Thrombin potently enhances swelling-sensitive glutamate efflux from cultured astrocytes

High concentrations of thrombin (Thr) have been linked to neuronal damage in cerebral ischemia and traumatic brain injury. In the present study we found that Thr markedly enhanced swelling-activated efflux of (3)H-glutamate from cultured astrocytes exposed to hyposmotic medium. Thr (0.5-5 U/mL) elicited small (3)H-glutamate efflux under isosmotic conditions and increased the hyposmotic glutamate efflux by 5- to 10-fold, the maximum effect being observed at 15% osmolarity reduction. These Thr effects involve its protease activity and are fully mimicked by SFFLRN, the synthetic peptide activating protease-activated receptor-1. Thr potentiation of (3)H-glutamate efflux was largely dependent on a Thr-elicited increases in cytosolic Ca(2+) (Ca(2+) (i)) concentration ([Ca(2+)](i)). Preventing Ca(2+) (i) rise by treatment with EGTA-AM or with the phospholipase C blocker U73122 reduced the Thr-increased glutamate efflux by 68%. The protein kinase C blockers Go6976 or chelerythrine reduced the Thr effect by 19%-22%, while Ca/calmodulin blocker W7 caused a 63% inhibition. In addition to this Ca(2+)-sensitive pathway, Thr effect on glutamate efflux also involved activation of phosphoinositide-3 kinase (PI3K), since it was reduced by the PI3K inhibitor wortmannin (51% inhibition). Treating cells with EGTA-AM plus wortmannin essentially abolished Thr-dependent glutamate efflux. Thr-activated glutamate release was potently inhibited by the blockers of the volume-sensitive anion permeability pathway, NPPB (IC(50) 15.8 microM), DCPIB (IC(50) 4.2 microM), and tamoxifen (IC(50) 6.6 microM. These results suggest that Thr may contribute to the excitotoxic neuronal injury by elevating extracellular glutamate release from glial cells. Therefore, this work may aid in search of neuroprotective strategies for treating cerebral ischemia and brain trauma.

Swelling-Activated K+ Efflux and Regulatory Volume Decrease Efficiency in Human Bronchial Epithelial Cells

This study describes the correlation between cell swelling-induced K+ efflux and volume regulation efficiency evaluated with agents known to modulate ion channel activity and/or intracellular signaling processes in a human bronchial epithelial cell line, 16HBE14o(-1). Cells on permeable filter supports, differentiated into polarized monolayers, were monitored continuously at room temperature for changes in cell height (T(c)), as an index of cell volume, whereas (86)Rb efflux was assessed for K+ channel activity. The sudden reduction in osmolality of both the apical and basolateral perfusates (from 290 to 170 mosmol/kg H(2)O) evoked a rapid increase in cell volume by 35%. Subsequently, the regulatory volume decrease (RVD) restored cell volume almost completely (to 94% of the isosmotic value). The basolateral (86)Rb efflux markedly increased during the hyposmotic shock, from 0.50 +/- 0.03 min(-1) to a peak value of 6.32 +/- 0.07 min(-1), while apical (86)Rb efflux was negligible. Channel blockers, such as GdCl(3) (0.5 mM), quinine (0.5 mM) and 5-nitro-2-(3-phenyl-propylamino) benzoic acid (NPPB, 100 microM), abolished the RVD. The protein tyrosine kinase inhibitors tyrphostin 23 (100 microM) and genistein (150 microM) attenuated the RVD. All agents decreased variably the hyposmosis-induced elevation in (86)Rb efflux, whereas NPPB induced a complete block, suggesting a link between basolateral K(+) and Cl(-1) efflux. Forskolin-mediated activation of adenylyl cyclase stimulated the RVD with a concomitant increase in basolateral (86)Rb efflux. These data suggest that the basolateral extrusion of K+ and Cl(-1) from 16HBE14o(-1) cells in response to cell swelling determines RVD efficiency.

