Induction of the reactive chlorine-responsive transcription factor RclR in Escherichia coli following ingestion by neutrophils

Abstract

Neutrophils generate hypochlorous acid (HOCl) and related reactive chlorine species as part of their defence against invading microorganisms. In isolation, bacteria respond to reactive chlorine species by upregulating responses that provide defence against oxidative challenge. Key questions are whether these responses are induced when bacteria are phagocytosed by neutrophils, and whether this provides them with a survival advantage. We investigated RclR, a transcriptional activator of the rclABC operon in Escherichia coli that has been shown to be specifically activated by reactive chlorine species. We first measured induction by individual reactive chlorine species, and showed that HOCl itself activates the response, as do chloramines (products of HOCl reacting with amines) provided they are cell permeable. Strong RclR activation was seen in E. coli following phagocytosis by neutrophils, beginning within 5 min and persisting for 40 min. RclR activation was suppressed by inhibitors of NOX2 and myeloperoxidase, providing strong evidence that it was due to HOCl production in the phagosome. RclR activation demonstrates that HOCl, or a derived chloramine, enters phagocytosed bacteria in sufficient amount to induce this response. Although RclR was induced in wild-type bacteria following phagocytosis, we detected no greater sensitivity to neutrophil killing of mutants lacking genes in the rclABC operon.

Redox-Mediated Inactivation of the Transcriptional Repressor RcrR is Responsible for Uropathogenic Escherichia coli’s Increased Resistance to Reactive Chlorine Species

“…1D ). The RclR regulon consists of rclA , rclB , and rclC and is induced through a HOCl-sensing mechanism of the transcriptional activator RclR both in lab culture and during phagocytosis, although its expression did not result in increased survival in the phagosome of neutrophils ( 26 , 72 ). RclA was recently identified as a HOSCN reductase that protects E. coli from the oxidizing effects of hypothiocyanous acid, another antimicrobial oxidant generated by MPO ( 73 ).…”

Site-specific decreases in DNA methylation in replicating cells following exposure to oxidative stress

“…It is well known that oxidants can impact gene expression through direct oxidation of transcription factors and associated regulatory proteins (29,30). HOCl exposure activates several transcription factors in bacterial systems, resulting in the upregulation of genes that protect the organism from oxidative stress (31)(32)(33)(34). Likewise in mammalian cells, HOCl-induced modified gene expression has been observed through its action on stress-sensing transcription factors such as Nrf2 (NF-E2-related factor 2) and NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells), both through the oxidation of the regulatory proteins Keap-1 and IκB (35)(36)(37)(38)(39).…”

Redox-mediated inactivation of the transcriptional repressor C3600 makes uropathogenicEscherichia coliexquisitely resistant to reactive chlorine species

“…1D). The RclR regulon consists of rclA, rclB, and rclC and is induced through a HOCl-sensing mechanism of the transcriptional activator RclR both in lab culture and during phagocytosis (27,69). RclA was recently identified as a Cu (II) reductase that protects E. coli from HOCl-and Custress (35).…”