Molecular biology of stress responses

Mutations and functional analysis of 14-3-3 stress response protein from Triticum aestivum: An evolutionary analysis through in silico structural biochemistry approach

Wheat (Triticum aestivum), having high nutritional values is one of the staple food of most of the countries in the world. The productivity of the crop decreases drastically when it encounters various abiotic stresses, most common of which are heat, drought, flood and salinity. There is a crucial role of stress response proteins for the survival of the crops in stress conditions. So the study of wheat stress response proteins is of great importance to raise wheat production in different stress conditions. In this study, we analysed 14-3-3 protein, a stress response protein that is expressed in three major stresses, for example heat, drought and salinity and helps the plants to survive in those conditions. Effect of mutations in the 14-3-3 sequence was predicted using its domain, secondary structure and multiple sequence alignment of amino acid sequences from wheat and its related species. The functional diversity of the protein in different species was correlated with mutations, change in secondary structure and the evolutionary relatedness of the protein in different species. This is the first novel work for analysing the mutational effect on the structure and function of a stress response protein (14-3-3) from Triticum aestivum and its related species.

The global effect of heat on gene expression in cultured bovine mammary epithelial cells

Heat stress (HS) in hot climates is a major cause that strongly negatively affects milk yield in dairy cattle, leading to immeasurable economic loss. The heat stress response of bovine mammary epithelial cells (BMECs) is one component of the acute systemic response to HS. Gene networks of BMECs respond to environmental heat loads with both intra- and extracellular signals that coordinate cellular and whole-animal metabolism. Our experimental objective was to characterize the direct effects of heat stress on the cultured bovine mammary epithelial cells by microarray analyses. The data identified 2716 differentially expressed genes in 43,000 transcripts which were changed significantly between heat-stressed and normal bovine mammary epithelial cells (fold change ≥2, P ≤ 0.001). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that these differentially expressed genes are involved in different pathways that regulate cytoskeleton, cell cycle, and stress response processes. Our study provides an overview of gene expression profile and the interaction between gene expression and heat stress, which will lead to further understanding of the potential effects of heat stress on bovine mammary glands.

Upregulation of heat shock protein 32 in Sertoli cells alleviates the impairments caused by heat shock-induced apoptosis in mouse testis

Heat stress results in apoptosis in testicular germ cells. A small heat shock protein (hsp), hsp32, is induced by heat stress in the testis, but little is known about its definitive function in physiological processes. To clarify the underlying role of hsp32, hsp32 expression and related signals in the heat shock pathway were analysed in mouse testes and Sertoli cells after heat stress in vivo and in vitro; meanwhile, expression of hsp32 was silenced only in the Sertoli cells using three different small interfering RNAs (siRNAs) to further verify the functional role of hsp32 in Sertoli cells, and hsp32-derived carbon monoxide (CO) contents in cultured media were analysed to clarify whether hsp32-derived CO involve in the apoptosis regulation mechanisms. The results from the in vivo experiment showed that the high expression levels of hsp32 (P < 0.05) were observed whether chronic, moderate or acute, transient heat exposure. The in vitro experiment showed that acute, transient heat exposure resulted in increases in Sertoli cells apoptosis (P < 0.01), the expression of hsp32 and caspase-3 activity; hsp32-siRNA knockdown of hsp32 expression resulted in upregulated apoptosis (P < 0.01) and caspase-3 activity (P < 0.01) in the Sertoli cells and hyperthermia increases CO (P < 0.01) release by Sertoli cells. The results suggested that upregulating hsp32 in Sertoli cells inhibits caspase-3 activity and alleviates heat-induced impairments in mouse testis; hsp32-derived CO may involve in the regulation mechanism.

