Cell cycle-dependent association of HSP70 with specific cellular proteins

A colorimetric sensor array for the classification of biologically relevant tri-, di- and mono-phosphates

A cyclic tetrapeptide paired with six commercially available indicators provides a chemosensing array able to classify biological phosphate derivatives.

The Nuclear and DNA-Associated Molecular Chaperone Network

Maintenance of a healthy and functional proteome in all cellular compartments is critical to cell and organismal homeostasis. Yet, our understanding of the proteostasis process within the nucleus is limited. Here, we discuss the identified roles of the major molecular chaperones Hsp90, Hsp70, and Hsp60 with client proteins working in diverse DNA-associated pathways. The unique challenges facing proteins in the nucleus are considered as well as the conserved features of the molecular chaperone system in facilitating DNA-linked processes. As nuclear protein inclusions are a common feature of protein-aggregation diseases (e.g., neurodegeneration), a better understanding of nuclear proteostasis is warranted.

CLEC14a-HSP70-1A interaction regulates HSP70-1A-induced angiogenesis

CLEC14a (C-type lectin domain family 14 member) is a tumor endothelial cell marker protein that is known to play an important role in tumor angiogenesis, but the basic molecular mechanisms underlying this function have not yet been clearly elucidated. In this study, using various proteomic tools, we isolated a 70-kDa protein that interacts with the C-type lectin-like domain of CLEC14a (CLEC14a-CTLD) and identified it as heat shock protein 70-1A (HSP70-1A). Co-immunoprecipitation showed that HSP70-1A and CLEC14a interact on endothelial cells. In vitro binding analyses identified that HSP70-1A specifically associates with the region between amino acids 43 and 69 of CLEC14a-CTLD. Competitive blocking experiments indicated that this interacting region of CLEC14a-CTLD significantly inhibits HSP70-1A-induced extracellular signal-regulated kinase (ERK) phosphorylation and endothelial tube formation by directly inhibiting CLEC14a-CTLD-mediated endothelial cell-cell contacts. Our data suggest that the specific interaction of HSP70-1A with CLEC14a may play a critical role in HSP70-1A-induced angiogenesis and that the HSP70-1A-interacting region of CLEC14a-CTLD may be a useful tool for inhibiting HSP70-1A-induced angiogenesis.

Differential effect of thermal stress on HSP70 expression, nitric oxide production and cell proliferation among native and crossbred dairy cattle

In a tropical country like India, thermal stress is one of the major factors which significantly affects the productivity of dairy cattle. The present study was aimed to identify the effect of heat and cold stress on cell viability, mitogen stimulation indices, nitric oxide production and HSP70 expression in Sahiwal and Holstein crossbred (Frieswal) population in India. The results indicated that the Sahiwal breed can better withstand the effect of heat and cold stress significantly (P<0.05) when compared to the crossbred cattle due to the higher survivability of the Peripheral Blood Mononuclear Cells (PBMCs) and Phytohemagglutinin (PHA-P) mitogen based stimulation indices. The study also revealed the significant differences (P<0.05) in the level of nitric oxide (µM) production amongst the pre and post thermal stressed samples of Sahiwal and Frieswal crossbred samples. Further, the expression of HSP70 was significantly (P<0.05) higher in Sahiwal compared to Frieswal immediately after heat/cold shock to 6h of recovery as indirect ELISA analysis showed gradual rise in the Hsp70 protein concentration (ng/ml) immediately after heat and cold stress (0h) and reached the peak at 6h of recovery. Western blot and immune fluorescent assay results were also corroborated with the findings of indirect ELISA. In Sahiwal cattle the mRNA expression of HSP70 and its protein concentration were higher (P<0.05) during peak summer (44°C) and winter (10°C) as compared to Frieswal cattle. This investigation supports the earlier information on the higher adaptability of indigenous cattle breeds to hot and humid conditions compared to the crossbreds of temperate cattle breeds.

Hsp70 architecture: the formation of novel polymeric structures of Hsp70.1 and Hsc70 after proteotoxic stress

Heat induces Hsp70.1 (HSPA1) and Hsc70 (HSPA8) to form complex detergent insoluble cytoplasmic and nuclear structures that are distinct from the cytoskeleton and internal cell membranes. These novel structures have not been observed by earlier immunofluorescence studies as they are obscured by the abundance of soluble Hsp70.1/Hsc70 present in cells. While resistant to detergents, these Hsp70 structures display complex intracellular dynamics and are efficiently disaggregated by ATP, indicating that this pool of Hsp70.1/Hsc70 retains native function and regulation. Hsp70.1 promotes the repair of proteotoxic damage and cell survival after stress. In heated fibroblasts expressing Hsp70.1, Hsp70.1 and Hsc70 complexes are efficiently disaggregated before the cells undergo-heat induced apoptosis. In the absence of Hsp70.1, fibroblasts have increased rates of heat-induced apoptosis and maintain stable insoluble Hsc70 structures. The differences in the intracellular distribution of Hsp70.1 and Hsc70, combined with the ability of Hsp70.1, but not Hsc70, to promote the disaggregation of insoluble Hsp70.1/Hsc70 complexes, indicate that these two closely related proteins perform distinctly different cellular functions in heated cells.

Exercise training and work task induced metabolic and stress-related mRNA and protein responses in myalgic muscles

The aim was to assess mRNA and/or protein levels of heat shock proteins, cytokines, growth regulating, and metabolic proteins in myalgic muscle at rest and in response to work tasks and prolonged exercise training. A randomized controlled trial included 28 females with trapezius myalgia and 16 healthy controls. Those with myalgia performed ~7 hrs repetitive stressful work and were subsequently randomized to 10 weeks of specific strength training, general fitness training, or reference intervention. Muscles biopsies were taken from the trapezius muscle at baseline, after work and after 10 weeks intervention. The main findings are that the capacity of carbohydrate oxidation was reduced in myalgic compared with healthy muscle. Repetitive stressful work increased mRNA content for heat shock proteins and decreased levels of key regulators for growth and oxidative metabolism. In contrast, prolonged general fitness as well as specific strength training decreased mRNA content of heat shock protein while the capacity of carbohydrate oxidation was increased only after specific strength training.

Basal and stress-induced Hsp70 are modulated by ataxin-3

Regulation of basal and induced levels of hsp70 is critical for cellular homeostasis. Ataxin-3 is a deubiquitinase with several cellular functions including transcriptional regulation and maintenance of protein homeostasis. While investigating potential roles of ataxin-3 in response to cellular stress, it appeared that ataxin-3 regulated hsp70. Basal levels of hsp70 were lower in ataxin-3 knockout (KO) mouse brain from 2 to 63 weeks of age and hsp70 was also lower in fibroblasts from ataxin-3 KO mice. Transfecting KO cells with ataxin-3 rescued basal levels of hsp70 protein. Western blots of representative chaperones including hsp110, hsp90, hsp70, hsc70, hsp60, hsp40/hdj2, and hsp25 indicated that only hsp70 was appreciably altered in KO fibroblasts and KO mouse brain. Turnover of hsp70 protein was similar in wild-type (WT) and KO cells; however, basal hsp70 promoter reporter activity was decreased in ataxin-3 KO cells. Transfecting ataxin-3 restored hsp70 basal promoter activity in KO fibroblasts to levels of promoter activity in WT cells; however, mutations that inactivated deubiquitinase activity or the ubiquitin interacting motifs did not restore full activity to hsp70 basal promoter activity. Hsp70 protein and promoter activity were higher in WT compared to KO cells exposed to heat shock and azetidine-2-carboxylic acid, but WT and KO cells had similar levels in response to cadmium. Heat shock factor-1 had decreased levels and increased turnover in ataxin-3 KO fibroblasts. Data in this study are consistent with ataxin-3 regulating basal level of hsp70 as well as modulating hsp70 in response to a subset of cellular stresses.

