Long-Distance Effects of H-NS Binding in the Control of hilD Expression in the Salmonella SPI1 Locus
Long-Distance Effects of H-NS Binding in the Control of hilD Expression in the Salmonella SPI1 Locus
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DOI：
10.1128/jb.00308-21
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发表时间：
2021-11-01
影响因子：
3.2
通讯作者：
Slauch, James M.
中科院分区：
文献类型：
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作者：
Kalafatis, Marinos;Slauch, James M.
鼠伤寒沙门氏菌利用沙门氏菌致病岛1(SPI1)携带的三型分泌系统(T3SS)侵袭肠道上皮细胞，引起炎症性腹泻。HILA激活T3SS结构基因的表达。高侵袭位点A(HILA)的表达受转录因子HILD、HILC和RTSA控制，这些转录因子在一个复杂的前馈调控环中发挥作用。类核相关蛋白H-NS是一种异种沉默蛋白，对SPI1的表达有重要影响。在这项工作中，我们使用基因技术证明了HILD周围染色体区域的破坏对H-NS介导的HILD启动子的抑制具有顺式影响；这种影响不对称地发生在跨越prgH-HILD基因间隔区的4kb以上。插入在该区域不同位置的CAT盒也因与HILD启动子的接近而被沉默。我们确定了一个假定的H-NS成核位点，它的突变导致该基因座的去抑制。此外，我们从遗传学上证明，HILD取消了H-NS介导的沉默来激活HILD启动子。相反，H-NS介导的对HILA启动子的抑制是通过其对HILD的控制来实现的，后者直接激活HILA转录。同样，prgH启动子的激活，尽管是在被H-NS沉默的区域，但严格依赖于Hila。综上所述，我们提出了一个模型，在该模型中，H-NS在HILD启动子区域内成核，从而聚合并发挥其抑制作用。因此，H-NS介导的对SPI1的抑制主要是通过控制HIRD的表达，而HIRD能够克服H-NS而自我激活。重要的是，食源性致病菌沙门氏菌的成员依赖于III型分泌系统来入侵肠道上皮细胞并启动感染。这个系统是通过水平基因转移获得的，基本上创造了沙门氏菌属。这一关键毒力因子的表达受复杂的调控网络控制。类核蛋白H-NS是一种水平获得的基因组基因座的全球抑制因子。在这里，我们确定了这个系统中H-NS调控的关键位置，并表明在一个令人惊讶的大区域内DNA的改变会影响这种调控，从而提供了关于H-NS作用机制的重要信息。
Salmonella enterica serovar Typhimurium utilizes a type three secretion system (T3SS) carried on the Salmonella pathogenicity island 1 (SPI1) to invade intestinal epithelial cells and induce inflammatory diarrhea. HilA activates expression of the T3SS structural genes. Expression of hyper invasion locus A (hilA) is controlled by the transcription factors HilD, HilC, and RtsA, which act in a complex feed-forward regulatory loop. The nucleoid-associated protein H-NS is a xenogeneic silencer that has a major effect on SPI1 expression. In this work, we use genetic techniques to show that disruptions of the chromosomal region surrounding hilD have a cis effect on H-NS-mediated repression of the hilD promoter; this effect occurs asymmetrically over;4 kb spanning the prgH-hilD intergenic region. CAT cassettes inserted at various positions in this region are also silenced in relation to the proximity to the hilD promoter. We identify a putative H-NS nucleation site, and its mutation results in derepression of the locus. Furthermore, we genetically show that HilD abrogates H-NS-mediated silencing to activate the hilD promoter. In contrast, H-NS-mediated repression of the hilA promoter, downstream of hilD, is through its control of HilD, which directly activates hilA transcription. Likewise, activation of the prgH promoter, although in a region silenced by H-NS, is strictly dependent on HilA. In summary, we propose a model in which H-NS nucleates within the hilD promoter region to polymerize and exert its repressive effect. Thus, H-NS-mediated repression of SPI1 is primarily through the control of hilD expression, with HilD capable of overcoming H-NS to autoactivate.IMPORTANCE Members of the foodborne pathogen Salmonella rely on a type III secretion system to invade intestinal epithelial cells and initiate infection. This system was acquired through horizontal gene transfer, essentially creating the Salmonella genus. Expression of this critical virulence factor is controlled by a complex regulatory network. The nucleoid protein H-NS is a global repressor of horizontally acquired genomic loci. Here, we identify the critical site of H-NS regulation in this system and show that alterations to the DNA over a surprisingly large region affect this regulation, providing important information regarding the mechanism of H-NS action.