Thermo and pH stable ATP-independent chaperone activity of heat-inducible Hsp70 from Pennisetum glaucum

Heat shock proteins (Hsps) are a class of molecular chaperones that play an essential role in preserving cellular functions under stressful conditions. The over production of recombinant proteins often causes cellular stress that results in aggregation/misfolding of proteins, which sometimes leads to the formation of inclusion bodies. Here we report the cloning and characterization of heat-inducible PgHsp70 from Pennisetum glaucum, a heat and drought tolerant plant that showed stability and chaperone activity at elevated temperatures. The predicted amino acid sequence of PgHsp70 revealed a high homology with Hsp70 from other plants, and the overall 3D structure homology modeling is similar to that of the constitutively expressed bovine cytosolic Heat Shock Cognate (HSC)-70. The purified recombinant protein had an apparent molecular mass of 70 kDa and displayed optimal chaperone activity at 50 degrees C, and pH 8.0. Under these conditions, the T(1/2) of PgHsp70 increased from 10 to 15 h in the presence of glycerol. The PgHsp70 exhibited a higher chaperone activity towards glutamate dehydrogenase than alcohol dehydrogenase. The expression of recombinant carbonic anhydrase (CA) in E. coli in a catalytically active soluble form rather than in inclusion bodies was made feasible by co-expression of PgHsp70. Circular dichroism (CD) studies of the recombinant PgHsp70 did not reveal any discernible changes in the alpha-helix content, with increase in temperature from 35 to 85 degrees C, thus suggesting a critical role of alpha-helix content in maintaining the chaperone activity.

Expression of stress gene networks in tomato lines susceptible and resistant to Tomato yellow leaf curl virus in response to abiotic stresses

The defense response to several abiotic stresses has been compared in two tomato inbred lines issued from the same breeding program, one susceptible and the other resistant to Tomato yellow leaf curl virus (TYLCV) infection. The level of oxidative burst and the amounts of key regulatory stress proteins: pathogenesis-related proteins (PRs), heat shock proteins (HSPs) and mitogen-activated protein kinases (MAPKs) were appraised following treatments with NaCl, H(2)O(2), and ethanol. Significant differences in the response of the two tomato genotypes to these stresses have been found for HSPs and MAPKs patterns at the level of down-regulation but not activation. The higher abundance of HSPs and MAPKs in tomatoes resistant to TYLCV could result in enhanced defense capacity against abiotic stresses.

Genetic engineering for heat tolerance in plants

High temperature tolerance has been genetically engineered in plants mainly by over-expressing the heat shock protein genes or indirectly by altering levels of heat shock transcription factor proteins. Apart from heat shock proteins, thermotolerance has also been altered by elevating levels of osmolytes, increasing levels of cell detoxification enzymes and through altering membrane fluidity. It is suggested that Hsps may be directly implicated in thermotolerance as agents that minimize damage to cell proteins. The other three above approaches leading to thermotolerance in transgenic experiments though operate in their own specific ways but indirectly might be aiding in creation of more reductive and energy-rich cellular environment, thereby minimizing the accumulation of damaged proteins. Intervention in protein metabolism such that accumulation of damaged proteins is minimized thus appears to be the main target for genetically-engineering crops against high temperature stress.

Transcriptomic identification of candidate genes involved in sunflower responses to chilling and salt stresses based on cDNA microarray analysis

BACKGROUND

Considering that sunflower production is expanding to arid regions, tolerance to abiotic stresses as drought, low temperatures and salinity arises as one of the main constrains nowadays. Differential organ-specific sunflower ESTs (expressed sequence tags) were previously generated by a subtractive hybridization method that included a considerable number of putative abiotic stress associated sequences. The objective of this work is to analyze concerted gene expression profiles of organ-specific ESTs by fluorescence microarray assay, in response to high sodium chloride concentration and chilling treatments with the aim to identify and follow up candidate genes for early responses to abiotic stress in sunflower.

