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Hha is a negative modulator of transcription of hilA, the Salmonella enterica serovar Typhimurium invasion gene transcriptional activator.

ABSTRACT: An early step in the establishment of Salmonella enterica serovar Typhimurium murine infection is the penetration of the intestinal mucosa of the small intestine. The majority of the genes responsible for the Salmonella invasive phenotype are encoded on Salmonella pathogenicity island 1, and their transcription is controlled by the hilA transcriptional activator. The expression of hilA is regulated by environmental signals including oxygen, osmolarity, pH, and growth phase such that the presence of any one suboptimal condition results in repression of hilA expression and the invasive phenotype. We have conducted a search for negative regulators of hilA by introduction of a Salmonella enterica serovar Typhimurium chromosomal DNA gene bank into a Salmonella enterica serovar Typhimurium hilA::Tn5lacZY reporter strain. This screen has identified the hha gene as a regulator that exerts a negative influence on hilA expression. Plasmid-encoded hha significantly reduces hilA::Tn5lacZY chromosomal expression, as well as expression of the invasion genes invF, prgH, and sipC. An hha null mutation results in substantial derepression of both chromosomally encoded and plasmid-encoded hilA::Tn5lacZY expression. Introduction of plasmid-encoded hha into strain SL1344 results in attenuation of invasion using in vitro and in vivo assays. Importantly, purified Hha protein was found to bind to a hilA DNA promoter fragment, suggesting that the regulatory activity of the Hha protein occurs at the hilA promoter. These data add detail to the developing model of the regulation of Salmonella invasion genes.

SUBMITTER: Fahlen TF

PROVIDER: S-EPMC95493 | biostudies-literature | 2001 Nov

REPOSITORIES: biostudies-literature

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Hha is a negative modulator of transcription of hilA, the Salmonella enterica serovar Typhimurium invasion gene transcriptional activator.

Fahlen T F TF Wilson R L RL Boddicker J D JD Jones B D BD

Journal of bacteriology 20011101 22

An early step in the establishment of Salmonella enterica serovar Typhimurium murine infection is the penetration of the intestinal mucosa of the small intestine. The majority of the genes responsible for the Salmonella invasive phenotype are encoded on Salmonella pathogenicity island 1, and their transcription is controlled by the hilA transcriptional activator. The expression of hilA is regulated by environmental signals including oxygen, osmolarity, pH, and growth phase such that the presence ...[more]

PMID: 11673432

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Project description:Penetration of intestinal epithelial cells by Salmonella enterica serovar Typhimurium requires the expression of invasion genes, found in Salmonella pathogenicity island 1 (SPI1), that encode components of a type III secretion apparatus. These genes are controlled in a complex manner by regulators within SPI1, including HilA and InvF, and those outside SPI1, such as the two-component regulators PhoP/PhoQ and BarA/SirA. We report here that epithelial cell invasion requires the serovar Typhimurium homologue of Escherichia coli csrA, which encodes a regulator that alters the stability of specific mRNA targets. A deletion mutant of csrA was unable to efficiently invade cultured epithelial cells and showed reduced expression of four tested SPI1 genes, hilA, invF, sipC, and prgH. Overexpression of csrA from an induced araBAD promoter also negatively affected the expression of these genes, indicating that CsrA can act as both a positive and a negative regulator of SPI1 genes and suggesting that the bacterium must tightly control the level or activity of CsrA to achieve maximal invasion. We found that CsrA affected hilA, a regulator of the other three genes we tested, probably by controlling one or more genetic elements that regulate hilA. We also found that both the loss and the overexpression of csrA reduced the expression of two regulators of hilA, hilC and hilD, suggesting that csrA exerts its control of hilA through one or both of these regulators. We further found, however, that CsrA could affect the expression of both invF and sipC independent of its effects on hilA. One additional striking phenotype of the csrA mutant, not observed in a comparable E. coli mutant, was its slow growth. Phenotypic revertants that had normal growth rates, while maintaining the csrA mutation, were common. These suppressed strains, however, did not recover the ability to invade cultured cells, indicating that the csrA-mediated loss of invasion cannot be attributed simply to poor growth and that the growth and invasion deficits of the csrA mutant arise from effects of CsrA on different targets.

