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Hyperosmotic Stress (hyperosmotic + stress)

Distribution by Scientific Domains

Life Sciences	90%

Selected Abstracts

Hyperosmotic Stress in Murine Hybridoma Cells: Effects on Antibody Transcription, Translation, Posttranslational Processing, and the Cell Cycle

BIOTECHNOLOGY PROGRESS, Issue 2 2004
Zhe Sun
Mechanisms for increased antibody production in batch cultures of murine hybridoma cells in response to hyperosmotic stress were investigated. The rates of immunoglobulin transcription and protein translation and posttranslational processing were determined in control and hyperosmotic cultures. Changes in immunoglobulin transcription played a minor role in the increase in antibody production in response to hyperosmotic stress. In contrast, protein translation increased substantially in response to osmotic stress. However, the antibody translation rate remained relatively constant after correcting for the overall increase in protein translation. Cell size and intracellular antibody pool also increased in response to hyperosmolarity. The intracellular antibody pool increased proportionately with the increase in cell size, indicating that hyperosmotic cultures do not selectively increase their intracellular antibody population. Changes in cell cycle distribution in response to osmotic stress and the relationship between the cell cycle and antibody production were also evaluated. Hyperosmotic stress altered the cell cycle distribution, increasing the fraction of the cells in S-phase. However, this change was uncorrelated with the increase in antibody production rate. Immunoglobulin degradation was relatively low (,15%) and remained largely unchanged in response to hyperosmotic stress. There was no apparent increase in immunoglobulin stability as a result of osmotic stress. Antibody secretion rates increased approximately 50% in response to osmotic stress, with a commensurate increase in the antibody assembly rate. The rate of transit through the entire posttranslational processing apparatus increased, particularly for immunoglobulin light chains. The levels of endoplasmic reticulum chaperones did not increase as a fraction of the total cellular protein but were increased on a per cell basis as the result of an increase in total cellular protein. A difference in the interactions between the immunoglobulin heavy chains and BiP/GRP78 was observed in response to hyperosmotic conditions. This change in interaction may be correlated with the decrease in transit time through the posttranslational pathways. The increase in the posttranslational processing rate appears to be commensurate with the increase in antibody production in response to hyperosmotic stress. [source]

Hyperosmotic stress induces Axl activation and cleavage in cerebral endothelial cells

JOURNAL OF NEUROCHEMISTRY, Issue 1 2008
Imola Wilhelm
Abstract Because of the relative impermeability of the blood-brain barrier (BBB), many drugs are unable to reach the CNS in therapeutically relevant concentration. One method to deliver drugs to the CNS is the osmotic opening of the BBB using mannitol. Hyperosmotic mannitol induces a strong phosphorylation on tyrosine residues in a broad spectrum of proteins in cerebral endothelial cells, the principal components of the BBB. Previously, we have shown that among targets of tyrosine phosphorylation are ,-catenin, extracellular signal-regulated kinase 1/2 and the non-receptor tyrosine kinase Src. The aim of this study was to identify new signalling pathways activated by hypertonicity in cerebral endothelial cells. Using an antibody array and immunoprecipitation we identified the receptor tyrosine kinase Axl to become tyrosine phosphorylated in response to hyperosmotic mannitol. Besides activation, Axl was also cleaved in response to osmotic stress. Degradation of Axl proved to be metalloproteinase- and proteasome-dependent and resulted in 50,55 kDa C-terminal products which remained phosphorylated even after degradation. Specific knockdown of Axl increased the rate of apoptosis in hyperosmotic mannitol-treated cells; therefore, we assume that activation of Axl may be a protective mechanism against hypertonicity-induced apoptosis. Our results identify Axl as an important element of osmotic stress-induced signalling. [source]

Hyperosmotic Stress in Murine Hybridoma Cells: Effects on Antibody Transcription, Translation, Posttranslational Processing, and the Cell Cycle

Ion transport and osmotic adjustment in Escherichia coli in response to ionic and non-ionic osmotica

