ups1, an Arabidopsis thaliana camalexin accumulation mutant defective in multiple defence signalling pathways

We report the characterization of an Arabidopsis thaliana mutant, ups1, isolated on the basis of reduced expression of phosphoribosylanthranilate transferase, a tryptophan biosynthetic enzyme. ups1 also exhibits defects in a wide range of defence responses. After infection with Pseudomonas syringae or Botrytis cinerea, the expression of genes regulated by both the salicylic acid and jasmonic acid/ethylene pathways is reduced in ups1 compared with wild type. Camalexin accumulation in ups1 is greatly reduced after infection with these two pathogens, as well as after amino acid starvation or oxidative stress. Reactive oxygen species (ROS)-mediated gene expression is also compromised in ups1 indicating that this mutant is defective in signalling pathways activated in response to both biotic and abiotic stress. The fact that all three major defence signalling pathways are disrupted in ups1, together with the oxidative stress phenotype, leads us to suggest that UPS1 is involved in ROS signal transduction.     

Cytokinin action in response to abiotic and biotic stresses in plants

The phytohormone cytokinin was originally discovered as a regulator of cell division. Later, it was described to be involved in regulating numerous processes in plant growth and development including meristem activity, tissue patterning, and organ size. More recently, diverse functions for cytokinin in the response to abiotic and biotic stresses have been reported. Cytokinin is required for the defence against high light stress and to protect plants from a novel type of abiotic stress caused by an altered photoperiod. Additionally, cytokinin has a role in the response to temperature, drought, osmotic, salt, and nutrient stress. Similarly, the full response to certain plant pathogens and herbivores requires a functional cytokinin signalling pathway. Conversely, different types of stress impact cytokinin homeostasis. The diverse functions of cytokinin in responses to stress and crosstalk with other hormones are described. Its emerging roles as a priming agent and as a regulator of growth‐defence trade‐offs are discussed.     

Hyperosmosis enhances radiation and hydroxyurea resistance of Schizosaccharomyces pombe checkpoint mutants through the spindle checkpoint and delayed cytokinesis

The DNA damage and stress response pathways interact to regulate cellular responses to genotoxins and environmental stresses. How these pathways interact in Schizosaccharomyces pombe is not well understood. We demonstrate that osmotic stress suppresses the DNA damage sensitivity of checkpoint mutants, and that this occurs through three distinct cell cycle delays. A delay in G2/M is dependent on Srk1. Progression through mitosis is halted by the Mad2‐dependent spindle checkpoint. Finally, cytokinesis is impaired by modulating Cdc25 expression. These three delays, imposed by osmotic stress, together compensate for the loss of checkpoint signalling.     

Gene correlation networks reveal the transcriptomic response to elevated nitrogen in a photosynthetic sponge

Nutrient levels in coastal environments have been increasing globally due to elevated inputs of sewage and terrigenous sediments carrying fertilizers. Yet, despite their immense filtering capacities, marine sponges appear to be less affected by elevated nutrients than sympatric benthic organisms, such as corals. While the molecular‐level stress response of sponges to elevated seawater temperatures and other toxicants has been defined, this study represents the first global gene expression analysis of how sponges respond to elevated nitrogen. Gene correlation network analysis revealed that sponge gene modules, coded by colours, became either highly upregulated (Blue) or downregulated (Turquoise, Black, Brown) as nitrogen treatment levels increased. Gene Ontology enrichment analysis of the different modules revealed genes involved in cell signalling, immune response and flagella motility were affected by increasing nitrogen levels. Notably, a decrease in the regulation of NF‐kappaB signalling and an increase in protein degradation was identified, which is comparable to metabolic pathways associated with the sponge thermal stress response. These results highlight that Cymbastela stipitata can rapidly respond to changes in the external environment and identifies pathways that probably contribute to the ability of C. stipitata to tolerate short‐term nutrient pulses.     

