title: The Pseudomonas aeruginosa Vfr regulator controls global virulence factor expression through cyclic AMP-dependent and -independent mechanisms.
abstract: Vfr is a global regulator of virulence factor expression in the human pathogen Pseudomonas aeruginosa. Although indirect evidence suggests that Vfr activity is controlled by cyclic AMP (cAMP), it has been hypothesized that the putative cAMP binding pocket of Vfr may accommodate additional cyclic nucleotides. In this study, we used two different approaches to generate apo-Vfr and examined its ability to bind a representative set of virulence gene promoters in the absence and presence of different allosteric effectors. Of the cyclic nucleotides tested, only cAMP was able to restore DNA binding activity to apo-Vfr. In contrast, cGMP was capable of inhibiting cAMP-Vfr DNA binding. Further, we demonstrate that vfr expression is autoregulated and cAMP dependent and involves Vfr binding to a previously unidentified site within the vfr promoter region. Using a combination of in vitro and in vivo approaches, we show that cAMP is required for Vfr-dependent regulation of a specific subset of virulence genes. In contrast, we discovered that Vfr controls expression of the lasR promoter in a cAMP-independent manner. In summary, our data support a model in which Vfr controls virulence gene expression by distinct (cAMP-dependent and -independent) mechanisms, which may allow P. aeruginosa to fine-tune its virulence program in response to specific host cues or environments.
authors.affiliation: Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, NC 27599, USA.
authors.forename: Erin L
authors.initials: EL
authors.lastname: Fuchs
authors.forename: Evan D
authors.initials: ED
authors.lastname: Brutinel
authors.forename: Adriana K
authors.initials: AK
authors.lastname: Jones
authors.forename: Nanette B
authors.initials: NB
authors.lastname: Fulcher
authors.forename: Mark L
authors.initials: ML
authors.lastname: Urbanowski
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Yahr
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Wolfgang
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D000242:Cyclic AMP / Q000378:metabolism*; D002373:Cyclic AMP Receptor Protein / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism*; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002373:Cyclic AMP Receptor Protein; D004269:DNA, Bacterial; C091090:Vfr protein, Pseudomonas aeruginosa; D037521:Virulence Factors; D000242:Cyclic AMP