Nuclear Translocation of Soybean MPK6, GmMPK6, Is Mediated by Hydrogen Peroxide in Salt Stress

The plant mitogen-activated protein kinase (MPK) cascade, a highly conserved signal transduction system in eukaryotes, plays a crucial role in the plant’s response to environmental stimuli and phytohormones. It is well-known that nuclear translocation of MPKs is necessary for their activities in mammalian cells. However, the mechanism underlying nuclear translocation of plant MPKs is not well elucidated. In the previous study, it has been shown that soybean MPK6 (GmMPK6) is activated by phosphatidic acid (PA) and hydrogen peroxide (H2O2), which are two signaling molecules generated during salt stress. Using the two signaling molecules, we investigated how salt stress triggers its translocation to the nucleus. Our results show that the translocation of GmMPK6 to the nucleus is mediated by H2O2, but not by PA. Furthermore, the translocation was interrupted by diphenylene iodonium (DPI) (an inhibitor of RBOH), confirming that H2O2 is the signaling molecule for the nuclear translocation of GmMPK6 during salt stress.

Decreased ZO1 expression causes loss of time-dependent tight junction function in the liver of ob/ob mice

Diabetes patients are at a high risk of developing complications related to angiopathy and disruption of the signal transduction system. The liver is one of the multiple organs damaged during diabetes. Few studies have evaluated the morphological effects of adhesion factors in diabetic liver. The influence of diurnal variation has been observed in the expression and functioning of adhesion molecules to maintain tissue homeostasis associated with nutrient uptake. The present study demonstrated that the rhythm-influenced functioning of tight junction was impaired in the liver of ob/ob mice. The tight junctions of hepatocytes were loosened during the dark period in normal mice compared to those in ob/ob mice, where the hepatocyte gaps remained open throughout the day. The time-dependent expression of zonula occludens 1 (ZO1) in the liver plays a vital role in the functioning of the tight junction. The time-dependent expression of ZO1 was nullified and its expression was attenuated in the liver of ob/ob mice. ZO1 expression was inhibited at the mRNA and protein levels. The expression rhythm of ZO1 was found to be regulated by heat shock factor (HSF)1/2, the expression of which was reduced in the liver of ob/ob mice. The DNA-binding ability of HSF1/2 was decreased in the liver of ob/ob mice compared to that in normal mice. These findings suggest the involvement of impaired expression and functioning of adhesion factors in diabetic liver complications.

Multiple regulatory mechanisms control the production of CmrRST, an atypical signal transduction system in Clostridioides difficile

Clostridioides difficile, an intestinal pathogen and leading cause of nosocomial infection, exhibits extensive phenotypic heterogeneity through phase variation by site-specific recombination. The signal transduction system CmrRST, which encodes two response regulators (CmrR and CmrT) and a sensor kinase (CmrS), impacts C. difficile cell and colony morphology, surface and swimming motility, biofilm formation, and virulence in an animal model. CmrRST is subject to phase variation through site-specific recombination and reversible inversion of the ‘cmr switch’, and expression of cmrRST is also regulated by c-di-GMP through a riboswitch. The goal of this study was to determine how the cmr switch and c-di-GMP work together to regulate cmrRST expression. We generated “phase locked” strains by mutating key residues in the right inverted repeat flanking the cmr switch. Phenotypic characterization of these phase locked cmr-ON and -OFF strains demonstrates that they cannot switch between rough and smooth colony morphologies, respectively, or other CmrRST-associated phenotypes. Manipulation of c-di-GMP levels in these mutants showed that c-di-GMP promotes cmrRST expression and associated phenotypes independent of cmr switch orientation. We identified multiple promoters controlling cmrRST transcription, including one within the ON orientation of cmr switch and another that is positively autoregulated by CmrR. Overall, this work reveals a complex regulatory network that governs cmrRST expression and a unique intersection of phase variation and c-di-GMP signaling. These findings suggest that multiple environmental signals impact the production of this signaling transduction system.

An Intracellular Sensing and Signal Transduction System That Regulates the Metabolism of Polycyclic Aromatic Hydrocarbons in Bacteria

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed and have been found indoors, in the atmosphere, in terrestrial soils, in marine waters and sediments, and even in outer space. Bacteria may degrade PAHs via degradation pathways.

Evolutionary divergence of the Wsp signal transduction system in β- and γ-proteobacteria

