Extended longevity of Caenorhabditis elegans by knocking in extra copies of hsp70F, a homolog of mot-2 (mortalin)/mthsp70/Grp75

Hormesis in aging

Hormesis in aging is represented by mild stress-induced stimulation of protective mechanisms in cells and organisms resulting in biologically beneficial effects. Single or multiple exposure to low doses of otherwise harmful agents, such as irradiation, food limitation, heat stress, hypergravity, reactive oxygen species and other free radicals have a variety of anti-aging and longevity-extending hormetic effects. Detailed molecular mechanisms that bring about the hormetic effects are being increasingly understood, and comprise a cascade of stress response and other pathways of maintenance and repair. Although the extent of immediate hormetic effects after exposure to a particular stress may only be moderate, the chain of events following initial hormesis leads to biologically amplified effects that are much larger, synergistic and pleiotropic. A consequence of hormetic amplification is an increase in the homeodynamic space of a living system in terms of increased defence capacity and reduced load of damaged macromolecules. Hormetic strengthening of the homeodynamic space provides wider margins for metabolic fluctuation, stress tolerance, adaptation and survival. Hormesis thus counter-balances the progressive shrinkage of the homeodynamic space, which is the ultimate cause of aging, diseases and death. Healthy aging may be achieved by hormesis through mild and periodic, but not severe or chronic, physical and mental challenges, and by the use of nutritional hormesis incorporating mild stress-inducing molecules called hormetins. The established scientific foundations of hormesis are ready to pave the way for new and effective approaches in aging research and intervention.

Caenorhabditis elegans mitochondrial mutants as an investigative tool to study human neurodegenerative diseases associated with mitochondrial dysfunction

In humans, well over one hundred diseases have been linked to mitochondrial dysfunction and many of these are associated with neurodegeneration. At the root of most of these diseases lay ineffectual energy production, caused either by direct or indirect disruption to components of the mitochondrial electron transport chain. It is surprising then to learn that, in the nematode Caenorhabditis elegans, a collection of mutants which share disruptions in some of the same genes that cause mitochondrial pathogenesis in humans are in fact long-lived. Recently, we resolved this paradox by showing that the C. elegans "Mit mutants" only exhibit life extension in a defined window of mitochondrial dysfunction. Similar to humans, when mitochondrial dysfunction becomes too severe these mutants also exhibit pathogenic life reduction. We have proposed that life extension in the Mit mutants occurs as a by-product of compensatory processes specifically activated to maintain mitochondrial function. We have also proposed that similar kinds of processes may act to delay the symptomatic appearance in many human mitochondrial-associated disorders. In the present report, we describe our progress in using the Mit mutants as an investigative tool to study some of the processes potentially employed by human cells to offset pathological mitochondrial dysfunction.

Mortalin is a novel mediator of erythropoietin signaling

Erythropoietin (EPO) stimulates erythroid growth by enhancing the proliferation, maturation and survival of late-stage erythroid progenitor cells. However, the entire process of EPO stimulation remains undetermined. To further clarify the intracellular mechanisms by which EPO affects the growth of erythroid progenitor cells, we analyzed proteins obtained from purified human erythroid colony-forming cells (ECFCs) cultured with or without EPO, and one of the proteins apparently related with EPO stimuli was identified as mortalin (mthsp70/PBP74/Grp75/mot-2), which is a member of the heat shock protein 70 family of chaperones. The amount of mortalin mRNA in ECFCs increased in an EPO dose-dependent manner, and ECFC growth was dependent on the amount of mortalin. Furthermore, expression of mortalin in ECFCs was suppressed by a phosphatidylinositol 3-kinase inhibitor. Finally, we analyzed gene expression patterns in ECFCs cultured with or without EPO after treatment with mortalin small interfering RNA (siRNA) using a DNA microarray. When ECFCs treated with mortalin siRNA were cultured with EPO, the expression of several genes overlapped with the profile seen in control ECFCs cultured without EPO. Our data suggest that mortalin is involved in the mediation of EPO signaling and plays an important role in stimulating the growth of erythroid progenitor cells.

Anoxia tolerance in turtles: Metabolic regulation and gene expression

Freshwater turtles of the Trachemys and Chrysemys genera are champion facultative anaerobes able to survive for several months without oxygen during winter hibernation in cold water. They have been widely used as models to identify and understand the molecular mechanisms of natural anoxia tolerance and the molecular basis of the hypoxic/ischemic injuries that occur in oxygen-sensitive systems and underlie medical problems such as heart attack and stroke. Peter L. Lutz spent much of his career investigating turtle anaerobiosis with a particular focus on the mechanisms of brain ion homeostasis and neurotransmitter responses to anoxia exposure and the mechanisms that suppress brain ion channel function and neuronal excitability during anaerobiosis. Our interests intersected over the mechanisms of metabolic rate depression which is key to long term anoxia survival. Studies in my lab have shown that a key mechanism of metabolic arrest is reversible protein phosphorylation which provides coordinated suppression of the rates of multiple ATP-producing, ATP-utilizing and related cellular processes to allow organisms to enter a stable hypometabolic state. Anoxia tolerance is also supported by selective gene expression as revealed by recent studies using cDNA library and DNA array screening. New studies with both adult T. scripta elegans and hatchling C. picta marginata have identified prominent groups of genes that are up-regulated under anoxia in turtle organs, in several cases suggesting aspects of cell function and metabolic regulation that have not previously been associated with anaerobiosis. These groups of anoxia-responsive genes include mitochondrially-encoded subunits of electron transport chain proteins, iron storage proteins, antioxidant enzymes, serine protease inhibitors, transmembrane solute carriers, neurotransmitter receptors and transporters, and shock proteins.

Quantum dot-based mortalin staining as a visual assay for detection of induced senescence in cancer cells

Quantum dots (QDs) are fluorescent nanocrystals that are emerging as fine alternatives to the conventional organic dyes. They have several advantages including greater photostability and a wider range of excitation-emission wavelengths. By using mortalin staining as a model, we initially demonstrated that the QDs are more stable and provide better resolution in protein imaging in fixed cells. With the help of an internalizing antibody, we generated internalizing QD (i-QD) and demonstrated its inertness to cell replication, structure, and viability. Based on the superior resolution, stability and inertness, we propose the use of QD staining of mortalin as a cell-based visual assay to screen for senescence-inducing drugs, proteins, and siRNAs.

