cells with different sensitivity to ionizing radiation (IR)-induced DSBs, still incomplete are those specific proteins selectively recruited by γH2AX to decide different cell fates. Because the abundance of γH2AX indicates the extent of DSBs, we first identified IR-induced dose-dependent H2AX-interacting partners and found that Bcl-2-associated transcription factor 1 (BCLAF1/Btf) showed enhanced association with γH2AX only under high-dose radiation. In acutely irradiated cells, BCLAF1 promoted apoptosis of irreparable cells through disturbing p21-mediated inhibition of Caspase/cyclin E-dependent, mitochondrial-mediated pathways. Meanwhile, BCLAF1 co-localized with γH2AX foci in nuclei and stabilized the Ku70/DNA-PKcs complex therein, facilitating non-homologous end joining (NHEJ)-based DSB repair in surviving cells. In tumor cells, BCLAF1 was intrinsically suppressed, leading to formation of anti-apoptotic Ku70-Bax complexes and disruption of Ku70/DNA-PKcs complexes, all of which contribute to tumor-associated apoptotic resistance and cell survival with defective NHEJ DNA repair. For the first time, our studies reveal that, based on the extent of DNA damage, BCLAF1 is involved in the γH2AX-mediated regulation of apoptosis and DNA repair, and is a γH2AX-interacting tumor suppressor.
H2AX 是一种组蛋白 H2A 变体，在细胞对 DNA 双链断裂 (DSB) 的反应中起着关键作用。H2AX 通过丝氨酸 139 的快速磷酸化来感知 DSB，同时导致各种蛋白质与磷酸化的 γH2AX 焦点形成。然而，在对电离辐射 (IR) 诱导的 DSB 具有不同敏感性的细胞中，γH2AX 选择性招募的特定蛋白质决定不同细胞命运的机制仍不完整。由于 γH2AX 的丰度表明 DSB 的程度，我们首先鉴定了 IR 诱导的剂量依赖性 H2AX 相互作用伙伴，并发现 Bcl-2 相关转录因子 1 (BCLAF1/Btf) 仅在高剂量辐射下与 γH2AX 的结合增强。在急性照射的细胞中，BCLAF1 通过干扰 p21 介导的 Caspase/cyclin E 依赖性、线粒体介导的途径来促进不可修复细胞的凋亡。同时，BCLAF1 与核内的 γH2AX 焦点共定位，并稳定其中的 Ku70/DNA-PKcs 复合物，促进存活细胞中非同源末端连接 (NHEJ) 为基础的 DSB 修复。在肿瘤细胞中，BCLAF1 被内在抑制，导致抗凋亡的 Ku70-Bax 复合物的形成和 Ku70/DNA-PKcs 复合物的破坏，所有这些都有助于肿瘤相关的凋亡抵抗和细胞存活，并伴有缺陷的 NHEJ DNA 修复。我们的研究首次揭示了，基于 DNA 损伤的程度，BCLAF1 参与 γH2AX 介导的凋亡和 DNA 修复的调控，是一种 γH2AX 相互作用的肿瘤抑制因子。