The association of CaM and Hsp70 regulates S-phase arrest and apoptosis in a spatially and temporally dependent manner in human cells

The cell cycle is controlled by regulators functioning at the right time and at the right place. We have found that calmodulin (CaM) has specific distribution patterns during different cell-cycle stages. Here, we identify cell-cycle-specific binding proteins of CaM and examine their function during cell-cycle progression. We first applied immunoprecipitation methods to isolate CaM-binding proteins from cell lysates obtained at different cell-cycle phases and then identified these proteins using mass spectrometry methods. A total of 41 proteins were identified including zinc finger proteins, ribosomal proteins, and heat shock proteins operating in a Ca(2+)-dependent or independent manner. Fifteen proteins were shown to interact with CaM in a cell-phase-specific manner. The association of the selected proteins and CaM were confirmed with in vitro immunoprecipitation and immunostaining methods. One of the identified proteins, heat shock protein 70 (Hsp70), was further studied with respect to its cell-cycle-related function. In vivo fluorescence resonance energy transfer (FRET) analysis showed that the interaction of CaM and Hsp70 was found in the nucleus during the S phase. Overexpression of Hsp70 is shown to arrest cells at S phase and, thus, induce cell apoptosis. When we disrupted the CaM-Hsp70 association with HSP70 truncation without the CaM-binding domain, we found that S-phase arrest and apoptosis could be rescued. The results suggest that the spatial and temporal association of CaM and Hsp70 can regulate cell-cycle progression and cell apoptosis.

Cooperation of salivary protein histatin 3 with heat shock cognate protein 70 relative to the G1/S transition in human gingival fibroblasts

Histatins, a family of salivary proteins, have antimicrobial activity. Candida albicans, which is killed by histatins, induces oral candidiasis in individuals with compromised immune systems. Although the functional significance of histatins has been documented, their biological and physiological functions against host cells have not been clarified. In this study, we found that histatin 3, a member of the histatin family, binds to heat shock cognate protein 70 (HSC70). These proteins were co-localized in the cytoplasm and nucleus in human gingival fibroblasts following non-heat and heat shock. Histatin 3 induced stimulation of DNA synthesis and cell survival in human gingival fibroblasts in a dose-dependent manner. This DNA synthesis was found to be dependent on HSC70 by knockdown experiments. The effect of heat shock on DNA synthesis induced by histatin 3 was approximately 2-fold higher than that of non-heat shock. When the histatin 3 uptake into cells was inhibited by monodansylcadaverine or when histatin 3 binding to HSC70 was precluded by 15-deoxyspergualin, DNA synthesis by histatin 3 was approximately 2-fold less than that without monodansylcadaverine or 15-deoxyspergualin. Although HSC70 directly bound to p27(Kip1) (a cyclin-dependent kinase inhibitor), histatin 3 increased the binding between those proteins but not with a peptide capable of binding to HSC70. Moreover histatin 3 prevented ATP-dependent dissociation of HSC70-p27(Kip1). ATP was unable to form a histatin 3-HSC70(D10N)-p27(Kip1) complex (HSC70(D10N) is a mutant attenuating ATPase activity). These findings suggest that histatin 3 may be involved in cell proliferation through the regulation of HSC70 and p27(Kip1) in oral cells.

Chaperones in cell cycle regulation and mitogenic signal transduction: a review

Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).

Heat shock proteins in immunity

This chapter focuses on immunological effects of eukaryotic and microbial heat shock proteins (HSPs), with molecular weights of about 60, 70, and 90 kDa. The search for tumor-specific antigens resulted in the identification of HSPs. They have been found to elicit a potent anti-cancer immune response mediated by the adoptive and innate immune system. Following receptor-mediated uptake of HSP (HSP70 and gp96) peptide complexes by antigen-presenting cells and representation of HSP-chaperoned peptides by MHC class I molecules, a CD8-specific T cell response is induced. Apart from chaperoning immunogenic peptides derived from tumors, bacterial and virally infected cells, they by themselves provide activatory signals for antigen-presenting cells and natural killer (NK) cells. After binding of peptide-free HSP70 to Toll-like receptors, the secretion of pro-inflammatory cytokines is initiated by antigen-presenting cells and thus results in a nonspecific stimulation of the immune system. Moreover, soluble as well as cell membrane-bound HSP70 on tumor cells can directly activate the cytolytic and migratory capacity of NK cells. Apart form cancer, HSPs of different origins, with a molecular weight of about 60, 70, and 90 kDa, also play a pivotal role in viral infections, including human and simian immunodeficiency virus (HIV, SIV), measles, and choriomeningitis. Moreover, HSPs have been found to induce tolerance against autoimmune diseases. In summary, depending on their mode of induction, intracellular/extracellular location, cellular origin (eukaryote/prokaryote), peptide loading status, intracellular ADP/ATP content, concentration, and route of application, HSPs either exert immune activation as danger signals in cancer immunity and mediate protection against infectious diseases or exhibit regulatory activities in controlling and preventing autoimmunity.

The effect of quercetin on pro-apoptotic activity of cisplatin in HeLa cells

It is well known that some tumour cells are very resistant to chemotherapy-induced cell death which indicate poor prognosis for patients. Thus the aim of the present study was to investigate the effect of quercetin on pro-apoptotic activity of cisplatin in human cervix carcinoma cells (HeLa). Three variants of experiments were performed. In the first one cells were incubated with studied drugs separately for 8 and 24h. In the second, drugs were added to the culture medium simultaneously. In third cisplatin or quercetin addition was followed by subsequent quercetin or cisplatin treatment, respectively. We observed different apoptotic effects, dependent on the drug succession. Preincubation of cells with quercetin followed by cisplatin treatment appeared to be the most effective and was correlated with strong activation of caspase-3 and inhibition of both heat shock proteins (Hsp72) and multi-drug resistance proteins (MRP) levels. Our results indicate that quercetin pretreatment sensitizes HeLa cells to cisplatin-induced apoptosis in HeLa cells.

Bioinformatic analysis of the nucleolus

The nucleolus is a plurifunctional, nuclear organelle, which is responsible for ribosome biogenesis and many other functions in eukaryotes, including RNA processing, viral replication and tumour suppression. Our knowledge of the human nucleolar proteome has been expanded dramatically by the two recent MS studies on isolated nucleoli from HeLa cells [Andersen, Lyon, Fox, Leung, Lam, Steen, Mann and Lamond (2002) Curr. Biol. 12, 1-11; Scherl, Coute, Deon, Calle, Kindbeiter, Sanchez, Greco, Hochstrasser and Diaz (2002) Mol. Biol. Cell 13, 4100-4109]. Nearly 400 proteins were identified within the nucleolar proteome so far in humans. Approx. 12% of the identified proteins were previously shown to be nucleolar in human cells and, as expected, nearly all of the known housekeeping proteins required for ribosome biogenesis were identified in these analyses. Surprisingly, approx. 30% represented either novel or uncharacterized proteins. This review focuses on how to apply the derived knowledge of this newly recognized nucleolar proteome, such as their amino acid/peptide composition and their homologies across species, to explore the function and dynamics of the nucleolus, and suggests ways to identify, in silico, possible functions of the novel/uncharacterized proteins and potential interaction networks within the human nucleolus, or between the nucleolus and other nuclear organelles, by drawing resources from the public domain.