RESULTS

Abiotic-related expressed genes were the target of this characterization through a gene expression analysis using an organ-specific cDNA fluorescence microarray approach in response to high salinity and low temperatures. The experiment included three independent replicates from leaf samples. We analyzed 317 unigenes previously isolated from differential organ-specific cDNA libraries from leaf, stem and flower at R1 and R4 developmental stage. A statistical analysis based on mean comparison by ANOVA and ordination by Principal Component Analysis allowed the detection of 80 candidate genes for either salinity and/or chilling stresses. Out of them, 50 genes were up or down regulated under both stresses, supporting common regulatory mechanisms and general responses to chilling and salinity. Interestingly 15 and 12 sequences were up regulated or down regulated specifically in one stress but not in the other, respectively. These genes are potentially involved in different regulatory mechanisms including transcription/translation/protein degradation/protein folding/ROS production or ROS-scavenging. Differential gene expression patterns were confirmed by qRT-PCR for 12.5% of the microarray candidate sequences.

CONCLUSION

Eighty genes isolated from organ-specific cDNA libraries were identified as candidate genes for sunflower early response to low temperatures and salinity. Microarray profiling of chilling and NaCl-treated sunflower leaves revealed dynamic changes in transcript abundance, including transcription factors, defense/stress related proteins, and effectors of homeostasis, all of which highlight the complexity of both stress responses. This study not only allowed the identification of common transcriptional changes to both stress conditions but also lead to the detection of stress-specific genes not previously reported in sunflower. This is the first organ-specific cDNA fluorescence microarray study addressing a simultaneous evaluation of concerted transcriptional changes in response to chilling and salinity stress in cultivated sunflower.

Expression of stress-response proteins upon whitefly-mediated inoculation of Tomato yellow leaf curl virus in susceptible and resistant tomato plants

To better understand the nature of resistance of tomato to the whitefly (Bemisia tabaci, B biotype)-transmitted Tomato yellow leaf curl virus (TYLCV), whiteflies and TYLCV were considered as particular cases of biotic stresses and virus resistance as a particular case of successful response to these stresses. Two inbred tomato lines issued from the same breeding program that used Solanum habrochaites as a TYLCV resistance source, one susceptible and the other resistant, were used to compare the expression of key proteins involved at different stages of the plant response with stresses: mitogen-activated protein kinases (MAPKs), cellular heat shock proteins (HSPs, proteases), and pathogenesis-related (PR) proteins. The two biotic stresses-non-viruliferous whitefly feeding and virus infection with viruliferous insects--led to a slow decline in abundance of MAPKs, HSPs, and chloroplast protease FtsH (but not chloroplast protease ClpC), and induced the activities of the PR proteins, beta-1,3-glucanase, and peroxidase. This decline was less pronounced in virus-resistant than in virus-susceptible lines. Contrary to whitefly infestation and virus infection, inoculation with the fungus Sclerotinia sclerotiorum induced a rapid accumulation of the stress proteins studied, followed by a decline; the virus-susceptible and -resistant tomato lines behaved similarly in response to the fungus.

Identification of new subgroup of HSP70 in Bythograeidae (hydrothermal crabs) and Xanthidae

Crabs of the Bythograeidae family (Crustacea: Brachyura: Bythogreoidea) are the only endemic crab family living in hydrothermal fields. The hydrothermal environment is characterized by unique ecological parameters, such as the high temperature gradient around the hydrothermal chimney (2-350 degrees C), a fluid environment containing high levels of metals and numerous gases. The 70-kDa Heat Shock Protein (HSP70) group is the most-studied HSP, because it is ubiquitous, and a strong positive correlation has been found between the amounts of HSP70 produced in response to stress, and the ability of the organism to withstand stressful conditions. The 70-kDa heat shock protein genes from Bythograeids (species analyzed: Bythograea thermydron, Cyanagraea praedator and Segonzacia mesatlantica) were characterized. Our results revealed that Bythograeidae possess genes which are similar with those present in Xanthids (coastal crabs). The deduced protein sequences displayed motifs distinct from those in the other crustacean HSC70/HSP70s available in the databases. Phylogenetic analysis showed that these members of HSP70 family identified in Bythograeidae and Xanthidae constitute a new subgroup within this family.

