Differential regulation of staphylococcal virulence by the sensor kinase SaeS in response to neutrophil-derived stimuli (original) (raw)
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PLoS pathogens, 2015
Bacterial pathogens often employ two-component systems (TCSs), typically consisting of a sensor kinase and a response regulator, to control expression of a set of virulence genes in response to changing host environments. In Staphylococcus aureus, the SaeRS TCS is essential for in vivo survival of the bacterium. The intramembrane-sensing histidine kinase SaeS contains, along with a C-terminal kinase domain, a simple N-terminal domain composed of two transmembrane helices and a nine amino acid-long extracytoplasmic linker peptide. As a molecular switch, SaeS maintains low but significant basal kinase activity and increases its kinase activity in response to inducing signals such as human neutrophil peptide 1 (HNP1). Here we show that the linker peptide of SaeS controls SaeS's basal kinase activity and that the amino acid sequence of the linker peptide is highly optimized for its function. Without the linker peptide, SaeS displays aberrantly elevated kinase activity even in the ab...
Two-Component Systems of S. aureus: Signaling and Sensing Mechanisms
Genes
Staphylococcus aureus encodes 16 two-component systems (TCSs) that enable the bacteria to sense and respond to changing environmental conditions. Considering the function of these TCSs in bacterial survival and their potential role as drug targets, it is important to understand the exact mechanisms underlying signal perception. The differences between the sensing of appropriate signals and the transcriptional activation of the TCS system are often not well described, and the signaling mechanisms are only partially understood. Here, we review present insights into which signals are sensed by histidine kinases in S. aureus to promote appropriate gene expression in response to diverse environmental challenges.
Infection and Immunity, 2014
The Staphylococcus aureus two-component regulatory system, GraRS, is involved in resistance to killing by distinct host defense cationic antimicrobial peptides (HD-CAPs). It is believed to regulate downstream target genes such as mprF and dltABCD to modify the S. aureus surface charge. However, the detailed mechanism(s) by which the histidine kinase, GraS, senses specific HD-CAPs is not well defined. Here, we studied a well-characterized clinical methicillin-resistant S. aureus (MRSA) strain (MW2), its isogenic graS deletion mutant (⌬graS strain), a nonameric extracellular loop mutant (⌬EL strain), and four residuespecific ⌬EL mutants (D37A, P39A, P39S, and D35G D37G D41G strains). The ⌬graS and ⌬EL strains were unable to induce mprF and dltA expression and, in turn, demonstrated significantly increased susceptibilities to daptomycin, polymyxin B, and two prototypical HD-CAPs (hNP-1 and RP-1). Further, P39A, P39S, and D35G-D37G-D41G ⌬EL mutations correlated with moderate increases in HD-CAP susceptibility. Reductions of mprF and dltA induction by PMB were also found in the ⌬EL mutants, suggesting these residues are pivotal to appropriate activation of the GraS sensor kinase. Importantly, a synthetic exogenous soluble EL mimic of GraS protected the parental MW2 strain against hNP-1-and RP-1-mediated killing, suggesting a direct interaction of the EL with HD-CAPs in GraS activation. In vivo, the ⌬graS and ⌬EL strains displayed dramatic reductions in achieved target tissue MRSA counts in an endocarditis model. Taken together, our results provide new insights into potential roles of GraS in S. aureus sensing of HD-CAPs to induce adaptive survival responses to these molecules.
The Role of Innate Immunity in Promoting SaeR/S-Mediated Virulence in Staphylococcus aureus
Journal of Innate Immunity, 2013
The ability of Staphylococcus aureus to infect tissues is dependent on precise control of virulence through gene-regulatory systems. While the SaeR/S two-component system has been shown to be a major regulator of S. aureus virulence, the influence of the host environment on SaeR/S-regulated genes (saeR/S targets) remains incompletely defined. Using QuantiGene 2.0 transcriptional assays, we examined expression of genes with the SaeR binding site in USA300 exposed to human and mouse neutrophils and host-derived peptides and during subcutaneous skin infection. We found that only some of the saeR/S targets, as opposed to the entire SaeR/S virulon, were activated within 5 and 10 min of interacting with human neutrophils as well as α-defensin. Furthermore, mouse neutrophils promoted transcription of saeR/S targets despite lacking α-defensin, and the murine skin environment elicited a distinctive expression profile of saeR/S targets. These findings indicate that saeR/S-mediated transcripti...