Interaction of the Hsp90 cochaperone cyclophilin 40 with Hsc70

The high-affinity ligand-binding form of unactivated steroid receptors exists as a multicomponent complex that includes heat shock protein (Hsp)90; one of the immunophilins cyclophilin 40 (CyP40), FKBP51, or FKBP52; and an additional p23 protein component. Assembly of this heterocomplex is mediated by Hsp70 in association with accessory chaperones Hsp40, Hip, and Hop. A conserved structural element incorporating a tetratricopeptide repeat (TPR) domain mediates the interaction of the immunophilins with Hsp90 by accommodating the C-terminal EEVD peptide of the chaperone through a network of electrostatic and hydrophobic interactions. TPR cochaperones recognize the EEVD structural motif common to both Hsp90 and Hsp70 through a highly conserved clamp domain. In the present study, we investigated in vitro the molecular interactions between CyP40 and FKBP52 and other stress-related components involved in steroid receptor assembly, namely Hsp70 and Hop. Using a binding protein-retention assay with CyP40 fused to glutathione S-transferase immobilized on glutathione-agarose, we have identified the constitutively expressed form of Hsp70, heat shock cognate (Hsc)70, as an additional target for CyP40. Deletion mapping studies showed the binding determinants to be similar to those for CyP40-Hsp90 interaction. Furthermore, a mutational analysis of CyP40 clamp domain residues confirmed the importance of this motif in CyP40-Hsc70 interaction. Additional residues thought to mediate binding specificity through hydrophobic interactions were also important for Hsc70 recognition. CyP40 was shown to have a preference for Hsp90 over Hsc70. Surprisingly, FKBP52 was unable to compete with CyP40 for Hsc70 binding, suggesting that FKBP52 discriminates between the TPR cochaperone-binding sites in Hsp90 and Hsp70. Hop, which contains multiple units of the TPR motif, was shown to be a direct competitor with CyP40 for Hsc70 binding. Similar to Hop, CyP40 was shown not to influence the adenosine triphosphatase activity of Hsc70. Our results suggest that CyP40 may have a modulating role in Hsc70 as well as Hsp90 cellular function.

Rapid, transient, and dose-dependent expression of hsp70 messenger RNA in the rat brain after morphine treatment

Induction of Hsp70 in the brain has been reported after intake of drugs of abuse like amphetamine and lysergic acid diethylamide. In this investigation, gene expression of Hsp70 and other heat shock genes in the rat brain was studied in response to morphine. Twenty milligrams per kilogram morphine intraperitoneally resulted in a marked induction of Hsp70 messenger RNA (mRNA) expression in the frontal cortex with a maximum increase of 13.2-fold after 2 hours. A moderate increase of Hsp27 mRNA expression (6.7-fold) could be observed after 4 hours, whereas mRNA expression of Hsp90 and of the constitutive Hsc70 did not exceed a mean factor of 1.8-fold during the 24 hours interval. The increase in Hsp70 mRNA was dose dependent, showing a significant elevation after doses ranging from 10 to 50 mg/kg morphine. In situ hybridization revealed enhanced Hsp70 mRNA expression mainly in cortical areas, in the hippocampus, in the paraventricular and supraoptic nuclei of the hypothalamus, in the locus coeruleus, as well in the pineal body. The double in situ hybridization technique revealed increased Hsp70 mRNA expression mainly in VGLUT1-positive neurons and to a lesser extent in olig1-positive oligodendroglia. Immunohistochemistry revealed a marked increase of Hsp70 protein in neuronal cells and blood vessels after 12 hours. In contrast to animal experiments, morphine did not increase Hsp70 mRNA expression in vitro in micro-opioid receptor (MOR1)-expressing human embryonic kidney 293 cells, suggesting no direct MOR1-mediated cellular effect. To exclude a body temperature-related morphine effect on Hsp70 mRNA expression, the temperature was recorded. Five to 20 mg/kg resulted in hyperthermia (maximum 40.6 degrees), whereas a high dose (50 mg/kg) that produced the highest mRNA induction, showed a clear hypothermia (minimum 37.2 degrees C). These findings argue against the possibility that Hsp70 induction by morphine is caused by its effect on body temperature. It may be speculated that increased expression of Hsp70 after morphine application protects brain structures against potentially hazardous effects of opiates.

Heat shock factor 1-mediated thermotolerance prevents cell death and results in G2/M cell cycle arrest

Mammalian cells respond to environmental stress by activating heat shock transcription factors (eg, Hsf1) that regulate increased synthesis of heat shock proteins (Hsps). Hsps prevent the disruption of normal cellular mitosis, meiosis, or differentiation by environmental stressors. To further characterize this stress response, transformed wild-type Hsf1+/+ and mutant Hsf1-/- mouse embryonic fibroblasts (MEFs) were exposed to (1) lethal heat (45 degrees C, 60 minutes), (2) conditioning heat (43 degrees C, 30 minutes), or (3) conditioning followed by lethal heat. Western blot analysis demonstrated that only Hsf1+/+ MEFs expressed inducible Hsp70s and Hsp25 following conditioning or conditioning and lethal heat. Exposure of either Hsf1+/+ or Hsf1-/- MEFs to lethal heat resulted in cell death. However, if conditioning heat was applied 6 hours before lethal heat, more than 85% of Hsf1+/+ MEFs survived, and cells in G2/M transiently increased 3-fold. In contrast, conditioned Hsf1-/- MEFs neither survived lethal heat nor exhibited this G2/M accumulation. Coinfection with adenoviral Hsp70 and Hsp25 constructs did not fully recreate thermotolerance in either Hsf1+/+ or Hsf1-/- MEFs, indicating other Hsf1-mediated gene expression is required for complete thermotolerance. These results demonstrate the necessity of Hsf1-mediated gene expression for thermotolerance and the involvement of cell cycle regulation, particularly the G2/M transition, in this thermotolerant response.

MSJ-1, a mouse testis-specific DnaJ protein, is highly expressed in haploid male germ cells and interacts with the testis-specific heat shock protein Hsp70-2

The MSJ-1 gene encodes a murine DnaJ homologue that is expressed specifically in adult testis. DnaJ proteins act as cochaperones of Hsp70 proteins in promoting diverse cellular functions. In this study we used recombinant MSJ-1 proteins to produce MSJ-1 antiserum and to carry out in vitro binding assays. In a wide immunoscreening of mouse tissues, affinity-purified MSJ-1 antibodies recognize a unique protein of 30 kDa in male germ cells only. MSJ-1 is able to interact with the testis-specific Hsp70-2 protein and can be coimmunoprecipitated with Hsp70-2 from spermatogenic cells; binding of these two chaperones is consistent with the presence of a third component, which is so far unknown. MSJ-1 is weakly detected in early round spermatids, and its protein content increases in cytodifferentiating spermatids where it colocalizes with the developing acrosome and their postnuclear region. Hsp70-2, which is known to be highly expressed in meiotic cells, shows a subcellular localization in late differentiating spermatids that overlaps that of MSJ-1. MSJ-1 is also maintained in testicular and epididymal spermatozoa, where it sharply demarcates into two distinct cell areas; the outer surface of the acrosomal vesicle, and the centrosomal area. On the whole, our findings are consistent with a role for MSJ-1 in acrosome formation and centrosome adjustment during spermatid development, whereas its presence in mature spermatozoa suggests a special function during fertilization, shortly afterward, or both.