Functional analysis of endo‐1,4‐β‐glucanases in response to Botrytis cinerea and Pseudomonas syringae reveals their involvement in plant–pathogen interactions

Plant cell wall modification is a critical component in stress responses. Endo‐1,4‐β‐glucanases (EGs) take part in cell wall editing processes, e.g. elongation, ripening and abscission. Here we studied the infection response of Solanum lycopersicum and Arabidopsis thaliana with impaired EGs. Transgenic TomCel1 and TomCel2 tomato antisense plants challenged with Pseudomonas syringae showed higher susceptibility, callose priming and increased jasmonic acid pathway marker gene expression. These two EGs could be resistance factors and may act as negative regulators of callose deposition, probably by interfering with the defence‐signalling network. A study of a set of Arabidopsis EG T‐DNA insertion mutants challenged with P. syringae and Botrytis cinerea revealed that the lack of other EGs interferes with infection phenotype, callose deposition, expression of signalling pathway marker genes and hormonal balance. We conclude that a lack of EGs could alter plant response to pathogens by modifying the properties of the cell wall and/or interfering with signalling pathways, contributing to generate the appropriate signalling outcomes. Analysis of microarray data demonstrates that EGs are differentially expressed upon many different plant–pathogen challenges, hormone treatments and many abiotic stresses. We found some Arabidopsis EG mutants with increased tolerance to osmotic and salt stress. Our results show that impairing EGs can alter plant–pathogen interactions and may contribute to appropriate signalling outcomes in many different biotic and abiotic plant stress responses.     

Signal transduction pathways through cytoprotective, apoptotic and hypertrophic stimuli: a comparative study in adult cardiac myocytes

In response to pathophysiological stresses, cardiac myocytes undergo hypertrophic growth or apoptosis. Multiple signalling pathways have been implicated in these responses and among them, kinases such as mitogen‐activated protein kinases (MAPKs) and Akt. However, the distinction between signalling pathways originally believed to be specific for either hypertrophy, apoptosis or cell survival is fading. The existing data, coming from different experimental systems, often are conflicting. In this study, we sought to compare aspects of intracellular signalling activated by diverse stimuli in a single experimental system, adult rat cardiac myocytes. Furthermore, we assessed the role of these stimuli in eliciting a particular cell phenotype, i.e. whether they promote hypertrophy, cell survival or apoptosis. The results demonstrate that the hypertrophic agonist phenylephrine is the most potent activator of MAPKs/mitogen and stress‐ activated kinase MSK1, although its effect on Akt phosphorylation is relatively minor. The pro‐apoptotic concentration of H₂O₂ activates strongly both MAPKs and PI3K/Akt pathways. Insulin‐like growth factor‐1 has a minimal effect on phosphorylation of MAPKs/MSK1, but it is a potent activator of Akt. In conclusion, hypertrophic, pro‐survival or apoptotic stimuli operate through the same signalling pathways with different time course and amplitude of kinase activation. Thus, to determine the effect of different stimuli on cell fate, it is important to assess signalling pathways as a network and not as a single pathway. Copyright © 2011 John Wiley & Sons, Ltd.     

The stressed synovium

This review focuses on the mechanisms of stress response in the synovial tissue of rheumatoid arthritis. The major stress factors, such as heat stress, shear stress, proinflammatory cytokines and oxidative stress, are discussed and reviewed, focusing on their potential to induce a stress response in the synovial tissue. Several pathways of stress signalling molecules are found to be activated in the synovial membrane of rheumatoid arthritis; of these the most important examples are heat shock proteins, mitogen-activated protein kinases, stress-activated protein kinases and molecules involved in the oxidative stress pathways. The expression of these pathways in vitro and in vivo as well as the consequences of stress signalling in the rheumatoid synovium are discussed. Stress signalling is part of a cellular response to potentially harmful stimuli and thus is essentially involved in the process of synovitis. Stress signalling pathways are therefore new and promising targets of future anti-rheumatic therapies.     

