RNA metabolism: strategies for regulation in the heat shock response

Mechanisms tailoring the expression of heat shock proteins to proteostasis challenges

All cells possess an internal stress response to cope with environmental and pathophysiological challenges. Upon stress, cells reprogram their molecular functions to activate a survival mechanism known as the heat shock response, which mediates the rapid induction of molecular chaperones such as the heat shock proteins (HSPs). This potent production overcomes the general suppression of gene expression and results in high levels of HSPs to subsequently refold or degrade misfolded proteins. Once the damage or stress is repaired or removed, cells terminate the production of HSPs and resume regular functions. Thus, fulfillment of the stress response requires swift and robust coordination between stress response activation and completion that is determined by the status of the cell. In recent years, single-cell fluorescence microscopy techniques have begun to be used in unravelling HSP-gene expression pathways, from DNA transcription to mRNA degradation. In this review, we will address the molecular mechanisms in different organisms and cell types that coordinate the expression of HSPs with signaling networks that act to reprogram gene transcription, mRNA translation, and decay and ensure protein quality control.

Recovery from heat shock requires the microRNA pathway in Caenorhabditis elegans

The heat shock response (HSR) is a highly conserved cellular process that promotes survival during stress. A hallmark of the HSR is the rapid induction of heat shock proteins (HSPs), such as HSP-70, by transcriptional activation. Once the stress is alleviated, HSPs return to near basal levels through incompletely understood mechanisms. Here, we show that the microRNA pathway acts during heat shock recovery in Caenorhabditis elegans. Depletion of the miRNA Argonaute, Argonaute Like Gene 1 (ALG-1), after an episode of heat shock resulted in decreased survival and perdurance of high hsp-70 levels. We present evidence that regulation of hsp-70 is dependent on miR-85 and sequences in the hsp-70 3’UTR that contain target sites for this miRNA. Regulation of hsp-70 by the miRNA pathway was found to be particularly important during recovery from HS, as animals that lacked miR-85 or its target sites in the hsp-70 3’UTR overexpressed HSP-70 and exhibited reduced viability. In summary, our findings show that down-regulation of hsp-70 by miR-85 after HS promotes survival, highlighting a previously unappreciated role for the miRNA pathway during recovery from stress.

In the natural world, organisms constantly face stressful conditions such as oxidative stress, pathogen infection, starvation and heat stress. While many studies have focused on the cellular response to stress, less is known about how gene expression re-sets after the stress has been ameliorated. Here, we show that the microRNA pathway plays a critical role during the recovery phase after an episode of heat shock in the nematode, Caenorhabditis elegans. Elevated temperatures induce high expression of heat shock proteins (HSPs), including HSP-70, that provide protection from the damaging effects of high heat. We found that restoration of basal levels of HSP-70 after heat shock depends on Argonaute Like Gene 1 and miR-85. Moreover, loss of miRNA-mediated repression of HSP-70 results in compromised survival following heat shock. Our study draws attention to the recovery phase of the heat shock response and highlights an important role for the microRNA pathway in re-establishing gene expression programs needed for organismal viability post stress.

A cold shock protein promotes high-temperature microbial growth through binding to diverse RNA species

Endowing mesophilic microorganisms with high-temperature resistance is highly desirable for industrial microbial fermentation. Here, we report a cold-shock protein (CspL) that is an RNA chaperone protein from a lactate producing thermophile strain (Bacillus coagulans 2–6), which is able to recombinantly confer strong high-temperature resistance to other microorganisms. Transgenic cspL expression massively enhanced high-temperature growth of Escherichia coli (a 2.4-fold biomass increase at 45 °C) and eukaryote Saccharomyces cerevisiae (a 2.6-fold biomass increase at 36 °C). Importantly, we also found that CspL promotes growth rates at normal temperatures. Mechanistically, bio-layer interferometry characterized CspL’s nucleotide-binding functions in vitro, while in vivo we used RNA-Seq and RIP-Seq to reveal CspL’s global effects on mRNA accumulation and CspL’s direct RNA binding targets, respectively. Thus, beyond establishing how a cold-shock protein chaperone provides high-temperature resistance, our study introduces a strategy that may facilitate industrial thermal fermentation.

Pharmacologic Approaches for Adapting Proteostasis in the Secretory Pathway to Ameliorate Protein Conformational Diseases

Maintenance of the proteome, ensuring the proper locations, proper conformations, appropriate concentrations, etc., is essential to preserve the health of an organism in the face of environmental insults, infectious diseases, and the challenges associated with aging. Maintaining the proteome is even more difficult in the background of inherited mutations that render a given protein and others handled by the same proteostasis machinery misfolding prone and/or aggregation prone. Maintenance of the proteome or maintaining proteostasis requires the orchestration of protein synthesis, folding, trafficking, and degradation by way of highly conserved, interacting, and competitive proteostasis pathways. Each subcellular compartment has a unique proteostasis network compromising common and specialized proteostasis maintenance pathways. Stress-responsive signaling pathways detect the misfolding and/or aggregation of proteins in specific subcellular compartments using stress sensors and respond by generating an active transcription factor. Subsequent transcriptional programs up-regulate proteostasis network capacity (i.e., ability to fold and degrade proteins in that compartment). Stress-responsive signaling pathways can also be linked by way of signaling cascades to nontranscriptional means to reestablish proteostasis (e.g., by translational attenuation). Proteostasis is also strongly influenced by the inherent kinetics and thermodynamics of the folding, misfolding, and aggregation of individual proteins, and these sequence-based attributes in combination with proteostasis network capacity together influence proteostasis. In this review, we will focus on the growing body of evidence that proteostasis deficits leading to human pathology can be reversed by pharmacologic adaptation of proteostasis network capacity through stress-responsive signaling pathway activation. The power of this approach will be exemplified by focusing on the ATF6 arm of the unfolded protein response stress responsive-signaling pathway that regulates proteostasis network capacity of the secretory pathway.

Environmental influences on RNA processing: Biochemical, molecular and genetic regulators of cellular response

RNA processing has emerged as a key mechanistic step in the regulation of the cellular response to environmental perturbation. Recent work has uncovered extensive remodeling of transcriptome composition upon environmental perturbation and linked the impacts of this molecular plasticity to health and disease outcomes. These isoform changes and their underlying mechanisms are varied-involving alternative sites of transcription initiation, alternative splicing, and alternative cleavage at the 3' end of the mRNA. The mechanisms and consequences of differential RNA processing have been characterized across a range of common environmental insults, including chemical stimuli, immune stimuli, heat stress, and cancer pathogenesis. In each case, there are perturbation-specific contributions of local (cis) regulatory elements or global (trans) factors and downstream consequences. Overall, it is clear that choices in isoform usage involve a balance between the usage of specific genetic elements (i.e., splice sites, polyadenylation sites) and the timing at which certain decisions are made (i.e., transcription elongation rate). Fine-tuned cellular responses to environmental perturbation are often dependent on the genetic makeup of the cell. Genetic analyses of interindividual variation in splicing have identified genetic effects on splicing that contribute to variation in complex traits. Finally, the increase in the number of tissue types and environmental conditions analyzed for RNA processing is paralleled by the need to develop appropriate analytical tools. The combination of large datasets, novel methods and conditions explored promises to provide a much greater understanding of the role of RNA processing response in human phenotypic variation. This article is categorized under: RNA Processing > RNA Editing and Modification RNA Evolution and Genomics > Computational Analyses of RNA RNA Processing > Splicing Mechanisms RNA Processing > Splicing Regulation/Alternative Splicing.