Molecular chaperones regulate p53 and suppress senescence programs

Many types of cancer cells constitutively express major molecular chaperones at high levels. Recent findings demonstrate that specific depletion of individual chaperones, including various members of the Hsp70 family, small heat shock proteins, or VCP/p97, leads to activation of p53 pathway and subsequently triggers cellular senescence. Here, we discuss a possibility that in cancer cells high levels of chaperones serve to keep the p53 signaling under control, thus allowing cancer cells to evade the default senescence and form tumors.

Analyses of human-chimpanzee orthologous gene pairs to explore evolutionary hypotheses of aging

Compared to chimpanzees (Pan troglodytes), the onset of aging appears to be delayed in the human species. Herein, we studied human-chimpanzee orthologous gene pairs to investigate the selective forces acting on genes associated with aging in different model systems, which allowed us to explore evolutionary hypotheses of aging. Our results show that aging-associated genes tend to be under purifying selection and stronger-than-average functional constraints. We found little evidence of accelerated evolution in aging-associated genes in the hominid or human lineages, and pathways previously related to aging were largely conserved between humans and chimpanzees. In particular, genes associated with aging in non-mammalian model organisms and cellular systems appear to be under stronger functional constraints than those associated with aging in mammals. One gene that might have undergone rapid evolution in hominids is the Werner syndrome gene. Overall, our findings offer novel insights regarding the evolutionary forces acting on genes associated with aging in model systems. We propose that genes associated with aging in model organisms may be part of conserved pathways related to pleiotropic effects on aging that might not regulate species differences in aging.

On why decreasing protein synthesis can increase lifespan

An explanation is offered for the increased lifespan of Caenorhabditis elegans when mRNA translation is inhibited due to loss of the initiation factor IFE-2 [Hansen, M., Taubert, T., Crawford, D., Libina, N., Lee, S.-J., Kenyon, C., 2007. Lifespan extension by conditions that inhibit translation in Caenorhabditis elegans. Ageing Cell 6, 95-110; Pan, K.Z., Palter, J.E., Rogers, A.N., Olsen, A., Chen, D., Lithgow, G.J., Kapahi, P., 2007. Inhibition of mRNA translation extends lifespan in Caenorhabditis elegans. Ageing Cell 6, 111-119; Syntichaki, P., Troulinaki, K., Tavernarakis, N., 2007. eIF4E function in somatic cells modulates ageing in Caenorhabditis elegans. Nature 445, 922-926]. It is suggested that the general reduction of protein synthesis, due to the decreased frequency of mRNA translation, also lowers the cellular load of erroneously synthesized polypeptides which the constitutive protein homeostatic apparatus (proteases and chaperones proteins) normally eliminates. This situation results in "spare" proteolytic and chaperone function which can then deal with those proteins modified post-synthetically, e.g. by oxidation and/or glycation, which are thought to contribute to the senescent phenotype. This increased availability of proteolytic and chaperone functions may thereby contribute to the observed increase in organism stress resistance and lifespan.

Three faces of mortalin: a housekeeper, guardian and killer

Mortalin was first cloned as a mortality factor that existed in the cytoplasmic fractions of normal, but not in immortal, mouse fibroblasts. A decade of efforts have expanded its persona from a house keeper protein involved in mitochondrial import, energy generation and chaperoning of misfolded proteins, to a guardian of stress that has multiple binding partners and to a killer protein that contributes to carcinogenesis on one hand and to old age disorders on the other. Being proved to be an attractive target for cancer therapy, it also warrants attention from the perspectives of management of old age diseases and healthy aging.

Knockdown of mitochondrial heat shock protein 70 promotes progeria-like phenotypes in caenorhabditis elegans

Mitochondrial heat shock protein 70 (mthsp70) functions as a mitochondrial import motor and is essential in mitochondrial biogenesis and energy generation in eukaryotic cells. HSP-6 (hsp70F) is a nematode orthologue of mthsp70. Knockdown of HSP-6 by RNA interference in young adult nematodes caused a reduction in the levels of ATP-2, HSP-60 and CLK-1, leading to abnormal mitochondrial morphology and lower ATP levels. As a result, RNA interference-treated worms had lower motility, defects in oogenesis, earlier accumulation of autofluorescent material, and a shorter life span. These are the major phenotypes observed during the aging of worms, suggesting that the reduction of HSP-6 causes early aging or progeria-like phenotypes. The amount of HSP-6 became dramatically reduced at the expected mean life span in not only wild-type but also in long and short life span mutant worms (wild-type, daf-2, and daf-16). Mitochondrial HSP-60 and ATP-2 were also reduced following the reduction of HSP-6 during aging. These results suggest that the reduction of HSP-6 causes defects in mitochondrial function at the final stage of aging, leading to mortality.

Mortalin is regulated by APOE in hippocampus of AD patients and by human APOE in TR mice

Mortalin is a chaperone protein associated with cell survival, stress response, intracellular trafficking, control of cell proliferation, mitochondrial biogenesis, and cell fate determination. Human APOE targeted replacement (TR) mice have been used to elucidate the role of APOE4 in Alzheimer's disease (AD), since these animals express the APOE4 gene without the classical pathological signatures of AD. Using proteomics we found that mortalin isoforms are differentially expressed in the hippocampus of APOE4 TR mice compared with the APOE3 (control) TR mice. We also observed that these mortalin isoforms are differentially phosphorylated. Then we studied mortalin expression in patients with AD (genotypes APOE 3/3 and APOE 4/4) compared with patients without AD (genotype APOE 3/3). We observed that mortalin isoforms are also differentially expressed in the hippocampi of patients with AD, and that the expression of these mortalin isoforms is regulated by the APOE genotype. We propose that the differential regulation of mortalin in AD and by the APOE genotype is a cellular defense mechanism responding to increases in oxidative stress.

Heat-shock transcription factor (HSF)-1 pathway required for Caenorhabditis elegans immunity

Innate immunity comprises physical barriers, pattern-recognition receptors, antimicrobial substances, phagocytosis, and fever. Here we report that increased temperature results in the activation of a conserved pathway involving the heat-shock (HS) transcription factor (HSF)-1 that enhances immunity in the invertebrate Caenorhabditis elegans. The HSF-1 defense response is independent of the p38 MAPK/PMK-1 pathway and requires a system of chaperones including small and 90-kDa inducible HS proteins. In addition, HSF-1 is needed for the effects of the DAF-2 insulin-like pathway in defense to pathogens, indicating that interacting pathways control stress response, aging, and immunity. The results also show that HSF-1 is required for C. elegans immunity against Pseudomonas aeruginosa, Salmonella enterica, Yersinia pestis, and Enterococcus faecalis, indicating that HSF-1 is part of a multipathogen defense pathway. Considering that several coinducers of HSF-1 are currently in clinical trials, this work opens the possibility that activation of HSF-1 could be used to boost immunity to treat infectious diseases and immunodeficiencies.

