ThetibAdherence Locus of EnterotoxigenicEscherichia coliIs Regulated by Cyclic AMP Receptor Protein

Abstract

Enterotoxigenic Escherichia coli (ETEC) is a Gram-negative enteric pathogen that causes profuse watery diarrhea through the elaboration of heat-labile and/or heat-stable toxins. Virulence is also dependent upon the expression of adhesive pili and afimbrial adhesins that allow the pathogen to adhere to the intestinal epithelium or mucosa. Both types of enterotoxins are regulated at the level of transcription by cyclic AMP (cAMP) receptor protein (CRP). To further our understanding of virulence gene regulation, an in silico approach was used to identify putative CRP binding sites in the genome of H10407 (O78:H11), an ETEC strain that was originally isolated from the stool of a Bangledeshi patient with cholera-like symptoms circa 1971. One of the predicted binding sites was located within an intergenic region upstream of tibDBCA. TibA is an autotransporter and afimbrial adhesin that is glycosylated by TibC. Expression of the TibA glycoprotein was abolished in an H10407 crp mutant and restored when crp was provided in trans. TibA-dependent aggregation was also abolished in a cyaA::kan strain and restored by addition of exogenous cAMP to the growth medium. DNase I footprinting confirmed that the predicted site upstream of tibDBCA is bound by CRP. Point mutations within the CRP binding site were found to abolish or significantly impair CRP-dependent activation of the tibDB promoter. Thus, these studies demonstrate that CRP positively regulates the expression of the glycosylated afimbrial adhesin TibA through occupancy of a binding site within tibDBp.More than 100 genes in Escherichia coli and many other bacterial species are regulated by cyclic AMP (cAMP) receptor protein (CRP) through direct and indirect pathways (12,33,36,42,75,76). For CRP, DNA binding is cAMP dependent and the position of a CRP binding site relative to RNA polymerase largely determines whether it functions as an activator or a repressor of a particular gene or operon. With respect to the transcription start site, CRP binding sites centered at or near Ϫ62, Ϫ72, Ϫ83, or Ϫ93 are typical for class I CRPdependent promoters. Class II promoters have a binding site centered at or near Ϫ41. 5 (16, 24, 50). Class III promoters are more complex in that they usually require an additional transcription factor or multiple CRP binding sites (24). In comparison to class I and class II promoters, class III and CRPrepressed promoters display a greater range of binding site positions (33).In addition to regulating the expression of metabolic and housekeeping genes, CRP has been shown to regulate the expression of many virulence factors. For example, CRP positively regulates the expression of Pla, a surface-exposed protease of Yersinia pestis that is necessary for the establishment of primary pneumonic plague and facilitates dissemination of the bacterium during bubonic plague (46, 49). In Vibrio vulnificus, a marine bacterium that causes gastroenteritis when ingested with contaminated seafood, CRP positively regulates the expression of a cytolytic hemolysin and a he...

Transcriptional Modulation of Enterotoxigenic Escherichia coli Virulence Genes in Response to Epithelial Cell Interactions

“…However, the studies do appear to affirm a central role of cAMP and the cAMP receptor protein (CRP) in modulation (41) of known (22) and putative (42) virulence genes, including genes involved in flagellar biosynthesis (7), whose expression is known to be under the control of crp (43). Interestingly, the crp gene is itself negatively autoregulated by the cAMP-CRP complex (44).…”

“…To construct transcriptional reporter fusions, regions upstream of the gene of interest were amplified by PCR and cloned into pHKLac1, a promoterless lacZYA reporter plasmid (22) containing an R6K␥ origin of replication and HK022 phage attP site for integration into the respective HK022 chromosomal attB site (23). Briefly, a 935-bp amplicon containing the eaeH promoter region (from Ϫ594 to ϩ341 of eaeH) was PCR-amplified using primers jf032812.1 (5=-GATCGGATCCGATCCCATAGTTTATCCGG-3=) and jf032812.2 (5=-GATCGAATTCTTCCCGAGCCACTCCTG-3=) and directionally cloned into the corresponding BamHI and EcoRI sites (respectively underlined in sequences listed above) of pHKLac1, resulting in plasmid pQL002.…”

Analysis of Global Transcriptional Profiles of Enterotoxigenic Escherichia coli Isolate E24377A

“…To date, the majority of the ETEC transcriptional studies have focused on the ETEC rns regulon (11), which has largely been associated with the regulation of CF expression (3,9,23), although binding motifs have been identified adjacent to other genes (44). No regulator has been identified that is associated with the expression of the enterotoxins.…”

EnterotoxigenicEscherichia coli

“…16 We're Here! Coincident with these events, genes governing the metabolism of key signaling molecules including the AI-2 autoinducer and c-di-GMP, as well as crp encoding the cAMP receptor protein (CRP), a major regulator of essential virulence traits, 17,18 are significantly modulated as bacteria move from planktonic to adherent populations. Although the precise impact of these signals on the expression of ETEC virulence genes is still being determined, the major changes in surface architecture of these pathogens upon interaction with intestinal cells clearly suggest that these organisms are programmed to respond to their environment in an orchestrated fashion that involves the modulation of both pathovar-specific genes like etpA and those genes encoding highly conserved features such as type 1 fimbriae.…”