Transcriptional profiles of plasticity for desiccation stress in Drosophila

We examined the transcriptional responses of desiccation resistance candidate genes in populations of Drosophila melanogaster divergent for desiccation resistance and in capacity to improve resistance via phenotypic plasticity. Adult females from temperate and tropical eastern Australian populations were exposed to a rapid desiccation hardening (RDH) treatment, and groups without RDH to acute desiccation stress, and the transcript expression of 12 candidate desiccation genes were temporally profiled during, and in recovery from stress. We found that desiccation exposure resulted in largely transitory, stress-specific transcriptional changes in all but one gene. However linking the expression profiles to the population-level phenotypic divergence was difficult given subtle, and time-point specific population expression variation. Nonetheless, rapid desiccation hardening had the largest effect on gene expression, resulting in distinct molecular profiles. We report a hitherto uncharacterised desiccation molecular hardening response where prior exposure essentially 'primes' genes to respond to subsequent stress without discernible transcript changes prior to stress. This, taken together with some population gene expression variation of several bona fide desiccation candidates associated with different water balance strategies speaks of the complexity of natural desiccation resistance and plasticity and provides new avenues for understanding the molecular basis of a trait of ecological significance.

Stress Beyond Translation: Poxviruses and More

Poxviruses are large double-stranded DNA viruses that form viral factories in the cytoplasm of host cells. These viruses encode their own transcription machinery, but rely on host translation for protein synthesis. Thus, poxviruses have to cope with and, in most cases, reprogram host translation regulation. Granule structures, called antiviral granules (AVGs), have been observed surrounding poxvirus viral factories. AVG formation is associated with abortive poxvirus infection, and AVGs contain proteins that are typically found in stress granules (SGs). With certain mutant poxviruses lack of immunoregulatory factor(s), we can specifically examine the mechanisms that drive the formation of these structures. In fact, cytoplasmic macromolecular complexes form during many viral infections and contain sensing molecules that can help reprogram transcription. More importantly, the similarity between AVGs and cytoplasmic structures formed during RNA and DNA sensing events prompts us to reconsider the cause and consequence of these AVGs. In this review, we first summarize recent findings regarding how poxvirus manipulates host translation. Next, we compare and contrast SGs and AVGs. Finally, we review recent findings regarding RNA- and especially DNA-sensing bodies observed during viral infection.

Spatial analysis of gene regulation reveals new insights into the molecular basis of upper thermal limits

The cellular stress response has long been the primary model for studying the molecular basis of thermal adaptation, yet the link between gene expression, RNA metabolism and physiological responses to thermal stress remains largely unexplored. We address this by comparing the transcriptional and physiological responses of three geographically distinct populations of Drosophila melanogaster from eastern Australia in response to, and recovery from, a severe heat stress with and without a prestress hardening treatment. We focus on starvin (stv), recently identified as an important thermally responsive gene. Intriguingly, stv encodes seven transcripts from alternative transcription sites and alternative splicing, yet appears to be rapidly heat inducible. First, we show genetic differences in upper thermal limits of the populations tested. We then demonstrate that the stv locus does not ubiquitously respond to thermal stress but is expressed as three distinct thermal and temporal RNA phenotypes (isoforms). The shorter transcript isoforms are rapidly upregulated under stress in all populations and show similar molecular signatures to heat-shock proteins. Multiple stress exposures seem to generate a reserve of pre-mRNAs, effectively 'priming' the cells for subsequent stress. Remarkably, we demonstrate a bypass in the splicing blockade in these isoforms, suggesting an essential role for these transcripts under heat stress. Temporal profiles for the weakly heat responsive stv isoform subset show opposing patterns in the two most divergent populations. Innate and induced transcriptome responses to hyperthermia are complex, and warrant moving beyond gene-level analyses.

Widespread inhibition of posttranscriptional splicing shapes the cellular transcriptome following heat shock

During heat shock and other proteotoxic stresses, cells regulate multiple steps in gene expression in order to globally repress protein synthesis and selectively upregulate stress response proteins. Splicing of several mRNAs is known to be inhibited during heat stress, often meditated by SRp38, but the extent and specificity of this effect have remained unclear. Here, we examined splicing regulation genome-wide during heat shock in mouse fibroblasts. We observed widespread retention of introns in transcripts from ∼1,700 genes, which were enriched for tRNA synthetase, nuclear pore, and spliceosome functions. Transcripts with retained introns were largely nuclear and untranslated. However, a group of 580+ genes biased for oxidation reduction and protein folding functions continued to be efficiently spliced. Interestingly, these unaffected transcripts are mostly cotranscriptionally spliced under both normal and stress conditions, whereas splicing-inhibited transcripts are mostly spliced posttranscriptionally. Altogether, our data demonstrate widespread repression of splicing in the mammalian heat stress response, disproportionately affecting posttranscriptionally spliced genes.

New levels of transcriptome complexity at upper thermal limits in wild Drosophila revealed by exon expression analysis

While the cellular heat-shock response has been a paradigm for studying the impact of thermal stress on RNA metabolism and gene expression, the genome-wide response to thermal stress and its connection to physiological stress resistance remain largely unexplored. Here, we address this issue using an array-based exon expression analysis to interrogate the transcriptome in recently established Drosophila melanogaster stocks during severe thermal stress and recovery. We first demonstrated the efficacy of exon-level analyses to reveal a level of thermally induced transcriptome complexity extending well beyond gene-level analyses. Next, we showed that the upper range of both the cellular and physiological thermal stress response profoundly affected message expression and processing in D. melanogaster, limiting expression to a small subset of transcripts, many that share features of known rapidly responding stress genes. As predicted from cellular heat-shock research, constitutive splicing was blocked in a set of novel genes; we did not detect changes to alternative splicing during heat stress, but rather induction of intronless isoforms of known heat-responsive genes. We observed transcriptome plasticity in the form of differential isoform expression during recovery from heat shock, mediated by multiple mechanisms including alternative transcription and alternative splicing. This affected genes involved in DNA regulation, immune response, and thermotolerance. These patterns highlight the complex nature of innate transcriptome responses under stress and potential for adaptive shifts through plasticity and evolved genetic responses at different hierarchical levels.