The chaperone function of hsp70 is required for protection against stress-induced apoptosis

Cellular stress can trigger a process of self-destruction known as apoptosis. Cells can also respond to stress by adaptive changes that increase their ability to tolerate normally lethal conditions. Expression of the major heat-inducible protein hsp70 protects cells from heat-induced apoptosis. hsp70 has been reported to act in some situations upstream or downstream of caspase activation, and its protective effects have been said to be either dependent on or independent of its ability to inhibit JNK activation. Purified hsp70 has been shown to block procaspase processing in vitro but is unable to inhibit the activity of active caspase 3. Since some aspects of hsp70 function can occur in the absence of its chaperone activity, we examined whether hsp70 lacking its ATPase domain or the C-terminal EEVD sequence that is essential for peptide binding was required for the prevention of apoptosis. We generated stable cell lines with tetracycline-regulated expression of hsp70, hsc70, and chaperone-defective hsp70 mutants lacking the ATPase domain or the C-terminal EEVD sequence or containing AAAA in place of EEVD. Overexpression of hsp70 or hsc70 protected cells from heat shock-induced cell death by preventing the processing of procaspases 9 and 3. This required the chaperone function of hsp70 since hsp70 mutant proteins did not prevent procaspase processing or provide protection from apoptosis. JNK activation was inhibited by both hsp70 and hsc70 and by each of the hsp70 domain mutant proteins. The chaperoning activity of hsp70 is therefore not required for inhibition of JNK activation, and JNK inhibition was not sufficient for the prevention of apoptosis. Release of cytochrome c from mitochondria was inhibited in cells expressing full-length hsp70 but not in cells expressing the protein with ATPase deleted. Together with the recently identified ability of hsp70 to inhibit cytochrome c-mediated procaspase 9 processing in vitro, these data demonstrate that hsp70 can affect the apoptotic pathway at the levels of both cytochrome c release and initiator caspase activation and that the chaperone function of hsp70 is required for these effects.

Hyperactive forms of the Pdr1p transcription factor fail to respond to positive regulation by the hsp70 protein Pdr13p

Multidrug resistance in Saccharomyces cerevisiae is commonly associated with the overproduction of ATP-binding cassette transporter proteins such as Pdr5p or Yor1p. The Cys6-Zn(II)2 cluster-containing transcription factors Pdr1p and Pdr3p are key regulators of expression of these pleiotropic drug resistance (PDR) loci. Previous experiments have demonstrated that the Hsp70 protein encoded by the PDR13 gene is a positive regulator of Pdr1p function. We have examined the mechanism underlying the control of Pdr1p by Pdr13p. Expression of deletion, insertion and amino acid substitution mutant variants of Pdr1p suggest that the centre region of the transcription factor is the target for Pdr13p-mediated positive regulation. Immunological and fusion protein analyses demonstrate that Pdr13p is located in the cytoplasm, while Pdr1p is found in the nucleus. Biochemical fractionation experiments indicate that Pdr13p is associated with a high-molecular-weight complex and suggest the association of some fraction of Pdr13p with ribosomes.

Heat-induced alterations in the localization of HSP72 and HSP73 as measured by indirect immunohistochemistry and immunogold electron microscopy

The heat shock proteins are a family of stress-inducible proteins that act as molecular chaperones for nascent proteins and assist in protection and repair of proteins whose conformation is altered by stress. HSP72 and HSP73 are two major cytosolic/nuclear stress proteins of mammalian cells, with extensive sequence homology. HSP73 is constitutively expressed, whereas HSP72 is highly stress-inducible. However, it is unclear why two isoforms are expressed and whether these two proteins have different functions in the cell. To assist in the delineation of function, we have completed a detailed study of the localization of HSP72 and HSP73 in the cell before and after heat stress, using two different methods of detection. By indirect immunohistochemistry, the localization of these two proteins is similar, cytoplasmic and nuclear in nonstressed cells with a translocation to nucleoli immediately after heat. By the more sensitive immunogold electron microscopy technique, differences in localization were noted. In nonstressed cells, HSP72 was primarily nuclear, localized in heterochromatic regions and in nucleoli. HSP73 was distributed throughout the cell, with most cytoplasmic label associated with mitochondria. Mitotic chromosomes were also heavily labeled. After stress, HSP72 concentrated in nuclei and nucleoli and HSP73 localized to nuclei, nucleoli, and cytoplasm, with increased label over mitochondria. These differences in localization suggest that the HSP72 and HSP73 may associate with different proteins or complexes and hence have different but overlapping functions in the cell.

Cellular method for evaluation of noxiousness of inorganic pollutants in industrial wastes: calculation of a safety index for monitoring sludge discharge

This article deals with a biological test of safety applicable to industrial wastes. The test is based on the measurement of the growth rate of cultured human cells exposed to waste samples with different dilutions. As a first approach, 15 chemicals in which discharge concentrations are submitted to sanitary regulations were tested one by one. For Zn, Cu, Ni, Cd, Ag, Co, Mg, sulfates, and fluorides, it was possible to detect concentrations that are below the allowed limit. For Hg, Al, As(V), Cr(III), Fe, and Pb, the concentrations that affect cell growth are higher than the allowed limit. Tests were also performed using actual samples (liquid effluent from a laundry and sludge from waste-water treatment plants). Results indicate that, in contrast to chemical analyses, the current biological test has the advantage of providing an indication of global toxicity, integrating all substances and factors that can be harmful to life processes. From the sludge data and the observed threshold of concentration that does not affect cell growth, a numeric safety index has been calculated which indicates the amount of sludge that could be dispersed, as a fertilizer, per hectare of agricultural soil. Such an index could be conveniently used for designing sewage sludge disposal strategies.

73-kDa heat shock cognate protein interacts directly with P27Kip1, a cyclin-dependent kinase inhibitor, during G1/S transition

Although heat shock proteins (HSPs) were discovered as inducible proteins by the physical stress to protect cells, recent evidence has suggested that HSPs are likely involved in cell cycle control under normal conditions without stress. In the present study, we demonstrated that 73hsc (heat shock cognate protein), which belongs to the HSP70 family of molecular chaperones, interacts with P27Kip1, an inhibitor of cyclin-dependent kinase, during G1/S transition. 73hsc was detected in the immunoprecipitates with anti-P27Kip1 antibody and, vice versa, P27Kip1 was present in the immunoprecipitates with anti-73hsc antibody by Western blotting using growth-stimulated rat thyroid FRTL-5 cells. This complex formation of 73hsc and P27Kip1 was cell cycle dependent and its maximum formation was observed at G1/S transition where the level of P27Kip1 dramatically decreased. ATP dissociated this complex formation in a dose-dependent manner. These data indicated that 73hsc might be involved in the cell cycle progression through the regulation of cell cycle regulators such as P27Kip1.

