JH Institute of Molecular Medicine, Jamia Hamdard, New Delhi, India.
Molecular Infection and Functional Biology Lab, Kusuma School of Biological Sciences, Indian Institute of Technology-Delhi, New Delhi, India.
mBio. 2018 Jun 19;9(3):e01017-18. doi: 10.1128/mBio.01017-18.
The genome of , the causal organism of tuberculosis (TB), encodes a unique protein family known as the PE/PPE/PGRS family, present exclusively in the genus and nowhere else in the living kingdom, with largely unexplored functions. We describe the functional significance of the PGRS domain of Rv0297, a member of this family. analyses revealed the presence of intrinsically disordered stretches and putative endoplasmic reticulum (ER) localization signals in the PGRS domain of Rv0297 (Rv0297PGRS). The PGRS domain aids in ER localization, which was shown by infecting macrophage cells with and by overexpressing the protein by transfection in macrophage cells followed by activation of the unfolded protein response, as evident from increased expression of GRP78/GRP94 and CHOP/ATF4, leading to disruption of intracellular Ca homeostasis and increased nitric oxide (NO) and reactive oxygen species (ROS) production. The consequent activation of the effector caspase-8 resulted in apoptosis of macrophages, which was Toll-like receptor 4 (TLR4) dependent. Administration of recombinant Rv0297PGRS (rRv0297PGRS) also exhibited similar effects. These results implicate a hitherto-unknown role of the PGRS domain of the PE_PGRS protein family in ER stress-mediated cell death through TLR4. Since this protein is already known to be present at later stages of infection in human granulomas it points to the possibility of it being employed by for its dissemination via an apoptotic mechanism. Apoptosis is generally thought to be a defense mechanism in protecting the host against in early stages of infection. However, apoptosis during later stages in lung granulomas may favor the bacterium in disseminating the disease. ER stress has been found to induce apoptosis in TB granulomas, in zones where apoptotic macrophages accumulate in mice and humans. In this study, we report ER stress-mediated apoptosis of host cells by the Rv0297-encoded PE_PGRS5 protein of exceptionally present in the pathogenic genus. The PGRS domain of Rv0297 aids the protein in localizing to the ER and induces the unfolded protein response followed by apoptosis of macrophages. The effect of the Rv0297PGRS domain was found to be TLR4 dependent. This study presents novel insights on the strategies employed by to disseminate the disease.
结核分枝杆菌（TB）的病原体 基因组编码了一个独特的蛋白家族，称为 PE/PPE/PGRS 家族，仅存在于分枝杆菌属，而在生命体王国的其他地方都不存在，其功能很大程度上仍未被探索。我们描述了该家族成员 Rv0297 的 PGRS 结构域的功能意义。结构分析表明，Rv0297（Rv0297PGRS）的 PGRS 结构域存在固有无序延伸和内质网（ER）定位信号。PGRS 结构域有助于 ER 定位，这通过感染巨噬细胞细胞的实验和通过转染在巨噬细胞细胞中过表达该蛋白并随后激活未折叠蛋白反应来证明，这从 GRP78/GRP94 和 CHOP/ATF4 的表达增加以及细胞内 Ca 平衡的破坏和一氧化氮（NO）和活性氧（ROS）的产生增加中显而易见。随后效应半胱氨酸蛋白酶-8 的激活导致巨噬细胞凋亡，这是 Toll 样受体 4（TLR4）依赖性的。重组 Rv0297PGRS（rRv0297PGRS）的给药也表现出类似的效果。这些结果表明，PE_PGRS 蛋白家族的 PGRS 结构域在通过 TLR4 介导的 ER 应激诱导细胞死亡方面具有未知的作用。由于该蛋白已经在人类肉芽肿的感染后期阶段被发现存在，这表明它可能被 用于通过凋亡机制进行传播。凋亡通常被认为是宿主在感染早期阶段抵御 的防御机制。然而，在肺肉芽肿的后期阶段，凋亡可能有利于细菌传播疾病。内质网应激已被发现可诱导 TB 肉芽肿中的细胞凋亡，在这种情况下，凋亡的巨噬细胞在小鼠和人类中积累。在这项研究中，我们报告了由 Rv0297 编码的结核分枝杆菌的 PE_PGRS5 蛋白通过内质网应激诱导宿主细胞凋亡，这种蛋白异常存在于致病性的分枝杆菌属中。Rv0297 的 PGRS 结构域有助于该蛋白定位于内质网，并诱导未折叠蛋白反应，随后导致巨噬细胞凋亡。Rv0297PGRS 结构域的作用被发现依赖于 TLR4。这项研究提供了结核分枝杆菌传播疾病的新策略的新见解。
