Evolution of the cellular stress proteome: from monophyletic origin to ubiquitous function

Animal performance and stress: responses and tolerance limits at different levels of biological organisation

Recent advances in molecular biology and the use of DNA microarrays for gene expression profiling are providing new insights into the animal stress response, particularly the effects of stress on gene regulation. However, interpretation of the complex transcriptional changes that occur during stress still poses many challenges because the relationship between changes at the transcriptional level and other levels of biological organisation is not well understood. To confront these challenges, a conceptual model linking physiological and transcriptional responses to stress would be helpful. Here, we provide the basis for one such model by synthesising data from organismal, endocrine, cellular, molecular, and genomic studies. We show using available examples from ectothermic vertebrates that reduced oxygen levels and oxidative stress are common to many stress conditions and that the responses to different types of stress, such as environmental, handling and confinement stress, often converge at the challenge of dealing with oxygen imbalance and oxidative stress. As a result, a common set of stress responses exists that is largely independent of the type of stressor applied. These common responses include the repair of DNA and protein damage, cell cycle arrest or apoptosis, changes in cellular metabolism that reflect the transition from a state of cellular growth to one of cellular repair, the release of stress hormones, changes in mitochondrial densities and properties, changes in oxygen transport capacities and changes in cardio-respiratory function. Changes at the transcriptional level recapitulate these common responses, with many stress-responsive genes functioning in cell cycle control, regulation of transcription, protein turnover, metabolism, and cellular repair. These common transcriptional responses to stress appear coordinated by only a limited number of stress-inducible and redox-sensitive transcription factors and signal transduction pathways, such as the immediate early genes c-fos and c-jun, the transcription factors NFkappaB and HIF-1alpha, and the JNK and p38 kinase signalling pathways. As an example of environmental stress responses, we present temperature response curves at organismal, cellular and molecular levels. Acclimation and physiological adjustments that can shift the threshold temperatures for the onset of these responses are discussed and include, for example, adjustments of the oxygen delivery system, the heat shock response, cellular repair system, and transcriptome. Ultimately, however, an organism's ability to cope with environmental change is largely determined by its ability to maintain aerobic scope and to prevent loss in performance. These systemic constraints can determine an organism's long-term survival well before cellular and molecular functions are disturbed. The conceptual model we propose here discusses some of the crosslinks between responses at different levels of biological organisation and the central role of oxygen balance and oxidative stress in eliciting these responses with the aim to help the interpretation of environmental genomic data in the context of organismal function and performance.

Classification of fixed urological cells using Raman tweezers

In this paper we report on preliminary investigations into using Raman tweezers to classify urological cell lines. This builds on earlier work within the group, whereby Raman tweezer methodologies were developed, and the application of this technique to differentiate between live prostate cancer (CaP) and bladder cells lines (PC-3 and MGH-U1 respectively) was demonstrated.In this present study we analysed chemically fixed cells using two different fixative methods; SurePath (a commercial available liquid based cytology media) and 4% v/v formalin/PBS fixatives. The study has been expanded from our previous live cell study to include the androgen sensitive CaP cell line LNCaP, primary benign prostate hyperplasia (BPH) cells as well as primary urethral cells. Raman light from the cells was collected using a 514.5 nm Ar-ion laser excitation source in back-scattering configuration mode.Principal component-linear discriminate analysis (PC-LDA) models of resulting cell spectra were generated and these were validated using a blind comparison. Sensitivities and specificities of > 72% and 90% respectively, for SurePath fixed cells, and > 93% and 98% respectively for 4% v/v formalin/PBS fixed cells was achieved. The higher prediction results for the formalin fixed cells can be attributed to a better signal-to-noise ratio for spectra obtained from these cells.Following on from this work, urological cell lines were exposed to urine for up to 12 hours to determine the effect of urine on the ability to classify these cells. Results indicate that urine has no detrimental effect on prediction results.