Chemical and biological approaches for adapting proteostasis to ameliorate protein misfolding and aggregation diseases: progress and prognosis

Maintaining the proteome to preserve the health of an organism in the face of developmental changes, environmental insults, infectious diseases, and rigors of aging is a formidable task. The challenge is magnified by the inheritance of mutations that render individual proteins subject to misfolding and/or aggregation. Maintenance of the proteome requires the orchestration of protein synthesis, folding, degradation, and trafficking by highly conserved/deeply integrated cellular networks. In humans, no less than 2000 genes are involved. Stress sensors detect the misfolding and aggregation of proteins in specific organelles and respond by activating stress-responsive signaling pathways. These culminate in transcriptional and posttranscriptional programs that up-regulate the homeostatic mechanisms unique to that organelle. Proteostasis is also strongly influenced by the general properties of protein folding that are intrinsic to every proteome. These include the kinetics and thermodynamics of the folding, misfolding, and aggregation of individual proteins. We examine a growing body of evidence establishing that when cellular proteostasis goes awry, it can be reestablished by deliberate chemical and biological interventions. We start with approaches that employ chemicals or biological agents to enhance the general capacity of the proteostasis network. We then introduce chemical approaches to prevent the misfolding or aggregation of specific proteins through direct binding interactions. We finish with evidence that synergy is achieved with the combination of mechanistically distinct approaches to reestablish organismal proteostasis.

Transcriptional response of hepatic largemouth bass (Micropterus salmoides) mRNA upon exposure to environmental contaminants

Microarrays enable gene transcript expression changes in near-whole genomes to be assessed in response to environmental stimuli. We utilized oligonucleotide microarrays and subsequent gene set enrichment analysis (GSEA) to assess patterns of gene expression changes in male largemouth bass (Micropterus salmoides) hepatic tissues after a 96 h exposure to common environmental contaminants. Fish were exposed to atrazine, cadmium chloride, PCB 126, phenanthrene and toxaphene via intraperitoneal injection with target body burdens of 3.0, 0.00067, 2.5, 50 and 100 µg g(-1), respectively. This was conducted in an effort to identify potential biomarkers of exposure. The expressions of 4, 126, 118, 137 and 58 mRNA transcripts were significantly (P ≤ 0.001, fold change ≥2×) affected by exposure to atrazine, cadmium chloride, PCB 126, phenanthrene and toxaphene exposures, respectively. GSEA revealed that none, four, five, five and three biological function gene ontology categories were significantly influenced by exposure to these chemicals, respectively. We observed that cadmium chloride elicited ethanol metabolism responses, and along with PCB 126 and phenanthrene affected transcripts associated with protein biosynthesis. PCB 126, phenanthrene and toxaphene also influenced one-carbon compound metabolism while PCB 126 and phenanthrene affected mRNA transcription and mRNA export from the nucleus and may have induced an antiestrogenic response. Atrazine was found to alter the expression of few hepatic transcripts. This work has highlighted several biological processes of interest that may be helpful in the development of gene transcript biomarkers of chemical exposure in fish.

Heat shock-induced SRSF10 dephosphorylation displays thermotolerance mediated by Hsp27

Gene regulation in response to environmental stress is critical for the survival of all organisms. From Saccharomyces cerevisiae to humans, it has been observed that splicing of mRNA precursors is repressed upon heat shock. However, a mild heat pretreatment often prevents splicing inhibition in response to a subsequent and more severe heat shock, a phenomenon called splicing thermotolerance. We have shown previously that the splicing regulator SRSF10 (formerly SRp38) is specifically dephosphorylated by the phosphatase PP1 in response to heat shock and that dephosphorylated SRSF10 is responsible for splicing repression caused by heat shock. Here we report that a mild heat shock protects SRSF10 from dephosphorylation during a second and more severe heat shock. Furthermore, this "thermotolerance" of SRSF10 phosphorylation, like that of splicing, requires de novo protein synthesis, specifically the synthesis of heat shock proteins. Indeed, overexpression of one of these proteins, Hsp27, inhibits SRSF10 dephosphorylation in response to heat shock and does so by interaction with SRSF10. Our data thus provide evidence that splicing thermotolerance is acquired through maintenance of SRSF10 phosphorylation and that this is mediated at least in part by Hsp27.

Molecular characterization of a putative heat shock protein cognate gene in Rhynchosciara americana

An hsc70 homologue gene (Rahsc70) of the diptera Rhynchosciara americana was isolated and characterized. We were able to determine the mRNA sequence from an EST of salivary gland cDNA library, and a Rahsc70 cDNA cassette was used as a probe to isolate the genomic region from a genomic library. The mRNA expression of this gene parallels the 2B puff expansion, suggesting its involvement in protein processing, since this larval period corresponds to a high synthetic activity period. During heat shock stress conditions, hsc70 expression decreased. In situ hybridization of polytene chromosomes showed that the Rahsc70 gene is located near the C3 DNA puff. The cellular localization of Hsc70 protein showed this protein in the cytoplasm and in the nucleus.

Ubiquitin-mediated proteolysis of HuR by heat shock

The RNA-binding protein HuR regulates the stability and translation of numerous mRNAs encoding stress-response and proliferative proteins. Although its post-transcriptional influence has been linked primarily to its cytoplasmic translocation, here we report that moderate heat shock (HS) potently reduces HuR levels, thereby altering the expression of HuR target mRNAs. HS did not change HuR mRNA levels or de novo translation, but instead reduced HuR protein stability. Supporting the involvement of the ubiquitin-proteasome system in this process were results showing that (1) HuR was ubiquitinated in vitro and in intact cells, (2) proteasome inhibition increased HuR abundance after HS, and (3) the HuR kinase checkpoint kinase 2 protected against the loss of HuR by HS. Within a central, HS-labile approximately 110-amino-acid region, K182 was found to be essential for HuR ubiquitination and proteolysis as mutant HuR(K182R) was left virtually unubiquitinated and was refractory to HS-triggered degradation. Our findings reveal that HS transiently lowers HuR by proteolysis linked to K182 ubiquitination and that HuR reduction enhances cell survival following HS.

The pOT and pLOB vector systems: improving ease of transgene expression in Botrytis cinerea

This paper outlines the construction of a novel vector system comprising interchangeable terminators, as well as a multiple cloning site (MCS), to facilitate the transformation of the fungal plant pathogen Botrytis cinerea. Previous molecular studies on B. cinerea have relied upon the pLOB1 based vector system (controlled by the Aspergillus nidulans oliC promoter and a region reported to be the B. cinerea tubA terminator). Investigations, however, have revealed that, rather than the genuine B. cinerea tubA terminator, the pLOB1 terminator fragment is from another gene locus within the genome. Because previous studies have found that terminators aide in transcript stability, the main aims of this study were to develop and evaluate both vector systems, pOT (controlled by the A. nidulans oliC promoter and A. nidulans trpC terminator) and pLOB, with a range of exogenous genes, including enhanced green fluorescent protein (eGFP), monomeric red fluorescent protein (mRFP), luciferase (LUC) and beta-glucuronidase (GUS). Our investigations demonstrate that pLOB and pOT based vectors are capable of expressing all four reporter genes and may be applied to future molecular studies on B. cinerea and other related ascomycetes. Additionally, this is the first reported expression of mRFP and LUC in B. cinerea.