ENVIRONMENTAL MICROBIOLOGY, Issue 1 2009
Lana Shabala
Summary Bacteria respond to osmotic stress by a substantial increase in the intracellular osmolality, adjusting their cell turgor for altered growth conditions. Using Escherichia coli as a model organism we demonstrate here that bacterial responses to hyperosmotic stress specifically depend on the nature of osmoticum used. We show that increasing acute hyperosmotic NaCl stress above ,1.0 Os kg,1 causes a dose-dependent K+ leak from the cell, resulting in a substantial decrease in cytosolic K+ content and a concurrent accumulation of Na+ in the cell. At the same time, isotonic sucrose or mannitol treatment (non-ionic osmotica) results in a gradual increase of the net K+ uptake. Ion flux data are consistent with growth experiments showing that bacterial growth is impaired by NaCl at the concentration resulting in a switch from net K+ uptake to efflux. Microarray experiments reveal that about 40% of upregulated genes shared no similarity in their responses to NaCl and sucrose treatment, further suggesting specificity of osmotic adjustment in E. coli to ionic and non-ionic osmotica. The observed differences are explained by the specificity of the stress-induced changes in the membrane potential of bacterial cells highlighting the importance of voltage-gated K+ transporters for bacterial adaptation to hyperosmotic stress. [source]

Hog1p mitogen-activated protein kinase determines acetic acid resistance in Saccharomyces cerevisiae

FEMS YEAST RESEARCH, Issue 8 2006
Mehdi Mollapour
Abstract When glucose-repressed, Saccharomyces cerevisiae cannot use acetic acid as a carbon source and is inhibited in growth by high levels of this compound, especially at low pH. Cultures exposed to a 100 mM acetate stress activate both the Hog1p and Slt2p stress-activated MAP kinases. Nevertheless, only active Hog1p, not Slt2p, is needed for the acquisition of acetate resistance. Hog1p undergoes more rapid activation by acetate in pH 4.5, than in pH 6.8 cultures, an indication that the acid may have to enter the cells in order to generate the Hog1p activatory signal. Acetate activation of Hog1p is absent in the ssk1, and pbs2, mutants, but is present in sho1, and ste11,, showing that it involves the Sln1p branch of the high-osmolarity glycerol (HOG) pathway signaling to Pbs2p. In low-pH (pH 4.5) cultures, the acetate-activated Hog1p, although conferring acetate resistance, does not generate the GPD1 gene or intracellular glycerol inductions that are hallmarks of activation of the HOG pathway by hyperosmotic stress. [source]

Fungicide activity through activation of a fungal signalling pathway

MOLECULAR MICROBIOLOGY, Issue 6 2004
Kaihei Kojima
Summary Fungicides generally inhibit enzymatic reactions involved in fungal cellular biosynthesis. Here we report, for the first time, an example of fungicidal effects through hyperactivation of a fungal signal transduction pathway. The OSC1 gene, encoding a MAP kinase (MAPK) related to yeast Hog1, was isolated from the fungal pathogen Colletotrichum lagenarium that causes cucumber anthracnose. The osc1 knockout mutants were sensitive to high osmotic stress and showed increased resistance to the fungicide fludioxonil, indicating that Osc1 is involved in responses to hyperosmotic stress and sensitivity to fludioxonil. The Osc1 MAPK is phosphorylated under high osmotic conditions, indicating activation of Osc1 by high osmotic stress. Importantly, fludioxonil treatment also activates phosphorylation of Osc1, suggesting that improper activation of Osc1 by fludioxonil has negative effects on fungal growth. In the presence of fludioxonil, the wild-type fungus was not able to infect the host plant because of a failure of appressorium-mediated penetration, whereas osc1 mutants successfully infected plants. Analysis using a OSC1- GFP fusion gene indicated that Osc1 is rapidly translocated to the nucleus in appressorial cells after the addition of fludioxonil, suggesting that fludioxonil impairs the function of infection structures by activation of Osc1. Furthermore, fludioxonil activates Hog1-type MAPKs in the plant pathogenic fungi Cochliobolus heterostrophus and Botrytis cinerea. These results strongly suggest that fludioxonil acts as a fungicide, in part, through activation of the MAPK cascade in fungal pathogens. [source]

Mitochondrial proline oxidation is affected by hyperosmotic stress in durum wheat seedlings