Effects of cadmium on cellular protein and glutathione synthesis and expression of stress proteins in eastern oysters, Crassostrea virginica Gmelin

Cadmium (Cd) is an important toxicant in estuarine and coastal environments that can strongly affect energy balance of aquatic organisms by increasing the organism's basal energy demand and reducing its aerobic capacity. Mechanisms of cadmium-induced increase in basal metabolic costs are not well understood and may involve elevated detoxification costs due to the synthesis of cellular protective proteins and glutathione. We studied the short-term effects of cadmium exposure (4 h) on protein and glutathione (GSH) synthesis and expression of stress proteins (heat shock proteins HSP60, HSP70 and HSP90) and metallothioneins in isolated gill and hepatopancreas cells of the eastern oyster, Crassostrea virginica. Our study showed that exposure to cadmium resulted in a dose-dependent increase in the rate of protein synthesis in oyster cells, which reached 150% of the control at the highest tested Cd level (2000 micromol l(-1)). GSH synthesis was significantly inhibited by the highest Cd concentrations, especially in hepatopancreas, which resulted in a slight but significant decrease in the total GSH concentrations. Elevated protein synthesis was associated with the increased expression of metallothioneins and heat shock proteins. Interestingly, stress protein response differed considerably between gill and hepatopancreas cells. In hepatopancreas, expression of metallothionein mRNA (measured by real-time PCR) increased 2-8-fold in response to Cd exposure, whereas no significant increase in metallothionein expression was found in Cd-exposed gill cells. By contrast, HSP60 and HSP70 protein levels increased significantly in Cd-exposed gill cells (by 1.5-2-fold) but not in hepatopancreas. No change in HSP90 expression was detected in response to Cd exposure in oyster cells. These data indicate that metallothionein expression may provide sufficient protection against Cd-induced damage to intracellular proteins in hepatopancreas, alleviating the need for overexpression of molecular chaperones. By contrast, Cd detoxification mechanisms such as inducible metallothioneins and GSH appear to be insufficient to fully prevent protein damage in gill cells, thus necessitating induction of HSPs as a secondary line of cellular defense. Therefore, gills are likely to be among the most Cd-sensitive tissues in oysters, which may have important implications for impaired oxygen uptake contributing to energy misbalance and reduced aerobic scope in Cd-exposed oysters.

Effects of cyclic hypoxia on gene expression and reproduction in a grass shrimp, Palaemonetes pugio

Cyclic changes in dissolved oxygen occur naturally in shallow estuarine systems, yet little is known about the adaptations and responses of estuarine organisms to cyclic hypoxia. Here we examine the responses of Palaemonetes pugio, a species of grass shrimp, to cyclic hypoxia (1.5-8 mg/l dissolved oxygen; 4.20-22.42 kPa) at both the molecular and organismal levels. We measured alterations in gene expression in hepatopancreas tissue of female grass shrimp using custom cDNA macroarrays. After short-term (3-d) exposure to cyclic hypoxia, mitochondrial manganese superoxide dismutase (MnSOD) was upregulated and 70-kd heat shock proteins (HSP70) were downregulated. After 7-d exposure, nuclear genes encoding mitochondrial proteins (ribosomal protein S2, ATP synthase, very-long-chain specific acyl-CoA dehydrogenase [VLCAD]) were downregulated, whereas mitochondrial phosphoenol pyruvate carboxykinase (PEP Cbk) was upregulated. After 14 d, vitellogenin and apolipoprotein A1 were upregulated. Taken together, these changes suggest a shift in metabolism toward gluconeogenesis and lipid export. Long-term (77-d) exposure to hypoxia showed that profiles of gene expression returned to pre-exposure levels. These molecular responses differ markedly from those induced by chronic hypoxia. At the organismal level, cyclic hypoxia reduces the number of broods and eggs a female can produce. Demographic analysis showed a lower estimated rate of population growth in grass shrimp exposed to both continuous and short-term cyclic hypoxia, suggesting population-level impacts on grass shrimp.

Functional identification of an osmotic response element (ORE) in the promoter region of the killifish deiodinase 2 gene (FhDio2)

The physiological role played by thyroid hormones (TH) in hydro-osmotic homeostasis in fish remains a controversial issue. Previous studies have shown that in Fundulus heteroclitus (killifish) hypo-osmotic stress increases liver iodothyronine deiodinase type 2 (D2) mRNA and D2 activity. In this study we identified two conserved osmotic response element (ORE) motifs in the promoter region of the killifish D2 gene (FhDio2) and examined their possible role in the transcriptional regulation of FhDio2 during hypo-osmotic stress. As assessed by the electrophoretic mobility shift assay, results from in vivo and in vitro experiments demonstrate that exposure to an abrupt hyposmotic challenge triggers in the liver of killifish a strong nuclear recruitment of a putative osmotic response element binding protein (OREBP). This protein-DNA binding is time-dependent, attains a maximum within 2-8 h after the osmotic stress, and is followed by a significant increase in D2 activity. Furthermore, protein-DNA binding and the subsequent elevation in enzyme activity were blocked by the tyrosine kinase inhibitor genistein. Thus, during hypo-osmotic stress, a putative OREBP kinase-activated pathway stimulates FhDio2 transcription and enzymatic activity. These data and the fact that D2 is the major enzyme providing local intracellular T(3) suggest that TH plays a direct role in osmoregulation in fish, possibly by participating in hepatic ammonia metabolism. This study provides important insight into the physiological role of TH in hydro-osmotic homeostasis in fish.

