College of Life Science and Technology, Huazhong Agricultural University, Wuhan, China.
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, Nanning, China.
Front Cell Infect Microbiol. 2022 Apr 4;12:877265. doi: 10.3389/fcimb.2022.877265. eCollection 2022.
The normal operation of the endoplasmic reticulum (ER) is critical for cells and organisms. However, ER stress, caused by imbalanced protein folding, occurs frequently, which perturbs the function of the ER and even results in cell apoptosis eventually. Many insults can induce ER stress; pathogen infection is one of them. Most of the genes involved in ER stress have been reported to be upregulated in (Mtb) granulomas of humans and mice, implicating that infection with Mtb can induce ER stress. However, little is known about the molecular mechanism of Mtb induction of ER stress. Here, we reveal that protein CDP-diglyceride hydrolase of Mycobacteriumn (CdhM) could target the ER and cause abnormal ER morphology and cell death. RNA-seq analysis suggests that most of the ER stress-involved genes were modulated by CdhM. Further assessed by biochemical experiments, the transcription and protein levels of ER stress markers BiP and CHOP, as well as the levels of XBP1 splicing and eIF2α phosphorylation, were significantly increased by CdhM, confirming that CdhM could induce ER stress alone or during infection. A single conserved amino acid mutant of CdhM, including L44A, G96A, H150A, and W175A, was incapable of inducing ER stress, which indicates that induction of ER stress by CdhM is specific and functional. Furthermore, CdhM-induced ER stress could also promote apoptosis of macrophages during Mtb infection. Overexpression of CdhM conferred a significant benefit for Mtb replication by releasing Mtb into extracellular during infection of macrophage , as presented in CFU assays. Overall, our study identified a novel Mtb effector protein CdhM which may promote Mtb dissemination and proliferation by induction of ER stress and apoptosis and provided new insight into the physiological significance of induction of ER stress in tuberculosis (TB) granulomas.
内质网（ER）的正常运作对细胞和生物体至关重要。然而，由于蛋白质折叠失衡导致的内质网应激经常发生，这扰乱了内质网的功能，最终甚至导致细胞凋亡。许多因素都可以诱导内质网应激；病原体感染就是其中之一。已报道，与内质网应激相关的大多数基因在人类和小鼠的（Mtb）肉芽肿中上调，这表明感染 Mtb 可以诱导内质网应激。然而，对于 Mtb 诱导内质网应激的分子机制知之甚少。在这里，我们揭示分枝杆菌 CDP-二酰基甘油水解酶（CdhM）蛋白可以靶向内质网并导致内质网形态异常和细胞死亡。RNA-seq 分析表明，大多数内质网应激相关基因都受到 CdhM 的调节。进一步通过生化实验评估，内质网应激标志物 BiP 和 CHOP 的转录和蛋白水平，以及 XBP1 剪接和 eIF2α 磷酸化的水平，均显著增加，这证实了 CdhM 可以单独或在感染期间诱导内质网应激。CdhM 的单个保守氨基酸突变体，包括 L44A、G96A、H150A 和 W175A，不能诱导内质网应激，这表明 CdhM 诱导内质网应激是特异且有功能的。此外，CdhM 诱导的内质网应激也可以促进 Mtb 感染期间巨噬细胞的凋亡。CFU 测定显示，CdhM 的过表达通过在感染巨噬细胞期间将 Mtb 释放到细胞外，为 Mtb 的复制提供了显著的益处。总的来说，我们的研究鉴定了一种新的 Mtb 效应蛋白 CdhM，它可能通过诱导内质网应激和细胞凋亡来促进 Mtb 的传播和增殖，并为结核（TB）肉芽肿中内质网应激的诱导提供了新的见解。