On the brotherhood of the mitochondrial chaperones mortalin and heat shock protein 60

The heat shock chaperones mortalin/mitochondrial heat shock protein 70 (mtHsp70) and Hsp60 are found in multiple subcellular sites and function in the folding and intracellular trafficking of many proteins. The chaperoning activity of these 2 proteins involves different structural and functional mechanisms. In spite of providing an excellent model for an evolutionarily conserved molecular "brotherhood", their individual functions, although overlapping, are nonredundant. As they travel to various locations, both chaperones acquire different binding partners and exert a more divergent involvement in tumorigenesis, cellular senescence, and immunology. An understanding of their functional biology may lead to novel designing and development of therapeutic strategies for cancer and aging.

Is (your cellular response to) stress killing you?

Free radicals provide a generally accepted explanation for age-related decline in tissue function. However, the free radical hypothesis does not provide a mechanistic course of action to explain exactly how damage to macromolecules translates into the recognizable pathophysiology of aged organisms. Recent advances in the fields of DNA damage and cellular senescence point towards a substantial role for the DNA damage response, rather than DNA mutations per se, in the genesis of cellular and/or tissue damage. Furthermore, several studies suggest that protein damage can be at least as important as DNA damage in bringing about the aging phenotype. Here we propose that a "protein damage response," namely the ER/UPR (endoplasmic reticulum/unfolded protein) stress response is likely to play an important role in the aging process.

Structural and functional differences between mouse mot-1 and mot-2 proteins that differ in two amino acids

Chaperone functions mediated by the heat-shock protein (HSP) family constitute a fundamental mechanism that governs the life span of organisms. Here we investigated the chaperone activities of the mitochondrial HSP70 protein, mortalin, which is a heat-uninducible stress protein involved in immortalization and tumorigenesis. There are two mortalin alleles, mot-1 and mot-2, in mouse, encoding two distinct proteins. Whereas an overexpression of mot-1-induced senescence in NIH 3T3 cells, overexpression of mot-2 promoted their malignant properties. Here, we provide evidence that mot-1 possesses very low chaperone activity as compared to mot-2. A "lazy lid" hypothesis is proposed for their differential aging phenotypes.

Using Caenorhabditis elegans as a model for aging and age-related diseases

During the last three decades the soil nematode C. elegans has become a prominent model organism for studying aging. Initially research in the C. elegans aging field was focused on the genetics of aging and single gene mutations that dramatically increased the life span of the worm. Undoubtedly, the existence of such mutations is one of the main reasons for the popularity of the worm as model system for studying aging. However, today many different approaches are being used in the C. elegans aging field in addition to genetic manipulations that influence life span. For example, environmental manipulations such as caloric restriction and hormetic treatments, evolutionary studies, population studies, models of age-related diseases, and drug screening for compounds that extend life span are now being investigated using this nematode. This review will focus on the most recent developments in C. elegans aging research with the aim of illustrating the diversity of the field.

Lifespan extension of Caenorhabditis elegans following repeated mild hormetic heat treatments

Mild hormetic heat treatments early in life can significantly increase the lifespan of the nematode C. elegans. We have examined the effects of heat treatments at different ages and show that treatments early in life cause the largest increases in lifespan. We also find that repeated mild heat treatments throughout life have a larger effect on lifespan compared to a single mild heat treatment early in life. We hypothesize that the magnitude of the hormetic effect is related to the levels of heat shock protein expression. Following heat treatment young worms show a dramatic increase in the levels of the small heat shock protein HSP-16 whereas old worms are a 100-fold less responsive. The levels of the heat shock proteins HSP-4 and HSP-16 correlate well with the effects on lifespan by the hormetic treatments.

Checkpoint proteins control survival of the postmitotic cells in Caenorhabditis elegans

Checkpoints are evolutionarily conserved signaling mechanisms that arrest cell division and alter cellular stress resistance in response to DNA damage or stalled replication forks. To study the consequences of loss of checkpoint functions in whole animals, checkpoint genes were inactivated in the nematode C. elegans. We show that checkpoint proteins are not only essential for normal development but also determine adult somatic maintenance. Checkpoint proteins play a role in the survival of postmitotic adult cells.

Upregulation of mortalin/mthsp70/Grp75 contributes to human carcinogenesis

Mortalin, also known as mthsp70/GRP75/PBP74, interacts with the tumor suppressor protein p53 and inactivates its transcriptional activation and apoptotic functions. Here, we examined the level of mortalin expression in a large variety of tumor tissues, tumor-derived and in vitro immortalized human cells. It was elevated in many human tumors, and in all of the tumor-derived and in vitro immortalized cells. In human embryonic fibroblasts immortalized with an expression plasmid for hTERT, the telomerase catalytic subunit, with or without human papillomavirus E6 and E7 genes, we found that subclones with spontaneously increased mortalin expression levels became anchorage-independent and acquired the ability to form tumors in nude mice. Furthermore, overexpression of mortalin was sufficient to increase the malignancy of breast carcinoma cells. The study demonstrates that upregulation of mortalin contributes significantly to tumorigenesis, and thus is a good candidate target for cancer therapy.

Hormetic modulation of aging and longevity by mild heat stress

Aging is characterized by a stochastic accumulation of molecular damage, progressive failure of maintenance and repair, and consequent onset of age-related diseases. Applying hormesis in aging research and therapy is based on the principle of stimulation of maintenance and repair pathways by repeated exposure to mild stress. In a series of experimental studies we have shown that repetitive mild heat stress has anti-aging hormetic effects on growth and various other cellular and biochemical characteristics of human skin fibroblasts undergoing aging in vitro. These effects include the maintenance of stress protein profiles, reduction in the accumulation of oxidatively and glycoxidatively damaged proteins, stimulation of the proteasomal activities for the degradation of abnormal proteins, improved cellular resistance to ethanol, hydrogen peroxide and ultraviolet-B rays, and enhanced levels of various antioxidant enzymes. Anti-aging hormetic effects of mild heat shock appear to be facilitated by reducing protein damage and protein aggregation by activating internal antioxidant, repair and degradation processes.

