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Expression of ToxR, the transcriptional activator of the virulence factors in Vibrio cholerae, is modulated by the heat shock response.

ABSTRACT: The toxR gene of Vibrio cholerae encodes a transmembrane, DNA-binding protein that positively controls transcription of the genes for cholera toxin, TCP pili, and other proteins important in cholera pathogenesis. Nucleotide sequence analysis of the toxR upstream region has revealed that the heat shock gene htpG, encoding the bacterial homologue of the eukaryotic Hsp90 protein, was located immediately upstream and was divergently transcribed from toxR. Using lacZ transcriptional fusions, we have shown that neither toxR nor htpG expression was regulated by ToxR. However, the growth temperature had a coordinate but reciprocal effect on the expression from both the toxR and htpG promoters in V. cholerae; the decrease of toxR expression between 22 degrees C and 37 degrees C was proportional to the increase of htpG expression observed within that temperature range. A similar pattern of expression of the htpG and toxR promoters was observed in the heterologous host Escherichia coli, where this regulation was controlled by the level of the E. coli rpoH (htpR) gene product, sigma-32. Consistent with the temperature-regulated expression of the V. cholerae htpG promoter in E. coli, a sequence similar to the consensus sequence of the E. coli heat shock promoters was detected upstream from the V. cholerae htpG gene. We propose a model in which the regulation of toxR expression by temperature is controlled by the level of sigma-32 (RpoH) RNA polymerase.

SUBMITTER: Parsot C

PROVIDER: S-EPMC55281 | biostudies-other | 1990 Dec

REPOSITORIES: biostudies-other

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Expression of ToxR, the transcriptional activator of the virulence factors in Vibrio cholerae, is modulated by the heat shock response.

Parsot C C Mekalanos J J JJ

Proceedings of the National Academy of Sciences of the United States of America 19901201 24

The toxR gene of Vibrio cholerae encodes a transmembrane, DNA-binding protein that positively controls transcription of the genes for cholera toxin, TCP pili, and other proteins important in cholera pathogenesis. Nucleotide sequence analysis of the toxR upstream region has revealed that the heat shock gene htpG, encoding the bacterial homologue of the eukaryotic Hsp90 protein, was located immediately upstream and was divergently transcribed from toxR. Using lacZ transcriptional fusions, we have ...[more]

PMID: 2124707

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Project description:UnlabelledVibrio cholerae is an aquatic organism that causes the severe acute diarrheal disease cholera. The ability of V. cholerae to cause disease is dependent upon the production of two critical virulence determinants, cholera toxin (CT) and the toxin-coregulated pilus (TCP). The expression of the genes that encode for CT and TCP production is under the control of a hierarchical regulatory system called the ToxR regulon, which functions to activate virulence gene expression in response to in vivo stimuli. Cyclic dipeptides have been found to be produced by numerous bacteria, yet their biological function remains unknown. V. cholerae has been shown to produce cyclo(Phe-Pro). Previous studies in our laboratory demonstrated that cyclo(Phe-Pro) inhibited V. cholerae virulence factor production. For this study, we report on the mechanism by which cyclo(Phe-Pro) inhibited virulence factor production. We have demonstrated that exogenous cyclo(Phe-Pro) activated the expression of leuO, a LysR-family regulator that had not been previously associated with V. cholerae virulence. Increased leuO expression repressed aphA transcription, which resulted in downregulation of the ToxR regulon and attenuated CT and TCP production. The cyclo(Phe-Pro)-dependent induction of leuO expression was found to be dependent upon the virulence regulator ToxR. Cyclo(Phe-Pro) did not affect toxR transcription or ToxR protein levels but appeared to enhance the ToxR-dependent transcription of leuO. These results have identified leuO as a new component of the ToxR regulon and demonstrate for the first time that ToxR is capable of downregulating virulence gene expression in response to an environmental cue.ImportanceThe ToxR regulon has been a focus of cholera research for more than three decades. During this time, a model has emerged wherein ToxR functions to activate the expression of Vibrio cholerae virulence factors upon host entry. V. cholerae and other enteric bacteria produce cyclo(Phe-Pro), a cyclic dipeptide that we identified as an inhibitor of V. cholerae virulence factor production. This finding suggested that cyclo(Phe-Pro) was a negative effector of virulence factor production and represented a molecule that could potentially be exploited for therapeutic development. In this work, we investigated the mechanism by which cyclo(Phe-Pro) inhibited virulence factor production. We found that cyclo(Phe-Pro) signaled through ToxR to activate the expression of leuO, a new virulence regulator that functioned to repress virulence factor production. Our results have identified a new arm of the ToxR regulon and suggest that ToxR may play a broader role in pathogenesis than previously known.

Project description:UnlabelledToxR is a major virulence gene regulator in Vibrio cholerae. Although constitutively expressed under many laboratory conditions, our previous work demonstrated that the level of ToxR increases significantly when cells are grown in the presence of the 4 amino acids asparagine, arginine, glutamate, and serine (NRES). We show here that the increase in ToxR production in response to NRES requires the Var/Csr global regulatory circuit. The VarS/VarA two-component system controls the amount of active CsrA, a small RNA-binding protein involved in the regulation of a wide range of cellular processes. Our data show that a varA mutant, which is expected to overproduce active CsrA, had elevated levels of ToxR in the absence of the NRES stimulus. Conversely, specific amino acid substitutions in CsrA were associated with defects in ToxR production in response to NRES. These data indicate that CsrA is a positive regulator of ToxR levels. Unlike previously described effects of CsrA on virulence gene regulation, the effects of CsrA on ToxR were not mediated through quorum sensing and HapR. CsrA is likely essential in V. cholerae, since a complete deletion of csrA was not possible; however, point mutations in CsrA were tolerated well. The CsrA Arg6His mutant had wild-type growth in vitro but was severely attenuated in the infant mouse model of V. cholerae infection, showing that CsrA is critical for pathogenesis. This study has broad implications for our understanding of how V. cholerae integrates its response to environmental cues with the regulation of important virulence genes.ImportanceIn order to colonize the human host, Vibrio cholerae must sense and respond to environmental signals to ensure appropriate expression of genes required for pathogenesis. Uncovering how V. cholerae senses its environment and activates its virulence gene repertoire is critical for our understanding of how V. cholerae transitions from its natural aquatic habitat to the human host. Here we demonstrate a previously unknown link between the global regulator CsrA and the major V. cholerae virulence gene regulator ToxR. The role of CsrA in the cell is to receive input from the environment and coordinate an appropriate cellular response. By linking environmental sensing to the ToxR regulon, CsrA effectively acts as a switch that controls pathogenesis in response to specific signals. We demonstrate that CsrA is critical for virulence in the infant mouse model of V. cholerae infection, consistent with its role as an in vivo regulator of virulence gene expression.

Dataset Information

Expression of ToxR, the transcriptional activator of the virulence factors in Vibrio cholerae, is modulated by the heat shock response.

Publications

Expression of ToxR, the transcriptional activator of the virulence factors in Vibrio cholerae, is modulated by the heat shock response.

Similar Datasets

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