Mechanisms of Activation and Regulation of the Heat Shock-Sensitive Signaling Pathways

Heat shock (HS), like many other stresses, induces specific and highly regulated signaling cascades that promote cellular homeostasis. The three major mitogen-activated protein kinases (MAPK) and protein kinase B (PKB/Akt) are the most notable of these HS-stimulated pathways. Their activation occurs rapidly and sooner than the transcriptional upregulation of heat shock proteins (Hsp), which generate a transient state of extreme resistance against subsequent thermal stress. The direct connection of these signaling pathways to cellular death or survival mechanisms suggests that they contribute importantly to the HS response. Some of them may counteract early noxious effects of heat, while others may bolster key apoptosis events. The triggering events responsible for activating these pathways are unclear. Protein denaturation, specific and nonspecific receptor activation, membrane alteration and chromatin structure perturbation are potential initiating factors.

Mild exercise training, cardioprotection and stress genes profile

To improve current knowledge of the molecular mechanisms underlying exercise-induced cardioprotection in a rat model of mild exercise training, Sprague-Dawley rats were trained to run on a treadmill up to 55% of their maximal oxygen uptake for 1 h/day, 3 days/week, 14 weeks, with age-matched sedentary controls (n = 20/group). Rats were sacrificed 48 h after the last training session. Despite lack of cardiac hypertrophy, training decreased blood hemoglobin (7.94 +/- 0.21 mM vs. 8.78 +/- 0.23 mM, mean +/- SE, P = 0.01) and increased both plasma malondialdehyde (0.139 +/- 0.005 mM vs. 0.085 +/- 0.009 mM, P = 0.05) and the activity of Mn-superoxide dismutase (11.6 +/- 0.6 vs. 16.5 +/- 1.6 mU/microg, P = 0.01), whereas total superoxide dismutase activity was unaffected. When subjected to 30-min ischemia followed by 90-min reperfusion, hearts from trained rats (n = 5) displayed reduced infarct size as compared to controls (37.26 +/- 0.92% vs. 49.09 +/- 2.11% of risk area, P = 0.04). The biochemical analyses in the myocardium, which included gene expression profiles, real-time PCR, Western blot and determination of enzymatic activity, showed training-induced upregulation of the following mRNAs and/or proteins: growth-arrest and DNA-damage induced 153 (GADD153/CHOP), heme-oxygenase-1 (HO-1), cyclooxygenase-2 (Cox-2), heat-shock protein 70/72 (HSP70/72), whereas heat-shock protein 60 (HSP60) and glucose-regulated protein 75 (GRP75) were decreased. As a whole, these data indicate that mild exercise training activates a second window of myocardial protection against ischemia/reperfusion by upregulating a number of protective genes, thereby warranting further investigation in man.

Transcriptional profiling of Alzheimer blood mononuclear cells by microarray

We evaluated pathomechanisms and systemic manifestations of Alzheimer disease (AD), an aging-related dementing neurodegenerative disorder, by expression profiling. Blood mononuclear cell (BMC) transcriptomes of sporadic AD subjects and aged-matched normal elderly controls (NEC) were compared using the human NIA microarray. Relative to the NEC samples, the Alzheimer BMC exhibited a significant decline in the expression of genes concerned with cytoskeletal maintenance, cellular trafficking, cellular stress response, redox homeostasis, transcription and DNA repair. We observed decreased expression of several genes which may impact amyloid-beta production and the processing of the microtubule-associated protein tau. The microarray results were validated by quantitative real time PCR and revealed gender differences in the levels of altered gene expression. Our findings attest to the systemic nature of gene dys-regulation in sporadic AD, implicate disruption of cytoskeletal integrity, DNA repair mechanisms and cellular defenses in this condition, and suggest novel pathways of beta-amyloid deposition in this disease. BMC are highly accessible and may reflect molecular events germane to the neuropathophysiology of AD.

Evaluation of the activities of the medfly and Drosophila hsp70 promoters in vivo in germ-line transformed medflies

The promoter of the hsp70 gene of Drosophila melanogaster has been widely used for the expression of foreign genes in other insects. It has been generally assumed that because this gene is highly conserved, its promoter will function efficiently in other species. We report the results of a quantitative comparison of the activities of the medfly and D. melanogaster hsp70 promoters in vivo in transformed medflies. We constructed transformed lines containing the lacZ reporter gene under the control of the two promoters by using Minos-mediated germ-line transformation. The activity of each promoter was evaluated in 15 transformed lines by beta-galactosidase quantitative assays. The heat-inducible activity of the medfly promoter was found several times higher than the respective activity of the heterologous D. melanogaster promoter. These results were confirmed by northern blot analysis and indicate that the D. melanogaster promoter does not work efficiently in medfly. The -263/+105 medfly promoter region that was used in this study was found able to drive heat shock expression of the lacZ reporter gene in all stages of medfly, except early embryonic stages, in a similar fashion to the endogenous hsp70 genes. However the heat inducible RNA levels driven from this promoter region were significantly lower than the endogenous hsp70 RNA levels, suggesting that additional upstream and/or downstream sequences to the -263/+105 region may be necessary for optimum function of the medfly hsp70 promoter in vivo.

Use of physiological constraints to identify quantitative design principles for gene expression in yeast adaptation to heat shock

Background

Understanding the relationship between gene expression changes, enzyme activity shifts, and the corresponding physiological adaptive response of organisms to environmental cues is crucial in explaining how cells cope with stress. For example, adaptation of yeast to heat shock involves a characteristic profile of changes to the expression levels of genes coding for enzymes of the glycolytic pathway and some of its branches. The experimental determination of changes in gene expression profiles provides a descriptive picture of the adaptive response to stress. However, it does not explain why a particular profile is selected for any given response.

Results

We used mathematical models and analysis of in silico gene expression profiles (GEPs) to understand how changes in gene expression correlate to an efficient response of yeast cells to heat shock. An exhaustive set of GEPs, matched with the corresponding set of enzyme activities, was simulated and analyzed. The effectiveness of each profile in the response to heat shock was evaluated according to relevant physiological and functional criteria. The small subset of GEPs that lead to effective physiological responses after heat shock was identified as the result of the tuning of several evolutionary criteria. The experimentally observed transcriptional changes in response to heat shock belong to this set and can be explained by quantitative design principles at the physiological level that ultimately constrain changes in gene expression.

Conclusion

Our theoretical approach suggests a method for understanding the combined effect of changes in the expression of multiple genes on the activity of metabolic pathways, and consequently on the adaptation of cellular metabolism to heat shock. This method identifies quantitative design principles that facilitate understating the response of the cell to stress.