The accumulation and synthesis of betaine in winter skate (Leucoraja ocellata)

The present study investigated aspects of betaine metabolism in an elasmobranch fish, the winter skate (Leucoraja ocellata). Based on the level of choline dehydrogenase (ChoDH) activity, the liver and kidney appear to be the major sites of betaine synthesis and the mitochondrial localization of ChoDH and betaine aldehyde dehydrogenase (BADH) indicates that the metabolic organization of betaine synthesis in winter skate is similar to other vertebrates. Food deprivation did not affect white muscle betaine content, and prolonged starvation (70 days) appeared to decrease the total hepatic betaine synthetic capacity. There was no decrease in ChoDH or BADH activity at the mitochondrial level with starvation, suggesting any decrease is due to catabolism of hepatic reserves rather than downregulation of betaine synthesis. Skates fed a high betaine diet (frozen squid approximately 55 micromol g(-1)) had elevated white muscle betaine content compared to those fed a low betaine diet (frozen herring <2 micromol g(-1)); however, high dietary betaine intake did not affect the activity of betaine synthesizing enzymes in liver. Acclimation to elevated salinity (120 and 130% seawater) did not result in an increase in white muscle betaine content. Taken as a whole, the present data suggest that diet is a major determinant of muscle betaine in the winter skate and that betaine is of marginal importance as an intracellular osmolyte in this species.

Induction of the galanin-like peptide gene expression in the posterior pituitary gland after acute osmotic stimulus in rats

Galanin-like peptide (GALP) is a 60 amino-acid peptide, and the GALP mRNA is restricted to pituicytes in the posterior pituitary gland (PP) and neurons in the hypothalamic arcuate nucleus (Arc). We examined whether the GALP gene expression in the PP and Arc would be induced after intraperitoneal (i.p.) administration of hypertonic saline, that is, acute osmotic stimulus, in rats. The dose-response (2.8, 4.5, 6.0 and 9.0% NaCl) and time-course (6.0% NaCl, 1, 3, 6, 12 and 24h) effects of acute osmotic stimulus on GALP mRNA levels in the PP and Arc were examined in rats by using in situ hybridization histochemistry. Plasma osmolality and plasma sodium concentration increased significantly at 1h, and returned to control level at 6h after i.p. administration of hypertonic saline (6.0% NaCl). The GALP mRNA level in the PP increased significantly 3 and 6h after i.p. administration of hypertonic saline (6.0% NaCl), but the level in the Arc did not change. These results showed that acute osmotic stimulus-induced GALP gene expression in the pituicyte of the PP, but not in the neurons in the Arc, and the gene expression in the pituicyte might be regulated by plasma osmolality and/or plasma sodium concentration.

Calcium and cytoskeleton signaling during cell volume regulation in isolated nematocytes of Aiptasia mutabilis (Cnidaria: Anthozoa)

Cell volume regulation has not been completely clarified in Coelenterates. The present investigation focuses on cell volume regulation under anisosmotic conditions, both hyposmotic and hypertonic, and on the underlying signals in nematocytes isolated from the Coelenterate Aiptasia mutabilis living in sea water. Nematocytes, once isolated from acontia, that were submitted to either hyposmotic (35%) and hypertonic shock (45%) show RVD and RVI capabilities, respectively. In order to ascertain the role of Ca2+ in triggering such regulatory mechanisms and the possible involvement of cytoskeleton components, tests were performed by employing either Ca2+ free conditions, Gd3+ as Ca2+ channel blockers, TFP as calmodulin inhibitor, colchicine as microtubule inhibitor and cytochalasin B as microfilament polymerization inhibitor. Results show that isolated nematocytes of A. mutabilis can regulate their volume upon both hyposmotic and hypertonic challenge. Ca2+ both from external medium and from internal stores is needed to perform RVD mechanisms, whereas, intracellular Ca2+ seems to be mainly involved in RVI. Moreover cytoskeletal components may play an important role since a significant RVD and RVI inhibition was observed in treated cells. On the basis of our observations further studies are warranted to further verify the role of signals, including phosphatases and phosphorylases, in cell volume regulation of primitive eukaryotic cells.

