Co‐ordinate regulation of Salmonella typhimurium invasion genes by environmental and regulatory factors is mediated by control of hilA expression

Bajaj, Vivek; Lucas, Robin L.; Hwang, Clara; Lee, Catherine A.

doi:10.1046/j.1365-2958.1996.d01-1718.x

Cited by 434 publications

(561 citation statements)

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“…Conversely, the PhoP/Q system that activates SPI-2 expression is known to shut down SPI-1 activity (Bajaj et al, 1996;Behlau and Miller, 1993). These and similar mechanisms are considered to coordinate the cross-talk between the different SPIs, with huge impact on Salmonella virulence (Fabrega and Vila, 2013).…”

Section: Salmonella As a Model Organism For Host-pathogen Interactionmentioning

confidence: 99%

Dual RNA-seq of pathogen and host

2012

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SummaryThe infection of a eukaryotic host cell by a bacterial pathogen is one of the most intimate examples of cross-kingdom interactions in biology. Infection processes are highly relevant from both a basic research as well as a clinical point of view. Sophisticated mechanisms have evolved in the pathogen to manipulate the host response and vice versa host cells have developed a wide range of anti-microbial defense strategies to combat bacterial invasion and clear infections.However, it is this diversity and complexity that makes infection research so challenging to technically address as common approaches have either been optimized for bacterial or eukaryotic organisms. Instead, methods are required that are able to deal with the often dramatic discrepancy between host and pathogen with respect to various cellular properties and processes. One class of cellular macromolecules that exemplify this host-pathogen heterogeneity is given by their transcriptomes: Bacterial transcripts differ from their eukaryotic counterparts in many aspects that involve both quantitative and qualitative traits. The entity of RNA transcripts present in a cell is of paramount interest as it reflects the cell's physiological state under the given condition. Genome-wide transcriptomic techniques such as RNA-seq have therefore been used for single-organism analyses for several years, but their applicability has been limited for infection studies.The present work describes the establishment of a novel transcriptomic approach for infection biology which we have termed "Dual RNA-seq". Using this technology, it was intended to shed light particularly on the contribution of non-protein-encoding transcripts to virulence, as these classes have mostly evaded previous infection studies due to the lack of suitable methods. The performance of Dual RNA-seq was evaluated in an in vitro infection model based on the important facultative intracellular pathogen Salmonella enterica serovar Typhimurium and different human cell lines. Dual RNA-seq was found to be capable of capturing all major bacterial and human transcript classes and proved reproducible. During the course of these experiments, a previously largely uncharacterized bacterial small non-coding RNA (sRNA), referred to as STnc440, was identified as one of the most strongly induced genes in intracellular Salmonella.Interestingly, while inhibition of STnc440 expression has been previously shown to cause a virulence defect in different animal models of Salmonellosis, the underlying molecular mechanisms have remained obscure. Here, classical genetics, transcriptomics and biochemical assays proposed a complex model of Salmonella gene expression control that is orchestrated by this sRNA. In particular, STnc440 was found to be involved in the regulation of multiple bacterial target mRNAs by direct base pair interaction with consequences for Salmonella virulence and

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Section: Salmonella As a Model Organism For Host-pathogen Interactionmentioning

confidence: 99%

Dual RNA-seq of pathogen and host

2012

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“…Expression of SPI1 invasion and effector genes responds to multiple environmental signals and is decreased under conditions of high oxygen, low osmolarity, low pH, and stationaryphase growth (5,11,16,25). Many regulatory proteins influence invasion gene expression (31,32), but the key regulator is the SPI1-encoded HilA protein, which can activate their transcription directly (1,4,28) or by increasing expression of the activator InvF (9).…”

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DNA-Binding Activities of the HilC and HilD Virulence Regulatory Proteins ofSalmonella entericaSerovar Typhimurium