Salt stress response in rice: genetics, molecular biology, and comparative genomics

Significant progress has been made in unraveling the molecular biology of rice in the past two decades. Today, rice stands as a forerunner amongst the cereals in terms of details known on its genetics. Evidence show that salt tolerance in plants is a quantitative trait. Several traditional cultivars, landraces, and wild types of rice like Pokkali, CSR types, and Porteresia coarctata appear as promising materials for donation of requisite salt tolerance genes. A large number of quantitative trait loci (QTL) have been identified for salt tolerance in rice through generation of recombinant inbred lines and are being mapped using different types of DNA markers. Salt-tolerant transgenic rice plants have been produced using a host of different genes and transcript profiling by micro- and macroarray-based methods has opened the gates for the discovery of novel salt stress mechanisms in rice, and comparative genomics is turning out to be a critical input in this respect. In this paper, we present a comprehensive review of the genetic, molecular biology, and comparative genomics effort towards the generation of salt-tolerant rice. From the data on comprehensive transcript expression profiling of clones representing salt-stress-associated genes of rice, it is shown that transcriptional and translational machineries are important determinants in controlling salt stress response, and gene expression response in tolerant and susceptible rice plants differs mainly in quantitative terms.

Heat-shock response down-regulates interleukin-18 expression in murine peritoneal macrophages

BACKGROUND INFORMATION

The heat-shock response is a self-defence mechanism that protects cells and organisms from a wide range of harmful stresses. Recent studies revealed that it involved the regulation of cytokine expression. Interleukin-18 (IL-18) is an important cytokine in mediating immune response.

RESULTS

We studied interferon-gamma (IFN-gamma)-induced IL-18 expression in heat-shock-treated murine peritoneal macrophages. Our results showed that the heat-shock response significantly inhibited the expression of IFN-gamma-induced pro-inflammatory cytokine IL-18. Interferon consensus sequence binding protein (ICSBP) is a transcription factor that binds to the promoter of IL-18 and regulates the transcription of IL-18. Further research on the down-regulation mechanism showed that the DNA-binding activity of ICSBP was greatly reduced by the heat shock response.

CONCLUSIONS

These results suggest that the inhibitory effect of heat-shock response on IL-18 production in IFN-gamma-stimulated macrophages is related to the suppression of the binding activity of ICSBP.

Asymmetric modulation of a catecholamine-regulated protein in the rat brain, following quinpirole administration

We previously reported a brain-specific 40 kDa catecholamine-regulated protein (CRP40) that binds dopamine (DA) and related catecholamines. CPR40 shares significant sequence homology with human heat shock protein (Hsp70), GRP78/BIP, and human #BQ24193 protein. Recent studies with the DA D(2) receptor antagonist, haloperidol, demonstrated a significant increase in expression of CRP40 in the striatum (STR). The objective of the present study was to investigate CRP40 expression in various brain regions following treatments with the DA D(2)/D(3) receptor agonist quinpirole (QNP) in rats and examine possible relationships between neurochemical parameters and locomotor activity. Rats received injections of either QNP (0.5 mg/kg, for 27 days every third day) or saline (SAL) and their locomotor activities were measured for 90 min after each injection. At injection 9, QNP-treated rats showed locomotor activity that was significantly greater than SAL controls (F(2,28) = 3.88, P < 0.05, Duncan's multiple range test, P < 0.05). Neurochemically, acute QNP-treated rats demonstrated significant differential expression of CRP40 in the left/right prefrontal cortex (PFC) relative to SAL-treated rats (-17.76 +/- 2.10%, -10.35 +/- 1.23%, P < 0.001). Chronic QNP significantly decreased CRP40 expression in the STR, ventral tegmental area (VTA), and left/right PFC (-24.85+/- 2.10%, -18.15 +/- 5.64%, -49.13 +/- 7.05%, -25 +/- 3.63%, P < 0.001). Finally, chronic QNP treatment resulted in a significant increase in CRP40 levels in the nucleus accumbens (NA) (+39.32 +/- 7.00%, P < 0.001). Heat shock protein (i.e., Hsp70 or Hsc70) expression remained unaltered following QNP treatment. Since QNP is a DA D(2)/D(3) agonist, alterations in CRP40 expression following QNP treatment suggest the protein's function in dopaminergic neurotransmission.