Thermoregulation in the life cycle of nematodes

An unanswered question in the biology of many parasites is the mechanism by which environmental (or external) and intrinsic signals are integrated to determine the switch from one developmental stage to the next. This is particularly pertinent for nematode parasites, many of which have a free-living stage in the environment prior to infection of the mammalian host, or for parasites such as filarial nematodes, which utilise an insect vector for transmission. The environmental changes experienced by a parasite upon infection of a mammalian host are extremely complex and poorly understood. However, the ability of a parasite to sense its new environment must be intrinsically linked to its developmental programme, as progression of the life cycle is dependent upon the infection event. In this review, the relationship between temperature and development in filarial nematodes and in the free-living species Caenorhabditis elegans is summarised, with a focus on the role of heat shock factor and heat shock protein 90 in the nematode life cycle.

Nutrient-gene interaction in ageing and successful ageing. A single nutrient (zinc) and some target genes related to inflammatory/immune response

In this paper, we reviewed data regarding to the pivotal role played by the zinc-gene interaction in affecting some relevant cytokines (IL-6 and TNF-alpha) and heat shock proteins (Hsp70-2) in ageing, successful ageing (nonagenarians) and in some age-related diseases (atherosclerosis and infections). The polymorphisms of the genes codifying these proteins are predictive on one hand in longevity, such as IL-6 -174G/C locus, on the other hand 1267 Hsp70-2A/B or TNF-alpha -308G/A polymorphisms are associated to worsening atherosclerosis or severe infections, respectively, rather than longevity. Taking into account that longevity has a strong genetic component but, at the same time, is affected by life style and environmental factors, the analysis of these polymorphisms in association to some immune parameters (NK cell cytotoxicity) and nutritional factors (zinc) is a useful tool to unravel the role played by these genetic factors in longevity and in the appearance of age-related diseases. Indeed, these polymorphisms are associated with chronic inflammation, low zinc ion bioavailability, depressed innate immune response and high gene expression of metallothioneins, which have a limited zinc release for an optimal innate immune response in ageing. Therefore, the nutrient (zinc)-gene (IL-6, TNF-alpha and Hsp70-2) interaction is pivotal to keep under control the inflammatory/immune response with subsequent longevity, indicating these genes as "robust" for "healthy ageing".

Comparative analysis of the expressed genome of the infective juvenile entomopathogenic nematode, Heterorhabditis bacteriophora

We report the first cDNA-sequencing project of the entomopathogenic nematode, Heterorhabditis bacteriophora. A total of 1246 expressed sequence tags (ESTs) were generated by random sequencing of clones from a cDNA library of the infective juvenile stage. The ESTs were annotated resulting in 1072 useful ESTs that were categorized into functional categories according to Kyoto Encyclopedia of Genes and Genomes. Approximately 459 of 1072 ESTs (43%) had significant similarities to annotated sequences in GenBank. Of these, 417 had significant similarities to the free-living nematode Caenorhanditis elegans proteins. Most ESTs (18%) belonged to the genetic information processing category followed by metabolism (15% ESTs) and environmental information processing (15%) pathways. Several interesting ESTs were found that may have roles in the infectivity and survival of infective juveniles. These included proteases, dauer pathway genes (akt-1, pdk-1 & daf-7) and aging and stress resistance genes such as superoxide dismutase (sod-4), heat shock genes (hsp-4 & hsp-6), and eat genes, and signaling proteins like G-protein coupled receptors, regulators of G-protein signaling (rgs), and serine/threonine kinases. Other interesting ESTs include systemic RNAi defective protein (sid-1), ribonuclease III family members (rnh-2 &rnc) and transposase gene (Tc3A). About 67% of the ESTs did not find matches in any of the searched databases suggesting potentially novel genes in this enomopathogenic nematode. Note: Sequences described in this paper have been deposited in Genbank under the accessions DN 152655-DN 152999, and DN 153000-DN 153726.

Functional and phenotypic relevance of differentially expressed proteins in calcineurin mutants ofCaenorhabditis elegans

Calcineurin is a heterodimeric serine/threonine protein phosphatase, important for many cellular processes such as T-cell regulation, cardiac hypertrophy and kidney development. We previously reported the characterization of Caenorhabditis elegans calcineurin mutants as providing a simple but excellent genetic model system for studying in vivo functions of calcineurin. Calcineurin loss-of-function mutants, cnb-1(lf), and gain-of-function mutants, tax-6(gf), show certain opposite phenotypes as well as some similar phenotypes. In order to explain the phenotypic similarity observed in both loss-of-function and gain-of-function mutants, we examined the proteins that followed similar trends in both mutants relative to wild-type worms by using 2-DE. Interestingly, VHA-13, HSP-6 and phosphoenolpyruvate carboxykinase are down-regulated in both mutants. A total of 96 differentially regulated proteins were identified by MALDI-TOF/MS. Among these, 42 proteins are up-regulated and 54 proteins are down-regulated in calcineurin mutants. Furthermore, knock-down of about 30% of the genes, which are down-regulated in calcineurin mutants, showed some of the phenotypes of calcineurin-null mutants. This analysis suggests the functional relevance of these proteins to calcineurin activity in C. elegans.

Understanding and modulating ageing

Ageing is characterized by a progressive accumulation of molecular damage in nucleic acids, proteins and lipids. The inefficiency and failure of maintenance, repair and turnover pathways is the main cause of age-related accumulation of damage. Research in molecular gerontology is aimed at understanding the genetic and epigenetic regulation of survival and maintenance mechanisms at the levels of transcription, post-transcriptional processing, post-translational modifications, and interactions among various gene products. Concurrently, several approaches are being tried and tested to modulate ageing in a wide variety of organisms. The ultimate aim of such studies is to improve the quality of human life in old age and prolong the health-span. Various gerontomodulatory approaches include gene therapy, hormonal supplementation, nutritional modulation and intervention by free radical scavengers and other molecules. A recent approach is that of applying hormesis in ageing research and therapy, which is based on the principle of stimulation of maintenance and repair pathways by repeated exposure to mild stress. A combination of molecular, physiological and psychological modulatory approaches can realize "healthy ageing" as an achievable goal in the not-so-distant future.

