Sensing cytosolic RpsL by macrophages induces lysosomal cell death and termination of bacterial infection.
Sensing cytosolic RpsL by macrophages induces lysosomal cell death and termination of bacterial infection.
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巨噬细胞感测胞质 RpsL 诱导溶酶体细胞死亡并终止细菌感染
DOI：
10.1371/journal.ppat.1004704
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发表时间：
2015-03
期刊：
影响因子：
6.7
通讯作者：
Luo ZQ
中科院分区：
文献类型：
--
作者：
Zhu W;Tao L;Quick ML;Joyce JA;Qu JM;Luo ZQ
细胞内细菌病原体嗜肺军团菌引起强烈的宿主反应，并已被证明是一个有价值的模型，发现新的免疫监视途径。我们以前的工作表明，一个环境分离的L。嗜肺菌诱导非典型形式的细胞死亡，导致原代小鼠巨噬细胞中细菌复制的限制。在这里，我们表明，这种限制也发生在感染野生型临床分离株。重要的是，我们发现核糖体蛋白RpsL中第88位残基（K88 R）的赖氨酸到精氨酸的突变不仅赋予细菌对链霉素的抗性，更重要的是，严重减弱了宿主细胞死亡的诱导，并使L. pneumophila在原代小鼠巨噬细胞中复制。虽然赋予类似的抗性链霉素，K43 N突变RpsL不允许生产性细胞内细菌复制。进一步的分析表明，RpsL能够通过参与溶酶体膜透化的途径有效地诱导巨噬细胞死亡; K88 R突变体激发类似的反应，但效力较低。此外，组织蛋白酶B是一种溶酶体蛋白酶，在膜完整性丧失后释放到胞质溶胶中后导致细胞死亡，是有效的RpsL诱导的巨噬细胞死亡所必需的。此外，尽管组织蛋白酶B在延迟RpsL诱导的细胞死亡中起关键作用，但缺乏组织蛋白酶B的巨噬细胞不支持L的生产性细胞内复制。携带野生型RpsL的嗜肺菌。这表明其他尚未鉴定的成分参与了细菌复制的限制。我们的研究结果表明，RpsL作为一种调节剂，在细菌之间的相互作用，如L。pneumophila和原代小鼠巨噬细胞通过触发限制细胞内细菌复制的独特细胞途径。感染期间宿主细胞的死亡可以由一种或多种微生物分子触发;这种“活或死”的选择为解剖免疫识别机制以及鉴定负责这种反应的微生物分子提供了有效手段。我们发现，由携带野生型RpsL（细菌核糖体的S12组分）的嗜肺军团菌菌株感染原代小鼠巨噬细胞，通过独立于三种炎性半胱天冬酶（半胱天冬酶1、7和11）的机制导致巨噬细胞死亡。重要的是，尽管两者都以难以区分的效力赋予对链霉素的抗性，但RpsL中的K88 R而不是K43 N突变使L.在巨噬细胞中复制。纯化的RpsL和RpsLK 43 N物理递送到巨噬细胞中通过诱导溶酶体膜的损伤和组织蛋白酶的释放而引起细胞死亡。我们还发现，溶酶体蛋白酶组织蛋白酶B是必需的有效RpsL诱导的细胞死亡，但它的缺乏是不足以支持细胞内的细菌复制的巨噬细胞。因此，RpsL作为免疫诱导分子起作用以触发一个或多个信号传导级联，其导致溶酶体细胞死亡以及细菌复制的终止。
The intracellular bacterial pathogen Legionella pneumophila provokes strong host responses and has proven to be a valuable model for the discovery of novel immunosurveillance pathways. Our previous work revealed that an environmental isolate of L. pneumophila induces a noncanonical form of cell death, leading to restriction of bacterial replication in primary mouse macrophages. Here we show that such restriction also occurs in infections with wild type clinical isolates. Importantly, we found that a lysine to arginine mutation at residue 88 (K88R) in the ribosome protein RpsL that not only confers bacterial resistance to streptomycin, but more importantly, severely attenuated the induction of host cell death and enabled L. pneumophila to replicate in primary mouse macrophages. Although conferring similar resistance to streptomycin, a K43N mutation in RpsL does not allow productive intracellular bacterial replication. Further analysis indicated that RpsL is capable of effectively inducing macrophage death via a pathway involved in lysosomal membrane permeabilization; the K88R mutant elicits similar responses but is less potent. Moreover, cathepsin B, a lysosomal protease that causes cell death after being released into the cytosol upon the loss of membrane integrity, is required for efficient RpsL-induced macrophage death. Furthermore, despite the critical role of cathepsin B in delaying RpsL-induced cell death, macrophages lacking cathepsin B do not support productive intracellular replication of L. pneumophila harboring wild type RpsL. This suggests the involvement of other yet unidentified components in the restriction of bacterial replication. Our results identified RpsL as a regulator in the interactions between bacteria such as L. pneumophila and primary mouse macrophages by triggering unique cellular pathways that restrict intracellular bacterial replication. The death of the host cell during infection can be triggered by one or more microbial molecules; this “live or die” selection provides effective means for the dissection of immune recognition mechanisms as well as for the identification of the microbial molecules responsible for such responses. We found that infection of primary mouse macrophages by Legionella pneumophila strains harboring wild type RpsL, the S12 component of the bacterial ribosome, causes macrophage death by a mechanism independent of the three inflammatory caspases, caspase 1, 7 and 11. Importantly, although both confer resistance to streptomycin at indistinguishable effectiveness, the K88R, but not the K43N mutation in RpsL enables L. pneumophila to replicate in macrophages. Purified RpsL and RpsLK43N physically delivered into macrophages cause cell death by inducing damage to lysosomal membranes and the release of cathepsins. We also found that the lysosomal protease cathepsin B is required for efficient RpsL-induced cell death but its absence is not sufficient for macrophages to support intracellular bacterial replication. Thus, RpsL functions as an immune induction molecule to trigger one or more signaling cascades that leads to lysosomal cell death as well as the termination of bacterial replication.
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