Proteomic profiling of a parasitic wasp exposed to constant and fluctuating cold exposure

When insects are exposed to fluctuating thermal regimes (FTRs) (i.e., cold exposure alternating with periodic short pulses to high temperature), in contrast to constant low temperature (CLT), mortality due to accumulation of chill injuries is markedly reduced. To investigate the physiological processes behind the positive impact of FTR, based on a holistic approach, two-dimensional electrophoresis (2-DE) analysis were performed with the parasitic wasp Aphidius colemani. Parasitoid proteomes revealed 369 well-distinguishable protein spots, where the overall response to cold exposure was clearly specific to treatments (CLT versus FTR). The reduced mortality under FTR was associated with up-regulation of several proteins playing key roles in energy metabolism (glycolysis, TCA cycle, synthesis and conversion of ATP), protein chaperoning (Hsp70/Hsp90), and protein degradation (proteasome). Our results also support the idea that cytoskeleton components, particularly actin arrangement, could play a role in the higher survival rates of insects under FTR.

An inducible 70 kDa-class heat shock protein is constitutively expressed during early development and diapause in the annual killifish Austrofundulus limnaeus

The annual killifish Austrofundulus limnaeus inhabits ephemeral ponds in regions of northern South America, where they survive the periodic drying of their habitat as diapausing embryos. These diapausing embryos are highly resistant to a number of environmental insults such as high temperature, dehydration, anoxia, and increased salinity. Molecular chaperones are known to play a role in stabilizing protein structure and function during events of cellular stress. Relative levels of heat shock protein (Hsp)70 were measured in developing and diapausing embryos of A. limnaeus using quantitative Western blots. An inducible or embryo-specific form of Hsp70 is expressed during embryonic development in A. limnaeus and is elevated during diapause II in this species. Constitutive expression of Hsp70 during development may afford these embryos protection from environmental stresses during development more quickly than relying on the induction of a classic heat shock response.

Cell cycle checkpoints: the role and evaluation for early diagnosis of senescence, cardiovascular, cancer, and neurodegenerative diseases

Maintenance of genomic integrity is critical for prevention of a wide variety of adverse cellular effects including apoptosis, cellular senescence, and malignant cell transformation. Under stress conditions and even during an unperturbed cell cycle, checkpoint proteins play the key role in genome maintenance by and mediating cellular response to DNA damage, and represent an essential part of the "cellular stress response proteome". Intact checkpoint signal transduction cascades check the presence of genome damage, trigger cell cycle arrest, and forward the information to the protein core of cell cycle machinery, replication apparatus, repair, and/or apoptotic protein cores. Genetic checkpoint defects lead to syndromes that demonstrate chromosomal instability, increased sensitivity to genotoxic stress, tissue degeneration, developmental retardation, premature aging, and cancer predisposition that is most extensively studied for the ATM-checkpoint mutated in Ataxia telangiectasia. Tissue specific epigenetic control over the function of cell cycle checkpoints can be, further, misregulated by aberrant DNA methylation status. The consequent checkpoint dysregulation may result in tissue specific degenerative processes such as degeneration and calcification of heart aortic valves, diabetic cardiomyopathy, hyperhomocysteinemic cerebrovascular, peripheral vascular and coronary heart diseases, neurodegenerative disorders (Alzheimer and Parkinson diseases, amyotrophic lateral sclerosis, glaucoma), and accelerated aging frequently accompanied with cancer. This review focuses on the checkpoints shown to be crucial for unperturbed cell cycle regulation, dysregulation of which might be considered as a potential molecular marker for early diagnosis of and therapy efficiency in neurodegenerative, cardiovascular and cancer diseases. An application of the most potent detection technologies such as "Disease Proteomics and Transcriptomics" also considered here, allows a most specific selection of diagnostic markers.