2002

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The HilC and HilD proteins of Salmonella enterica serovar Typhimurium are members of the AraC/XylS family of transcription regulators. They are encoded on Salmonella pathogenicity island 1 (SPI1) and control expression of the hilA gene, which encodes the major transcriptional activator for many genes encoded on SPI1 and elsewhere that contribute to invasion of host cells. Gel electrophoretic shift and DNase footprinting assays revealed that purified HilC and HilD proteins can bind to multiple regions in the hilA and hilC promoters and to a single region in the hilD promoter. Although both HilC and -D proteins can bind to the same DNA regions, they showed different dependencies on the sequence and lengths of their DNA targets. To identify the binding-sequence specificity of HilC and HilD, a series of single base substitutions changing each position in a DNA fragment corresponding to positions ؊92 to ؊52 of the hilC promoter was tested for binding to HilC and HilD in a gel shift DNA-binding assay. This mutational analysis in combination with sequence alignments allowed deduction of consensus sequences for binding of both proteins. The consensus sequences overlap but differ so that HilC can bind to both types of sites but HilD only to one. The hilA and hilC promoters contain multiple binding sites of each type, whereas the hilD promoter contains a site that binds HilC but not HilD without additional binding elements. The HilC and HilD proteins had no major effect on transcription from the hilA or hilD promoters using purified proteins in vitro but changed the choice of promoter at hilC. These results are consistent with a model derived from analysis of lacZ fusions stating that HilC and HilD enhance hilA expression by counteracting a repressing activity.

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“…Northern blotting indicated that the gene downstream of the prgH operon, orgA, did not reside on the same mRNA transcript nor did phoP appear to regulate levels of the orgA transcript, in contrast to the prgH transcript. However, work by another group indicated that an orgA::lacZY fusion is repressed by a phoP(Con) serovar strain of Typhimurium (3).…”

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Transcriptional Organization and Function of Invasion Genes within Salmonella enterica Serovar Typhimurium Pathogenicity Island 1, Including the prgH , prgI , prgJ , prgK , orgA , orgB , and orgC Genes

2000

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Salmonella enterica serovar Typhimurium initiates infection of a host by inducing its own uptake into specialized M cells which reside within the epithelium overlaying Peyer's patches. Entry of Salmonella into intestinal epithelial cells is dependent upon invasion genes that are clustered together in Salmonella pathogenicity island 1 (SPI-1). Upon contact between serovar Typhimurium and epithelial cells targeted for bacterial internalization, bacterial proteins are injected into the host cell through a type III secretion system that leads to internalization of the bacteria. Previous work has established that the prgH, -I, -J, and -K and orgA genes reside in SPI-1, and the products of these genes are predicted to be components of the invasion secretion apparatus. We report that an error in the published orgA DNA sequence has been identified so that this region encodes two small genes rather than a single large open reading frame. These genes have been designated orgA and orgB. Additionally, an opening reading frame downstream of orgB, which we have designated orgC, has been identified and partially characterized. Previously published work has indicated that the prgH, -I, -J, and -K genes are transcribed from a promoter distinct from that used by the gene immediately downstream, orgA. Here, we present experiments indicating that orgA expression is driven by the prgH promoter. In addition, using reverse transcriptase PCR analysis, we have found that this polycistronic message extends downstream of prgH to include a total of 10 genes. To more fully characterize this invasion operon, we demonstrate that the prgH, prgI, prgJ, prgK, orgA, and orgB genes are each required for invasion and secretion, while orgC is not essential for the invasive phenotype.Salmonella infections are an important health problem in both the developing and developed world (9,32,34). Pathogenic Salmonella species cause infections that range in severity from self-limiting gastroenteritis to life-threatening systemic dissemination (45). After entry into a host, the bacteria establish infection by attaching to and invading specialized M cells associated with Peyer's patches in the small intestine (5,23,26). Following M-cell invasion and destruction, host-restricted Salmonella species cause localized destruction of the intestinal epithelium (gastroenteritis). In contrast, passage of hostadapted Salmonella species through M cells allows rapid dissemination to the mesenteric lymph nodes and then to the liver and spleen, where unchecked growth causes death (25).A critical determinant in the development of Salmonella disease is the ability of the bacteria to invade cells. Salmonella enterica serovar Typhimurium mutants that are unable to invade tissue culture cells are defective in their ability to invade and destroy M cells (26,43). This defect severely limits the ability of the bacteria to initiate infection and reduces their virulence in mice (14,24,43). Genes required for Salmonella internalization into mammalian cells have been identified (4, 7, ...

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**Co‐ordinate regulation of Salmonella typhimurium invasion genes by environmental and regulatory factors is mediated by control of hilA expression**

Cited by 434 publications

References 44 publications

Dual RNA-seq of pathogen and host

Dual RNA-seq of pathogen and host

DNA-Binding Activities of the HilC and HilD Virulence Regulatory Proteins ofSalmonella entericaSerovar Typhimurium

Transcriptional Organization and Function of Invasion Genes within Salmonella enterica Serovar Typhimurium Pathogenicity Island 1, Including the prgH , prgI , prgJ , prgK , orgA , orgB , and orgC Genes

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