Activation of the Cpx Envelope Stress Response Down-regulates Expression of Several LEE-encoded genes in Enteropathogenic Escherichia coli

Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E9; Cancer Research UK, London Research Institute, Clare Hall Laboratories, Blanche Lane, South Mimms, EN6 3LD

^* To whom correspondence should be addressed. Email: traivio{at}ualberta.ca.

	Abstract

The Cpx two-component system regulates an extracytoplasmic stress response that functions to rid the envelope of misfolded and mislocalized proteins that may interfere with normal cellular processes. The Cpx pathway is also involved in pathogenesis. This study investigated the role of the Cpx response in enteropathogenic Escherichia coli (EPEC) type III secretion (T3S). It was determined that a functional Cpx pathway is not required for T3S, but that pathway activation inhibits secretion by reducing the cellular pools of T3S substrates. The EPEC type III secretion system (T3SS) structural components as well as a number of its substrates are encoded on the locus of enterocyte effacement (LEE) pathogenicity island. Transcriptional fusions to the five major operons of the LEE were constructed and examined under Cpx pathway activating conditions. Induction of the Cpx response caused a decrease in the transcription of several LEE operons, having the most pronounced effect on LEE4 and LEE5. Collectively, these two operons encode components of the T3S translocation apparatus, the bacterial adhesin intimin, and the translocated bacterial receptor Tir. These data show for the first time that activation of the Cpx envelope stress response in EPEC inhibits T3S of both translocators and effectors, likely through down-regulation of LEE transcription. Coupled with recent findings, our results suggest that Cpx-mediated down-regulation of virulence is a conserved theme in a number of bacterial pathogens.