Department of Microbial and Molecular Pathogenesis, Texas A&M Health Science Center, Bryan, TX 77807, USA.
Cell Microbiol. 2011 Oct;13(10):1479-96. doi: 10.1111/j.1462-5822.2011.01634.x. Epub 2011 Jul 4.
The bacterial virulence factors Shiga toxins (Stxs) are expressed by Shigella dysenteriae serotype 1 and certain Escherichia coli strains. Stxs are protein synthesis inhibitors and induce apoptosis in many cell types. Stxs induce apoptosis via prolonged endoplasmic reticulum stress signalling to activate both extrinsic and intrinsic pathways in human myeloid cells. Studies have shown that autophagy, a lysosome-dependent catabolic process, may be associated with activation of pro-survival or death processes. It is currently unknown if autophagy contributes to apoptosis or protects cells from Stxs. To study cellular responses to Stxs, we intoxicated toxin-sensitive cells (THP-1 and HK-2 cells), and toxin-resistant cells (primary human monocyte-derived macrophages) and examined toxin intracellular trafficking and autophagosome formation. Stxs translocated to different cell compartments in toxin-resistant versus toxin-sensitive cells. Confocal microscopy revealed autophagosome formation in both toxin-resistant and toxin-sensitive cells. Proteolytic cleavage of Atg5 and Beclin-1 plays pivotal roles in switching non-cytotoxic autophagy to cell death signalling. We detected cleaved forms of Atg5 and Beclin-1 in Stx-treated toxin-sensitive cells, while cleaved caspases, calpains, Atg5 and Beclin-1 were not detected in toxin-resistant primary human monocytes and macrophages. These findings suggest that toxin sensitivity correlates with caspase and calpain activation, leading to Atg5 and Beclin-1 cleavage.
志贺氏菌血清型 1 和某些大肠杆菌菌株可表达细菌毒力因子志贺毒素（Stxs）。Stxs 是蛋白质合成抑制剂，可诱导多种细胞类型发生细胞凋亡。Stxs 通过延长内质网应激信号来诱导细胞凋亡，从而激活人髓样细胞中的外在和内在途径。研究表明，自噬是一种溶酶体依赖性的分解代谢过程，可能与激活促生存或死亡过程有关。目前尚不清楚自噬是否有助于细胞凋亡或防止细胞受到 Stxs 的侵害。为了研究细胞对 Stxs 的反应，我们用毒素感染了对毒素敏感的细胞（THP-1 和 HK-2 细胞）和对毒素有抗性的细胞（原代人单核细胞衍生的巨噬细胞），并检查了毒素的细胞内转运和自噬体的形成。Stxs 在对毒素有抗性的细胞和对毒素敏感的细胞中转位到不同的细胞区室。共聚焦显微镜显示，自噬体在对毒素有抗性的细胞和对毒素敏感的细胞中均有形成。Atg5 和 Beclin-1 的蛋白水解切割在将非细胞毒性自噬转换为细胞死亡信号中起着关键作用。我们在 Stx 处理的对毒素敏感的细胞中检测到了切割形式的 Atg5 和 Beclin-1，而在对毒素有抗性的原代人单核细胞和巨噬细胞中则没有检测到切割的 caspase、钙蛋白酶、Atg5 和 Beclin-1。这些发现表明，对毒素的敏感性与 caspase 和钙蛋白酶的激活相关，从而导致 Atg5 和 Beclin-1 的切割。