Kinetics of pore formation by the Bacillus thuringiensis toxin Cry1Ac

After binding to specific receptors, Cry toxins form pores in the midgut apical membrane of susceptible insects. The receptors could form part of the pore structure or simply catalyze pore formation and consequently be recycled. To discriminate between these possibilities, the kinetics of pore formation in brush border membrane vesicles isolated from Manduca sexta was studied with an osmotic swelling assay. Pore formation, as deduced from changes in membrane permeability induced by Cry1Ac during a 60-min incubation period, was strongly dose-dependent, but rapidly reached a maximum as toxin concentration was increased. Following exposure of the vesicles to the toxin, the osmotic swelling rate reached a maximum shortly after a delay period. Under these conditions, at relatively high toxin concentrations, the maximal osmotic swelling rate increased linearly with toxin concentration. When vesicles were incubated for a short time with the toxin and then rapidly cooled to prevent the formation of new pores before and during the osmotic swelling experiment, a plateau in the rate of pore formation was observed as toxin concentration was increased. Taken together, these results suggest that the receptors do not act as simple catalysts of pore formation, but remain associated with the pores once they are formed.

Stable Agrobacterium-mediated genetic transformation of London plane tree (Platanus acerifolia Willd.)

London plane tree (Platanus acerifolia Willd.) is an important tree in urban landscaping but it suffers from a number of negative traits which genetic engineering could be used to address. As with many woody species, P. acerifolia has appeared recalcitrant to genetic transformation. However, the recent development of a method for regenerating shoots from P. acerifolia leaf explants suggests that such material could be a target for gene-transfer. Using an Agrobacterium tumefaciens strain in which the T-DNA carries the histochemically detected reporter gene beta-glucuronidase (GUS), we have followed the transfer of genes from Agrobacterium to leaf explants of Platanus acerifolia. Using this system, we have identified a set of inoculation and co-cultivation conditions (notably: the pre-treatment of leaf explants with 0.4 M mannitol, an inoculation period of 10 min, a bacterial OD(600) of 0.8-1.0 and a co-cultivation period of 5 days) that permit a good frequency and reliability of transient gene-transfer. Optimum levels of antibiotics for bacterial elimination and kanamycin-resistant shoot regeneration were also established. By applying these parameters, we recovered eight independent stably transformed shoots that were kanamycin-resistant and contained the nptII T-DNA gene, as confirmed by PCR analysis. Furthermore, Southern blot analysis confirmed that, in at least five of these lines, the transgene was associated with high molecular weight DNA, so indicating integration into the plant genome.

Stable Agrobacterium-mediated genetic transformation of London plane tree (Platanus acerifolia Willd.)

London plane tree (Platanus acerifolia Willd.) is an important tree in urban landscaping but it suffers from a number of negative traits which genetic engineering could be used to address. As with many woody species, P. acerifolia has appeared recalcitrant to genetic transformation. However, the recent development of a method for regenerating shoots from P. acerifolia leaf explants suggests that such material could be a target for gene-transfer. Using an Agrobacterium tumefaciens strain in which the T-DNA carries the histochemically detected reporter gene beta-glucuronidase (GUS), we have followed the transfer of genes from Agrobacterium to leaf explants of Platanus acerifolia. Using this system, we have identified a set of inoculation and co-cultivation conditions (notably: the pre-treatment of leaf explants with 0.4 M mannitol, an inoculation period of 10 min, a bacterial OD(600) of 0.8-1.0 and a co-cultivation period of 5 days) that permit a good frequency and reliability of transient gene-transfer. Optimum levels of antibiotics for bacterial elimination and kanamycin-resistant shoot regeneration were also established. By applying these parameters, we recovered eight independent stably transformed shoots that were kanamycin-resistant and contained the nptII T-DNA gene, as confirmed by PCR analysis. Furthermore, Southern blot analysis confirmed that, in at least five of these lines, the transgene was associated with high molecular weight DNA, so indicating integration into the plant genome.

An integrated analysis of the effects of Esculentin 1-21 on Saccharomyces cerevisiae

The antimicrobial peptide esculentin 1-21 (Esc 1-21) is a shorter synthetic version of the 46-residue peptide occurring in the Rana esculenta skin secretion. Here we propose an integrated proteomic and transcriptomic approach to interpret the biological effects of this peptide on Saccharomyces cerevisiae. We further investigated the response to this peptide by correlating the results of the transcriptome and proteome analysis with phenotypic effects. The results show that S. cerevisiae adapts to Esc 1-21 using the High Osmolarity Glycerol (HOG) pathway involved in osmotic tolerance and cell wall maintenance. Comparative proteomics reveals that Esc 1-21 causes downregulation of enzymes of the lower glycolytic pathway and in genes involved in spindle body formation and remodelling of cell-wall synthesis. Moreover the peptide induces downexpression of protein actin within 45 min and cells pre-treated with peptide show less sensitivity to osmotic stress and increased sensitivity to heat shock stress. The results obtained with the two different methodologies are in agreement at the cellular process levels. A combined approach may help elucidate the main aspects related to the effects of this peptide on the eukaryotic cell. The employment of different technologies may reveal the potential and limitations of each adapted approach in a prospective application for drug screening.