The C. elegans ortholog of mammalian Ku70, interacts with insulin-like signaling to modulate stress resistance and life span

The mammalian Ku heterodimer has important roles in DNA double strand break repair, telomere maintenance, cell cycle checkpoint-arrest, tumor suppression, and cellular stress resistance. To investigate the evolutionarily conserved functions of Ku, we knocked down expression by RNA interference (RNAi) of Ku genes in C. elegans. We found that C. elegans Ku70 (CKU-70) is required for resistance to genotoxic stress, regulates cytotoxic stress responses, and influences aging. The latter effects are dependent on an IGF-1/insulin-like signaling pathway previously shown to affect life span. Reduction of CKU-70 activity amplifies the aging phenotype of long-lived insulin receptor daf-2 mutations in a daf-16-dependent manner. These observations support the view that organismal stress resistance determines life span and Ku70 modulates these effects.

Defense against protein carbonylation by DnaK/DnaJ and proteases of the heat shock regulon

Protein carbonylation is an irreversible oxidative modification that increases during organism aging and bacterial growth arrest. We analyzed whether the heat shock regulon has a role in defending Escherichia coli cells against this deleterious modification upon entry into stationary phase. Providing the cell with ectopically elevated levels of the heat shock transcription factor, sigma32, effectively reduced stasis-induced carbonylation. Separate overproduction of the major chaperone systems, DnaK/DnaJ and GroEL/GroES, established that the former of these is more important in counteracting protein carbonylation. Deletion of the heat shock proteases Lon and HslVU enhanced carbonylation whereas a clpP deletion alone had no effect. However, ClpP appears to have a role in reducing protein carbonyls in cells lacking Lon and HslVU. Proteomic immunodetection of carbonylated proteins in the wild-type, lon, and hslVU strains demonstrated that the same spectrum of proteins displayed a higher load of carbonyl groups in the lon and hslVU mutants. These proteins included the beta-subunit of RNA polymerase, elongation factors Tu and G, the E1 subunit of the pyruvate dehydrogenase complex, isocitrate dehydrogenase, 6-phosphogluconate dehydrogenase, and serine hydroxymethyltranferase.

Ageing and metabolism: drug discovery opportunities

There has recently been significant progress in our understanding of the mechanisms that regulate ageing, and it has been shown that changes in single genes can dramatically extend lifespan and increase resistance to many diseases. Furthermore, many of these genes belong to evolutionarily conserved pathways that also control energy metabolism. In this review, we describe the shared molecular machinery that regulates ageing and energy metabolism. Although drugs to slow ageing face severe regulatory hurdles, it is likely that an understanding of ageing pathways will help to identify novel drug targets to treat metabolic disorders and other age-related diseases.

Longevity genes: from primitive organisms to humans

Recent results indicate that the longevity of both invertebrates and vertebrates can be altered through genetic manipulation and pharmacological intervention. Most of these interventions involve alterations of one or more of the following: insulin/IGF-I signaling pathway, caloric intake, stress resistance and nuclear structure. How longevity regulation relates to aging per se is less clear, but longevity increases are usually accompanied by extended periods of good health. How these results will translate to primate aging and longevity remains to be shown.

Paeoniflorin, a novel heat shock protein-inducing compound

Heat shock proteins (HSPs) are induced by various physical, chemical, and biological stresses. HSPs are known to function as molecular chaperones, and they not only regulate various processes of protein biogenesis but also function as lifeguards against proteotoxic stresses. Because it is very useful to discover nontoxic chaperone-inducing compounds, we searched for them in herbal medicines. Some herbal medicines had positive effects on the induction of HSPs (Hsp70, Hsp40, and Hsp27) in cultured mammalian cells. We next examined 2 major constituents of these herbal medicines, glycyrrhizin and paeoniflorin, with previously defined chemical structures. Glycyrrhizin had an enhancing effect on the HSP induction by heat shock but could not induce HSPs by itself. In contrast, paeoniflorin had not only an enhancing effect but also an inducing effect by itself on HSP expression. Thus, paeoniflorin might be termed a chaperone inducer and glycyrrhizin a chaperone coinducer. Treatment of cells with paeoniflorin but not glycyrrhizin resulted in enhanced phosphorylation and acquisition of the deoxyribonucleic acid-binding ability of heat shock transcription factor 1 (HSF1), as well as the formation of characteristic HSF1 granules in the nucleus, suggesting that the induction of HSPs by paeoniflorin is mediated by the activation of HSF1. Also, thermotolerance was induced by treatment with paeoniflorin but not glycyrrhizin. Paeoniflorin had no toxic effect at concentrations as high as 80 microg/ mL (166.4 microM). To our knowledge, this is the first report on the induction of HSPs by herbal medicines.

Imminent approaches towards molecular interventions in ageing

Ageing is an innate feature of living organisms. Sensational progress in its molecular understanding in the last decade has culminated into a highly complex picture. Emerging from this complexity are the distinctive roles of some of the tumor suppressor pathways including p53 and pRB in maintenance of senescence phenotype, and telomere maintaining pathways in its escape. We discuss here the current scenario of molecular ageing and the use of modern approaches for its intervention in culture system, at least. Many of the tools we describe here are the newly emergent functional RNA tools that are proved to be fruitful in decoding the human genome. These post-genomic technologies will help us in the discovery of gene targets for interventions aiming to improve the quality at later years of life beyond their mere algebraic extension.

Life long calorie restriction increases heat shock proteins and proteasome activity in soleus muscles of Fisher 344 rats

Heat shock proteins (HSP's) closely interact with 20S proteasome and have been shown to maintain catalytic activity, responsible for the prevention of protein aggregation. A decrease in both proteasome activity and heat shock proteins (HSP's) has been observed with age. We investigated whether life-long calorie restriction (CR), a natural intervention, which prolongs life span, could prevent the age-associated decline in HSP's and restore the proteolytic activity of the 20S proteasome in skeletal muscle. Hence, we investigated HSP's and proteasome activity in the soleus muscle from 12-mo-old (Adult) and 26-28 mo old ad libitum fed (Old), and 26-28 mo old CR (Old-CR; fed 40% of ad libitum for their lifespan) male Fisher 344 rats. Trypsin-like proteasome activity in Old rats was significantly less than both Adult and Old-CR rats. Furthermore, no significant changes where found in chymotrypsin-like proteasome activity due to age or diet. Levels of HSP 72 and 25 were significantly less in Old animals when compared to both Adult and Old-CR rats. In contrast, HSP 90 was elevated in Old rats by 220% compared to adult animals and life-long calorie restriction caused a significant induction (150%) compared to age-matched ad libitum fed animals. Protein carbonyls were significantly elevated in Old when compared to Adult rats, but showed no significant decline due to life long CR. This study shows that HSP's may be largely responsible for the restoration of the trypsin-like activity of the 20S proteasome with age. The large increase in HSP 90 is intriguing and further studies are required to elucidate its role in maintaining 20S proteasome function.

