Tyrolean Cancer Research Institute, 6020 Innsbruck, Austria.
Mol Biol Cell. 2012 Jun;23(11):2226-34. doi: 10.1091/mbc.E11-06-0535. Epub 2012 Apr 4.
Forkhead box O (FOXO) transcription factors control diverse cellular functions, such as cell death, metabolism, and longevity. We analyzed FOXO3/FKHRL1 expression and subcellular localization in tumor sections of neuroblastoma patients and observed a correlation between nuclear FOXO3 and high caspase-8 expression. In neuroblastoma caspase-8 is frequently silenced by DNA methylation. Conditional FOXO3 activated caspase-8 gene expression but did not change the DNA-methylation pattern of regulatory sequences in the caspase-8 gene. Instead, FOXO3 induced phosphorylation of its binding partner ATM and of the ATM downstream target cAMP-responsive element binding protein (CREB), which was critical for FOXO3-mediated caspase-8 expression. Caspase-8 levels above a critical threshold sensitized neuroblastoma cells to tumor necrosis factor-related apoptosis-inducing ligand-induced cell death. The DNA-demethylating drug 5-Aza-2-deoxycytidine (5-azadC) induced rapid nuclear accumulation of FOXO3, ATM-dependent CREB phosphorylation, and caspase-8 expression in a FOXO3-dependent manner. This indicates that 5-azadC activates the FOXO3-ATM-CREB signaling pathway, which contributes to caspase-8 expression. The combined data suggest that FOXO3 is activated by 5-azadC treatment and triggers expression of caspase-8 in caspase-8-negative neuroblastoma, which may have important implication for metastasis, therapy, and death resistance of this childhood malignancy.
叉头框 O（FOXO）转录因子控制着多种细胞功能，如细胞死亡、代谢和寿命。我们分析了神经母细胞瘤患者肿瘤组织中 FOXO3/FKHRL1 的表达和亚细胞定位，观察到核 FOXO3 与高 caspase-8 表达之间存在相关性。在神经母细胞瘤中，caspase-8 常因 DNA 甲基化而沉默。条件性 FOXO3 激活 caspase-8 基因表达，但不改变 caspase-8 基因调控序列的 DNA 甲基化模式。相反，FOXO3 诱导其结合伙伴 ATM 和 ATM 下游靶标 cAMP 反应元件结合蛋白（CREB）的磷酸化，这对于 FOXO3 介导的 caspase-8 表达至关重要。临界阈值以上的 caspase-8 水平使神经母细胞瘤细胞对肿瘤坏死因子相关凋亡诱导配体诱导的细胞死亡敏感。DNA 去甲基化药物 5-氮杂-2′-脱氧胞苷（5-azadC）以 FOXO3 依赖的方式诱导 FOXO3 的快速核积累、ATM 依赖性 CREB 磷酸化和 caspase-8 表达。这表明 5-azadC 激活 FOXO3-ATM-CREB 信号通路，促进 caspase-8 表达。综合数据表明，FOXO3 被 5-azadC 处理激活，并触发 caspase-8 在 caspase-8 阴性神经母细胞瘤中的表达，这可能对该儿童恶性肿瘤的转移、治疗和耐药性具有重要意义。