Preferential Phosphorylation of Focal Adhesion Kinase Tyrosine 861 Is Critical for Mediating an Anti-apoptotic Response to Hyperosmotic Stress

The results presented here demonstrate that focal adhesion kinase (FAK) Tyr-861 is the predominant tyrosine phosphorylation site stimulated by hyperosmotic stress in a variety of cell types, including epithelial cell lines (ileum-derived IEC-18, colon-derived Caco2, and stomach-derived NCI-N87), FAK null fibroblasts re-expressing FAK, and Src family kinase triple null fibroblasts (SYF cells) in which c-Src has been restored (YF cells). We show that hyperosmotic stress-stimulated FAK phosphorylation in epithelial cells is inhibited by Src family kinase inhibitors PP2 and SU6656 and that it does not occur in SYF cells. Unexpectedly, hyperosmotic stress-induced phosphorylation of FAK at Tyr-397, Tyr-576, and most dramatically at Tyr-861 was completely insensitive to the F-actin-disrupting agents, latrunculin A and cytochalasin D. Finally, we show that in FAK null cells exposed to hyperosmotic stress or growth factor withdrawal, re-expression of wild type FAK restored cell survival, whereas re-expression of FAK mutated from tyrosine to phenylalanine at position 861 (FAKY861F) did not. Our results indicate that FAK Tyr-861 phosphorylation is required for mammalian cell survival of hyperosmotic stress. Furthermore, the results suggest that FAK is an upstream regulator (rather than downstream effector) of F-actin reorganization in response to hyperosmotic stress. We propose that FAK/c-Src bipartite enzyme is a sensor of cytoplasmic shrinkage, and that the phosphorylation on FAK Tyr-861 by Src and subsequent reorganization of F-actin can initiate an anti-apoptotic signaling pathway that protects cells from hyperosmotic stress.

[Effects of salt stress on the contents of chlorophyll and organic solutes in Aeluropus littoralis var. sinensis Debeaux]

After seedlings of Aeluropus sinensis var. sinensis Debeaux were treated with different NaCl concentrations (0-200 mmol/L) for 14 days, some physiological indexes were measured. The higher the NaCl concentration, the more the growth of A. sinensis was inhibited. The increase in root/shoot ratio suggests that the shoots are more sensitive to salinity than the roots. The diminished leaf area may reduce the transpiration rate, and the root mainly grew longitudinally, which may help the root to reach the water source under the high salinity conditions. Chl a contents increased, so did Chl b, but the Chl a/Chl b ratio declined, which implies the stimulation of Chl a accepted from NaCl is smaller than that of Chl b. After salt treatment, the organic solute contents increased (P<0.05), the proline, amino acids and soluble sugar contents increased more than organic acids, the increase in soluble carbohydrate may inhibit photosynthesis in feedback. The percentage of sucrose in soluble carbohydrates increased too. Although the organic dry weight of whole plant declined, the proportion of organic dry weight in total dry weight increased, and the osmotic potential of plant cell juice declined, which implies that the contribution of organic matter to osmotic adjustment increased with salinity. That is, A. sinensis had ability to tolerate salinity to a certain degree.