REDD1, an inhibitor of mTOR signalling,is regulated by the CUL4A–DDB1 ubiquitin ligase

The cellular response to hypoxia involves several signalling pathways that mediate adaptation and survival. REDD1 (regulated in development and DNA damage responses 1), a hypoxia‐inducible factor‐1 target gene, has a crucial role in inhibiting mammalian target of rapamycin complex 1 (mTORC1) signalling during hypoxic stress. However, little is known about the signalling pathways and post‐translational modifications that regulate REDD1 function. Here, we show that REDD1 is subject to ubiquitin‐mediated degradation mediated by the CUL4A–DDB1–ROC1–β‐TRCP E3 ligase complex and through the activity of glycogen synthase kinase 3β. Furthermore, REDD1 degradation is crucially required for the restoration of mTOR signalling as cells recover from hypoxic stress. Our findings define a mechanism underlying REDD1 degradation and its importance for regulating mTOR signalling.     

Autoantibody systems in rheumatoid arthritis: specificity, sensitivity and diagnostic value

This review focuses on the mechanisms of stress response in the synovial tissue of rheumatoid arthritis. The major stress factors, such as heat stress, shear stress, proinflammatory cytokines and oxidative stress, are discussed and reviewed, focusing on their potential to induce a stress response in the synovial tissue. Several pathways of stress signalling molecules are found to be activated in the synovial membrane of rheumatoid arthritis; of these the most important examples are heat shock proteins, mitogen-activated protein kinases, stress-activated protein kinases and molecules involved in the oxidative stress pathways. The expression of these pathways in vitro and in vivo as well as the consequences of stress signalling in the rheumatoid synovium are discussed. Stress signalling is part of a cellular response to potentially harmful stimuli and thus is essentially involved in the process of synovitis. Stress signalling pathways are therefore new and promising targets of future anti-rheumatic therapies.     

Signalling mucin Msb2 Regulates adaptation to thermal stress in Candida albicans

Temperature is a potent inducer of fungal dimorphism. Multiple signalling pathways control the response to growth at high temperature, but the sensors that regulate these pathways are poorly defined. We show here that the signalling mucin Msb2 is a global regulator of temperature stress in the fungal pathogen Candida albicans. Msb2 was required for survival and hyphae formation at 42°C. The cytoplasmic signalling domain of Msb2 regulated temperature‐dependent activation of the CEK mitogen activated proteins kinase (MAPK) pathway. The extracellular glycosylated domain of Msb2 (100‐900 amino acid residues) had a new and unexpected role in regulating the protein kinase C (PKC) pathway. Msb2 also regulated temperature‐dependent induction of genes encoding regulators and targets of the unfolded protein response (UPR), which is a protein quality control (QC) pathway in the endoplasmic reticulum that controls protein folding/degradation in response to high temperature and other stresses. The heat shock protein and cell wall component Ssa1 was also required for hyphae formation and survival at 42°C and regulated the CEK and PKC pathways.     

Lipid peroxidation and apoptotic response in rat brain areas induced by long‐term administration of nandrolone: the mutual crosstalk between ROS and NF‐kB

The aim of this study was to evaluate the played by oxidative stress in the apoptotic response in different brain areas of rats chronically treated with supra‐physiological doses of nandrolone decanoate (ND). Immunohistochemical study and Western blot analysis were performed to evaluate cells' apoptosis and to measure the effects of expression of specific mediators, such as NF‐κB (nuclear factor kappa‐light‐chain‐enhancer of activated B cells), Bcl‐2 (B‐cell lymphoma 2), SMAC/DIABLO (second mitochondria‐derived activator of caspases/direct IAP‐binding protein with low PI) and VMAT2 (vesicular monoamine transporter 2) on apoptosis. The results of the present study indicate that a long‐term administration of ND promotes oxidative injury in rat brain specific areas. A link between oxidative stress and NF‐κB signalling pathways is supported by our results. In addition to high levels of oxidative stress, we consistently observed a strong immunopositivity to NF‐κB. It has been argued that one of the pathways leading to the activation of NF‐κB could be under reactive oxygen species (ROS)‐mediated control. In fact, growing evidence suggests that although in limited doses, endogenous ROS may play an activating role in NF‐κB signalling, while above a certain threshold, they may negatively impact upon this signalling. However, a mutual crosstalk between ROS and NF‐κB exists and recent studies have shown that ROS activity is subject to negative feedback regulation by NF‐κB, and that this negative regulation of ROS is the means through which NF‐κB counters programmed cells.     