Turning up the heat: The effects of thermal acclimation on the kinetics of hsp70 gene expression in the eurythermal goby, Gillichthys mirabilis

Most organisms respond to temperature fluctuations by altering the expression of an evolutionarily conserved family of proteins known as heat shock proteins (Hsps). Studies have shown Hsp expression and the activation of HSF1, one of the primary regulators of Hsp transcription, are highly malleable, varying with the recent thermal history of the organism; however, the mechanisms that confer plasticity to the regulation of this ubiquitous response are not well-understood. This study furthers our knowledge in this area by characterizing the activation kinetics of HSF1 and the corresponding transcription of hsp70 in the liver of the eurythermal goby, Gillichthys mirabilis, following a month-long acclimation at 13, 21 or 28 degrees C. Our data revealed HSF1 DNA-binding kinetics varied as a function of acclimation temperature and magnitude/duration of exposure, with gobies acclimated at 21 degrees C exhibiting the most robust response. Hsp70 mRNA followed a similar pattern with induction first occurring in the 13 and 21 degrees C fish, and then most robustly in the 28 degrees C group at 36 degrees C. The hsp70 mRNA induction pattern was corroborated by levels of HSF1 DNA-binding activity in each group and may have been lowest in the 28 degrees C group due to the 2-fold greater levels of hsp70 protein prior to thermal exposure. This study illustrates the integral role of HSF1 as a key regulator of Hsp induction and helps explain the plasticity of this response in ectothermic organisms.

Sequencing and expression pattern of inducible heat shock gene products in the European flat oyster, Ostrea edulis

Heat shock proteins are a multigene family of polypeptides composed of the constitutively-expressed heat shock cognate (HSC) members and of the stress-inducible (HSP) proteins, whose expression is specifically induced by stress factors. Constitutive and inducible 70 kDa isoforms are reported in vertebrates and invertebrates. HSCs are expressed in all bivalve molluscs studied to date, while the occurrence of strictly heat-inducible HSPs seems a distinctive feature of oysters. To gain more insight into the molecular features of the Ostrea edulis HSP70, we have cloned and sequenced the gene product putatively encoding for the heat-inducible isoform HSP69 and examined the pattern of expression after heat exposure. Four different clones of approximately 1794 bp were obtained that share a high degree of homology with heat-inducible HSP70 from other bivalves. Amino acid sequence comparisons indicated that the main structural features of the heat-inducible HSP70 are highly conserved within the O. edulis HSP70 clones, while lower sequence homology occurred with respect to HSC70 transcripts. Northern blot analysis indicated that HSP69 mRNA was absent in control animals but induced after heat shock (1 h at 32 degrees C or higher). Induction was detectable immediately after heat shock, reaching a maximum after 2 to 3 h of post-stress recovery at 18 degrees C, and decreasing thereafter. A phylogenetic analysis of the HSP70 family members from oyster and other bivalves revealed a substantial conservation in the evolutionary pattern among constitutive and inducible gene products, from invertebrates to higher vertebrates.

Differential HSP70 gene expression in the Mediterranean mussel exposed to various stressors

HSP70 gene expression was studied by quantitative RT-PCR after cloning and sequencing of two different HSP70 gene fragments from the digestive gland of Mytilus galloprovincialis, called MgHSP70 and MgHSC70. Heat shock (1h at 35 degrees C) caused rapid induction of MgHSP70, while no change was observed for MgHSC70. Hg(2+) (150 microg/L for different time periods) significantly induced MgHSP70 expression that reached maximum levels after 24h, decreasing thereafter. MgHSC70 expression was inhibited after 1 day and induced after a 6-day exposure to Hg(2+). A 1-week exposure to Cr(6+) (1, 10, and 50 ng/L) induced and inhibited MgHSC70 and MgHSP70 transcript levels, respectively. MgHSC70 and MgHSP70 appear to play different roles in cell protection; the former is induced after acute stress and/or during the earlier phase of the response while the latter is induced by chronic stress. The present results provide new insights into mechanisms used by mussels to adapt to stressful environments.

Cell signalling and the control of pre-mRNA splicing

The transcripts of most metazoan protein-coding genes are alternatively spliced, but the mechanisms that are involved in the control of splicing are not well understood. Recent evidence supports the potential of both extra- and intracellular signalling to the splicing machinery as a means of regulating gene expression, and indicates that this form of gene control is widespread and mechanistically complex. However, important questions about these pathways need to be answered before this method of post-transcriptional regulation can be fully appreciated.

Translational regulation of Hsp90 mRNA. AUG-proximal 5'-untranslated region elements essential for preferential heat shock translation

Heat shock in Drosophila results in repression of most normal (non-heat shock) mRNA translation and the preferential translation of the heat shock mRNAs. The sequence elements that confer preferential translation have been localized to the 5'-untranslated region (5'-UTR) for Hsp22 and Hsp70 mRNAs (in Drosophila). Hsp90 mRNA is unique among the heat shock mRNAs in having extensive secondary structure in its 5'-UTR and being abundantly represented in the non-heat shocked cell. In this study, we show that Hsp90 mRNA translation is inefficient at normal growth temperature, and substantially activated by heat shock. Its preferential translation is not based on an IRES-mediated translation pathway, because overexpression of eIF4E-BP inhibits its translation (and the translation of Hsp70 mRNA). The ability of Hsp90 mRNA to be preferentially translated is conferred by its 5'-UTR, but, in contrast to Hsp22 and -70, is primarily influenced by nucleotides close to the AUG initiation codon. We present a model to account for Hsp90 mRNA translation, incorporating results indicating that heat shock inhibits eIF4F activity, and that Hsp90 mRNA translation is sensitive to eIF4F inactivation.

Magnitude and Duration of Thermal Stress Determine Kinetics ofhspGene Regulation in the GobyGillichthys mirabilis

The stress-induced transcription of heat shock genes is controlled by heat shock transcription factor 1 (HSF1), which becomes activated in response to heat and other protein denaturants. In previous research on the eurythermal goby Gillichthys mirabilis, thermal activation of HSF1 was shown to vary as a function of acclimation temperature, suggesting the mechanistic importance of HSF1 activation to the plasticity of heat shock protein (Hsp) induction temperature. We examined the effect of season on the thermal activation of HSF1 in G. mirabilis, as well as the relative kinetics of HSF1 activation and Hsp70 mRNA production at ecologically relevant temperatures. There was no predictable seasonality in the thermal activation of HSF1, perhaps due to the existence of stressors, in addition to heat, acting in the field. Concentrations of Hsp70, a negative regulator of HSF1, as well as those of HSF1, varied with collection date. The rapidity of HSF1 activation and of Hsp70 mRNA synthesis increased with laboratory exposure temperature. Furthermore, Hsp70 mRNA production was more sustained at 35 degrees C than at 30 degrees C. Therefore, both the magnitude and the duration of a heat shock are important in determining the intensity of heat shock gene induction.