Journal of Bacteriology, 2008
The two-component system SaeRS of Staphylococcus aureus is closely involved in the regulation of major virulence factors. However, little is known about the signals leading to saeRS activation. A total of four overlapping transcripts (T1 to T4) from three different transcription starting points are expressed in the sae operon. We used a -galactosidase reporter assay to characterize the putative promoter regions within the saeRS upstream region. The main transcript T2 is probably generated by endoribonucleolytic processing of the T1 transcript. Only two distinct promoter elements (P1 and P3) could be detected within the saeRS upstream region. The P3 promoter, upstream of saeRS, generates the T3 transcript, includes a cis-acting enhancer element and is repressed by saeRS. The most distal P1 promoter is strongly autoregulated, activated by agr, and repressed by sigma factor B. In strain Newman a mutation within the histidine kinase SaeS leads to a constitutively activated sae system. Evaluation of different external signals revealed that the P1 promoter in strain ISP479R and strain UAMS-1 is inhibited by low pH and high NaCl concentrations but activated by hydrogen peroxide. The most prominent induction of P1 was observed at subinhibitory concentrations of ␣-defensins in various S. aureus strains, with the exception of strain ISP479R and strain COL. P1 was not activated by the antimicrobial peptides LL37 and daptomycin. In summary, the results indicate that the sensor molecule SaeS is activated by alteration within the membrane allowing the pathogen to react to phagocytosis related effector molecules.
Staphylococcus aureus pathogenesis in diverse host environments
Pathogens and disease, 2017
Staphylococcus aureus (S. aureus) is an eminent human pathogen that can colonize the human host and cause severe, life-threatening illnesses. This bacterium can reside in and infect a wide range of host tissues, ranging from superficial surfaces like the skin to deeper tissues such as in the gastrointestinal tract, heart and bones. Due to its multifaceted lifestyle, S. aureus uses complex regulatory networks to sense diverse signals that enable it to adapt to different environments and modulate virulence. In this mini-review, we explore well-characterized environmental and host cues that S. aureus responds to and describe how this pathogen modulates virulence in response to these signals. Lastly, we highlight therapeutic approaches undertaken by several groups to inhibit both signaling and the cognate regulators that sense and transmit these signals downstream.
2020
The ability of Staphylococcus aureus to infect many different tissue sites is enabled, in part, by its Transcriptional Regulatory Network (TRN) that coordinates its gene expression to respond to different environments. We elucidated the organization and activity of this TRN by applying Independent Component Analysis (ICA) to a compendium of 108 RNAseq expression profiles from two S. aureus clinical strains (TCH1516 and LAC). ICA decomposed the S. aureus transcriptome into 29 independently modulated sets of genes (i-modulons) that revealed (1) high confidence associations between 21 i-modulons and known regulators; (2) an association between an i-modulon and σS, whose regulatory role was previously undefined; (3) the regulatory organization of 65 virulence factors in the form of three i-modulons associated with AgrR, SaeR and Vim-3, (4) the roles of three key transcription factors (codY, Fur and ccpA) in coordinating the metabolic and regulatory networks; and (5) a low dimensional re...
Sensory deprivation in Staphylococcus aureus
Nature communications, 2018
Bacteria use two-component systems (TCSs) to sense and respond to environmental changes. The core genome of the major human pathogen Staphylococcus aureus encodes 16 TCSs, one of which (WalRK) is essential. Here we show that S. aureus can be deprived of its complete sensorial TCS network and still survive under growth arrest conditions similarly to wild-type bacteria. Under replicating conditions, however, the WalRK system is necessary and sufficient to maintain bacterial growth, indicating that sensing through TCSs is mostly dispensable for living under constant environmental conditions. Characterization of S. aureus derivatives containing individual TCSs reveals that each TCS appears to be autonomous and self-sufficient to sense and respond to specific environmental cues, although some level of cross-regulation between non-cognate sensor-response regulator pairs occurs in vivo. This organization, if confirmed in other bacterial species, may provide a general evolutionarily mechani...
