Stress-induced apoptosis is mediated primarily through the intrinsic pathway that involves caspase-9. We previously reported that in caspase-9-deficient cells, a protein complex containing ATG5 and Fas-associated death domain (FADD) facilitated caspase-8 activation and cell death in response to endoplasmic reticulum (ER) stress. Here, we investigated whether this complex could be activated by other forms of cell stress. We show that diverse stress stimuli, including etoposide, brefeldin A and paclitaxel, as well as heat stress and gamma-irradiation, caused formation of a complex containing ATG5-ATG12, FADD and caspase-8 leading to activation of downstream caspases in caspase-9-deficient cells. We termed this complex the ‘stressosome’. However, in these cells, only ER stress and heat shock led to stressosome-dependent cell death. Using in silico molecular modelling, we propose the structure of the stressosome complex, with FADD acting as an adaptor protein, interacting with pro-caspase-8 through their respective death effector domains (DEDs) and interacting with ATG5-ATG12 through its death domain (DD). This suggests that the complex could be regulated by cellular FADD-like interleukin-1β-converting enzyme–inhibitory protein (cFLIP_L), which was confirmed experimentally. This study provides strong evidence for an alternative mechanism of caspase-8 activation involving the stressosome complex.

中文翻译：

---

应激体，一种激活 caspase-8 的信号复合物，以 ATG5 介导的方式响应细胞应激而组装

应激诱导的细胞凋亡主要通过涉及 caspase-9 的内在途径介导。我们之前报道过，在 caspase-9 缺陷细胞中，含有 ATG5 和 Fas 相关死亡结构域 (FADD) 的蛋白质复合物促进了 caspase-8 活化和细胞死亡，以响应内质网 (ER) 应激。在这里，我们研究了这种复合物是否可以被其他形式的细胞应激激活。我们发现不同的应激刺激，包括依托泊苷、布雷菲德菌素 A 和紫杉醇，以及热应激和伽马射线照射，导致形成含有 ATG5-ATG12、FADD 和 caspase-8 的复合物，从而激活 caspase-9 中的下游 caspase - 缺陷细胞。我们将这种复合体称为“应激体”。然而，在这些细胞中，只有 ER 应激和热休克导致应激体依赖性细胞死亡。使用在计算机分子建模中，我们提出了应激体复合物的结构，FADD 作为衔接蛋白，通过各自的死亡效应域 (DED) 与 pro-caspase-8 相互作用，并通过其死亡域 (DD) 与 ATG5-ATG12 相互作用）。这表明该复合物可以受到细胞 FADD 样白介素 1β 转换酶抑制蛋白 (cFLIP _L ) 的调节，这已通过实验得到证实。这项研究为涉及应激体复合物的 caspase-8 激活的替代机制提供了强有力的证据。