Luciferase activity and synthesis of Hsp70 and Hsp90 are insensitive to 50Hz electromagnetic fields

The activity of luciferase expressed in transfected 34i cells has been monitored under 50Hz EMF and heat shock. While heat shock decreased the luciferase activity, short exposure to EMFs did not, the luciferase expressed in cells exposed to EMFs at 300-3000 microT showing the same activity as that of control cells. To further analyse whether EMF and thermal stress display similar effects, the relative rate of Hsp90 and Hsp70 synthesis was investigated. Hsp90 and Hsp70 synthesis, while induced by a short thermal stress, was not increased by EMF exposure. These results, contrary to previously proposed similarities between thermal stress and EMF effects at a cellular level, indicate that protein denaturation and misfolding caused by thermal stress and responsible both for a loss of luciferase activity and for an induction of Hsp, are not necessarily induced by exposure to EMFs.

Characterization of the heat shock response in the gills of sea lampreys and a brook lamprey at different intervals of their life cycles

The heat shock response (HSR) was characterized in the gills of two lamprey species that differ with respect to their adult life history. In vivo labelling with [35S]methionine revealed an enhanced synthesis of heat shock proteins (HSPs) having approximate molecular weights of 70 kDa (HSP70) and 90 kDa (HSP90) following heat treatment. Induction of the HSR occurred in larval lampreys (ammocoetes) following temperature elevations of 13-16 degrees C for the parasitic species, the sea lamprey (Petromyzon marinus) and 16-20 degrees C for the nonparasitic species, the brook lamprey (Lampetra appendix). The case in L. appendix represents the greatest increase in temperature required to induce the HSR in gill tissue among aquatic poikilotherms studied to data and induction occurs within a temperature range (25-29 degrees C) not normally experienced by these animals. Western blotting detected the presence of 70 and 90 kDa HSPs and HSP70 levels were greater in post-metamorphic L. appendix than in ammocoetes both before and after heat shock. The HSR of lampreys appears to be induced during times of emergency when large, rapid temperature increases are experienced. The high set-point temperature for induction of the response may be a consequence of both the environments they presently inhabit and their experiences during evolution.

Cryptic expression of the 70-kDa heat shock protein, hsp72, in gerbil hippocampus after transient ischemia

The 70 kDa heat shock protein, hsp72, is known to be induced following transient global ischemia in brain, as detected by immunocytochemistry and in situ hybridization techniques. However, while hsp72 mRNA is expressed rapidly following postischemic recirculation, immunocytochemistry fails to detect hsp72 protein for many hours after such insults, even in cell populations that readily express Fos and other proteins encoded by ischemia-induced mRNAs. In the present study, hsp72 expression in gerbil hippocampus was compared by immunocytochemistry and immunoblot methods at several intervals following 10 min ischemia. As established in previous studies, hsp72 immunoreactivity remained undetectable in postischemic neurons at 6 h following such insults. In contrast, immunoblots of dissected gerbil hippocampus demonstrated nearly maximal accumulation of hsp72 at this time point. These results indicate that the protein is present, but cryptic to detection in perfusion-fixed sections, during early recirculation. The constitutively expressed heat shock cognate protein, hsc70, did not show significant changes in level or distribution by either method, except for a decrease in CA1 staining at 48 h. These results confirm that hsp72 rapidly accumulates to high levels in postischemic hippocampus, and suggest that further studies of its subcellular localization during this interval may offer insight into its functional role as a component of the stress response in neurons after such insults.

Intracellular distribution of stress glycoproteins in a heat-resistant cell model expressing human HSP70

Heat stress results in the cellular accumulation of heat-shock proteins (HSP) and increased protein glycosylation. Among known stress glycoproteins, GP50 and GP62 are associated with the expression of thermotolerance. In the present study, we characterized subcellular localization and redistribution of GP62 and GP50 in a rodent cell line, M21, before and after cellular heat-stress. M21 cells are heat-resistant cells that overexpress human HSP70 and also have concomitantly high GP62 levels. Cellular fractionation by differential centrifugation showed that GP62 and GP50 was present in each subcellular fraction. However, each stress glycoprotein exhibited a characteristic kinetic pattern of redistribution during cellular recovery after heat stress. For example, glycosylated GP62 was seen predominantly in the mitochondria before heat-stress. Immediately after heat-stress, its presence in the mitochondrial fraction was dramatically reduced, while it increased in lysosomes, microsomes and cytosol. By 1 h after heat stress, it had largely disappeared from microsomal and cytosolic fractions. After 24 h, all subcellular fractions showed only trace amounts of residual GP62. By comparison, GP50 was also highest in the mitochondrial fraction before heat-stress, redistributed like GP62 immediately after heat stress, but remained relatively unchanged thereafter. In contrast to GP62, GP50 showed little redistribution during 24 h after heat-stress and remained at high concentrations in all cell fractions, including microsomes. Distribution of GP50 and GP62 before and after heat stress, based on differential centrifugation, was consistent with immunolocalization data. Following heat stress, both GP50 and GP62 showed a partial overlap in distribution with HSP70. The above results indicate that each stress glycoprotein has a specific subcellular location, both before and after heat stress. The presence of GP62 in virtually all cell fractions is consistent with a multifunctional role for GP62 in the cellular stress response.

HSP70-2 is required for CDC2 kinase activity in meiosis I of mouse spermatocytes

Cyclin B-dependent CDC2 kinase activity has a key role in triggering the G2/M-phase transition during the mitotic and meiotic cell cycles. The Hsp70-2 gene is expressed only in spermatogenic cells at a significant level. In Hsp70-2 gene knock-out (Hsp70-2(−/−)) mice, primary spermatocytes fail to complete meiosis I, suggesting a link between HSP70-2 heat-shock protein and CDC2 kinase activity during this phase of spermatogenesis. Members of the HSP70 protein family are molecular chaperones that mediate protein de novo folding, translocation and multimer assembly. This study used immunoprecipitation-coupled western blot and in vitro reconstitution experiments to show that HSP70-2 interacts with CDC2 in the mouse testis, appears to be a molecular chaperone for CDC2, and is required for CDC2/cyclin B1 complex formation. Previous studies reported that most CDC2 kinase activity in the mouse testis is present in pachytene spermatocytes. Although CDC2 kinase activity for histone H1 was present in the testis of wild-type mice, it was nearly absent from the testis of Hsp70-2(−/−) mice, probably due to defective CDC2/cyclin B1 complex formation. Furthermore, addition of HSP70-2 to freshly prepared extracts of testis from Hsp70-2(−/−) mice not only restored CDC2/cyclin B1 complex formation but also reconstituted CDC2 kinase activity in vitro. It appears that one cause of failure to complete meiosis I during spermatogenesis in Hsp70-2(−/−) mice is disruption of CDC2/cyclin B1 assembly in pachytene spermatocytes, thereby preventing development of the CDC2 kinase activity required to trigger G2/M-phase transition. These studies provide novel in vivo evidence for a link between an HSP70 molecular chaperone and CDC2 kinase activity essential for the meiotic cell cycle in spermatogenesis.