Journal of Bacteriology, 2010
Staphylococcus aureus uses the SaeRS two-component system to control the expression of many virulence factors such as alpha-hemolysin and coagulase; however, the molecular mechanism of this signaling has not yet been elucidated. Here, using the P1 promoter of the sae operon as a model target DNA, we demonstrated that the unphosphorylated response regulator SaeR does not bind to the P1 promoter DNA, while its C-terminal DNA binding domain alone does. The DNA binding activity of full-length SaeR could be restored by sensor kinase SaeS-induced phosphorylation. Phosphorylated SaeR is more resistant to digestion by trypsin, suggesting conformational changes. DNase I footprinting assays revealed that the SaeR protection region in the P1 promoter contains a direct repeat sequence (GTTAAN 6 GTTAA [where N is any nucleotide]). This sequence is critical to the binding of phosphorylated SaeR. Mutational changes in the repeat sequence greatly reduced both the in vitro binding of SaeR and the in vivo function of the P1 promoter. From these results, we concluded that SaeR recognizes the direct repeat sequence as a binding site and that binding requires phosphorylation by SaeS.
Cross-talk between Two Nucleotide-signaling Pathways in Staphylococcus aureus
Journal of Biological Chemistry, 2015
Background: Nucleotide-signaling pathways are complex systems that allow bacteria to rapidly respond to stress. Results: Cyclic diadenosine monophosphate is essential for the growth of S. aureus, and its signaling network is intricately interconnected with the stringent response. Conclusion: Cross-talk between different nucleotide-signaling networks is more common than previously anticipated. Significance: Bacteria have evolved intricate signaling networks to survive. Nucleotide-signaling pathways are found in all kingdoms of life and are utilized to coordinate a rapid response to external stimuli. The stringent response alarmones guanosine tetra-(ppGpp) and pentaphosphate (pppGpp) control a global response allowing cells to adapt to starvation conditions such as amino acid depletion. One more recently discovered signaling nucleotide is the secondary messenger cyclic diadenosine monophosphate (c-di-AMP). Here, we demonstrate that this signaling nucleotide is essential for the growth of Staphylococcus aureus, and its increased production during late growth phases indicates that c-di-AMP controls processes that are important for the survival of cells in stationary phase. By examining the transcriptional profile of cells with high levels of c-di-AMP, we reveal a significant overlap with a stringent response transcription signature. Examination of the intracellular nucleotide levels under stress conditions provides further evidence that high levels of c-di-AMP lead to an activation of the stringent response through a RelA/SpoT homologue (RSH) enzymedependent increase in the (p)ppGpp levels. This activation is shown to be indirect as c-di-AMP does not interact directly with the RSH protein. Our data extend this interconnection further by showing that the S. aureus c-di-AMP phosphodiesterase enzyme GdpP is inhibited in a dose-dependent manner by ppGpp, which itself is not a substrate for this enzyme. Altogether, these findings add a new layer of complexity to our understanding of nucleotide signaling in bacteria as they highlight intricate interconnections between different nucleotidesignaling networks. When faced with unfavorable environmental conditions, bacteria employ a variety of small nucleotide-signaling molecules that allow them to rapidly alter cellular physiology to promote survival. Under nutrient limiting conditions, the signaling nucleotide cyclic adenosine monophosphate (cAMP) controls the acquisition of alternative sugar sources (1), whereas the stringent response alarmones guanosine tetra-(ppGpp) 3 and pentaphosphate (pppGpp) control a transcriptional response allowing cells to adapt during stresses such as amino acid deprivation, carbon source starvation, fatty acid depletion, or osmotic stress (2-4). The stringent response is best characterized in Gram-negative bacteria, where (p)ppGpp is synthesized by the monofunctional enzyme RelA or the bifunctional enzyme SpoT, which also contains hydrolase activity (5). These nucleotides are then responsible for controlling a cellular switch resulting in the down-regulation of pathways involved in active growth and the up-regulation of genes involved in stress adaptation (6). For numerous bacterial species, it has been reported that (p)ppGpp is vital for controlling the transition of bacteria into stationary phase, biofilm formation, sporulation, virulence, antibiotic tolerance, and more recently bacterial persistence (7-10). This is also the case for the Gram-positive bacterial pathogen Staphylococcus aureus, where high levels of (p)ppGpp have been shown to affect the virulence of this organism by promoting the formation of persistent and chronic infections (11-14). In S. aureus, as well as other Gram-positive species, (p)ppGpp is synthesized in response to amino acid deprivation by RSH, a bifunctional RelA/SpoT homologue (RSH) that contains both a synthase and a hydrolase domain (15, 16). S. aureus also produces two other synthases, RelP and RelQ, both of which are monofunctional and transcription of the corresponding genes increases when cells are exposed to cell walltargeting antimicrobials (17). A more recently discovered signaling nucleotide is the secondary messenger cyclic diadenosine monophosphate (c-di-AMP), which is predominantly produced by Gram-positive