Serratia marcescens ShlA Pore-Forming Toxin Is Responsible for Early Induction of Autophagy in Host Cells and Is Transcriptionally Regulated by RcsB
Serratia marcescens ShlA Pore-Forming Toxin Is Responsible for Early Induction of Autophagy in Host Cells and Is Transcriptionally Regulated by RcsB
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DOI：
10.1128/iai.01682-14
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发表时间：
2014-09-01
影响因子：
3.1
通讯作者：
Garcia Vescovi, Eleonora
中科院分区：
文献类型：
--
作者：
Di Venanzio, Gisela;Stepanenko, Tatiana M.;Garcia Vescovi, Eleonora
粘质沙雷氏菌是一种革兰氏阴性细菌，在各种环境中茁壮成长，并与大量宿主相互作用。作为一种人类机会致病菌，近年来其临床发病率增加，是危及生命的医院感染的原因。S. marcescens产生许多具有毒性作用的外蛋白，包括ShlA成孔毒素，其已被归类为其最有效的细胞毒素。然而，控制ShlA表达的调节机制以及其对宿主的作用仍不清楚。我们证明了S.粘质虫在宿主非吞噬细胞中引起自噬反应。在这项工作中，我们确定ShlA的表达是负责的自噬反应，促进之前的细菌内化上皮细胞。我们表明，菌株不能表达ShlA不再能够诱导这种自噬机制，而异源表达的ShlA/ShlB足以赋予非侵入性大肠杆菌的能力，触发自噬。我们还表明，shlBA窝藏在其启动子区的RcsB调节器的结合基序。RcsB依赖性控制的shlBA构成了一个前馈调节机制，允许相互作用与鞭毛生物发生调节。在回路的顶部，活化的RcsB通过结合至flhDC启动子区下调鞭毛的表达，从而阻止FliA活化的shlBA转录。同时，ShlBA启动子内的RcsB相互作用抑制ShlA表达。该电路提供多个接入点以微调ShlA生产。这些发现也加强了RcsB在协调沙雷氏菌毒力因子表达中的作用。
Serratia marcescens is a Gram-negative bacterium that thrives in a wide variety of ambient niches and interacts with an ample range of hosts. As an opportunistic human pathogen, it has increased its clinical incidence in recent years, being responsible for life-threatening nosocomial infections. S. marcescens produces numerous exoproteins with toxic effects, including the ShlA pore-forming toxin, which has been catalogued as its most potent cytotoxin. However, the regulatory mechanisms that govern ShlA expression, as well as its action toward the host, have remained unclear. We have shown that S. marcescens elicits an autophagic response in host nonphagocytic cells. In this work, we determine that the expression of ShlA is responsible for the autophagic response that is promoted prior to bacterial internalization in epithelial cells. We show that a strain unable to express ShlA is no longer able to induce this autophagic mechanism, while heterologous expression of ShlA/ShlB suffices to confer on noninvasive Escherichia coli the capacity to trigger autophagy. We also demonstrate that shlBA harbors a binding motif for the RcsB regulator in its promoter region. RcsB-dependent control of shlBA constitutes a feed-forward regulatory mechanism that allows interplay with flagellar-biogenesis regulation. At the top of the circuit, activated RcsB downregulates expression of flagella by binding to the flhDC promoter region, preventing FliA-activated transcription of shlBA. Simultaneously, RcsB interaction within the shlBA promoter represses ShlA expression. This circuit offers multiple access points to fine-tune ShlA production. These findings also strengthen the case for an RcsB role in orchestrating the expression of Serratia virulence factors.