Influence of the Cpx Extracytoplasmic-Stress-Responsive Pathway on Yersinia sp.-Eukaryotic Cell Contact

Abstract

The extracytoplasmic-stress-responsive CpxRA two-component signal transduction pathway allows bacteria to adapt to growth in extreme environments. It controls the production of periplasmic protein folding and degradation factors, which aids in the biogenesis of multicomponent virulence determinants that span the bacterial envelope. This is true of the Yersinia pseudotuberculosis Ysc-Yop type III secretion system. However, despite using a second-site suppressor mutation to restore Yop effector secretion by yersiniae defective in the CpxA sensor kinase, these bacteria poorly translocated Yops into target eukaryotic cells. Investigation of this phenotype herein revealed that the expression of genes which encode several surface-located adhesins is also influenced by the Cpx pathway. In particular, the expression and surface localization of invasin, an adhesin that engages ␤1-integrins on the eukaryotic cell surface, are severely restricted by the removal of CpxA. This reduces bacterial association with eukaryotic cells, which could be suppressed by the ectopic production of CpxA, invasin, or RovA, a positive activator of inv expression. In turn, these infected eukaryotic cells then became susceptible to intoxication by translocated Yop effectors. In contrast, bacteria harboring an in-frame deletion of cpxR, which encodes the cognate response regulator, displayed an enhanced ability to interact with cell monolayers, as well as elevated inv and rovA transcription. This phenotype could be drastically suppressed by providing a wild-type copy of cpxR in trans. We propose a mechanism of inv regulation influenced by the direct negative effects of phosphorylated CpxR on inv and rovA transcription. In this fashion, sensing of extracytoplasmic stress by CpxAR contributes to productive Yersinia sp.-eukaryotic cell interactions.

Activation of the Cpx Envelope Stress Response Down-Regulates Expression of Several Locus of Enterocyte Effacement-Encoded Genes in Enteropathogenic Escherichia coli

“…Another subset of the Cpx regulon includes genes involved in adherence. CpxRϳP has been shown to bind upstream of the promoter regions of genes involved in motility and chemotaxis and those encoding the adhesive appendages curli and P pili and the Yersinia adhesin, invasin (5,13,17,29). These findings, coupled with the discovery that the Cpx pathway is activated upon contact with hydrophobic surfaces through the outer membrane lipoprotein NlpE (50), suggest that the Cpx response is intimately involved in attachment.…”

Signal Integration by the Two-Component Signal Transduction Response Regulator CpxR

“…The existence of point mutations in the CpxA gene (the so-called CpxA* alleles) that lead to constitutively activated CpxR-dependent targets (e.g., PcpxP and PdegP [10,12,37,42,45]) has been interpreted in terms of a mutant protein defective in phosphatase activity and suggests that the WT protein exhibits phosphatase activity in vivo. The observations that, compared to WT cells, cpxA null mutants can exhibit substantially greater PcpxP activity (4,(8)(9)(10)35; this paper) and can express elevated steady-state levels of CpxR (P. DiGuiseppe-Champion and T. Silhavy, personal communication) provide further support. If this hypothesis is correct, then the two activities must exist in an equilibrium that can be shifted in response to specific stimuli.…”

Characterization of the CpxRA Regulon in Haemophilus ducreyi

“…As observed in similar studies performed with E. coli (47), inactivation of the response regulator (i.e., cpxR) did not have much effect on overall gene expression (data not shown). With the working assumption that a cpxA deletion mutant should have a highly phosphorylated CpxR protein (10,32,68), we next compared the global expression profile of the wild-type strain with that of the cpxA mutant. Regulated genes were defined as those with a minimum 2-fold transcriptional change (P Ͻ 0.05).…”