ANNALS OF APPLIED BIOLOGY, Issue 1 2010
M. Soccio
The important role of plant mitochondria in the adaptation to environmental stresses at subcellular level has recently emerged. In particular, an important mitochondrial mechanism involved in the resistance to environmental stresses is the inhibition of proline oxidation. In order to study this physiological mechanism, we used both washed and purified durum wheat (Triticum durum) mitochondria (DWM) isolated from early seedlings germinated in two different NaCl solutions leading to either moderate or severe damage to growth. To assess the contribution of the osmotic component of stress, a parallel investigation was performed using hyperosmotic mannitol solutions. Comparison of the oxygen uptake rate in the course of proline oxidation, with that of the malate plus glutamate substrate pair and that of succinate showed that an early inhibition of proline oxidation occurs under stress. The drop of the proline-dependent oxygen uptake rate was as a result of a heavy inhibition of proline dehydrogenase (ProDH); on the other hand, malate plus glutamate-dependent and succinate-dependent oxidations were less inhibited, being the maintenance of oxygen uptake rate not dependent on alternative oxidase (AOX) pathway; in fact, DWM-AOX activity did not show any increase under our experimental stress conditions. The selective inhibition of proline oxidation should be considered a mitochondrial adaptation to stress rather than damage to mitochondrial oxidative properties. This result was achieved by means of a novel approach based on the comparison between oxygen uptake rates of washed and purified organelles. [source]

Chondroprotective role of the osmotically sensitive ion channel transient receptor potential vanilloid 4: Age- and sex-dependent progression of osteoarthritis in Trpv4 -deficient mice

ARTHRITIS & RHEUMATISM, Issue 10 2010
Andrea L. Clark
Objective Mechanical loading significantly influences the physiology and pathology of articular cartilage, although the mechanisms of mechanical signal transduction are not fully understood. Transient receptor potential vanilloid 4 (TRPV4) is a Ca++ -permeable ion channel that is highly expressed by articular chondrocytes and can be gated by osmotic and mechanical stimuli. The goal of this study was to determine the role of Trpv4 in the structure of the mouse knee joint and to determine whether Trpv4,/, mice exhibit altered Ca++ signaling in response to osmotic challenge. Methods Knee joints of Trpv4,/, mice were examined histologically and by microfocal computed tomography for osteoarthritic changes and bone structure at ages 4, 6, 9, and 12 months. Fluorescence imaging was used to quantify chondrocytic Ca++ signaling within intact femoral cartilage in response to osmotic stimuli. Results Deletion of Trpv4 resulted in severe osteoarthritic changes, including cartilage fibrillation, eburnation, and loss of proteoglycans, that were dependent on age and male sex. Subchondral bone volume and calcified meniscal volume were greatly increased, again in male mice. Chondrocytes from Trpv4+/+ mice demonstrated significant Ca++ responses to hypo-osmotic stress but not to hyperosmotic stress. The response to hypo-osmotic stress or to the TRPV4 agonist 4,-phorbol 12,13-didecanoate was eliminated in Trpv4,/, mice. Conclusion Deletion of Trpv4 leads to a lack of osmotically induced Ca++ signaling in articular chondrocytes, accompanied by progressive, sex-dependent increases in bone density and osteoarthritic joint degeneration. These findings suggest a critical role for TRPV4-mediated Ca++ signaling in the maintenance of joint health and normal skeletal structure. [source]

Hyperosmotic Stress in Murine Hybridoma Cells: Effects on Antibody Transcription, Translation, Posttranslational Processing, and the Cell Cycle

Two mitogen-activated protein kinase signalling cascades mediate basal resistance to antifungal plant defensins in Fusarium graminearum

CELLULAR MICROBIOLOGY, Issue 6 2007
Vellaisamy Ramamoorthy
Summary Antifungal defensins, MsDef1 and MtDef4, from Medicago spp., inhibit the growth of Fusarium graminearum, which causes head blight disease in cereals. In order to determine the signalling cascades that are modulated by these defensins, we have isolated several insertional mutants of F. graminearum that exhibit hypersensitivity to MsDef1, but not to MtDef4. The molecular characterization of two of these mutants, designated enhanced sensitivity to defensin (esd), has revealed that the Mgv1 and Gpmk1 MAP kinase signalling cascades play a major role in regulating sensitivity of F. graminearum to MsDef1, but not to MtDef4. The Hog1 MAP kinase signalling cascade, which is responsible for adaptation of this fungus to hyperosmotic stress, does not participate in the fungal response to these defensins. Significantly, the esd mutants also exhibit hypersensitivity to other tested defensins and are highly compromised in their pathogenesis on wheat heads and tomato fruits. The studies reported here for the first time implicate two MAP kinase signalling cascades in a plant defensin-mediated alteration of fungal growth. Based on our findings, we propose that specific MAP kinase signalling cascades are essential for protection of a fungal pathogen from the antimicrobial proteins of its host plant. [source]