RyhB, an Iron-Responsive Small RNA Molecule, Regulates Shigella dysenteriae Virulence

Abstract

Regulation of bacterial gene expression by small RNA (sRNA) molecules is an increasingly recognized phenomenon but one that is not yet fully understood. We show that the sRNA RyhB suppresses several virulence-associated phenotypes of Shigella dysenteriae, a causative agent of bacillary dysentery in humans. The virulence genes repressed by S. dysenteriae RyhB include those encoding the type III secretion apparatus, its secreted effectors, and specific chaperones. Suppression of Shigella virulence occurs via RyhB-dependent repression of the transcriptional activator VirB, leading to reduced expression of genes within the VirB regulon. Efficient repression of virB is mediated by a single-stranded region of RyhB that is distinct from the region required for repression of Shigella sodB. Regulation of virB by RyhB implicates iron as an environmental factor contributing to the complex regulation of Shigella virulence determinants.Shigella species, which are closely related to Escherichia coli, cause bacillary dysentery, a disease associated with invasion of the colonic epithelium and provocation of an intense inflammatory response (12). Using cultured epithelial cells to measure bacterial invasion (invasion assay) (8) and intercellular spread (plaque assay) (22), investigators have identified a number of the genes required for Shigella pathogenesis. Many Shigella virulence-associated genes, including those encoding the type III secretion apparatus (mxi and spa genes), its secreted effectors (ipaA-D, ipgD, icsB, and virA), and specific chaperones (ipgC, ipgA, ipgE, and spa15), map to a 220-kbp virulence plasmid. Expression of these Shigella virulence determinants is highly regulated in response to environmental signals, such as temperature, osmolarity, and pH (12). This complex regulation is accomplished primarily by the transcriptional activators VirF and VirB (1). Transcription of many Shigella virulence-associated genes, including those encoding the type III secretion system (TTSS), is positively regulated by direct binding of VirB to the regulated promoters. Transcription of virB, in turn, is controlled primarily by the opposing activities of VirF, a transcriptional activator, and HNS, a transcriptional repressor. (For a review of the regulation of Shigella virulence gene expression, see reference 6.) VirF and VirB are both required to induce expression of virulence determinants that allow efficient invasion of epithelial cells by Shigella, an essential step in disease initiation. While the regulation of Shigella virulence has been the focus of intense investigation, the identification and characterization of all contributing environmental factors and regulatory elements have not yet been achieved.Noncoding RNA molecules (ncRNAs) control diverse cellular functions in organisms ranging from bacteria to humans. Although it is known that ncRNAs employ a variety of mechanisms, including methylation of rRNA, inhibition of translation or transcription, and sequestration of regulatory proteins (11, 13, 21), the full spectr...

Genome-Wide Analysis of Small RNAs Expressed by Yersinia pestis Identifies a Regulator of the Yop-Ysc Type III Secretion System

“…vesicatoria, the sRNA xS13, which is responsive to high salt concentrations and high temperatures, has been suggested to be an indirect positive regulator of secretion by affecting the levels of a key transcriptional regulator of the T3SS (64). In Shigella dysenteriae, the iron-responsive sRNA RyhB has been implicated in the repression of the transcriptional activator VirB, which leads to reduced transcription of T3SS genes (65). Interestingly, Y. pestis encodes 2 RyhB sRNAs (RyhB1 and RyhB2), which could also influence the regulation of the T3SS (31,66).…”

The Small RNA RyhB Contributes to Siderophore Production and Virulence of Uropathogenic Escherichia coli

“…In S. flexneri, RyhB represses the expression of ydeP, a gene required for the virulence-associated phenotype of extreme acid resistance (21). In S. dysenteriae, effector protein secretion, plaque formation, and invasion of eukaryotic epithelial cells are suppressed by RyhB through regulation of virB (23). In V. cholerae, RyhB modulates the expression of several genes controlling motility, chemotaxis, and biofilm formation.…”

“…Thus, RyhB plays an essential role in bacteria that require adaptation to iron starvation. Moreover, this sRNA also contributes to many pathogenicity determinants, such as acid resistance in Shigella flexneri (21); eukaryotic cell invasion and cell-to-cell spread in Shigella dysenteriae (22,23); motility, chemotaxis, and biofilm formation in Vibrio cholerae (24,25); biosynthesis of capsular polysaccharide and iron acquisition in Klebsiella pneumoniae (26); and oxidative stress resistance, survival inside human macrophages, and iron acquisition in Salmonella enterica serovar Typhi (27).…”

Esre: A novel essential non‐coding RNA in Escherichia coli

“…They regulate their target genes with similar mechanism, via binding with their targets by base pairing to regulate the expression of target genes. They usually share same sequences with their targets for base pairing, which are the basis of sRNA targets prediction by bioinformatics [3,[25][26][27]. Up to now, only limited essential sRNAs have been found in bacteria.…”