Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, Oregon, United States of America.
PLoS One. 2010 May 4;5(5):e10474. doi: 10.1371/journal.pone.0010474.
Inhibition of macrophage apoptosis by Mycobacterium tuberculosis has been proposed as one of the virulence mechanisms whereby the pathogen avoids the host defense. The mechanisms by which M. tuberculosis H37Rv strain suppress apoptosis and escapes human macrophage killing was investigated.
METHODOLOGY/PRINCIPAL FINDINGS: The screening of a transposon mutant bank identified several mutants, which, in contrast to the wild-type bacterium, had impaired ability to inhibit apoptosis of macrophages. Among the identified genes, Rv3659c (31G12 mutant) belongs to an operon reminiscent of type IV pili. The Rv3654c and Rv3655c putative proteins in a seven-gene operon are secreted into the macrophage cytoplasm and suppress apoptosis by blocking the extrinsic pathway. The operon is highly expressed when the bacterium is within macrophages, compared to the expression level in the extracellular environment. Rv3654c recognizes the polypyrimidine tract binding Protein-associated Splicing Factor (PSF) and cleaves it, diminishing the availability of caspase-8. While M. tuberculosis inhibits apoptosis by the extrinsic pathway, the pathogen does not appear to affect the intrinsic pathway. Inactivation of the intrinsic pathway by pharmacologic agents afftects M. tuberculosis and induces cell necrosis. Likewise, inactivation of PSF by siRNA significantly decreased the level of caspase-8 in macrophages.
While M. tuberculosis inhibits the extrinsic pathway of apoptosis, it appears to activate the intrinsic pathway leading to macrophage necrosis as a potential exit strategy.
结核分枝杆菌抑制巨噬细胞凋亡被认为是病原体逃避宿主防御的一种毒力机制。本研究旨在探讨结核分枝杆菌 H37Rv 株抑制凋亡和逃避人巨噬细胞杀伤的机制。
方法/主要发现：转座子突变体库的筛选发现了几个突变体，与野生型细菌相比，这些突变体抑制巨噬细胞凋亡的能力受损。在鉴定的基因中，Rv3659c（31G12 突变体）属于类似于 IV 型菌毛的操纵子。七个基因操纵子中的 Rv3654c 和 Rv3655c 假定蛋白分泌到巨噬细胞质中，通过阻断外在途径抑制凋亡。与胞外环境中的表达水平相比，当细菌在巨噬细胞内时，该操纵子的表达水平高度上调。Rv3654c 识别多嘧啶 tract 结合蛋白相关剪接因子（PSF）并切割它，从而减少 caspase-8 的可用性。虽然结核分枝杆菌通过外在途径抑制细胞凋亡，但病原体似乎不影响内在途径。通过药物使内在途径失活会影响结核分枝杆菌并诱导细胞坏死。同样，用 siRNA 使 PSF 失活显著降低了巨噬细胞中 caspase-8 的水平。
虽然结核分枝杆菌抑制细胞凋亡的外在途径，但它似乎激活了内在途径，导致巨噬细胞坏死，这可能是一种潜在的逃逸策略。