Complexes between nascent polypeptides and their molecular chaperones in the cytosol of mammalian cells

Folding of newly synthesized proteins in vivo is believed to be facilitated by the cooperative interaction of a defined group of proteins known as molecular chaperones. We investigated the direct interaction of chaperones with nascent polypeptides in the cytosol of mammalian cells by multiple methods. A new approach using a polyclonal antibody to puromycin allowed us to tag and capture a population of truncated nascent polypeptides with no bias as to the identity of the bound chaperones. In addition, antibodies that recognize the cytosolic chaperones hsp70, CCT (TRiC), hsp40, p48 (Hip), and hsp90 were compared on the basis of their ability to coprecipitate nascent polypeptides, both before and after chemical cross-linking. By all three approaches, hsp70 was found to be the predominant chaperone bound to nascent polypeptides. The interaction between hsp70 and nascent polypeptides is apparently dynamic under physiological conditions but can be stabilized by depletion of ATP or by cross-linking. The cytosolic chaperonin CCT was found to bind primarily to full-length, newly synthesized actin, and tubulin. We demonstrate and caution that nascent polypeptides have a propensity for binding many proteins nonspecifically in cell lysates. Although current models of protein folding in vivo have described additional components in contact with nascent polypeptides, our data indicate that the hsp70 and, perhaps, the hsp90 families are the predominant classes of molecular chaperones that interact with the general population of cytosolic nascent polypeptides.

Nuclear translocation of constitutive heat shock protein 70 during S phase in synchronous macroplasmodia of Physarum polycephalum

The level of constitutive heat shock protein 70 (HSC70) in Physarum polycephalum was analyzed by means of Western blots during the synchronous cell cycle of macroplasmodia. Total amounts as well as nuclear and cytoplasmic contents were determined separately and evaluated densitometrically. A drastic increase of nuclear HSC70 was observed 10-40 min after the initiation of S phase (600% of the M phase value) and thereafter a slow decline toward the next M phase. Total HSC levels showed a slight (30%) increase during S phase whereas cytoplasmic HSC70 was about 30% lower during S phase compared to mitosis.

Distinct effect of hypoxia on endothelial cell proliferation and cycling

Endothelial cells (EC) occupy a strategic location in the vasculature as a barrier between the intravascular compartment and underlying tissues; as such, they are often exposed to stresses, such as decreases in ambient oxygen, diminished metabolic substrate, or changes in temperature, that could affect their ability to divide and proliferate. The present study characterizes cell counts, cell cycle distribution, and bromodeoxyuridine incorporation in pulmonary artery and aortic EC exposed to acute and/or chronic hypoxia and other cellular stresses. During hypoxia, EC division slows but does not arrest; progression through the G1-to-S transition point and/or progression from S to G2/M is altered with an increased percent of EC in S phase. These changes in EC cell cycle distribution with hypoxia are dependent on the origin of the EC as well as the ambient oxygen concentration; moreover, they are distinct from changes observed with elevated temperature or glucose deprivation. and differ from the quiescent pattern induced by serum deprivation or high-density confluence. These findings demonstrate that hypoxia exerts a distinct effect on the cell cycle distribution and proliferation of EC.

Tissue-specific differences in heat shock protein hsc70 and hsp70 in the control and hyperthermic rabbit

The ability to resolve protein members of the hsp70 multigene family by two-dimensional Western blotting permitted the characterization of antibodies which were specific in discriminating constitutively expressed hsc70 isoforms from stress-inducible hsp70 isoforms. This antibody characterization demonstrated that basal levels of hsp70 isoforms were present in the cerebellum of the control rabbit and that these were elevated following hyperthermia, whereas levels of hsc70 were similar in control and hyperthermic tissue. Multiple isoforms of hsp70 were detected but tissue-specific differences were not apparent in various organs of the rabbit. However, species differences were observed as fewer hsp70 isoforms were noted in rat and mouse. In the control rabbit, higher levels of hsc70 protein were present in neural tissues compared to non-neural tissues. Following physiologically relevant hyperthermia, induction of hsp70 was greatest in non-neural tissues such as liver, heart, muscle, spleen, and kidney compared to regions of the nervous system. These studies suggest that the amount of preexisting constitutive hsc70 protein may influence the level of induction of hsp70 in the stress response. Given this observation, caution is required in the employment of hsp70 induction as an index of cellular stress since endogenous levels of hsc70, and perhaps hsp70, may modulate the level of induction.

Differential expression of heat shock 70 proteins in primary cultures from rat cerebellum

While a number of studies have described the heat shock response in established cell lines and in primary cultures of cells derived from the nervous system, there has been no systematic analysis comparing expression and localization of the inducible heat shock 70 (hsp70) proteins and the constitutively synthesized members of the family (hsc70) in neurons and glia. In the present communication, we utilized specific probes to compare the expression of hsp70 and hsc70 mRNAs and proteins in two types of primary cultures, astroglial and neuro-astroglial, from postnatal rat cerebellum. Conditions were adjusted to maintain physiological numbers of microglia in both types of culture, and cultures were analyzed at a number of different time points following a precisely defined heat shock. The northern, in situ hybridization and immunohistochemical analyses resulted in a number of novel observations concerning the nature of the heat shock response in these neuronal and glial cells. In postnatal day 4-5 cultures, hsp70 mRNA levels were elevated for at least 10 h in both types of culture, but in situ hybridization analysis showed no evidence for hsp70 mRNAs in neurons. Microglia were the only cell type in which hsp70 was detected in non-stressed cultures and this cell type contained the highest concentrations of hsp70 proteins in stressed cultures. Hsc70 mRNA levels were also increased after heat shock, but the increase was more transient. Hsc70 mRNAs and proteins were present in all cell types, again with the highest concentrations being present in microglia. Hsc70 mRNAs and proteins were localized in the cytoplasm at all time points examined, with hsc70 protein also being localized in nucleoli. Hsp70 mRNAs and proteins were diffusely localized over nuclei of astrocytes, as well as of most microglia. Hsp70, but not hsc70, was localized on chromosomes in glia once they had resumed cell division after heat shock, suggesting a role for hsp70 either in targeting damaged chromosomal proteins or in cell division. Some cytoplasmic hsp70 was observed in astrocytes of the mixed neuro-astroglial cultures and a delayed hsp70 immunoreactivity was observed in granule neurons in these cultures, suggesting either that translation of low levels of hsp70 mRNAs was more efficient in neurons, or that glial-neuronal translocation of hsp70 proteins had taken place. These results suggest that metabolism and functions of different heat shock protein family members may not always be identical and that care must be taken in extrapolation of results from one cell type to another.

Comparison of flow cytometry and western blotting to measure Hsp70

The levels of constitutive and inducible forms of heat shock protein 70 (hsp73 and hsp72, respectively) through the cell cycle were measured in CHO cells by flow cytometry and Western blotting at various times after heating. Cells were labeled with antibody C92 (hsp72) or N27 (hsp73) and propidium iodide prior to analysis by flow cytometry. Cells were heated for 15 min at 45 degrees C, then analyzed from 3 to 36 h later. There was about a tenfold increase in hsp72 in early S phase cells beginning within 6 h after heating and these cells gradually cycled though S phase so by 36 h most of them had divided. When CHO cells were exposed to 10 microM sodium vanadate, an inhibitor of tyrosine phosphatase, for 24 h prior to heating, the induction of hsp72 in early S phase cells was almost completely inhibited. Heated cells did not express hsp73 in a cell-cycle-dependent manner. Hsp73 increased uniformly in all cells by 10 h after heating and sodium vanadate did not affect the expression. Quantitative comparisons of the relative levels of hsp72 and hsp73 measured by flow cytometry and Western blotting were in excellent agreement. Control and heated cells were labeled with Hoechst 33342 and sorted from G1, S, and G2/M phases and processed by Western blotting to verify the cell cycle dependent increase in hsp72 as measured by flow cytometry. Again there was excellent agreement between the Western blotting and flow cytometry results.