Dephosphorylated SRp38 acts as a splicing repressor in response to heat shock

The cellular response to stresses such as heat shock involves changes in gene expression. It is well known that the splicing of messenger RNA precursors is generally repressed on heat shock, but the factors responsible have not been identified. SRp38 is an SR protein splicing factor that functions as a general repressor of splicing. It is activated by dephosphorylation and required for splicing repression in M-phase cells. Here we show that SRp38 is also dephosphorylated on heat shock and that this dephosphorylation correlates with splicing inhibition. Notably, depletion of SRp38 from heat-shocked cell extracts derepresses splicing, and adding back dephosphorylated SRp38 specifically restores inhibition. We further show that dephosphorylated SRp38 interacts with a U1 small nuclear ribonucleoprotein particle (snRNP) protein, and that this interaction interferes with 5'-splice-site recognition by the U1 snRNP. Finally, SRp38-deficient DT40 cells show an altered cell-cycle profile consistent with a mitotic defect; they are also temperature sensitive and defective in recovery after heat shock. SRp38 thus plays a crucial role in cell survival under stress conditions by inhibiting the splicing machinery.

Chaperonin 60 and mitochondrial disease in Dictyostelium

The single Dictyostelium chaperonin 60 gene, hspA, was cloned, sequenced and characterized. Sequence comparisons and a three-dimensional model for the structure of the encoded protein showed that it exhibits the conserved sequence and structural features expected for its role as the Dictyostelium mitochondrial chaperonin 60. Dictyostelium hspA contains two introns and, unusually for a member of this major heat shock gene family, is not stress-inducible in response to heat, cold or cadmium ions. Although transcription of hspA is down regulated during early Dictyostelium development in response to starvation, the levels of the chaperonin 60 protein remain constant throughout the life cycle. Consistent with the essential role of chaperonin 60 in mitochondrial biogenesis, we were unable to isolate mutants in which the hspA gene had been disrupted. However, transformants were isolated that exhibited differing levels of antisense inhibition of chaperonin 60 expression, depending upon the number of copies of the antisense-expressing plasmid in the genome. Orientation in phototaxis (and thermotaxis) was severely impaired in all antisense transformants, while growth and morphogenesis were markedly defective only in transformants with higher levels of antisense inhibition. This pattern of phenotypes is similar to that reported previously to result from targeted disruption of the mitochondrial large subunit rRNA gene in a subpopulation of mitochondria. This suggests that, regardless of the nature of the underlying genetic defect, mitochondrial deficiency impairs signal transduction more sensitively than other cellular activities.

Regulation of cytochrome c oxidase subunit 1 (COX1) expression in Cryptococcus neoformans by temperature and host environment

In the study of differential gene expression of Cryptococcus neoformans, a transcript of COX1 (cytochrome oxidase c subunit 1) was identified in a serotype A strain. The transcript was upregulated at 37 degrees C compared to 30 degrees C and expressed by yeasts infecting the central nervous system. Northern analysis of COX1 from the serotype A strain revealed two polycistronic transcripts, a temperature-upregulated 2.3 kb transcript and a 1.9 kb transcript that was not affected by temperature. In contrast, COX1 in a serotype D strain showed only a 1.9 kb polycistronic transcript plus a 1.6 kb monocistronic message, and temperature had no effect on the transcripts. The sequence of COX1 revealed similar coding regions between the two strains, but the serotype D strain had five introns whereas no introns were found in the serotype A strain. The serotype D strain had reduced growth rates compared to the serotype A strain at 37 degrees C, but in an AD hybrid strain the serotype D COX1 gene could support efficient high temperature growth. These studies have revealed mitochondrial molecular differences between serotype A and D strains which show evolutionary divergence. It will be important to determine whether differences in mitochondrial structure and function can influence cryptococcosis.

Double-stranded RNA-dependent protein kinase (pkr) is essential for thermotolerance, accumulation of HSP70, and stabilization of ARE-containing HSP70 mRNA during stress

We have investigated the role of the double-stranded RNA-dependent protein kinase gene (pkr) in the regulation of the heat shock response. We show that the pkr gene is essential for efficient activation of the heat shock response and that pkr disruption profoundly inhibits heat shock protein 70 (HSP70) synthesis and blocks the development of thermotolerance. Despite these profound effects, pkr disruption did not markedly affect the activation of heat shock factor 1 by heat and did not reduce the rate of transcription of the HSP70 gene after heat shock. However, despite the lack of effect of pkr disruption on HSP70 gene transcription, we found a significant decrease in the expression of HSP70 mRNA in pkr-/- cells after heat shock. Kinetic studies of mRNA turnover suggested a block in the thermal stabilization of HSP70 mRNA in pkr-/- cells. As the thermal stabilization of HSP70 mRNA is thought to involve cis-acting A+U rich (ARE) elements in the 3'-untranslated region (UTR), we examined a potential role for pkr in this process. We found that a reporter beta-galactosidase mRNA destabilized by introduction of a functional ARE into the 3'-UTR became stabilized by heat but only in cells containing an intact pkr gene. Our studies suggest therefore that pkr plays a significant role in the stabilization of mRNA species containing ARE destruction sequences in the 3'-UTR and through this mechanism, contributes to the regulation of the heat shock response and other processes.

A 3'-UTR variant of the inducible porcine hsp70.2 gene affects mRNA stability

Large individual differences were observed in the abundance of transcripts from the hsp70.2 gene in primary fibroblast cultures sampled from 15 different pigs. While previously described functional promoter variants of this gene can partly account for the high variability of heat-induced increased abundance of transcripts, they are unrelated to the observed highly variable absolute amounts of hsp70.2 transcripts. Comparative sequence analysis revealed an alteration of the 3'-untranslated region (3'-UTR) sequences in these samples. The variant 3'-UTR allele proved to increase the half life of the hsp70.2 mRNA in reporter gene assays. It is suggested that the cellular stress response is significantly affected by the action and interaction of both promoter and 3'-UTR variants of the hsp70.2 gene.

Regulation of heat shock proteins, Hsp70 and Hsp64, in heat-shocked Malpighian tubules of Drosophila melanogaster larvae

It is known from earlier studies that the heat shock (HS) response in Malpighian tubules (MTs) of Drosophila larvae is different from that in other tissues because instead of the Hsp70 and other common heat shock proteins, Hsp64 and certain other new proteins are induced immediately after HS. In the present study, we examined the kinetics of the synthesis of Hsp70 and Hsp64 immediately after HS and during recovery from HS by 35S-methionine labeling and Western blotting. In addition, we also examined the transcriptional activity of hsp70 genes in larval MT cells at different times after HS by in situ hybridization and Northern blotting. The HS-induced synthesis of Hsp64 ceased by 1 hour of recovery from the HS when synthesis of the Hsp70 commenced. Our results revealed that the induced synthesis of Hsp64 immediately after HS was dependent on new transcription. Although the levels of Hsp70 in MT cells rapidly increased after its synthesis began during recovery, the levels of Hsp64 remained unaltered irrespective of its new synthesis occurring during or after HS. Inhibition of new Hsp64 synthesis by transcriptional or translational inhibitors also did not affect the total amount of this protein in MTs. The Hsp64 polypeptides synthesized in response to HS are degraded rapidly. Apparently, the cells in MTs maintain a balance between new synthesis of Hsp64 and its turnover so that under all conditions a more or less constant level of this protein is maintained. Although the Hsp70 synthesis started only after 1 hour of recovery, the hsp70 genes were transcriptionally activated immediately after HS and they continued to transcribe till at least 4 hours after the HS. The hsp70 transcripts in MT cells that recovered for 2 hours or longer did not contain the 3' untranslated regions (UTRs), which may allow their longer stability and translatability at normal temperature. Synthesis of Hsp70 during recovery period was dependent on continuing transcription. Assessment of the beta-galactosidase activity in 2 transgenic lines carrying the LacZ reporter gene under hsp70 promoter and different lengths of the 5'UTR suggested that the delayed translation of hsp70 transcripts in MTs is probably regulated by some elements in the 5'UTR.

