A previously uncharacterized two-component signaling system in uropathogenic Escherichia coli coordinates protection against host-derived oxidative stress with activation of hemolysin-mediated host cell pyroptosis.

Hongwei Gu,Xiao Hu,Xiaoyang Zhang,Wentong Cai,Jie Luo,Ganwu Li,Xuwang Cai,Xinyang Zhang,Joan Mecsas

doi:10.1371/journal.ppat.1010005

Abstract

Uropathogenic Escherichia coli (UPEC) deploy an array of virulence factors to successfully establish urinary tract infections. Hemolysin is a pore-forming toxin, and its expression correlates with the severity of UPEC infection. Two-component signaling systems (TCSs) are a major mechanism by which bacteria sense environmental cues and respond by initiating adaptive responses. Here, we began this study by characterizing a novel TCS (C3564/C3565, herein renamed orhK/orhR for oxidative resistance and hemolysis kinase/regulator) that is encoded on a UPEC pathogenicity island, using bioinformatic and biochemical approaches. A prevalence analysis indicates that orhK/orhR is highly associated with the UPEC pathotype, and it rarely occurs in other E. coli pathotypes tested. We then demonstrated that OrhK/OrhR directly activates the expression of a putative methionine sulfoxide reductase system (C3566/C3567) and hemolysin (HlyA) in response to host-derived hydrogen peroxide (H2O2) exposure. OrhK/OrhR increases UPEC resistance to H2O2 in vitro and survival in macrophages in cell culture via C3566/C3567. Additionally, OrhK/OrhR mediates hemolysin-induced renal epithelial cell and macrophage death via a pyroptosis pathway. Reducing intracellular H2O2 production by a chemical inhibitor impaired OrhK/OrhR-mediated activation of c3566-c3567 and hlyA. We also uncovered that UPEC links the two key virulence traits by cotranscribing the c3566-c3567 and hlyCABD operons. Taken together, our data suggest a paradigm in which a signal transduction system coordinates both bacterial pathogen defensive and offensive traits in the presence of host-derived signals; and this exquisite mechanism likely contributes to hemolysin-induced severe pathological outcomes.

Highlights

Uropathogenic Escherichia coli (UPEC) cause most urinary tract infections (UTIs) worldwide
We describe a virulence strategy employed by UPEC, i.e., the bacteria use a two-component signaling (TCS) system to coordinate oxidative stress resistance and hemolysin-mediated pyroptosis of host cells in response to host-derived oxidative signals
In searching for previously uncharacterized TCSs in pathogenic E. coli, we found that c3564 and c3565, which are located in the pheV genomic island in UPEC CFT073, are predicted to encode a TCS

Summary

Introduction

Uropathogenic Escherichia coli (UPEC) cause most urinary tract infections (UTIs) worldwide. Upon entry into the urethral opening, UPEC can ascend through the urethra and arrive at the bladder, where they can colonize and establish infection [3] Immune cells, such as macrophages and neutrophils, function as the first-line barriers to UPEC infection, usually by engulfing and killing the bacteria with reactive oxygen (ROS, e.g., H2O2), chlorine (RCS, e.g., HOCl) and nitrogen species (RNS, e.g., NO) [4,5,6]. Other defense systems in UPEC include the KatE catalase that decomposes H2O2 [9], and RpoS [10] regulator that elicits global response to withstand oxidative stress. As another strategy for survival, many bacterial pathogens encode toxins that can damage host cells in various ways [11,12], which can be deemed offensive activity. An effective and efficient coordination of defense and offense during infection is conceivably an important fitness factor for pathogens

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