Polyamines and abiotic stress: recent advances

In this review we will concentrate in the results published the last years regarding the involvement of polyamines in the plant responses to abiotic stresses, most remarkably on salt and drought stress. We will also turn to other types of abiotic stresses, less studied in relation to polyamine metabolism, such as mineral deficiencies, chilling, wounding, heavy metals, UV, ozone and paraquat, where polyamine metabolism is also modified. There is a great amount of data demonstrating that under many types of abiotic stresses, an accumulation of the three main polyamines putrescine, spermidine and spermine does occur. However, there are still many doubts concerning the role that polyamines play in stress tolerance. Several environmental challenges (osmotic stress, salinity, ozone, UV) are shown to induce ADC activity more than ODC. The rise in Put is mainly attributed to the increase in ADC activity as a consequence of the activation of ADC genes and their mRNA levels. On the other hand, free radicals are now accepted as important mediators of tissue injury and cell death. The polycationic nature of polyamines, positively charged at physiological pH, has attracted the attention of researchers and has led to the hypothesis that polyamines could affect physiological systems by binding to anionic sites, such as those associated with nucleic acids and membrane phospholipids. These amines, involved with the control of numerous cellular functions, including free radical scavenger and antioxidant activity, have been found to confer protection from abiotic stresses but their mode of action is not fully understood yet. In this review, we will also summarize information about the involvement of polyamines as antioxidants against the potential abiotic stress-derived oxidative damage.

Salt stress impact on the molecular structure and function of the photosynthetic apparatus--the protective role of polyamines

In the present study the green alga Scenedesmus obliquus was used to assess the effects of high salinity (high NaCl-concentration) on the structure and function of the photosynthetic apparatus and the possibility for alleviation by exogenous putrescine (Put). Chlorophyll fluorescence data revealed the range of the changes induced in the photosynthetic apparatus by different NaCl concentrations, which altogether pointed towards an increased excitation pressure. At the same time, changes in the levels of endogenous polyamine concentrations, both in cell and in isolated thylakoid preparations were also evidenced. Certain polyamine changes (Put reduction) were correlated with changes in the structure and function of the photosynthetic apparatus, such as the increase in the functional size of the antenna and the reduction in the density of active photosystem II reaction centers. Thus, exogenously added Put was used to compensate for this stress condition and to adjust the above mentioned changes, so that to confer some kind of tolerance to the photosynthetic apparatus against enhanced NaCl-salinity and permit cell growth even in NaCl concentrations that under natural conditions would be toxic.

Comparison of transcriptional responses to osmotic stresses induced by NaCl and sorbitol additions in Saccharomyces cerevisiae using DNA microarray

Transcriptional responses of laboratory and brewing strains of Saccharomyces cerevisiae to osmotic stresses induced by adding either NaCl or sorbitol to their cultures were compared by clustering DNA microarray data. Our results suggest that the difference in the transcriptional responses of the two strains between NaCl and sorbitol additions is small when the dynamics of the total change in gene expression are similar.

Seizure-promoting effect of blood-brain barrier disruption

PURPOSE

It is generally accepted that blood-brain barrier (BBB) failure occurs as a result of CNS diseases, including epilepsy. However, evidences also suggest that BBB failure may be an etiological factor contributing to the development of seizures.

METHODS

We monitored the onset of seizures in patients undergoing osmotic disruption of BBB (BBBD) followed by intraarterial chemotherapy (IAC) to treat primary brain lymphomas. Procedures were performed under barbiturate anesthesia. The effect of osmotic BBBD was also evaluated in naive pigs.

RESULTS

Focal motor seizures occurred immediately after BBBD in 25% of procedures and originated contralateral to the hemisphere of BBBD. No seizures were observed when BBB was not breached and only IAC was administered. The only predictors of seizures were positive indices of BBBD, namely elevation of serum S100beta levels and computed tomography (CT) scans. In a porcine model of BBBD, identical procedures generated an identical result, and sudden behavioral and electrographic (EEG) seizures correlated with successful BBB disruption. The contribution of tumor or chemotherapy to acute seizures was therefore excluded.

CONCLUSION

This is the first study to correlate extent of acute BBB openings and development of seizures in humans and in a large animal model of BBB opening. Acute vascular failure is sufficient to cause seizures in the absence of CNS pathologies or chemotherapy.