Is there an emerging endosymbiotic relationship between mycobacteria and the human host based on horizontal transfer of genetic sequences?

While not negating the seriousness of tuberculosis and the need to prevent and combat the disease effectively, the large percentage of infected, apparently healthy individuals who harbour latent infections warrants consideration whether an endosymbiotic relationship is being established between mycobacteria and man. By means of a gene decay process eliminating their most metabolically important pathogenic genes associated with an increasing need for host gene products during prolonged intracellular survival, mycobacteria appears to be undergoing a process of establishing a less dangerous relationship with its host. To have tolerated this relationship over time, humans must have benefited. This is suggested to have occurred via changes in DNA higher order structure altering combinatorially regulated gene expression allowing increased cerebrodiversity. It can be expected that, beyond a certain threshold, negative effects ensued, leading to neuropathology and increased susceptibility for certain psychiatric disorders. These processes have probably been happening since the earliest contact with mycobacteria, but recently may have become modified by the emergence of epidemic tuberculosis and waves of increased oxidative stress following the circumstances associated with the Industrial Revolution and the more recent AIDS pandemic. The organism seems to have uniquely exploited the normal stress reaction of the host. Genomic stresses include changes associated with glucocorticoid effects as well as upregulated reactive oxygen species and stress/(heat shock) protein production, the latter two of which result in host cell cycle delay. Subsequently replication dependent chromosomal fragile sites appear in the host genome and together with upregulated chaperonins and mobile element activation, the scene is set for sequence exchange between the organism and host. If proven, these events raise the possibility of modifying chromatin epigenetically to retain the proposed advantages while silencing pathogenicity factors.

The cellular response to heat stress in the gobyGillichthys mirabilis: a cDNA microarray and protein-level analysis

The cellular response to stress relies on the rapid induction of genes encoding proteins involved in preventing and repairing macromolecular damage incurred as a consequence of environmental insult. To increase our understanding of the scope of this response, a cDNA microarray, consisting of 9207 cDNA clones, was used to monitor gene expression changes in the gill and white muscle tissues of a eurythermic fish, Gillichthys mirabilis(Gobiidae) exposed to ecologically relevant heat stress. In each tissue, the induction or repression of over 200 genes was observed. These genes are associated with numerous biological processes, including the maintenance of protein homeostasis, cell cycle control, cytoskeletal reorganization,metabolic regulation and signal transduction, among many others. In both tissues, the molecular chaperones, certain transcription factors and a set of additional genes with various functions were induced in a similar manner;however, the majority of genes displayed tissue-specific responses. In gill,thermal stress induced the expression of the major structural components of the cytoskeleton, whereas these same genes did not respond to heat in muscle. In muscle, many genes involved in promoting cell growth and proliferation were repressed, perhaps to conserve energy for repair and replacement of damaged macromolecules, but a similar repression was not observed in the gill. Many of the observed changes in gene expression were similar to those described in model species whereas many others were unexpected. Measurements of the concentrations of the protein products of selected genes revealed that in each case an induction in mRNA synthesis correlated with an increase in protein production, though the timing and magnitude of the increase in protein was not consistently predicted by mRNA concentration, an important consideration in assessing the condition of the stressed cell using transcriptomic analysis.

Constitutive and inducible stress proteins dominate the proteome of the murine inner medullary collecting duct-3 (mIMCD3) cell line

A proteome map of the most abundant proteins in the murine inner medullary collecting duct (mIMCD3) cell line was generated by 2-dimensional gel electrophoresis (2D-GE) combined with MALDI-TOF/TOF mass spectrometry. The 2-D model map identifies 77 distinct constitutive proteins and a total of 86 spots including isoforms. Protein identification was based on both peptide mass fingerprinting (MS) and peptide fragmentation (MS/MS) data. High confidence Mascot scores were obtained in the database search, due to the high quality and the number of MS/MS spectra which provided matching sequence information to the database. A functional classification of the identified proteins showed that a high proportion were stress proteins, such as heat shock proteins and proteins with anti-oxidant activity. Other proteins identified were involved in cytoskeletal maintenance, metabolism and energy generation, as well as in translation, transcription, RNA processing and other cell cycle processes. Exposure of the mIMCD3 cells to hyperosmotic stress using 600 mOsmol/kg NaCl or Urea or 700 mOsmol/kg NaCl-Urea (50:50) resulted in the greatest proteome upregulation in 700 mosM NaCl-Urea and the greatest downregulation in 600 mosM NaCl. Several proteins with molecular chaperone function were induced, such as alpha-B crystallin, two Hsp70 isoforms, the osmotic stress protein (Osp94), as well as aldose reductase. Additional isoforms of the translation elongation factors Eef2 and Eef1a1 were induced. Characterization of the phosphoproteome of mIMCD3 cells with a phosphoprotein-specific stain showed a significant proportion of the proteome was phosphorylated. Additionally, exposure of mIMCD3 cells to 600 mOsmol/kg NaCl hyperosmotic stress resulted in a 1.8-fold higher phosphorylation level of the most acidic isoform of the heat shock protein Hsp27 compared to its phosphorylation level under iso-osmotic conditions.

