A novel two-component signaling system that activates transcription of an enterohemorrhagic Escherichia coli effector involved in remodeling of host actin

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is responsible for worldwide outbreaks of bloody diarrhea, hemorrhagic colitis, and life-threatening hemolytic uremic syndrome. After colonizing the large intestine, EHEC forms attaching and effacing (AE) lesions on intestinal epithelial cells. These lesions cause destruction of the microvilli and elicit actin rearrangement to form pedestals that cup each bacterium individually. EHEC responds to a signal produced by the intestinal microbial flora, autoinducer-3 (AI-3), and the host hormones epinephrine and norepinephrine to activate transcription of the genes involved in AE lesion formation. These three signals, involved in interkingdom communication, are sensed by bacterial sensor kinases. Here we describe a novel two-component system, QseEF (quorum-sensing E. coli regulators E and F), which is part of the AI-3/epinephrine/norepinephrine signaling system. QseE is the sensor kinase and QseF the response regulator. The qseEF genes are cotranscribed, and transcription of qseEF is activated by epinephrine through the QseC sensor. A qseF mutant does not form AE lesions. QseF activates transcription of the gene encoding EspFu, an effector protein translocated to the host cell by the EHEC, which mimics a eukaryotic SH2/SH3 adapter protein to engender actin polymerization during pedestal formation. Expression of the espFu gene from a plasmid restored AE lesion formation to the qseF mutant, suggesting that lack of espFu expression in this mutant was responsible for the loss of pedestal formation. These findings suggest the QseEF is a two-component system involved in the regulation of AE lesion formation by EHEC.