title: Small-molecule inhibitor of the Shigella flexneri master virulence regulator VirF.
abstract: VirF is an AraC family transcriptional activator that is required for the expression of virulence genes associated with invasion and cell-to-cell spread by Shigella flexneri, including multiple components of the type three secretion system (T3SS) machinery and effectors. We tested a small-molecule compound, SE-1 (formerly designated OSSL_051168), which we had identified as an effective inhibitor of the AraC family proteins RhaS and RhaR, for its ability to inhibit VirF. Cell-based reporter gene assays with Escherichia coli and Shigella, as well as in vitro DNA binding assays with purified VirF, demonstrated that SE-1 inhibited DNA binding and transcription activation (likely by blocking DNA binding) by VirF. Analysis of mRNA levels using real-time quantitative reverse transcription-PCR (qRT-PCR) further demonstrated that SE-1 reduced the expression of the VirF-dependent virulence genes icsA, virB, icsB, and ipaB in Shigella. We also performed eukaryotic cell invasion assays and found that SE-1 reduced invasion by Shigella. The effect of SE-1 on invasion required preincubation of Shigella with SE-1, in agreement with the hypothesis that SE-1 inhibited the expression of VirF-activated genes required for the formation of the T3SS apparatus and invasion. We found that the same concentrations of SE-1 had no detectable effects on the growth or metabolism of the bacterial cells or the eukaryotic host cells, respectively, indicating that the inhibition of invasion was not due to general toxicity. Overall, SE-1 appears to inhibit transcription activation by VirF, exhibits selectivity toward AraC family proteins, and has the potential to be developed into a novel antibacterial agent.
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA.
authors.forename: Veerendra
authors.initials: V
authors.lastname: Koppolu
authors.forename: Ichie
authors.initials: I
authors.lastname: Osaka
authors.forename: Jeff M
authors.initials: JM
authors.lastname: Skredenske
authors.forename: Bria
authors.initials: B
authors.lastname: Kettle
authors.forename: P Scott
authors.initials: PS
authors.lastname: Hefty
authors.forename: Jiaqin
authors.initials: J
authors.lastname: Li
authors.forename: Susan M
authors.initials: SM
authors.lastname: Egan
mesh_terms: D000818:Animals; D002460:Cell Line; D004269:DNA, Bacterial / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects; D005347:Fibroblasts / Q000187:drug effects / Q000382:microbiology; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D051379:Mice; D011485:Protein Binding / Q000187:drug effects; D011804:Quinolines / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D012763:Shigella flexneri / Q000187:drug effects*; D014157:Transcription Factors / Q000037:antagonists & inhibitors*; D015533:Transcriptional Activation / Q000187:drug effects; D037521:Virulence Factors / Q000037:antagonists & inhibitors*
chemical_list: C584457:1-butyl-4-nitromethyl-3-quinolin-2-yl-4H-quinoline; D004269:DNA, Bacterial; D011804:Quinolines; D014157:Transcription Factors; D037521:Virulence Factors