bFGF attenuates endoplasmic reticulum stress and mitochondrial injury on myocardial ischaemia/reperfusion via activation of PI3K/Akt/ERK1/2 pathway

Extensive research focused on finding effective strategies to prevent or improve recovery from myocardial ischaemia/reperfusion (I/R) injury. Basic fibroblast growth factor (bFGF) has been shown to have therapeutic potential in some heart disorders, including ischaemic injury. In this study, we demonstrate that bFGF administration can inhibit the endoplasmic reticulum (ER) stress and mitochondrial dysfunction induced in the heart in a mouse model of I/R injury. In vitro, bFGF exerts a protective effect by inhibiting the ER stress response and mitochondrial dysfunction proteins that are induced by tert‐Butyl hydroperoxide (TBHP) treatment. Both of these in vivo and in vitro effects are related to the activation of two downstream signalling pathways, PI3K/Akt and ERK1/2. Inhibition of these PI3K/Akt and ERK1/2 pathways by specific inhibitors, LY294002 and PD98059, partially reduces the protective effect of bFGF. Taken together, our results indicate that the cardioprotective role of bFGF involves the suppression of ER stress and mitochondrial dysfunction in ischaemic oxidative damage models and oxidative stress‐induced H9C2 cell injury; furthermore, these effects underlie the activation of the PI3K/Akt and ERK1/2 signalling pathways.     

The effects of extracellular adenosine 5′‐triphosphate on the tobacco proteome

Extracellular adenosine 5′‐triphosphate (eATP) is emerging as an important plant signalling compound capable of mobilising intracellular second messengers such as Ca²⁺, nitric oxide, and reactive oxygen species. However, the downstream molecular targets and the spectrum of physiological processes that eATP regulates are largely unknown. We used exogenous ATP and a non‐hydrolysable analogue as probes to identify the molecular and physiological effects of eATP‐mediated signalling in tobacco. 2‐DE coupled with MS/MS analysis revealed differential protein expression in response to perturbation of eATP signalling. These proteins are in several functional classes that included photosynthesis, mitochondrial ATP synthesis, and defence against oxidative stress, but the biggest response was in the pathogen defence‐related proteins. Consistent with this, impairment of eATP signalling induced resistance against the bacterial pathogen Erwinia carotovora subsp. carotovora. In addition, disease resistance activated by a fungal pathogen elicitor (xylanase from Trichoderma viride) was concomitant with eATP depletion. These results reveal several previously unknown putative molecular targets of eATP signalling, which pinpoint eATP as an important hub at which regulatory signals of some major primary metabolic pathways and defence responses are integrated.     

Regulation of chronological aging in Schizosaccharomyces pombe by the protein kinases Pka1 and Sck2

Budding yeast shows a progressive decline in viability after entering stationary phase, a phenomenon known as chronological aging. We show here that the fission yeast Schizosaccharomyces pombe also undergoes chronological aging and that the process is regulated by genes controlling two related nutrient signalling pathways. The first pathway includes the serine/threonine cAMP-activated protein kinase Pka1 and the second pathway comprises the serine/threonine kinase Sck2, a homologue of Saccharomyces cerevisiae SCH9. A double mutant for pka1 and sck2 displayed an additive effect on prolonging the fission yeast lifespan, suggesting that these genes regulate related but independent pathways. These long-lived mutants also accumulated less reactive oxygen species and had a delayed initiation of apoptosis compared with wild-type cells. We also found that strains carrying pka1 deletion but not those with sck2 deletion gained resistance to oxidative stress due to exposure to H(2)O(2) or menadione. On the other hand, the additional increase in lifespan shown by the Deltapka1Deltasck2 double-mutant strain correlated with an increased resistance to both oxidative stress and heat shock. These results underscore the importance of nutrient signalling pathways and reactive oxygen species on organismal lifespan and establish S. pombe as a new model organism to study the molecular mechanisms underlying aging.