Bacteria rapidly adapt to their environment by integrating external stimuli through diverse signal transduction systems. Pseudomonas aeruginosa , for example, senses surface-contact through the Wsp signal transduction system to trigger the production of cyclic di-GMP. Diverse mutations in wsp genes that manifest enhanced biofilm formation are frequently reported in clinical isolates of P. aeruginosa , and in biofilm studies of Pseudomonas spp. and Burkholderia cenocepacia . In contrast to the convergent phenotypes associated with comparable wsp mutations, we demonstrate that the Wsp system in B. cenocepacia does not impact intracellular cyclic di-GMP levels unlike that in Pseudomonas spp. Our current mechanistic understanding of the Wsp system is entirely based on the study of four Pseudomonas spp. and its phylogenetic distribution remains unknown. Here, we present a broad phylogenetic analysis to show that the Wsp system originated in the β-proteobacteria then horizontally transferred to Pseudomonas spp., the sole member of the γ-proteobacteria. Alignment of 794 independent Wsp systems with reported mutations from the literature identified key amino acid residues that fall within and outside annotated functional domains. Specific residues that are highly conserved but uniquely modified in B. cenocepacia likely define mechanistic differences among Wsp systems. We also find the greatest sequence variation in the extracellular sensory domain of WspA, indicating potential adaptations to diverse external stimuli beyond surface-contact sensing. This study emphasizes the need to better understand the breadth of functional diversity of the Wsp system as a major regulator of bacterial adaptation beyond B. cenocepacia and select Pseudomonas spp. Importance The Wsp signal transduction system serves as an important model system for studying how bacteria adapt to living in densely structured communities known as biofilms. Biofilms frequently cause chronic infections and environmental fouling, and they are very difficult to eradicate. In Pseudomonas aeruginosa , the Wsp system senses contact with a surface, which in turn activates specific genes that promote biofilm formation. We demonstrate that the Wsp system in Burkholderia cenocepacia regulates biofilm formation uniquely from that in Pseudomonas species. Furthermore, a broad phylogenetic analysis reveals the presence of the Wsp system in diverse bacterial species, and sequence analyses of 794 independent systems suggest that the core signaling components function similarly but with key differences that may alter what or how they sense. This study shows that Wsp systems are highly conserved and more broadly distributed than previously thought, and their unique differences likely reflect adaptations to distinct environments.

Evolutionary divergence of the Wsp signal transduction system in β- and γ-proteobacteria

Bacteria rapidly adapt to their environment by integrating external stimuli through diverse signal transduction systems. Pseudomonas aeruginosa, for example, senses surface-contact through the Wsp signal transduction system to trigger the production of cyclic di-GMP. Diverse mutations in wsp genes that manifest enhanced biofilm formation are frequently reported in clinical isolates of P. aeruginosa, and in biofilm studies of Pseudomonas spp. and Burkholderia cenocepacia. In contrast to the convergent phenotypes associated with comparable wsp mutations, we demonstrate that the Wsp system in B. cenocepacia does not impact intracellular cyclic di-GMP levels unlike that in Pseudomonas spp. Our current mechanistic understanding of the Wsp system is entirely based on the study of four Pseudomonas spp. and its phylogenetic distribution remains unknown. Here, we present the first broad phylogenetic analysis to date to show that the Wsp system originated in the β-proteobacteria then horizontally transferred to Pseudomonas spp., the sole member of the γ-proteobacteria. Alignment of 794 independent Wsp systems with reported mutations from the literature identified key amino acid residues that fall within and outside annotated functional domains. Specific residues that are highly conserved but uniquely modified in B. cenocepacia likely define mechanistic differences among Wsp systems. We also find the greatest sequence variation in the extracellular sensory domain of WspA, indicating potential adaptations to diverse external stimuli beyond surface-contact sensing. This study emphasizes the need to better understand the breadth of functional diversity of the Wsp system as a major regulator of bacterial adaptation beyond B. cenocepacia and select Pseudomonas spp.

Two-Component Signal Transduction System VraSR Contributes to Neuroinflammation in Streptococcus Suis Meningitis

Background: Streptococcus suis (S. suis) is an important zoonotic pathogen that can cause high morbidity and mortality in both humans and swine. As the most important life-threatening infection of the central nervous system (CNS), meningitis is an important symptom of S. suis infection. The VraSR is a critical two-component signal transduction system that affects S. suis ability to resist against host innate immune system and promotes the ability of S. suis to adhere to hBMEC. Whether and how VraSR contributes to the development of S. suis meningitis are currently unknown.Methods: The in vivo colonization, in vivo BBB permeability, histopathological examination and immunohistochemistry were applied to compare and characterize the degree of destruction of brain tissue in response to wild type SC19 and mutant ΔvraSR. Western blotting and real-time PCR were combined to identify the breakdown of tight junction proteins (TJ proteins). The secretion of proinflammatory cytokines and chemokines in the serum were detected on a BD FACSVerse flow cytometer.Results: We found an important role of VraSR regulatory system in S. suis SC19-induced meningitis. A mouse infection model demonstrated that ΔvraSR had significantly attenuated inflammatory lesions in the brain tissues compared with wild-type S. suis. In vitro, we characterized that SC19 could increase the blood-brain barrier (BBB) permeability through downregulating the TJ proteins compared with mutant ΔvraSR. Moreover, we found significant generation of proinflammatory cytokines and chemokines in the serum including IL-6, TNF-α, MCP-1, and IL-12p70 compared with ΔvraSR infected mice.Conclusions: For the first time, our work investigated the VraSR regulatory system of S. suis played an important role in streptococcal meningitis and revealed VraSR to be an important contributor to the disruption of TJ proteins. Characterization of these BBB disruption will facilitate further study of meningitis mechanisms in humans, thereby offering the development of novel preventative and therapeutic strategies against infection with S. suis.

Redox switching of an artificial transmembrane signal transduction system

An external redox signal delivered by ascorbic acid was used to trigger membrane translocation in a synthetic transduction system.