Soluble lytic transglycosylase SLT of Francisella novicida is involved in intracellular growth and immune suppression
Soluble lytic transglycosylase SLT of Francisella novicida is involved in intracellular growth and immune suppression
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DOI：
10.1371/journal.pone.0226778
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发表时间：
2019-12-26
期刊：
影响因子：
3.7
通讯作者：
Watarai, Masahisa
中科院分区：
文献类型：
--
作者：
Nakamura, Takemasa;Shimizu, Takashi;Watarai, Masahisa
土拉热弗朗西丝菌，A类生物恐怖主义制剂导致土拉菌病。F.土拉菌抑制宿主细胞的免疫应答并在细胞内增殖。然而，免疫抑制和细胞内生长的详细机制在很大程度上是未知的。我们建立了一个转座子突变体库来鉴定新的致病因子。土拉热。在750株F.土拉热亚种novicida（F. novicida），11株被分离为细胞毒性较小的菌株，并鉴定了负责细胞毒性的基因。其中，对编码可溶性裂解转糖基酶的slt的功能进行了详细的研究。与野生型菌株相比，slt缺失突变体（Delta slt）对人单核细胞系THP-1的毒性较小。虽然野生型菌株在THP-1细胞中增殖，但相比之下，细胞内Delta slt突变体的数量减少。Delta slt突变体在感染的早期阶段逃离吞噬体，但在自噬体内检测到突变体，随后在溶酶体中降解。此外，与野生型菌株相比，Delta slt突变体诱导宿主细胞产生高水平的细胞因子，如肿瘤坏死因子-α、白细胞介素（IL）-6和IL-1 β。这些结果表明F.杀线虫素是免疫抑制和逃避自噬以使其在宿主细胞中存活所必需的。
Francisella tularensis, a category-A bioterrorism agent causes tularemia. F. tularensis suppresses the immune response of host cells and intracellularly proliferates. However, the detailed mechanisms of immune suppression and intracellular growth are largely unknown. Here we developed a transposon mutant library to identify novel pathogenic factors of F. tularensis. Among 750 transposon mutants of F. tularensis subsp. novicida (F. novicida), 11 were isolated as less cytotoxic strains, and the genes responsible for cytotoxicity were identified. Among them, the function of slt, which encodes soluble lytic transglycosylase (SLT) was investigated in detail. An slt deletion mutant (Delta slt) was less toxic to the human monocyte cell line THP-1 vs the wild-type strain. Although the wild-type strain proliferated in THP-1 cells, the number of intracellular Delta slt mutant decreased in comparison. The Delta slt mutant escaped from phagosomes during the early stages of infection, but the mutant was detected within the autophagosome, followed by degradation in lysosomes. Moreover, the Delta slt mutant induced host cells to produce high levels of cytokines such as tumor necrosis factor-alpha, interleukin (IL)-6, and IL-1 beta, compared with the wild-type strain. These results suggest that the SLT of F. novicida is required for immune suppression and escape from autophagy to allow its survival in host cells.