AUTHOR=De la Cruz Miguel A. , Morgan Jason K. , Ares Miguel A. , Yáñez-Santos Jorge A. , Riordan James T. , Girón Jorge A. 

TITLE=The Two-Component System CpxRA Negatively Regulates the Locus of Enterocyte Effacement of Enterohemorrhagic Escherichia coli Involving σ32 and Lon protease

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=6

YEAR=2016

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2016.00011

DOI=10.3389/fcimb.2016.00011

ISSN=2235-2988

ABSTRACT=<p>Enterohemorrhagic <italic>Escherichia coli</italic> (EHEC) is a significant cause of serious human gastrointestinal disease worldwide. EHEC strains contain a pathogenicity island called the locus of enterocyte effacement (LEE), which encodes virulence factors responsible for damaging the gut mucosa. The Cpx envelope stress response of <italic>E. coli</italic> is controlled by a two-component system (TCS) consisting of a sensor histidine kinase (CpxA) and a cytoplasmic response regulator (CpxR). In this study, we investigated the role of CpxRA in the expression of LEE-encoded virulence factors of EHEC. We found that a mutation in <italic>cpxA</italic> significantly affected adherence of EHEC to human epithelial cells. Analysis of this mutant revealed the presence of high levels of CpxR which repressed transcription of <italic>grlA</italic> and <italic>ler</italic>, the main positive virulence regulators of the LEE, and influenced negatively the production of the type 3 secretion system–associated EspABD translocator proteins. It is known that CpxR activates <italic>rpoH</italic> (Sigma factor 32), which in turns activates transcription of the <italic>lon</italic> protease gene. We found that transcription levels of <italic>ler</italic> and <italic>grlA</italic> were significantly increased in the <italic>lon</italic> and <italic>cpxA lon</italic> mutants suggesting that <italic>lon</italic> is involved in down-regulating LEE genes. In addition, the <italic>Galleria mellonella</italic> model of infection was used to analyze the effect of the loss of the <italic>cpx</italic> and <italic>lon</italic> genes in EHEC's ability to kill the larvae. We found that the <italic>cpxA</italic> mutant was significantly deficient at killing the larvae however, the <italic>cpxA lon</italic> mutant which overexpresses LEE genes <italic>in vitro</italic>, was unable to kill the larvae, suggesting that virulence in the <italic>G. mellonella</italic> model is T3SS independent and that CpxA modulates virulence through a yet unknown EHEC-specific factor. Our data provides new insights and broadens our scope into the complex regulatory network of the LEE in which the CpxA sensor kinase plays an important role in a cascade involving both global and virulence regulators.</p>