Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada.
J Neurosci. 2010 Dec 15;30(50):16938-48. doi: 10.1523/JNEUROSCI.1598-10.2010.
An increasing body of evidence points to a key role of endoplasmic reticulum (ER) stress in acute and chronic neurodegenerative conditions. Extensive ER stress can trigger neuronal apoptosis, but the signaling pathways that regulate this cell death remain unclear. In the present study, we demonstrate that PUMA, a Bcl-2 homology 3 (BH3)-only member of the Bcl-2 family, is transcriptionally activated in cortical neurons by ER stress and is essential for ER-stress-induced cell death. PUMA is known to be a key transcriptional target of p53, but we have found that ER stress triggers PUMA induction and cell death through a p53-independent mechanism mediated by the ER-stress-inducible transcription factor ATF4 (activating transcription factor 4). Specifically, we demonstrate that ectopic expression of ATF4 sensitizes mouse cortical neurons to ER-stress-induced apoptosis and that ATF4-deficient neurons exhibit markedly reduced levels of PUMA expression and cell death. However, chromatin immunoprecipitation experiments suggest that ATF4 does not directly regulate the PUMA promoter. Rather, we found that ATF4 induces expression of the transcription factor CHOP (C/EBP homologous protein) and that CHOP in turn activates PUMA induction. Specifically, we demonstrate that CHOP binds to the PUMA promoter during ER stress and that CHOP knockdown attenuates PUMA induction and neuronal apoptosis. In summary, we have identified a key signaling pathway in ER-stress-induced neuronal death involving ATF4-CHOP-mediated transactivation of the proapoptotic Bcl-2 family member PUMA. We propose that this pathway may be an important therapeutic target relevant to a number of neurodegenerative conditions.
越来越多的证据表明内质网（ER）应激在急性和慢性神经退行性疾病中起着关键作用。广泛的 ER 应激会引发神经元凋亡，但调节这种细胞死亡的信号通路尚不清楚。在本研究中，我们证明了 PUMA，一种 Bcl-2 家族中的 BH3 仅成员，在皮质神经元中由 ER 应激转录激活，是 ER 应激诱导细胞死亡所必需的。PUMA 已知是 p53 的关键转录靶标，但我们发现 ER 应激通过由 ER 应激诱导的转录因子 ATF4（激活转录因子 4）介导的 p53 非依赖性机制触发 PUMA 诱导和细胞死亡。具体而言，我们证明了 ATF4 的异位表达使小鼠皮质神经元对 ER 应激诱导的凋亡敏感，并且 ATF4 缺陷神经元表现出明显降低的 PUMA 表达和细胞死亡水平。然而，染色质免疫沉淀实验表明 ATF4 不会直接调节 PUMA 启动子。相反，我们发现 ATF4 诱导转录因子 CHOP（C/EBP 同源蛋白）的表达，而 CHOP 反过来激活 PUMA 诱导。具体而言，我们证明 CHOP 在 ER 应激期间结合到 PUMA 启动子上，并且 CHOP 敲低减弱了 PUMA 诱导和神经元凋亡。总之，我们已经确定了 ER 应激诱导的神经元死亡中的关键信号通路，该通路涉及 ATF4-CHOP 介导的促凋亡 Bcl-2 家族成员 PUMA 的反式激活。我们提出，该途径可能是与多种神经退行性疾病相关的重要治疗靶标。
