RESUMO
Previous studies have shown that the MpeR transcriptional regulator produced by Neisseria gonorrhoeae represses the expression of mtrF, which encodes a putative inner membrane protein (MtrF). MtrF works as an accessory protein with the Mtr efflux pump, helping gonococci to resist high levels of diverse hydrophobic antimicrobials. Regulation of mpeR has been reported to occur by an iron-dependent mechanism involving Fur (ferric uptake regulator). Collectively, these observations suggest the presence of an interconnected regulatory system in gonococci that modulates the expression of efflux pump protein-encoding genes in an iron-responsive manner. Herein, we describe this connection and report that levels of gonococcal resistance to a substrate of the mtrCDE-encoded efflux pump can be modulated by MpeR and the availability of free iron. Using microarray analysis, we found that the mtrR gene, which encodes a direct repressor (MtrR) of mtrCDE, is an MpeR-repressed determinant in the late logarithmic phase of growth when free iron levels would be reduced due to bacterial consumption. This repression was enhanced under conditions of iron limitation and resulted in increased expression of the mtrCDE efflux pump operon. Furthermore, as judged by DNA-binding analysis, MpeR-mediated repression of mtrR was direct. Collectively, our results indicate that both genetic and physiologic parameters (e.g., iron availability) can influence the expression of the mtr efflux system and modulate levels of gonococcal susceptibility to efflux pump substrates.
Assuntos
Antibacterianos/farmacologia , Proteínas de Bactérias/genética , Regulação Bacteriana da Expressão Gênica , Proteínas Reguladoras de Ferro/genética , Ferro/metabolismo , Neisseria gonorrhoeae/genética , Proteínas de Bactérias/metabolismo , Farmacorresistência Bacteriana Múltipla/genética , Loci Gênicos , Humanos , Proteínas Reguladoras de Ferro/metabolismo , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Neisseria gonorrhoeae/efeitos dos fármacos , Óperon , Plasmídeos , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismoRESUMO
DNA-binding proteins that control expression of drug efflux pump genes have been termed "local regulators" as their encoding gene is often located adjacent to the gene(s) that they regulate. However, results from recent studies indicate that they can control genes outside efflux pump-encoding loci, which we term as being "off target." For example, the MtrR repressor was initially recognized for its ability to repress transcription of the mtrCDE-encoded efflux pump operon in the strict human pathogen Neisseria gonorrhoeae, but recent results from genetic and microarray studies have shown that it can control expression of nearly 70 genes scattered throughout the chromosome. One of the off-target MtrR-repressed genes is glnA, which encodes glutamine synthetase. Herein, we confirm the capacity of MtrR to repress glnA expression and provide evidence that such repression is due to its ability to negatively influence the binding of a second DNA-binding protein (FarR), which activates glnA. FarR was previously recognized as a transcriptional repressor of the farAB-encoded efflux pump operon. Thus, two DNA-binding proteins previously characterized as repressors of genes encoding efflux pumps that contribute to gonococcal resistance to antimicrobials can act in an opposing manner to modulate expression of a gene involved in basic metabolism.