Project description:UnlabelledSalmonella enterica pathogenicity island 1 (SPI-1) encodes proteins required for invasion of gut epithelial cells. The timing of invasion is tightly controlled by a complex regulatory network. The transcription factor (TF) HilD is the master regulator of this process and senses environmental signals associated with invasion. HilD activates transcription of genes within and outside SPI-1, including six other TFs. Thus, the transcriptional program associated with host cell invasion is controlled by at least 7 TFs. However, very few of the regulatory targets are known for these TFs, and the extent of the regulatory network is unclear. In this study, we used complementary genomic approaches to map the direct regulatory targets of all 7 TFs. Our data reveal a highly complex and interconnected network that includes many previously undescribed regulatory targets. Moreover, the network extends well beyond the 7 TFs, due to the inclusion of many additional TFs and noncoding RNAs. By comparing gene expression profiles of regulatory targets for the 7 TFs, we identified many uncharacterized genes that are likely to play direct roles in invasion. We also uncovered cross talk between SPI-1 regulation and other regulatory pathways, which, in turn, identified gene clusters that likely share related functions. Our data are freely available through an intuitive online browser and represent a valuable resource for the bacterial research community.ImportanceInvasion of epithelial cells is an early step during infection by Salmonella enterica and requires secretion of specific proteins into host cells via a type III secretion system (T3SS). Most T3SS-associated proteins required for invasion are encoded in a horizontally acquired genomic locus known as Salmonella pathogenicity island 1 (SPI-1). Multiple regulators respond to environmental signals to ensure appropriate timing of SPI-1 gene expression. In particular, there are seven transcription regulators that are known to be involved in coordinating expression of SPI-1 genes. We have used complementary genome-scale approaches to map the gene targets of these seven regulators. Our data reveal a highly complex and interconnected regulatory network that includes many previously undescribed target genes. Moreover, our data functionally implicate many uncharacterized genes in the invasion process and reveal cross talk between SPI-1 regulation and other regulatory pathways. All datasets are freely available through an intuitive online browser.

Project description:Salmonella enterica serovar Typhimurium (S. Typhimurium) is one of the leading causes of food-borne illnesses worldwide. To colonize the gastrointestinal tract, S. Typhimurium produces multiple virulence factors that facilitate cellular invasion. Chitinases have been recently emerging as virulence factors for various pathogenic bacterial species, and the S. Typhimurium genome contains two annotated chitinases: STM0018 (chiA) and STM0233. However, the role of these chitinases during S. Typhimurium pathogenesis is unknown. The putative chitinase STM0233 has not been studied previously, and only limited data exists on ChiA. Chitinases typically hydrolyze chitin polymers, which are absent in vertebrates. However, chiA expression was detected in infection models and purified ChiA cleaved carbohydrate subunits present on mammalian surface glycoproteins, indicating a role during pathogenesis. Here, we demonstrate that expression of chiA and STM0233 is upregulated in the mouse gut and that both chitinases facilitate epithelial cell adhesion and invasion. S. Typhimurium lacking both chitinases showed a 70% reduction in invasion of small intestinal epithelial cells in vitro. In a gastroenteritis mouse model, chitinase-deficient S. Typhimurium strains were also significantly attenuated in the invasion of small intestinal tissue. This reduced invasion resulted in significantly delayed S. Typhimurium dissemination to the spleen and the liver, but chitinases were not required for systemic survival. The invasion defect of the chitinase-deficient strain was rescued by the presence of wild-type S. Typhimurium, suggesting that chitinases are secreted. By analyzing N-linked glycans of small intestinal cells, we identified specific N-acetylglucosamine-containing glycans as potential extracellular targets of S. Typhimurium chitinases. This analysis also revealed a differential abundance of Lewis X/A-containing glycans that is likely a result of host cell modulation due to the detection of S. Typhimurium chitinases. Similar glycomic changes elicited by chitinase deficient strains indicate functional redundancy of the chitinases. Overall, our results demonstrate that S. Typhimurium chitinases contribute to intestinal adhesion and invasion through modulation of the host glycome.

Dataset Information

Hha is a negative modulator of transcription of hilA, the Salmonella enterica serovar Typhimurium invasion gene transcriptional activator.

Publications

Hha is a negative modulator of transcription of hilA, the Salmonella enterica serovar Typhimurium invasion gene transcriptional activator.

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