title: The SaeRS Two-Component System Is a Direct and Dominant Transcriptional Activator of Toxic Shock Syndrome Toxin 1 in Staphylococcus aureus.
abstract: Toxic shock syndrome toxin 1 (TSST-1) is a Staphylococcus aureus superantigen that has been implicated in both menstrual and nonmenstrual toxic shock syndrome (TSS). Despite the important role of TSST-1 in severe human disease, a comprehensive understanding of staphylococcal regulatory factors that control TSST-1 expression remains incomplete. The S. aureus exotoxin expression (Sae) operon contains a well-characterized two-component system that regulates a number of important exotoxins in S. aureus, although regulation of TSST-1 by the Sae system has not been investigated. We generated a defined deletion mutant of the Sae histidine kinase sensor (saeS) in the prototypic menstrual TSS strain S. aureus MN8. Mutation of saeS resulted in a complete loss of TSST-1 expression. Using both luciferase reporter experiments and quantitative real-time PCR, we demonstrate that the Sae system is an important transcriptional activator of TSST-1 expression. Recombinant SaeR was able to bind directly to the tst promoter to a region containing two SaeR consensus binding sites. Although the stand-alone SarA transcriptional regulator has been shown to be both a positive and a negative regulator of TSST-1, deletion of sarA in S. aureus MN8 resulted in a dramatic overexpression of TSST-1. As expected, mutation of agr also reduced TSST-1 expression, but this phenotype appeared to be independent of Sae. A double mutation of saeS and sarA resulted in the loss of TSST-1 expression. This work indicates that the Sae system is a dominant and direct transcriptional activator that is required for expression of TSST-1.
  
  
  
  The TSST-1 superantigen is an exotoxin, produced by some strains of S. aureus, that has a clear role in both menstrual and nonmenstrual TSS. Although the well-characterized agr quorum sensing system is a known positive regulator of TSST-1, the molecular mechanisms that directly control TSST-1 expression are only partially understood. Our studies demonstrate that the Sae two-component regulatory system is a positive transcriptional regulator that binds directly to the TSST-1 promoter, and furthermore, our data suggest that Sae is required for expression of TSST-1. This work highlights how major regulatory circuits can converge to fine-tune exotoxin expression and suggests that the Sae regulatory system may be an important target for antivirulence strategies.
authors.affiliation: Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada Lawson Health Research Institute, London, Ontario, Canada.
authors.forename: Miren L
authors.initials: ML
authors.lastname: Baroja
authors.affiliation: Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada Lawson Health Research Institute, London, Ontario, Canada.
authors.forename: Christine A
authors.initials: CA
authors.lastname: Herfst
authors.affiliation: Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.
authors.forename: Katherine J
authors.initials: KJ
authors.lastname: Kasper
authors.affiliation: Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.
authors.forename: Stacey X
authors.initials: SX
authors.lastname: Xu
authors.affiliation: Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Gillett
authors.affiliation: Corporate Research & Engineering, Kimberly-Clark Corporation, Roswell, Georgia, USA.
authors.forename: Jingru
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada Department of Surgery, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada Lawson Health Research Institute, London, Ontario, Canada.
authors.forename: Gregor
authors.initials: G
authors.lastname: Reid
authors.affiliation: Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada Lawson Health Research Institute, London, Ontario, Canada john.mccormick@uwo.ca.
authors.forename: John K
authors.initials: JK
authors.lastname: McCormick
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D004768:Enterotoxins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000235:genetics / Q000378:metabolism*; D018089:Superantigens / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004768:Enterotoxins; C492107:SarA protein, Staphylococcus aureus; D018089:Superantigens; C030107:enterotoxin F, Staphylococcal; D011494:Protein Kinases; C527351:SaeS protein, Staphylococcus aureus