Transcriptional Profiling of Target of RNAIII-Activating Protein, a Master Regulator of Staphylococcal Virulence

Abstract

Staphylococcus aureus is a gram-positive bacterium that is part of the normal healthy flora but that can become virulent and cause infections by producing biofilms and toxins. The production of virulence factors is regulated by cell-cell communication (quorum sensing) through the histidine phosphorylation of target of RNAIII-activating protein (TRAP), which is a 21-kDa protein that is highly conserved among staphylococci. Using microarray analysis, we show here that the expression and phosphorylation of TRAP upregulate the expression of most, if not all, toxins known to date, as well as their global regulator agr. In addition, we show here that the expression and phosphorylation of TRAP are also necessary for the expression of genes known to be necessary for the survival of the bacteria in a biofilm, like arc, pyr, and ure. TRAP is thus demonstrated to be a master regulator of staphylococcal pathogenesis.Staphylococcus aureus is a gram-positive bacterium that is part of the normal flora of the skin, but it can become pathogenic and cause fatal diseases once it forms a biofilm and/or produces toxins (18,25). Biofilm formation and toxin production are regulated by a quorum-sensing mechanism, where molecules produced and secreted by the bacteria (autoinducers) reach a threshold concentration and activate signal transduction pathways, leading to activation of the genes that encode virulence factors (22,27,32,35,37).To date, two staphylococcal quorum-sensing systems (SQS) have been described. SQS 1 consists of the autoinducer RNAIII-activating protein (RAP) and its target molecule, target of RNAIII-activating protein (TRAP) (4,5,20,21). SQS 2 consists of the molecules encoded by agr (28, 29). The bacteria secrete RAP, a 33-kDa protein, as they multiply (23); when RAP reaches a threshold concentration (in the mid-exponential phase of growth), RAP induces the histidine phosphorylation of its target molecule TRAP (5, 20). The phosphorylation of TRAP leads, in an as-yet-unknown mechanism, to the synthesis of SQS 2, which is composed of the products of the agr system. agr encodes two divergently transcribed transcripts, RNAII and RNAIII (28,29). RNAII encodes AgrA, AgrC, AgrD, and AgrB, where AgrD is a propeptide that yields an autoinducing peptide (AIP) that is processed and secreted with the aid of AgrB. Once agr is activated and AIP is secreted, AIP induces the phosphorylation of its receptor AgrC, leading to the production of the regulatory RNA molecule termed RNAIII (28). RNAIII upregulates the production of numerous secreted toxins (28). SQS 1 and SQS 2 interact with one another because once AIP is made in the mid-exponential phase of growth, it indirectly downregulates the phosphorylation of TRAP (5). The interplay between the phosphorylation of TRAP and AgrC by their respective autoinducers, RAP or AIP, regulates the expression of adhesion molecules or toxins Like typical sensors of classical two component systems, TRAP is histidine phosphorylated in the presence of RAP (5, 20); immunoelectron microscopy and West...

A Nonsense Mutation in agrA Accounts for the Defect in agr Expression and the Avirulence of Staphylococcus aureus 8325-4 traP :: kan

“…We find that the derivative of strain 8325-4 containing the traP mutation used in recent studies (5) has an adventitious stop codon in agrA that eliminates agr activation. This mutation is responsible for the failure of the traP mutant to express agr, for its avirulence in the murine abscess model (5), and for the identity of the traP transcriptome with that of agr (7). These findings are entirely consistent with two other reports (15,20) demonstrating that traP mutations have no effect on agr expression or virulence.…”

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