Regulation of Schizosaccharomyces pombe Atf1 protein levels by Sty1-mediated phosphorylation and heterodimerization with Pcr1

The Atf1 transcription factor plays a vital role in the ability of Schizosaccharomyces pombe cells to respond to various stress conditions. It regulates the expression of many genes in a stress-dependent manner, and its function is dependent upon the stress-activated MAPK, Sty1/Spc1. Moreover, Atf1 is directly phosphorylated by Sty1. Here we have investigated the role of such phosphorylation. Atf1 protein accumulates following stress, and this accumulation is lost in a strain defective in the Sty1 signaling pathway. In addition, accumulation of a mutant Atf1 protein that can no longer be phosphorylated is lost. Measurement of the half-life of Atf1 demonstrates that changes in Atf1 stability are responsible for this accumulation. Atf1 stability is also regulated by its heterodimeric partner, Pcr1. Similarly, Pcr1 levels are regulated by Atf1. Thus multiple pathways exist that ensure that Atf1 levels are appropriately regulated. Phosphorylation of Atf1 is important for cells to mount a robust response to H(2)O(2) stress, because the Atf1 phospho-mutant displays sensitivity to this stress, and induction of gene expression is lower than that observed in wild-type cells. Surprisingly, however, loss of Atf1 phosphorylation does not lead to the complete loss of stress-activated expression of Atf1 target genes. Accordingly, the Atf1 phospho-mutant does not display the same overall stress sensitivities as the atf1 deletion mutant. Taken together, these data suggest that Sty1 phosphorylation of Atf1 is not required for activation of Atf1 per se but rather for modulating its stability.

Stress-specific role of fission yeast Gcn5 histone acetyltransferase in programming a subset of stress response genes

Gcn5 is a coactivator protein that contributes to gene activation by acetylating specific lysine residues within the N termini of histone proteins. Gcn5 has been intensively studied in the budding yeast, Saccharomyces cerevisiae, but the features of genes that determine whether they require Gcn5 during activation have not been conclusively clarified. To allow comparison with S. cerevisiae, we have studied the genome-wide role of Gcn5 in the distantly related fission yeast, Schizosaccharomyces pombe. We show that Gcn5 is specifically required for adaptation to KCl- and CaCl(2)-mediated stress in S. pombe. We have characterized the genome-wide gene expression responses to KCl stress and show that Gcn5 is involved in the regulation of a subset of stress response genes. Gcn5 is most clearly associated with KCl-induced genes, but there is no correlation between Gcn5 dependence and the extent of their induction. Instead, Gcn5-dependent KCl-induced genes are specifically enriched in four different DNA motifs. The Gcn5-dependent KCl-induced genes are also associated with biological process gene ontology terms such as carbohydrate metabolism, glycolysis, and nicotinamide metabolism that together constitute a subset of the ontology parameters associated with KCl-induced genes.

Solute-inhibitor interactions in the plasmodial surface anion channel reveal complexities in the transport process

Human red blood cells infected with the malaria parasite Plasmodium falciparum have markedly increased permeabilities to diverse organic and inorganic solutes. The plasmodial surface anion channel (PSAC), recently identified with electrophysiological methods, contributes to the uptake of many small solutes. In this study, we explored the effects of known PSAC antagonists on transport of different solutes. We were surprised to find that the transport of two solutes, phenyltrimethylammonium and isoleucine, was only partially inhibited by concentrations of three inhibitors that abolish sorbitol or alanine uptake. Residual uptake via endogenous transporters could not account for this finding because uninfected red blood cells (RBCs) do not have adequate permeability for these solutes. In infected RBCs, the residual uptake of these solutes could be abolished by higher concentrations of specific and nonspecific PSAC antagonists. Adding sorbitol or alanine, permeant solutes that do not exhibit residual uptake, could also abolish it. The residual uptake did not exhibit anomalous mole fraction behavior and had a steep activation energy. These observations exclude uptake via unrelated pathways and instead point to differences in how PSAC recognizes and transports various solutes. We propose a possible model that also may help explain the unique selectivity properties of PSAC.