Post-genomics of the model haloarchaeon Halobacterium sp. NRC-1

Halobacteriumsp. NRC-1 is an extremely halophilic archaeon that is easily cultured and genetically tractable. Since its genome sequence was completed in 2000, a combination of genetic, transcriptomic, proteomic, and bioinformatic approaches have provided insights into both its extremophilic lifestyle as well as fundamental cellular processes common to all life forms. Here, we review post-genomic research on this archaeon, including investigations of DNA replication and repair systems, phototrophic, anaerobic, and other physiological capabilities, acidity of the proteome for function at high salinity, and role of lateral gene transfer in its evolution.

The significance of lipid composition for membrane activity: New concepts and ways of assessing function

In the last decade or so, it has been realised that membranes do not just have a lipid-bilayer structure in which proteins are embedded or with which they associate. Structures are dynamic and contain areas of heterogeneity which are vital for their formation. In this review, we discuss some of the ways in which these dynamic and heterogeneous structures have implications during stress and in relation to certain human diseases. A particular stress is that of temperature which may instigate adaptation in poikilotherms or appropriate defensive responses during fever in mammals. Recent data emphasise the role of membranes in sensing temperature changes and in controlling a regulatory loop with chaperone proteins. This loop seems to need the existence of specific membrane microdomains and also includes association of chaperone (heat stress) proteins with the membrane. The role of microdomains is then discussed further in relation to various human pathologies such as cardiovascular disease, cancer and neurodegenerative diseases. The concept of modifying membrane lipids (lipid therapy) as a means for treating such pathologies is then introduced. Examples are given when such methods have been shown to have benefit. In order to study membrane microheterogeneity in detail and to elucidate possible molecular mechanisms that account for alteration in membrane function, new methods are needed. In the second part of the review, we discuss ultra-sensitive and ultra-resolution imaging techniques. These include atomic force microscopy, single particle tracking, single particle tracing and various modern fluorescence methods. Finally, we deal with computing simulation of membrane systems. Such methods include coarse-grain techniques and Monte Carlo which offer further advances into molecular dynamics. As computational methods advance they will have more application by revealing the very subtle interactions that take place between the lipid and protein components of membranes - and which are so essential to their function.

Intracellular water homeostasis and the mammalian cellular osmotic stress response

The cellular response to osmotic stress ensures that the concentration of water inside the cell is maintained within a range that is compatible with biologic function. Single cell organisms are particularly dependent on mechanisms that permit adaptation to osmotic stress because each individual cell is directly exposed to the external environment. Mammals, however, limit osmotic stress by establishing an internal aqueous environment in which intravascular water and electrolytes are subject to sensitive and dynamic, organism-based homeostatic regulation. Recent studies of NFAT5/TonEBP, an essential mammalian osmoregulatory transcription factor, demonstrate the unexpected yet critical significance of cell-based osmotic regulation in vivo. These results highlight the fundamental importance of maintaining intracellular water homeostasis in the face of varying cellular metabolic activity and distinct tissue microenvironments.