Aging intervention, prevention, and therapy through hormesis

The phenomenon of hormesis is represented by mild stress-induced stimulation of maintenance and repair pathways resulting in beneficial effects for the cells and organisms. Anti-aging and life-prolonging effects of a wide variety of the so-called stressors, such as pro-oxidants, aldehydes, calorie restriction, irradiation, heat shock, and hypergravity, have been reported. Molecular mechanisms of hormesis due to different stresses are yet to be elucidated, but there are indications that relatively small individual hormetic effects become biologically amplified resulting in the collective significant improvement of cellular and organismic functions and survival. Accepting that some important issues with respect to establishing the optimal hormetic conditions still need to be resolved by future research, hormesis appears to be a promising and effective approach for modulating aging, for preventing or delaying the onset of age-related diseases, and for improving quality of life in old age.

Murine Models of Life Span Extension

Mice are excellent experimental models for genetic research and are being used to investigate the genetic component of organismal aging. Several mutant mice are known to possess defects in the growth hormone/insulin-like growth factor 1 (GH/IGF-1) neurohormonal pathway and exhibit dwarfism together with extended life span. Their phenotypes resemble those of mice subjected to caloric restriction. Targeted mutations that affect components of this pathway, including the GH receptor, p66Shc, and the IGF-1 receptor (IGF-1R), also extend life span; mutations that affect IGF-1R or downstream components of the pathway decouple longevity effects from dwarfism. These effects on life span may result from an increased capacity to resist oxidative damage.

The effects of temperature reduction on gene expression and oxidative stress in skeletal muscle from adult zebrafish

Longevity is inversely proportional to ambient temperature in ectothermic organisms such as fish. However, the mechanism by which reducing temperature over a physiological range increases life span is not known and available data are derived primarily from invertebrates. With a rodent-like longevity and abundant biological resources, the zebrafish is an ideal vertebrate ectothermic model in which to investigate this phenomenon. As an initial approach, the effects of a year-long 10 degrees C reduction in water temperature on global gene expression in tail skeletal muscle from adult zebrafish were determined using an oligonucleotide microarray representing 15,512 genes. Expression levels for approximately 600 genes were up-regulated by 1.7-fold or greater by the reduction in temperature, while a similar number of transcripts were down regulated by more than 1.7-fold. Using gene ontology (GO) classifications for molecular function, two functional groups, "oxygen and reactive oxygen species metabolism" and "response to oxidative stress," were found to be overrepresented among up-regulated genes. Transcripts levels for the genes in these two categories were increased by temperature reduction (TR). However, temperature reduction did not suppress lipid peroxidation potential, protein carbonyl content, or 8-oxoguanine level. Additional studies will be required to further delineate the role of altered gene expression and oxidative stress on the longevity-promoting effects of temperature reduction.

Tissue-specific changes of DNA repair protein Ku and mtHSP70 in aging rats and their retardation by caloric restriction

To provide an improved understanding of the molecular basis of the aging process, it is necessary to measure biological age on a tissue-specific basis. The role of DNA damage has emerged as a significant mechanism for determination of life span, and DNA repair genes and stress-response genes are also implicated in the aging process. In the present study, we investigated the changes of DNA-PK activity, especially Ku activity, in the various tissues including kidney, lung, testis and liver during aging and its correlation with mtHSP70 expression. We showed that the modulation of Ku activity during the aging process was highly tissue-specific as shown with highly impaired Ku activity in testis and unaffected Ku activity in liver with age, and the level of Ku70 or Ku80 was differentially expressed in each aging tissue. We found also that age-associated alteration of Ku70/80 was prevented or not prevented by caloric restriction (CR) in a tissue-specific manner. Age-related decline in Ku70 during the aging process was associated with the increase of mtHSP70, which could play a role as a predictive marker for aging related to Ku regulation, and CR retarded aging-induced mtHSP70.

The Bud Scar-Based Screening System for Hunting Human Genes Extending Life Span

We developed a high-throughput screening system that allows identification of genes prolonging life span in the budding yeast Saccharomyces cerevisiae. The method is based on isolating yeast mother cells with an extended number of cell divisions as indicated by the increased number of bud scars on their surface. Fluorescently labeled wheat germ agglutinin (WGA) was used for specific staining of bud scars. Screening of a human HepG2 cDNA expression library in yeast resulted in the isolation of several yeast transformants with a potentially prolonged life span. The budding yeast S. cerevisiae, one of the favorite models used to study aging, has been studied extensively for the better understanding of the mechanisms of human aging. Because human disease genes often have yeast counterparts, they can be studied efficiently in this organism. One interesting example is the WRN gene, the human DNA helicase, which participates in the DNA repair pathway. The mutation of the WRN gene causes Werner syndrome showing premature-aging phenotype. Budding yeast contains WRN homologue, SGS1, and its mutation results in shortening yeast life span. The knowledge gained from the studies of budding yeast will benefit studies in humans for better understanding of aging and aging-related disease.

Expression and Localization of GRP75 in Human Epithelial Tumors and Normal Tissues

Using differential display mRNA techniques, the authors found cDNA of the heat shock 70 protein known as GRP75 overexpressed in ovarian cancer cell lines. In the current study, the authors used immunohistochemistry to characterize the expression pattern of GRP75 in ovarian carcinomas and compared it with epithelial tumors originating from the female reproductive tract, epithelial neoplasms from non-gynecologic sites (colon, pancreas, breast, and lung), and various normal tissues. The authors also developed an antigen capture ELISA assay to determine if GRP75 can be detected in tumors, ascites, or sera of patients with advanced mullerian adenocarcinomas. All epithelial tumors from the ovary and the female reproductive tract were positive for GRP75 expression with moderate to strong staining intensity; stromal expression of GRP75 was generally weak or absent. Adenocarcinomas from the colon, lung, pancreas, and breast also stained strongly positive for GRP75. The epithelial cells of all normal tissues examined were positive for GRP75, and strong staining was also seen in the corpora lutea, hepatocytes, enteric neural plexus of the esophagus and colon, and placental cytotrophoblast and syncytiotrophoblast, and in subpopulations of pancreatic acinar cells. The ELISA assay detected GRP75 in tumor lysates and ascitic fluid, but not sera, of patients with mullerian adenocarcinomas. The authors conclude that GRP75 is highly expressed in both benign and malignant epithelium, as well as cells of specialized function from a variety of tissues.