Tissue- and development-specific induction and turnover of hsp70 transcripts from loci 87A and 87C after heat shock and during recovery inDrosophila melanogaster

The haploid genome of Drosophila melanogaster normally carries at least five nearly identical copies of heat-shock-inducible hsp70 genes, two copies at the 87A7 and three copies at the 87C1 chromosome sites. We used in situ hybridization of the cDNA, which hybridizes with transcripts of all five hsp70 genes, and of two 3′ untranslated region (3′UTR; specific for the 87A7- and 87C1-type hsp70 transcripts) riboprobes to cellular RNA to examine whether all these copies were similarly induced by heat shock in different cell types of D. melanogaster. Our results revealed remarkable differences not only in the heat-shock-inducibility of the hsp70 genes at the 87A7 and 87C1 loci, but also in their post-transcriptional metabolism, such as the stability of the transcripts and of their 3′UTRs in different cell types in developing embryos and in larval and adult tissues. Our results also revealed the constitutive presence of the heat-shock-inducible form of Hsp70 in a subset of late spermatogonial cells from the second-instar larval stage onwards. We suggest that the multiple copies of the stress-inducible hsp70 genes do not exist in the genome of D. melanogaster only to produce large amounts of the Hsp70 rapidly and at short notice, but that they are specifically regulated in a developmental-stage-specific manner. It is likely that the cost/benefit ratio of not producing or of producing a defined amount of Hsp70 under stress conditions varies for different cell types and under different physiological conditions and, accordingly, specific regulatory mechanisms operating at the transcriptional and post-transcriptional levels have evolved.

Microhabitats, thermal heterogeneity, and patterns of physiological stress in the rocky intertidal zone

Thermal stress has been considered to be among the most important determinants of organismal distribution in the rocky intertidal zone. Yet our understanding of how body temperatures experienced under field conditions vary in space and time, and of how these temperatures translate into physiological performance, is still rudimentary. We continuously monitored temperatures at a site in central California for a period of two years, using loggers designed to mimic the thermal characteristics of mussels, Mytilus californianus. Model mussel temperatures were recorded on both a horizontal and a vertical, north-facing microsite, and in an adjacent tidepool. We periodically measured levels of heat shock proteins (Hsp70), a measure of thermal stress, from mussels at each microsite. Mussel temperatures were consistently higher on the horizontal surface than on the vertical surface, and differences in body temperature between these sites were reflected in the amount of Hsp70. Seasonal peaks in extreme high temperatures ("acute" high temperatures) did not always coincide with peaks in average daily maxima ("chronic" high temperatures), suggesting that the time history of body temperature may be an important factor in determining levels of thermal stress. Temporal patterns in body temperature during low tide were decoupled from patterns in water temperature, suggesting that water temperature is an ineffective metric of thermal stress for intertidal organisms. This study demonstrates that spatial and temporal variability in thermal stress can be highly complex, and "snapshot" sampling of temperature and biochemical indices may not always be a reliable method for defining thermal stress at a site.

A novel gene that is up-regulated during recovery from cold shock in Drosophila melanogaster

Gene expression during recovery at 25 degrees C (rearing temperature) after cold shock (0 degrees C) was studied in Drosophila melanogaster using a subtraction technique. A novel gene (Frost, abbreviated as Fst) was considerably up-regulated during recovery after cold shock. In addition, a prolongation of cold shock was more effective for induction. In contrast to cold shock, Fst gene did not respond to heat shock. This gene is apparently the same as the unidentified gene, CG9434. Fst has high internal repeats not only in nucleotide but also in amino acid sequences. In addition, FST protein has a proline-rich region. The deduced amino acid sequence revealed a modular structure; i.e., a signal peptide in the N-terminal region followed by a long hydrophilic region. Therefore, this protein is likely to be directed into ER and secreted into extracellular space.

Heat shock and arsenite induce expression of the nonclassical class I histocompatibility HLA-G gene in tumor cell lines

The nonclassical histocompatibility class I gene HLA-G has a tissue-restricted expression. To explore mechanisms involved in HLA-G transcriptional regulation, we have investigated the effect of stress, including heat shock and arsenite treatment, on HLA-G expression in tumor cell lines. We show that stress induces an increase of the level of the different HLA-G alternative transcripts without affecting other MHC class I HLA-A, -B, -E, and -F transcripts. A heat shock element (HSE) that binds to heat shock factor 1 (HSF1) on stress conditions was further identified within the HLA-G promoter. Considering the ability of HLA-G to modulate the function of immunocompetent cells, we hypothesize a new feature of HLA-G as a signal regulating the immune response to stress.

Applications and pitfalls of stress-proteins in biomonitoring

The vast number of potentially hazardous chemicals and the complex interactions that can occur between them in environmental mixtures, call for inexpensive, early and sensitive endpoints that reflect their biological effect. The existing validated bioassays, mostly based on lethality or reproduction, have been shown to be inadequate in respect of their sensitivity, the duration and expense of the test. In contrast, changes at biochemical level are usually the first detectable responses to environmental perturbation. Because these alterations underlie all effects at higher organisational level, they have often been shown to be very sensitive indicators of pollution. Stress-proteins (also referred to as heat-shock proteins or hsp) have recently been recognised as being one of the primary defence mechanisms that are activated by the occurrence of denatured proteins in the cell. Four major stress-protein families of 90,70,60 and 16-24 kDa are the most prominent and are frequently referred to as hsp90, hsp70, hsp60 and low molecular weight (LMW) stress-proteins. Three aspects of stress-proteins have been characterised that are essential if they want to be used as biomarkers of pollution: (1) they are part of the cellular protective response; (2) their synthesis is likely to be induced by a large number of chemicals; and (3) they are highly conserved in all organisms from bacteria to plants and man. Also, field studies have shown (be it for a limited number of stressors) that the stress response can occur even at the minute concentrations of pollutants that are usually found in the environment. However, increasing knowledge on the kinetics and persistence of the stress response to complex environmental mixtures, on the influence of both physiological and environmental parameters (pH, eutrophication, ellipsis), on the constitutive levels of stress-proteins and on the acquisition of tolerance, is required before one could safely apply stress-proteins to assess on-site pollution. Still, included in a test battery of complementary bioassays, stress protein may be very valuable as tier I biomarkers, i.e. broad response biomarkers that are used for preliminary screening of the environment.