Mechanisms of high salinity tolerance in plants

Among abiotic stresses, high salinity stress is the most severe environmental stress, which impairs crop production on at least 20% of irrigated land worldwide. In response to high salinity stress, various genes get upregulated, the products of which are involved either directly or indirectly in plant protection. Some of the genes encoding osmolytes, ion channels, receptors, components of calcium signaling, and some other regulatory signaling factors or enzymes are able to confer salinity-tolerant phenotypes when transferred to sensitive plants. Overall, the susceptibility or tolerance to high salinity stress in plants is a coordinated action of multiple stress responsive genes, which also cross talk with other components of stress signal transduction pathways. High salinity exerts its negative impact mainly by disrupting the ionic and osmotic equilibrium of the cell. In saline soils, high levels of sodium ions lead to plant growth inhibition and even death; therefore, mechanisms of salinity tolerance involve sequestration of Na(+) and Cl(-) in vacuoles of the cells, blocking of Na(+) entry into the cell, Na(+) exclusion from the transpiration stream, and some other mechanisms that help in salinity tolerance. Understanding these mechanisms of stress tolerance, along with a plethora of genes involved in the stress signaling network, is important to improve high salinity stress tolerance in crops plants. This chapter first describes the adverse effect of salinity stress and general pathway for the plant stress response, followed by roles of various ion pumps, calcium, SOS pathways, ABA, transcription factors, mitogen-activated protein kinases, glycine betaine, proline, reactive oxygen species, and DEAD-box helicases in salinity stress tolerance. The cross-tolerance between stresses is also mentioned.

Improved conditions for production of recombinant plant sesquiterpene synthases in Escherichia coli

Amorpha-4,11-diene synthase (ADS) from Artemisia annua and (+)-germacrene synthase (GDS) from Zingiber officinale were expressed in Escherichia coli under different conditions to optimize the yield of active soluble protein. The cDNAs of these enzymes were inserted into the pET28 vector (Novagen) and expressed in four different bacterial strains; BL21 (DE3), BL21 (DE3) Tuner, BL21 (DE3) pLysS and BL21 (DE3) pLysS Tuner using different inducing agents (IPTG, The Inducer). The effects of induction under osmotic stress in the presence of glycine betaine and sorbitol were investigated. Although background expression for ADS was reduced when using pLysS strains, no significant difference was noted for ADS activity in soluble whole cell lysates after induction with either IPTG or The Inducer. For GDS, on the other hand, the change between BL21 (DE3) cells and BL21 (DE3) Tuner, induced with IPTG, leads to a twofold increase in enzyme activity in the soluble fraction while a reduction in activity is observed when using the pLysS strains. The same doubling of activity is observed for GDS when the commonly used BL.21 (DE3) is induced with The Inducer. Addition of 2.5 mM glycine betaine and 660 mM sorbitol to the bacterial growth media resulted in reduction of growth rate and biomass yield but under these conditions the best overall protein production, for both enzymes, was obtained. Compared to the standard conditions previously used in our laboratory the yield of soluble active protein was increased 7- and 2.5-fold for ADS and GDS, using BL21 (DE3) pLysS Tuner and BL21 (DE3), respectively.

Enhancement of thermal stability and inhibition of protein aggregation by osmolytic effect of hydroxyproline

A combination of spectroscopic, calorimetric, and microscopic studies to understand the effect of hydroxyproline on the thermal stability, conformation, biological activity, and aggregation of proteins has been investigated. Significantly increased protein stability and suppression of aggregation is achieved in the presence of hydroxyproline. For example, exceptional increase in the thermal stability of lysozyme up to 26.4 degrees C and myoglobin up to 31.8 degrees C is obtained in the presence of hydroxyproline. The increased thermal stability of the proteins is observed to be accompanied with significant rise of the catalytic activity. Hydroxyproline is observed to prevent lysozyme fibril formation in vitro. Fluorescence and circular dichroism studies indicate induction of tertiary structures of the studied proteins in the presence of hydroxyproline. Preferential hydration of the native state is found to be crucial for the mechanism of protein stabilization by hydroxyproline. We compared the effect of hydroxyproline to that of proline and observed similar increase in the activity and suppression of protein aggregation. The results demonstrate the use of hydroxyproline as a protein stabilizer and in the prevention of protein aggregation and fibril formation.

Effects of Osmolytes on Protein Folding and Aggregation in Cells

Nature has developed many strategies to ensure that the complex and challenging protein folding reaction occurs in vivo with adequate efficiency and fidelity for the success of the organism. Among the strategies widely employed in a huge range of species and cell types is the elaboration of small organic molecules called osmolytes that offset the potentially damaging effects of osmotic stress. While considerable knowledge has been gained in vitro regarding the influence of osmolytes on protein structure and folding, it is of great interest to probe the effects of osmolytes in cells. We have developed an in-cell fluorescent-labeling method that enables the study of protein stability and also protein aggregation in vivo. We utilize a genetically encoded tag called a tetra-Cys motif that binds specifically to a bis-arsenical fluorescein-based dye "FlAsH"; we inserted the tetra-Cys motif into a protein of interest in such a way that the FlAsH signal reported on the state of folding or aggregation of the protein. Then, we designed protocols to assess how various osmolytes influence the stability and propensity to aggregate of our protein of interest. These are described here. Not only are there potential biotechnological applications of osmolytes in the quest to produce greater quantities of well-folded proteins, but also osmolytes may serve as tools and points of departure for therapeutic intervention in protein folding and aggregation diseases. Having in vivo methods to analyze how osmolytes affect folding and aggregation enhances our ability to further these goals greatly.