Heat shock response by EBV-immortalized B-lymphocytes from centenarians and control subjects: a model to study the relevance of stress response in longevity

'Successful aging', i.e. the ability to attain old age in relatively good health, is believed to be related to the capability to cope with different environmental stresses. Independently of their specific differentiation, all body cells respond to hyperthermia and other stresses with the production of Heat Shock Proteins (HSPs) that play an important role in cell survival. We investigated the heat shock response in B-lymphoid cell lines from 44 centenarians and 23 younger subjects, by studying both HSP70 synthesis and cell survival after hyperthermic treatment. Interestingly, no significant difference could be found between the two age groups as far as HSP70 synthesis was concerned; moreover, cell lines from centenarians appeared to be less prone to heat-induced apoptosis than lines from younger controls. These results, which are in contrast with previous findings showing an age-related decrease of the HSP70 synthesis and of hyperthermic response, corroborate the above mentioned hypothesis that the biological success of centenarians is due to the preservation of the capability to cope with stresses. An A/C polymorphism identified in the promoter region of HSP70-1 gene had been previously shown to affect the probability to attain longevity in females. To investigate if this effect was related to any influence of this polymorphism on HSP70 protein synthesis the correlation between A/C polymorphism and protein synthesis was investigated. We found that cells from AA centenarian females displayed a lower synthesis of HSP70.

Hormetic Mechanisms of Anti-Aging and Rejuvenating Effects of Repeated Mild Heat Stress on Human Fibroblasts in Vitro

The phenomenon of hormesis is represented by mild stress-induced stimulation of maintenance and repair pathways, resulting in beneficial effects for cells and organisms. We have reported that repeated mild heat stress (RMHS) has anti-aging hormetic effects on growth and various cellular and biochemical characteristics of human skin fibroblasts undergoing aging in vitro. These effects of RMHS include the maintenance of the stress protein profile, reduction in the accumulation of oxidatively and glycoxidatively damaged proteins, stimulation of the activities of the proteasome and its 11S activator, improvement in cellular resistance to ethanol, hydrogen peroxide, and ultraviolet rays, and increased antioxidative activity of the cells. We have also reported that RMHS prolongs the lifespan of Drosophila. Others have reported anti-aging and life prolonging effects of a wide variety of so-called stressors, such as pro-oxidants, aldehydes, calorie restriction, irradiation, heat shock, and hypergravity. Although molecular mechanisms of hormesis are yet to be elucidated, there are indications that relatively small hormetic effects become biologically amplified, resulting in significant improvement of cellular and organic functions and survival. Hormesis, therefore, can be an effective approach for modulating aging, for preventing or delaying the onset of age-related diseases, and for improving the quality of life in old age.

A high-throughput screening system for genes extending life-span

We developed a high-throughput functional genomic screening system that allows identification of genes prolonging life-span in the baker's yeast Saccharomyces cerevisiae. The method is based on isolating yeast mother cells with extended number of cell divisions as indicated by the increased number of bud scars on their surface. Fluorescently labelled Wheat Germ Agglutinin was used for specific staining of chitin, a major component of bud scars. Screening of a human HepG2 cDNA expression library in yeast resulted in the isolation of 12 yeast transformants with a potentially prolonged life-span. The transgene in one of the lines was identified as ferritin light chain (FTL) and studied in more detail. Yeast cells containing FTL showed an enhanced iron and H(2)O(2) resistance, a reduced cell death rate and an increased number of cell divisions. Overexpression of FTL in the nematode Caenorhabditis elegans resulted in a life-span increase of 8% confirming our yeast observations in a multicellular organism. Our data demonstrate that this method permits a fast screening of libraries for hunting genes involved in ageing processes.

The life span determinant p66Shc localizes to mitochondria where it associates with mitochondrial heat shock protein 70 and regulates trans-membrane potential

P66Shc regulates life span in mammals and is a critical component of the apoptotic response to oxidative stress. It functions as a downstream target of the tumor suppressor p53 and is indispensable for the ability of oxidative stress-activated p53 to induce apoptosis. The molecular mechanisms underlying the apoptogenic effect of p66Shc are unknown. Here we report the following three findings. (i) The apoptosome can be properly activated in vitro in the absence of p66Shc only if purified cytochrome c is supplied. (ii) Cytochrome c release after oxidative signals is impaired in the absence of p66Shc. (iii) p66Shc induces the collapse of the mitochondrial trans-membrane potential after oxidative stress. Furthermore, we showed that a fraction of cytosolic p66Shc localizes within mitochondria where it forms a complex with mitochondrial Hsp70. Treatment of cells with ultraviolet radiation induced the dissociation of this complex and the release of monomeric p66Shc. We propose that p66Shc regulates the mitochondrial pathway of apoptosis by inducing mitochondrial damage after dissociation from an inhibitory protein complex. Genetic and biochemical evidence suggests that mitochondria regulate life span through their effects on the energetic metabolism (mitochondrial theory of aging). Our data suggest that mitochondrial regulation of apoptosis might also contribute to life span determination.

Mutations in chemosensory cilia cause resistance to paraquat in nematode Caenorhabditis elegans

The relationship between oxidative stress and longevity is a matter of concern in various organisms. We isolated mutants resistant to paraquat from nematode Caenorhabditis elegans. One mutant named mev-4 was long-lived and showed cross-resistance to heat and Dyf phenotype (defective in dye filling). Genetic and sequence analysis revealed that mev-4 had a nonsense mutation on the che-11 gene, homologues of which are involved in formation of cilia and flagella in other organisms. The paraquat resistance was commonly observed in various Dyf mutants and did not depend on the daf-16 gene, whereas the extension of life span did depend on it. Expression of antioxidant enzyme genes seemed normal. These results suggest that chemosensory neurons are a target of oxidative stress and influence longevity dependent on the daf-16 signaling in C. elegans.

Search for methuselah genes heats up

In a recent article, Morley and Morimoto confirm previous studies suggesting that the transcriptional activator heat shock factor 1 (HSF-1) regulates stress resistance genes that extend longevity independently of DAF-16. They also show that overexpression of HSF-1 in neurons or body-wall muscle cells is sufficient to extend longevity. The role of multiple transcription factors in extending life span in yeast and worms raises the possibility that many transcriptional regulators can contribute to longevity extension.

