School of Life Sciences, University of Nevada Las Vegas, Las Vegas, Nevada, USA.
Department of Microbiology and Immunology, Miller School of Medicine, University of Miami, Miami, Florida, USA.
J Bacteriol. 2022 Jul 19;204(7):e0013722. doi: 10.1128/jb.00137-22. Epub 2022 Jun 15.
Members of the AraC family of transcriptional regulators (AFTRs) control the expression of many genes important to cellular processes, including virulence. In species, the type III secretion system (T3SS), a key determinant for host cell invasion, is regulated by the three-tiered VirF/VirB/MxiE transcriptional cascade. Both VirF and MxiE belong to the AFTRs and are characterized as positive transcriptional regulators. Here, we identify a novel regulatory activity for MxiE and its coregulator IpgC, which manifests as a negative feedback loop in the VirF/VirB/MxiE transcriptional cascade. Our findings show that MxiE and IpgC downregulate the promoter and, hence, VirB protein production, thus decreasing VirB-dependent promoter activity at , one of the nearly 50 VirB-dependent genes. At the promoter, regions required for negative MxiE- and IpgC-dependent regulation were mapped and found to be coincident with regions required for positive VirF-dependent regulation. In tandem, negative MxiE- and IpgC-dependent regulation of the promoter only occurred in the presence of VirF, suggesting that MxiE and IpgC can function to counter VirF activation of the promoter. Lastly, MxiE and IpgC do not downregulate another VirF-activated promoter, , demonstrating that this negative feedback loop targets the promoter. Our study provides insight into a mechanism that may reprogram virulence gene expression following type III secretion and provides the impetus to examine if MxiE and IpgC homologs in other important bacterial pathogens, such as Burkholderia pseudomallei and Salmonella enterica serovars Typhimurium and Typhi, coordinate similar negative feedback loops. The large AraC family of transcriptional regulators (AFTRs) control virulence gene expression in many bacterial pathogens. In species, the AraC/XylS protein MxiE and its coregulator IpgC positively regulate the expression of type III secretion system genes within the three-tiered VirF/VirB/MxiE transcriptional cascade. Our findings suggest a negative feedback loop in the VirF/VirB/MxiE cascade, in which MxiE and IpgC counter VirF-dependent activation of the promoter, thus making this the first characterization of negative MxiE- and IpgC-dependent regulation. Our study provides insight into a mechanism that likely reprograms virulence gene expression following type III secretion, which has implications for other important bacterial pathogens with functional homologs of MxiE and IpgC.
AraC 家族转录调控因子（AFTRs）成员控制着许多对细胞过程重要的基因的表达，包括毒力。在 物种中，III 型分泌系统（T3SS）是宿主细胞入侵的关键决定因素，由三级 VirF/VirB/MxiE 转录级联调控。VirF 和 MxiE 均属于 AFTRs，其特征为正转录调控因子。在这里，我们发现了 MxiE 和其共调节剂 IpgC 的新调控活性，这表现为 VirF/VirB/MxiE 转录级联中的负反馈回路。我们的研究结果表明，MxiE 和 IpgC 下调 启动子，从而降低 VirB 蛋白的产生，从而降低 启动子活性，该启动子是近 50 个 VirB 依赖性基因之一。在 启动子上，鉴定出负调控所需的区域 MxiE- 和 IpgC- 依赖性，并且发现与正调控所需的区域 VirF- 依赖性一致。串联起来，只有在存在 VirF 的情况下，MxiE- 和 IpgC- 依赖性调节 启动子才会发生，这表明 MxiE 和 IpgC 可以起到对抗 VirF 激活 启动子的作用。最后，MxiE 和 IpgC 不会下调另一个 VirF 激活的启动子 ，表明该负反馈回路靶向 启动子。我们的研究提供了一种机制的见解，即在 III 型分泌后，这种机制可能重新编程 毒力基因表达，并促使人们检查其他重要细菌病原体（如 Burkholderia pseudomallei 和 Salmonella enterica serovars Typhimurium 和 Typhi）中的 MxiE 和 IpgC 同源物是否协调类似的负反馈回路。AraC 家族的转录调控因子（AFTRs）控制着许多细菌病原体的毒力基因表达。在 物种中，AraC/XylS 蛋白 MxiE 和其共调节剂 IpgC 在三级 VirF/VirB/MxiE 转录级联中正向调节 III 型分泌系统基因的表达。我们的研究结果表明，在 VirF/VirB/MxiE 级联中存在负反馈回路，其中 MxiE 和 IpgC 对抗 VirF 依赖性激活 启动子，从而首次对 MxiE- 和 IpgC- 依赖性负调控进行了表征。我们的研究提供了一种机制的见解，该机制可能在 III 型分泌后重新编程 毒力基因表达，这对具有 MxiE 和 IpgC 功能同源物的其他重要细菌病原体具有重要意义。