The two Saccharomyces cerevisiae SUA7 (TFIIB) transcripts differ at the 3'-end and respond differently to stress

Despite much information as to the structure and function of the general transcription factors, little is known about the regulation of their expression. Transcription of the Saccharomyces cerevisiae SUA7 (TFIIB) gene results in the formation of two discrete transcripts. It was originally reported that the two transcripts were derived from two promoters separated by approximately 80 bp. We have found that the two transcripts are instead derived from a common promoter and differ at the 3'-end by approximately 115 bp. The longer of the two transcripts has an unusually long 3'-untranslated region. We have analyzed the levels of these transcripts under different cell growth conditions and find that the relative amounts of the two transcripts vary. Approximately equal amounts of each transcript are observed during exponential growth, but stresses and growth limiting conditions lead to a decrease in the relative amount of the larger transcript. These results suggest that the expression of the SUA7 gene may be controlled by regulation of 3'-end formation or mRNA stability. One of the general transcription factors, then, may be subject to regulation by a general response of the mRNA processing machinery.

Expression of Drosophila homologue of senescence marker protein-30 during cold acclimation

Gene expression during cold acclimation at a moderately low temperature (15 degrees C) was studied in Drosophila melanogaster using a subtraction technique. A gene homologous to senescence marker protein-30 (SMP30), which has a Ca(2+)-binding function, was up-regulated at the transcription level after acclimation to 15 degrees C. This gene (henceforth referred to as Dca) was also expressed at a higher level in individuals reared at 15 degrees C from the egg stage than in those reared at 25 degrees C. Moreover, DCA mRNA increased at the senescent stage in Drosophila, although SMP30 is reported to decrease at senescent stages in mammals. In situ hybridization to polytene chromosomes revealed that the Dca gene was located at 88D on chromosome 3R. The 5' flanking region of this gene had AP-1 (a transcription factor of SMP30) binding sites, stress response element and some other transcription factor binding sites. The function of DCA was discussed in relation to the possible regulation of cytosolic Ca(2+) concentration.

Heat shock and arsenite induce expression of the nonclassical class I histocompatibility HLA-G gene in tumor cell lines

The nonclassical histocompatibility class I gene HLA-G has a tissue-restricted expression. To explore mechanisms involved in HLA-G transcriptional regulation, we have investigated the effect of stress, including heat shock and arsenite treatment, on HLA-G expression in tumor cell lines. We show that stress induces an increase of the level of the different HLA-G alternative transcripts without affecting other MHC class I HLA-A, -B, -E, and -F transcripts. A heat shock element (HSE) that binds to heat shock factor 1 (HSF1) on stress conditions was further identified within the HLA-G promoter. Considering the ability of HLA-G to modulate the function of immunocompetent cells, we hypothesize a new feature of HLA-G as a signal regulating the immune response to stress.

Dynamic changes in small nuclear ribonucleoproteins of heat-stressed and thermotolerant HeLa cells

Living organisms when subjected to various forms of environmental stress mount a physiological response to survive the long- and short-term ill-effects of the stress. The stress response may involve selective shut down of non-essential metabolic activities and the repair of macromolecular damage resulting from the stress. Messenger RNA splicing in cultured HeLa cells is one of the processes inhibited by heat stress. Splicing is protected from such inhibition in stress-preconditioned cells that have acquired a tolerant state characterised by increased cell survival and resistance to other environmental stresses. Stress tolerant cells have heat shock proteins (HSPs) that had been induced by the preconditioning process. To examine the biochemical changes induced by stress in the splicing apparatus, we analysed the small nuclear ribonucleoprotein (snRNP) particles associated with spliceosomes in normal, stressed, and stress tolerant cells. We show that (a) the spliceosomal component U4/U5/U6 snRNP particle is disassembled by heat stress into intermediates of splicing assembly, (b) prior induction of stress tolerance protects the structural and functional integrity of snRNPs if cells are subsequently exposed to a severe stress and (c) a novel 65 kDa protein is associated with small nuclear ribonucleoprotein particles in stress tolerant cells.

Regulated phosphorylation of the RNA polymerase II C-terminal domain (CTD)

The largest subunit of RNA polymerase II has an intriguing feature in its carboxyl-terminal domain (CTD) that consists of multiple repeats of an evolutionary conserved motif of seven amino acids. CTD phosphorylation plays a pivotal role in controlling mRNA synthesis and maturation. In exponentially growing cells, the phosphate turnover on the CTD is fast; it is blocked by common inhibitors of transcription, such as 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole and actinomycin D. Transcription-independent changes in CTD phosphorylation are observed at critical developmental stages, such as meiosis and early development.Key words: RNA polymerase II, phosphorylation, transcription inhibitors, cyclin-dependent kinases, development.

Thermotolerance of IVM-derived bovine oocytes and embryos after short-term heat shock

A series of experiments were designed to study the effect of elevated temperatures on developmental competence of bovine oocytes and embryos produced in vitro. In experiment 1, the effect of heat shock (HS) by a mild elevated temperature (40.5 degrees C) for 0, 30, or 60 min on the viability of in vitro matured (IVM) oocytes was tested following in vitro fertilization (IVF) and culture. No significant difference was observed between the control (39 degrees C) and the heat-treated groups in cleavage, blastocyst formation, or hatching (P > 0.05). In experiment 2, when the HS temperature was increased to 41.5 degrees C, neither the cleavage rate nor blastocyst development was affected by treatment. However, the rate of blastocyst hatching appeared lower in the HS groups (13% in control group vs. 3.9% and 5.6% in 30 min and 60 min, respectively; P < 0.05). When IVM oocytes were treated at 43 degrees C prior to IVF (experiment 3), no difference was detected in blastocyst and expanded blastocyst development following heat treatment for 0, 15, or 30 min, but heat treatment of oocytes for 45 or 60 min significantly reduced blastocyst and expanded blastocyst formation (P < 0.05). In experiment 4, the thermotolerance of day 3 and day 4 bovine IVF embryos were compared. When embryos were pre-treated with a mild elevated temperature (40.5 degrees C) for 1 hr, and then with a higher temperature (43 degrees C) for 1 hr, no improvement in thermotolerance of the embryos was observed as compared to those treated at 43 degrees C alone. However, a higher thermotolerance was observed in day 4 than day 3 embryos. In conclusion, treatment at 43 degrees C, but not 40.5 degrees C or 41.5 degrees C significantly reduced oocyte developmental competence. An increase in thermotolerance was observed from day 3 to day 4 of in vitro embryonic development, which corresponds to the maternal to zygotic transition of gene expression in bovine embryos.