Cui Yongyong, Zhao Deming, Sreevatsan Srinand, Liu Chunfa, Yang Wei, Song Zhiqi, Yang Lifeng, Barrow Paul, Zhou Xiangmei
State Key Laboratories for Agrobiotechnology, Key Lab of Animal Epidemiology and Zoonosis, Ministry of Agriculture, National Animal Transmissible Spongiform Encephalopathy Laboratory, College of Veterinary Medicine, China Agricultural University Beijing, China.
Veterinary Population Medicine Department, College of Veterinary Medicine, University of Minnesota St. Paul, MN, USA.
Front Cell Infect Microbiol. 2016 Dec 12;6:182. doi: 10.3389/fcimb.2016.00182. eCollection 2016.
Mycobacterium bovis () is highly adapted to macrophages and has developed multiple mechanisms to resist intracellular assaults. However, the host cells in turn deploy a multipronged defense mechanism to control bacterial infection. Endoplasmic reticulum (ER) stress-mediated apoptosis is one such primary defense mechanism. However, the role of interferon regulatory factor 3 (IRF3) between ER stress and apoptosis during infection is unknown. Here, we demonstrate that effectively induced apoptosis in murine macrophages. Caspase-12, caspase-9, and caspase-3 were activated over a 48 h infection period. The splicing of XBP-1 mRNA and the level of phosphorylation of eIF2α, indicators of ER stress, significantly increased at early time points after infection. The expansion of the ER compartment, a morphological hallmark of ER stress, was observed at 6 h. Pre-treatment of Raw 264.7 cells with 4-PBA (an ER stress-inhibitor) reduced the activation of the ER stress indicators, caspase activation and its downstream poly (ADP-ribose) polymerase (PARP) cleavage, phosphorylation of TBK1 and IRF3 and cytoplasmic co-localization of STING and TBK1. infection led to the interaction of activated IRF3 and cytoplasmic Bax leading to mitochondrial damage. Role of IRF3 in apoptosis was further confirmed by blocking this molecule with BX-795 that showed significant reduction expression of caspase-8 and caspase-3. Intracellular survival of increased in response to 4-PBA and BX-795. These findings indicate that STING-TBK1-IRF3 pathway mediates a crosstalk between ER stress and apoptosis during infection, which can effectively control intracellular bacteria.
牛分枝杆菌（Mycobacterium bovis）高度适应巨噬细胞，并已发展出多种机制来抵抗细胞内攻击。然而，宿主细胞反过来会部署多管齐下的防御机制来控制细菌感染。内质网（ER）应激介导的细胞凋亡就是这样一种主要防御机制。然而，在感染期间，干扰素调节因子3（IRF3）在内质网应激和细胞凋亡之间的作用尚不清楚。在这里，我们证明牛分枝杆菌能有效诱导小鼠巨噬细胞凋亡。在48小时的感染期内，半胱天冬酶-12、半胱天冬酶-9和半胱天冬酶-3被激活。XBP-1 mRNA的剪接以及内质网应激指标eIF2α的磷酸化水平在牛分枝杆菌感染后的早期时间点显著增加。在内质网应激的形态学标志——内质网腔扩张在6小时时被观察到。用4-PBA（一种内质网应激抑制剂）预处理Raw 264.7细胞可降低内质网应激指标的激活、半胱天冬酶激活及其下游聚（ADP-核糖）聚合酶（PARP）的切割、TBK1和IRF3的磷酸化以及STING和TBK1的细胞质共定位。牛分枝杆菌感染导致活化的IRF3与细胞质中的Bax相互作用，导致线粒体损伤。通过用BX-795阻断该分子进一步证实了IRF3在细胞凋亡中的作用，这显示半胱天冬酶-8和半胱天冬酶-3的表达显著降低。牛分枝杆菌的细胞内存活在对4-PBA和BX-795的反应中增加。这些发现表明，在牛分枝杆菌感染期间，STING-TBK1-IRF3途径介导了内质网应激和细胞凋亡之间的相互作用，这可以有效地控制细胞内细菌。