[The influence of sodium nitrite on the osmoresistance of Chinese hamster cells]

We have previously demonstrated that incubation of V-79 cells in the medium containing the nitric oxide donor, NaNO2, increases cell resistance to damaging effect of gamma-rays, UV radiation and hyperthermia. In the present study, we investigated the effects of the nitric oxide donor on the sensitivity of V-79 cells to changes in osmomolarity of the medium by adding different amounts of sodium chloride or water. We found that pretreatment of the cells with NaNO2 resulted in a significant increase in the number of growing cells in 48 h after the treatment. The osmomolarity-dependent morphological changes in cultured cells were also substantially diminished following NaNO2 treatment. This effect could be observed under both hyper- and hypoosmosis, and was dependent on concentration of sodium chloride in hypertonic medium (being maximal under 0.17 M NaCl) and on the amount of water in hypotonic medium (being maximal under 1.1 times the dilution with water). In the experiments with increased osmomolarity, we found that the observed increase in the number of growing cells following NaNO2 treatment was accompanied with a significant increase of the mitotic index. These findings indicate that nitric oxide increases cell resistance to the damaging effects of osmotic shock in the way which is similar to the protective effect of these molecules against radiation and hyperthermia. Similarities in the effects of NaNO2 under different conditions leading to cell damage suggest that nitric oxide might serve as the universal factor participating in recovery of damaged cells and mediating increased cellular resistance to the damaging conditions.

Domain-specific mechanosensory transmission of osmotic and enzymatic cell wall disturbances to the actin cytoskeleton

Plant protoplasts are embedded within surrounding cell walls and the cell wall-plasma membrane-cytoskeleton (WMC) structural continuum seems to be crucial for the proper functioning of plant cells. We have utilised the protoplast preparation methodology to study the organisation and the putative components of the WMC continuum. Application of an osmotic agent evoked plasmolysis of the Zea mays root apex cells which appeared to be cell type- and growth stage-specific. Simultaneous use of wall polysaccharide-digesting enzymes selectively severed linkages between the components of the WMC continuum which changed the plasmolytic patterns in various cell types. This was followed by a reorganisation of filamentous actin aimed to reinforce protoplast boundaries and maintain the functioning of intercellular contact sites, especially at the cross walls. Particularly strong effects were evoked by pectin-degrading enzymes. Such treatments demonstrated directly the differentiated composition of various wall domains surrounding individual cells with the pectin-enriched cross walls (synapses), and the cellulose-hemicellulose network dominating the side walls. The same wall-degrading enzymes were used for in vitro digestion of isolated Lupinus albus cell walls followed by the extraction of wall proteins. Selective release of proteins suggested the importance of wall polysaccharide-protein interactions in the maintenance of the functioning and mechanical stability of root cell walls.

Application of the Transfer Model to Understand How Naturally Occurring Osmolytes Affect Protein Stability

A primary thermodynamic goal in protein biochemistry is to attain a predictive understanding of the energetic changes responsible for solvent-induced folding and unfolding. This chapter demonstrates the use of Tanford's transfer model to predict solvent-dependent cooperative protein folding/unfolding free energy changes (m values). This approach provides a thermodynamic description of these free energy changes in terms of individual contributions from the peptide backbone and residue side chains. The quantitative success of the transfer model has been hindered for many years because of unresolved issues involving proper measurement of the group transfer-free energies of amino acid side chains and the peptide backbone unit. This chapter demonstrates what is necessary to design experiments properly so that reliable values of group transfer-free energies are obtainable. It then demonstrates how to derive a prediction of the m value for the description of protein folding/unfolding cooperativity and that the calculated values using the transfer model agree quite well with experimentally measured values.