MOLECULAR AND EVOLUTIONARY BASIS OF THE CELLULAR STRESS RESPONSE

The cellular stress response is a universal mechanism of extraordinary physiological/pathophysiological significance. It represents a defense reaction of cells to damage that environmental forces inflict on macromolecules. Many aspects of the cellular stress response are not stressor specific because cells monitor stress based on macromolecular damage without regard to the type of stress that causes such damage. Cellular mechanisms activated by DNA damage and protein damage are interconnected and share common elements. Other cellular responses directed at re-establishing homeostasis are stressor specific and often activated in parallel to the cellular stress response. All organisms have stress proteins, and universally conserved stress proteins can be regarded as the minimal stress proteome. Functional analysis of the minimal stress proteome yields information about key aspects of the cellular stress response, including physiological mechanisms of sensing membrane lipid, protein, and DNA damage; redox sensing and regulation; cell cycle control; macromolecular stabilization/repair; and control of energy metabolism. In addition, cells can quantify stress and activate a death program (apoptosis) when tolerance limits are exceeded.

Heat stress induces different forms of cell death in sea anemones and their endosymbiotic algae depending on temperature and duration

Bleaching of reef building corals and other symbiotic cnidarians due to the loss of their dinoflagellate algal symbionts (=zooxanthellae), and/or their photosynthetic pigments, is a common sign of environmental stress. Mass bleaching events are becoming an increasingly important cause of mortality and reef degradation on a global scale, linked by many to global climate change. However, the cellular mechanisms of stress-induced bleaching remain largely unresolved. In this study, the frequency of apoptosis-like and necrosis-like cell death was determined in the symbiotic sea anemone Aiptasia sp. using criteria that had previously been validated for this symbiosis as indicators of programmed cell death (PCD) and necrosis. Results indicate that PCD and necrosis occur simultaneously in both host tissues and zooxanthellae subject to environmentally relevant doses of heat stress. Frequency of PCD in the anemone endoderm increased within minutes of treatment. Peak rates of apoptosis-like cell death in the host were coincident with the timing of loss of zooxanthellae during bleaching. The proportion of apoptosis-like host cells subsequently declined while cell necrosis increased. In the zooxanthellae, both apoptosis-like and necrosis-like activity increased throughout the duration of the experiment (6 days), dependent on temperature dose. A stress-mediated PCD pathway is an important part of the thermal stress response in the sea anemone symbiosis and this study suggests that PCD may play different roles in different components of the symbiosis during bleaching.

The transcriptional response to hypoxic insult controlled by FRA-2

FRA-2 is involved in cellular differentiation and is also upregulated in response to ischemic injury to the brain. To shed light on the function of this transcription factor, a novel microarray analysis was utilized to identify FRA-2-dependent gene expression increased in the hypoxic response. Genes were identified that were upregulated by exposure of neuronally differentiated PC12 cells to hypoxia. Using a dominant negative construct to block FRA-2, a second subset of genes that were FRA-2 dependent was found. Cross comparison then allowed isolation of a list of genes that were induced in response to hypoxia in a FRA-2-dependent manner. These data suggest that FRA-2 is involved in the transcriptional control of neuroprotective genes and in the switch from aerobic to anaerobic metabolism.

Stress-related genomic responses during the course of heat acclimation and its association with ischemic-reperfusion cross-tolerance

Acclimation to heat is a biphasic process involving a transient perturbed phase followed by a long lasting period during which acclimatory homeostasis is developed. In this investigation, we used cDNA stress microarray (Clontech Laboratory) to characterize the stress-related genomic response during the course of heat acclimation and to test the hypotheses that 1) heat acclimation influences the threshold of activation of protective molecular signaling, and 2) heat-acclimation-mediated ischemic-reperfusion (I/R) protection is coupled with reprogrammed gene expression leading to altered capacity or responsiveness of protective-signaling pathways shared by heat and I/R cytoprotective systems. Rats were acclimated at 34°C for 0, 2, and 30 days.32P-labeled RNA samples prepared from the left ventricles of rats before and after subjection to heat stress (HS; 2 h, 41°C) or after I/R insult (ischemia: 75%, 45 min; reperfusion: 30 min) were hybridized onto the array membranes. Confirmatory RT-PCR of selected genes conducted on samples taken at 0, 30, and 60 min after HS or total ischemia was used to assess the promptness of the transcriptional response. Cluster analysis of the expressed genes indicated that acclimation involves a “two-tier” defense strategy: an immediate transient response peaking at the initial acclimating phase to maintain DNA and cellular integrity, and a sustained response, correlated with slowly developed adaptive, long-lasting cytoprotective signaling networks involving genes encoding proteins that are essential for the heat-shock response, antiapoptosis, and antioxidation. Gene activation was stress specific. Faster activation and suppression of signaling pathways shared by HS and I/R stressors probably contribute to heat-acclimation I/R cross-tolerance.