The determinants of lifespan in the nematode Caenorhabditis elegans: a short primer

Transparent, easily-maintained, amenable to genetic manipulation, and living for only a few weeks, the nematode Caenorhabditis elegans is a leading animal model for the study of the determinants of lifespan. The original genetic screen for increased longevity identified a mutant, age-1, with a defect in one component of a signal transduction pathway. This pathway functioned as a genetic switch and governed the decision whether to enter a specialized larval form, dauer, that enables the worm to withstand the scarcity of food or other stressful conditions. These age-1 worms had an increased tendency to become dauers, but if they did not adopt the dauer developmental pathway, they lived longer than wild type worms. age-1 and other longevity mutants with dauer phenotypes are vigorous, indicating that they do not suffer from a significant energy deficit, and stress resistant. Mutation of genes encoding mitochondrial components was found to be another means of extending the lifespan of the worm, although the associated phenotypes suggest a deficiency of available energy. While there are now many documented genetic manipulations which can extend the worm's lifespan, it has been difficult to come to definite conclusions as to the mechanism(s) by which lifespan is extended. The most carefully studied mutant strains have complex changes in gene expression and metabolism making it difficult to ascertain what changes are critical. The free radical theory of aging is the dominant biochemical theory of aging, and the phenotypes of the well-characterized longevity mutants worm can be accommodated to it. However discrete interventions to lower reactive oxygen species, or mitigate their effects, have not produced consistent easily-interpretable results in terms of lifespan extension. It has become clear that the insulin-dependent signalling mechanism that regulates lifespan in the worm functions in the context of a complex endocrine system and the hormonal control of aging is an emerging focus of research in worms and higher organisms.

ACE inhibition actively promotes cell survival by altering gene expression

We tested the effect of ACE inhibition on the survival of bovine retinal (REC) and choroidal (CEC) endothelial cells (EC) in culture. The ACE inhibitor captopril delayed the apoptotic tube collapse of REC on Matrigel for >15 days. Captopril treatment of confluent monolayers (2-8 weeks) followed by slow starvation (2-4 weeks) increased EC viability by approximately 200%. Two-week captopril exposures were sufficient to confer maximal protection. Only vehicle-treated EC demonstrated apoptotic features such as membrane blebbing and DNA laddering. By RT-PCR, the starvation marker p202 was upregulated only in starved cells. In REC, captopril upregulated the pro-survival proteins mortalin-2, uPA, and uPAR while downregulating the anti-growth sprouty-4 and tPA. In CEC, captopril also upregulated tPA and its inhibitor PAI-1. Amiloride (uPA inhibitor) blocked the captopril-induced increase in EC survival, secondary sprouting, and invasion in Matrigel. The pro-survival effects of captopril involve the reprogramming of genes involved in cell survival and immortalization.

Regulation of longevity in Caenorhabditis elegans by heat shock factor and molecular chaperones

The correlation between longevity and stress resistance observed in long-lived mutant animals suggests that the ability to sense and respond to environmental challenges could be important for the regulation of life span. We therefore examined the role of heat shock factor (HSF-1), a master transcriptional regulator of stress-inducible gene expression and protein folding homeostasis, in the regulation of longevity. Down-regulation of hsf-1 by RNA interference suppressed longevity of mutants in an insulin-like signaling (ILS) pathway that functions in the nervous system of Caenorhabditis elegans to influence aging. hsf-1 was also required for temperature-induced dauer larvae formation in an ILS mutant. Using tissue-specific expression of wild-type or dominant negative HSF-1, we demonstrated that HSF-1 acts in multiple tissues to regulate longevity. Down-regulation of individual molecular chaperones, transcriptional targets of HSF-1, also decreased longevity of long-lived mutant but not wild-type animals. However, suppression by individual chaperones was to a lesser extent, suggesting an important role for networks of chaperones. The interaction of ILS with HSF-1 could represent an important molecular strategy to couple the regulation of longevity with an ancient genetic switch that governs the ability of cells to sense and respond to stress.

An automated high-throughput assay for survival of the nematode Caenorhabditis elegans

Many genetic or environmental manipulations that extend life span in the nematode Caenorhabditis elegans (C. elegans) also enhance survival following acute stresses such as oxidative damage and thermal stress. This coupling of stress response and aging mechanisms has proved a useful tool in identifying new genes that affect the aging process without the need for performing lengthy life span analyses. Therefore, it is likely that this approach may also be applied to the identification of pharmacological agents that extend life span through enhanced resistance to oxygen radicals or other stressors. To facilitate high-throughput drug screens in the nematode, we have developed a microtitre plate survival assay that uses uptake of the fluorescent dye SYTOX green as a marker of nematode death. An increase in throughput compared with the conventional survival assay was achieved by combining automated worm-handling technology with automated real-time fluorescence detection. We have validated this assay by examining survival during acute heat stress and protection against oxidative stress with the superoxide dismutase/catalase mimetic Euk-134. We propose that this novel method of survival analysis will accelerate the discovery of new pharmacological interventions in aging and oxidative stress.

Physiological and molecular assessment of altered expression of Hsc70-1 in Arabidopsis. Evidence for pleiotropic consequences

Hsp70s function as molecular chaperones. The protective chaperone activities of hsp70 help to confer tolerance to heat, glucose deprivation, and drought. Overexpression of hsp70s in many organisms correlates with enhanced thermotolerance, altered growth, and development. To better understand the roles of hsp70 proteins in Arabidopsis, the molecular and physiological consequences of altered expression of the major heat shock cognate, Hsc70-1, were analyzed. Extensive efforts to achieve underexpression of Hsc70-1 mRNA using a full-length antisense cDNA resulted in no viable transgenic plants, suggesting that reduced expression is lethal. Constitutive overexpression of Hsc70-1 also appeared to be deleterious to viability, growth, and development because fewer transformants were recovered, and most were dwarfed with altered root systems. Despite being dwarfed, the overexpression plants progressed normally through four selected developmental stages. Heat treatment revealed that Hsc70-1 overexpression plants were more tolerant to heat shock (44 degrees C for 10 min). The elevated basal levels of HSC70-1 in transgenic plants led to delayed heat shock response of several heat shock genes. The data in this study suggest that tight regulation of Hsc70-1 expression is critical for the viability of Arabidopsis and that the functions of HSC70-1 contribute to optimum growth, development, thermotolerance, and regulation of the heat shock response.