Heat shock protein 70 binds caspase-activated DNase and enhances its activity in TCR-stimulated T cells

DNA fragmentation is a hallmark of cells undergoing apoptosis and is mediated mainly by the caspase-activated DNase (CAD or DNA-fragmentation factor 40 [DFF40]), which is activated when released from its inhibitor protein (ICAD or DFF45) upon apoptosis signals. Here we analyzed the effect of heat shock protein 70 (Hsp70) on CAD activity in T-cell receptor (TCR)-induced apoptosis using a T-cell line (TAg-Jurkat). Overexpression of Hsp70 significantly augmented the apoptotic cell death as well as DNA fragmentation in CD3/CD28- or staurosporine-stimulated cells. Following stimulation of cells with CD3/CD28 or staurosporine, Hsp70 was coprecipitated with free CAD, but not with CAD associated with ICAD. Furthermore, the purified Hsp70 dose-dependently augmented DNA-fragmentation activity of caspase-3-activated CAD in a cell-free system. Peptide-binding domain-deleted Hsp70 could neither bind nor augment its activity, while adenosine triphosphate (ATP)-binding domain-deleted Hsp70 or the peptide-binding domain itself bound CAD and augmented its activity. These results indicate that the the binding of Hsp70 to the activated CAD via the peptide-binding domain augments its activity. Although CAD lost its activity in an hour after being released from ICAD in vitro, its activity was retained after an hour of incubation in the presence of Hsp70, suggesting that Hsp70 may be involved in stabilization of CAD activity. Finally, CAD that had been coprecipitated with Hsp70 from the cell lysate of staurosporine-activated 293T cells induced chromatin DNA fragmentation and its activity was not inhibited by ICAD. These results suggest that Hsp70 binds free CAD in TCR-stimulated T cells to stabilize and augment its activity.

Heat stress-dependent DNA binding of Arabidopsis heat shock transcription factor HSF1 to heat shock gene promoters in Arabidopsis suspension culture cells in vivo

Using UV laser cross-linking and immunoprecipitation we measured the in vivo binding of Arabidopsis heat shock transcription factor HSF1 to the promoters of target genes, Hsp18.2 and Hsp70. The amplification of promoter sequences, co-precipitated with HSF1-specific antibodies, indicated that HSF1 is not bound in the absence of heat stress. Binding to promoter sequences of target genes is rapidly induced by heat stress, continues throughout the heat treatment, and declines during subsequent recovery at room temperature. The molecular mechanisms underlying the differences between Hsp18.2 and Hsp70 in the kinetics of HSF1/promoter binding and corresponding mRNA expression profiles are discussed.

Heat shock response inhibits IL-18 expression through the JNK pathway in murine peritoneal macrophages

Heat shock response has been implicated in cytoprotective effects from cellular damage and in the regulation of cytokine expression. We report the effect of heat shock on LPS-induced expression of IL-18, an important cytokine that has diverse immune regulatory effects on T cells, B cells, NK cells, and nonimmune cells. The augmentation of LPS-induced IL-18 mRNA and protein was significantly suppressed in murine peritoneal macrophages after 43 degrees C heat shock treatment. In addition, the JNK MAPK inhibitor SP600125 inhibited IL-18 mRNA transcription in a dose-dependent manner. To examine the possibility that the inhibition of IL-18 may be mediated through the inactivation of JNK, the activity of JNK was measured by using Western blot and kinase assays. Our data show that heat shock response decreased LPS-induced phosphorylation of JNK and its downstream substrate c-Jun. AP-1, a transcriptional factor composed of c-Jun, could regulate the expression of IL-18. Also, its DNA-binding activity was reduced by the heat shock response. These findings suggest that treatment of heat stress results in inhibition of IL-18 production in macrophages mainly through the JNK/AP-1 signaling pathway.