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Global impact of Salmonella type III secretion effector SteA on host cells

ABSTRACT: Salmonella enterica is a Gram-negative bacterium that causes gastroenteritis, bacteremia and typhoid fever in several animal species including humans. Its virulence is greatly dependent on two type III secretion systems (T3SSs), encoded in pathogenicity islands 1 (SPI1) and 2 (SPI2), respectively. These systems translocate proteins called effectors into eukaryotic host cell. Effectors interfere with certain host signal transduction pathways to allow the internalization of pathogens and their survival and proliferation inside vacuoles. SteA is one of the few Salmonella effectors that are substrates of both T3SSs. Nothing is known about the function of this protein inside the host cells. Here, we used gene arrays and bioinformatics analysis to study the genetic response of human epithelial cells to SteA. We found that constitutive synthesis of SteA in epithelial cells leads to induction of genes related to extracellular matrix organization and regulation of cell proliferation and serine/threonine kinase signaling pathways. SteA also represses genes related to immune processes and regulation of purine nucleotide synthesis and pathway-restricted SMAD protein phosphorylation. Consisted with this analysis a cell biology approach revealed that epithelial cells expressing steA show altered cell morphology, reduction of cytotoxicity, cell-cell adhesion and migration capability, and increase in endocytosis.

ORGANISM(S): Homo sapiens

PROVIDER: GSE51043 | GEO | 2014/05/28

SECONDARY ACCESSION(S): PRJNA219735

REPOSITORIES: GEO

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Project description:Background: Biofilm formation by Salmonella species enhances the capacity of these pathogenic bacteria to survive stresses that are commonly encountered within food processing and during host infection. The persistence of Salmonella within the food chain has become a major health concern, as biofilms can serve as a reservoir to contaminate food products. While the molecular mechanisms required for the survival of bacteria on surfaces are not fully understood, transcriptional studies of other bacteria have demonstrated that biofilm growth triggers the expression of specific sets of genes, compared with planktonic cells. Until now, most transcriptomic studies of Salmonella have focused on the effect of infection-relevant stressors on virulence and on comparing mutant and wild-type (WT). However little is known about the physiological responses taking place inside a Salmonella biofilm. Results: We have determined the transcriptomic and proteomic profiles of biofilms of Salmonella enterica serovar Typhimurium. We discovered that 124 of detectable proteins were differentially expressed in the biofilm compared with planktonic cells, and that 10% (433 genes) of S. Typhimurium genes showed a biofilm-specific pattern of transcription (i.e. a 2-fold or more change in the biofilm compared with planktonic cells). The genes that were significantly up-regulated implicated specific cellular processes in biofilm development including amino acid metabolism, cell motility, global regulation and tolerance to stress. We found that the most highly down-regulated genes in the biofilm were located on Salmonella Pathogenicity Island 2 (SPI2), but that a functional SPI2 secretion system regulator (ssrA) was required for WT biofilm formation. We identified STM0341 as a gene of unknown function that was needed for WT biofilm growth. Genes involved in tryptophan (trp) biosynthesis and transport were up-regulated in the biofilm. Deletion of trpE led to a decrease in bacterial attachment and we show that this biofilm defect is restored by exogenous tryptophan or indole. Conclusion: Biofilm growth of S. Typhimurium causes distinct changes in gene and protein expression. Our results show that aromatic amino acids make an important contribution to biofilm formation, and reveal that SPI2 genes, required for virulence in host cells, show opposing patterns of expression to biofilm-specific genes in S. Typhimurium.

Project description:To cause disease, Salmonella enterica serovar Typhimurium requires two type-III secretion systems, encoded on Salmonella Pathogenicity Islands 1 and 2 (SPI-1 and -2). These secretion systems serve to deliver virulence proteins, termed effectors, into the host cell cytosol. While the importance of these effector proteins to promote colonization and replication within the host has been established, the specific roles of individual secreted effectors in the disease process are not well understood. In this study, we used an in vivo gallbladder epithelial cell infection model to study the function of the SPI-2-encoded effector, SseL. Deletion of the sseL gene resulted in bacterial filamentation and elongation and unusual localization of Salmonella within infected epithelial cells. Infection with the ?sseL strain also caused dramatic changes in lipid metabolism and led to massive accumulation of lipid droplets in infected cells. Some of these changes were investigated through metabolomics of gallbladder tissue. This phenotype was directly attributed to the deubiquitinase activity of SseL, as a Salmonella strain carrying a single point mutation in the catalytic cysteine resulted in the same phenotype as the deletion mutant. Excessive buildup of lipids due to the absence of a functional sseL gene was also observed in S. Typhimurium-infected livers. These results demonstrate that SseL alters host lipid metabolism in infected epithelial cells by modifying ubiquitination patterns of cellular targets. Female C57BL/6 mice were infected with the indicated strain of Salmonella enterica serovar Typhimurium by oral gavage. Four gallbladders were collected and pooled per sample group and metabolites extracted using a mixture of methanol and chloroform. Extracts were infused into a 12-T Apex-Qe hybrid quadrupole-FT-ICR mass spectrometer equipped with an Apollo II electrospray ionization source, a quadrupole mass filter and a hexapole collision cell. Raw mass spectrometry data were processed as described elsewhere (Han et al. 2008. Metabolomics. 4:128-140). To identify differences in metabolite composition between different groups of samples, we filtered the list of masses for metabolites which were present on one set of samples but not the other. Additionally, we calculated the ratios between averaged intensities of metabolites from each group of mice. To assign possible metabolite identities, monoisotopic neutral masses of interest were queried against MassTrix (http://masstrix.org). Masses were searched against the Mus musculus database within a mass error of 3 ppm.

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Global impact of Salmonella type III secretion effector SteA on host cells

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