Heat shock protein hsp70 overexpression confers resistance against nitric oxide

Heat stress is known to render rat islet cells resistant against the toxic effects of nitric oxide, reactive oxygen intermediates and the islet cell toxin streptozotocin. We report here for the first time that protection against nitric oxide is mediated by the major heat shock protein, hsp70, even in the absence of heat stress. The human hsp70 gene was stably transfected into the rat insulinoma cell line RINm5F. Constitutive expression of hsp70 caused protection from NO-induced cell lysis which was of the same extent as seen after heat stressing cells. Our results identify hsp70 as a defence molecule against nitric oxide.

Relationship of lead-induced proteins to stress response proteins in astroglial cells

Astroglial cells are resistant to cell death and morphologic damage following lead (Pb) exposure at concentrations which elicit detrimental effects in neurons. A possible explanation may be that astroglial cells respond to Pb by increasing the expression of specific proteins, such as heat-shock proteins (HSPs), which confer resistance to low levels of Pb. However, there has been relatively limited information regarding the ability of Pb to evoke the synthesis of HSPs. In the current study, pulse-labeling of cultured astroglial proteins with [3H]-leucine was used to evaluate the nature of Pb-induced changes in protein expression. The effect of Pb on newly synthesized proteins was compared to the response elicited by heat-shock and oxidative injury. Immunoblot analysis was utilized to examine alterations in levels of various stress proteins including HSP27, HSP70, HSP90, and heme oxygenase-1 (HO-1). Even though Pb induced the synthesis of proteins with estimated molecular weights of 23 kDa, 32 kDa, 70 kDa, and 90 kDa, the accumulation of HSPs other than HO-1 was not observed. Hyperthermia and treatment with Na arsenite both resulted in enhanced expression of HSP70 and HO-1. In addition, exposure to hydrogen peroxide (H2O2), cadmium (Cd), and lipopolysaccharide (LPS) stimulated a rise in HO-1 levels. Although cellular insult failed to elicit an increase in either HSP27 or HSP90, cultured astroglia expressed readily detectable levels of both these proteins. Furthermore, Pb exposure resulted in the development of crosstolerance to subsequent injury by treatment with either Cd or H2O2. The results of this study indicate that Pb triggers a less conventional stress response in astroglial cells, which may provide enhanced resistance to the toxic effects of Pb.

The Epstein-Barr virus nuclear antigen leader protein associates with hsp72/hsc73

Epstein-Barr virus nuclear antigen leader protein (EBNA-LP) is important for primary B-lymphocyte growth transformation. We now demonstrate that the W repeat-encoded domain of EBNA-LP significantly associates with proteins of the heat shock protein 70 family (hsp72/hsc73). hsp72/hsc73 may mediate the previously observed interaction between EBNA-LP and the retinoblastoma protein or p53.

Cell cycle variation of Hsp70 levels in HeLa cells at 37 degrees C and after a heat shock

The expression of the 72 kD inducible heat shock protein (hsp72) has been reported to be cell cycle associated in unheated, synchronized HeLa cells. In this study, flow cytometry was used to investigate hsp72 levels through the cell cycle in HeLa cells by dual labeling with propidium iodide and antibodies against hsp72. The entire cell cycle distribution of hsp72 could be measured in a single sample of asynchronously growing cells. For unheated cells, the level of hsp72 increased about 30% from G1 to S phase, with about a 65% increase in G2/M, probably due to cell size differences. Neither mitotic selection nor serum stimulation induced a higher level of hsp72 than in the control cells. Western blot analysis of hsp72 from Hoechst-stained cells sorted from G1, mid-S, or G2/M showed that G1 cells had the lowest level of hsp72, with about a 30% increase in S phase and a 60% increase in G2/M, in good agreement with the flow cytometry results. These data conflict with previous reports by other laboratories which showed a 3-fold higher level of hsp72 in S phase than in G1 or G2. In contrast, heat shock (both acute and chronic) led to a non-uniform increase in hsp72 through the cell cycle. Most cells in mid S phase had high levels of hsp72, and a larger range in the levels of hsp72 were found in G1 and late S/G2/M phase cells.

MIDA1, a protein associated with Id, regulates cell growth

We have isolated cDNA clone encoding a protein that can associate with Id, a helix-loop-helix (HLH) protein. This protein is named MIDA1 (Mouse Id Associate 1), and its predicted amino acid sequence consists of Zuotin (a putative Z-DNA binding protein in yeast) homology region and tryptophan-mediated repeats similar to c-Myb oncoprotein. MIDA1 associates with the HLH region of Id with the conserved region adjacent to eukaryotic DnaJ conserved motif within the Zuotin homology region, although it does not have any canonical HLH motif. The addition of antisense oligonucleotide of MIDA1 inhibited growth of murine erythroleukemia cells without interfering with erythroid differentiation, indicating that it regulates cell growth.

Stable overexpression of human HSF-1 in murine cells suggests activation rather than expression of HSF-1 to be the key regulatory step in the heat shock gene expression

Transcription of the heat shock genes is regulated by the activation of the heat shock transcription factor (HSF-1). After heat shock, HSF-1 forms oligomers and binds to the heat shock element (HSE), which consists of several repeats of NGAAN located in the promoter region of the heat shock genes. HSF-1 is then phosphorylated, leading to the enhanced transcription of the heat shock genes likely by transactivation. We have stably overexpressed the human heat shock transcription factor-1 (HSF-1) in murine cells to investigate whether the regulation of the expression of the heat shock genes may partly reside at the level of HSF-1 expression. Human HSF-1 cDNA was cloned into a retroviral vector (pvhhsf-1) and was overexpressed in a murine fibroblast cell line. The overexpressed human HSF-1 is found in both the cytoplasm and nucleus of control cells but is translocated into the nucleus upon heat shock. Electrophoretic mobility shift analysis suggests that the human HSF-1 has constitutive DNA binding ability and its DNA binding ability is increased upon heat shock. Cross-linking experiments indicate that the overexpressed human HSF-1 is mainly a monomer under control conditions and forms oligomers upon heat shock. Immunoblotting shows that the human HSF-1 is phosphorylated upon heat shock and its apparent molecular weight is shifted up by at least 10 kDa. In spite of both the DNA binding ability and phosphorylation, the overexpression of human HSF-1 does not increase the transcription of murine HSP-70 mRNA or increase the synthesis of other HSPs after heat shock beyond that observed in control untransfected cells. An exception is the enhanced synthesis of a 47-50 kDa protein after heat shock and an apparent lack of induction of one HSP-70 kDa species when the protein pattern is analyzed by isoelectric focusing. Interestingly, cells overexpressing human HSF-1 show a 4-fold increase in the basal expression of luciferase when the plasmids containing the human HSP-70 promoter ligated to the luciferase reporter gene are transiently expressed in these cells. Murine cells overexpressing human HSF-1 are more resistant to the cytotoxic effects of heat when compared to the control untransfected cells, but the kinetics of thermotolerance development and decay is similar between HSF-1 transfected and untransfected cells. In conclusion, human HSF-1 protein in murine fibroblasts is modified in a similar fashion as the endogenous mouse HSF-1 after heat shock. However, the overexpression of HSF-1 does not result in overproduction of heat shock proteins after heat shock, perhaps because these cells contain abundant amounts of endogenous HSF-1.

Binding between wild-type p53 and hsp72 accumulated after UV and gamma-ray irradiation

We have investigated the increased levels of p53 and hsp72 after UV or gamma-ray irradiation and the association of these using two human glioblastoma cell lines. Human glioblastoma cell line A-172 exhibited no mutations in the p53 gene, whereas cell line T98G had a mutation in exon 7 of the p53 gene. In A-172, the level of wild-type p53 was increased by UV or gamma-ray irradiation. Although the level of mutant p53 in T98G was very high before irradiation, it was unchanged by UV or gamma-ray irradiation. Furthermore, in the A-172 cell line after UV or gamma-ray irradiation, wild-type p53 was co-immunoprecipitated with anti-hsp72/73 antibody, and accumulated hsp72 was also co-immunoprecipitated with anti-p53 antibody. These findings indicate that wild-type p53 accumulated by UV or gamma-ray irradiation is associated with hsp72 induced by these treatments.

Heat shock induces resistance in rat pancreatic islet cells against nitric oxide, oxygen radicals and streptozotocin toxicity in vitro

When cultures of pancreatic islet cells are exposed to the nitric oxide donor sodium nitroprusside, to enzymatically generated reactive oxygen intermediates or to streptozotocin cell lysis occurs after 4-12 h. We report here that a heat shock at 43 degrees C for 90 min reduces cell lysis from nitric oxide (0.45 mM sodium nitroprusside) by 70%, from reactive oxygen intermediates (12 mU xanthine oxidase and 0.05 mM hypoxanthine) by 80% and from streptozotocin (1.5 mM) by 90%. Heat shock induced resistance was observed immediately after termination of the 90 min culture at 43 degrees C and correlated with enhanced expression of hsp70. The occurrence of DNA strand breaks, a major early consequence of nitric oxide, reactive oxygen intermediates, or streptozotocin action, was not suppressed by heat shock treatment. However, the depletion of NAD+, the major cause of radical induced islet cell death, was suppressed after heat shock (P < 0.01). We conclude that pancreatic islet cells can rapidly activate defence mechanisms against nitric oxide, reactive oxygen intermediates and streptozotocin by culture at 43 degrees C. Islet cell survival is due to the prevention of lethal NAD+ depletion during DNA repair, probably by slowing down poly(ADP-ribose)polymerase activation.

HSP70 production and inhibition of cell proliferation in Molt-4 T-cells after cell-to-cell transmission of HTLV-I: effect of PGA1

Infection with HTLV-I is associated with leukemic transformation of mature CD4+ T lymphocytes. PGA1, a powerful inhibitor of tumour cell proliferation, can prevent the clonal expansion of HTLV-I-infected cells following acute infection of cord blood-derived mononuclear cells. Since the antiproliferative effect of PGA1 on HTLV-I transformed, chronically infected MT-2 cell line was associated with induction of HSP70, we have investigated the effect of PGA1 on cell cycle progression and HSP70 production in a leukemic T-cell line (Molt-4) shortly after exposure to HTLV-I in a cell-to-cell transmission model. Rate of cell proliferation and HSP70 expression were studied within one duplication cycle of Molt-4 cells after exposure to HTLV-I. Growth of both control and virus-exposed cultures was inhibited by treatment with PGA1 (4 micrograms/ml) and cell cycling was arrested preferentially at the G1/S interphase. Synthesis of HSP70 was induced within 3 h by PGA1 in control and virus-exposed Molt-4 cells and became undetectable from overnight onward, though the protein accumulated in the cells. The arrest of growth was observed from overnight up to 48 h so that treated cells almost missed one cycle. Interestingly, HSP70 transcript and protein persisted at remarkably high levels in Molt-4 cells exposed to HTLV-I in the absence of PGA1, showing that HSP70 expression can be directly activated during primary infection with this human retrovirus. Moreover, in these cocultures, treatment with PGA1 or heat shock was not able to increase further the elevated level of HSP70 found in untreated cocultures, suggesting that during the early period of the virus-transmission phase, HTLV-I could interfere with HSP70 induction by other inducers.

In vivo growth of a murine lymphoma cell line alters regulation of expression of HSP72

We have identified a murine B-cell lymphoma cell line, CH1, that has a much-diminished capacity to express increased levels of heat shock proteins in response to heat stress in vitro. In particular, these cells cannot synthesize the inducible 72-kDa heat shock protein (HSP72) which is normally expressed at high levels in stressed cells. We show here that CH1 fails to transcribe HSP72 mRNA after heat shock, even though the heat shock transcription factor, HSF, is activated correctly. After heat shock, HSF from CH1 is found in the nucleus and is phosphorylated, trimerized, and capable of binding the heat shock element. We propose that additional signals which CH1 cells are unable to transduce are normally required to activate hsp72 transcription in vitro. Surprisingly, we have found that when the CH1 cells are heated in situ in a mouse, they show normal expression of HSP72 mRNA and protein. Therefore, CH1 cells have a functional hsp72 gene which can be transcribed and translated when the cells are in an appropriate environment. A diffusible factor present in ascites fluid is capable of restoring normal HSP72 induction in CH1 cells. We conclude that as-yet-undefined factors are required for regulation of the hsp72 gene or, alternatively, that heat shock in vivo causes activation of hsp70 through a novel pathway which the defect in CH1 has exposed and which is distinct from that operating in vitro. This unique system offers an opportunity to study a physiologically relevant pathway of heat shock induction and to biochemically define effectors involved in the mammalian stress response.

Cytoplasmic HSP70 homologues of pea: differential expression in vegetative and embryonic organs

Eukaryotes express several cytoplasmic HSP70 genes, and their encoded proteins participate in diverse cellular processes. Three cDNAs encoding highly expressed cytoplasmic HSP70 homologues from Pisum sativum were cloned and characterized. They were designated PsHSP71.2, PsHSC71.0, and PsHSP70b. These HSP70 genes have different expression profiles in leaves: PsHSP71.2 is observed only in response to heat stress, PsHSC71.0 is present constitutively, and PsHSP70b is weakly constitutively expressed, but induced strongly in response to heat stress. In addition to being heat induced, the PsHSP71.2 mRNA is also expressed in zygotic, but not maternal organs of developing pea seeds, while PsHSC71.0 and PsHSP70b mRNAs are present in maternal and zygotic organs throughout seed development. Immunoblot analysis of parallel protein samples detects a 70 kDa polypeptide in all samples, and a 72 kDa polypeptide that corresponds to the PsHSP71.2 gene product is observed in cotyledons beginning at mid-maturation and in axes beginning between late maturation and desiccation. This polypeptide is not detected in the seed coat. The 72 kDa polypeptide remains abundant in both cotyledons and axes through germination, but declines substantially between 48 and 72 h after the onset of inbibition. Differential control of HSP70 expression during heat stress, seed maturation, and germination is consistent with the hypothesis that there are functional distinctions between cytoplasmic HSP70s.