Response of mammalian cells to metabolic stress; changes in cell physiology and structure/function of stress proteins

Transcriptomics-Based Screening Identifies Pharmacological Inhibition of Hsp90 as a Means to Defer Aging

Aging strongly influences human morbidity and mortality. Thus, aging-preventive compounds could greatly improve our health and lifespan. Here we screened for such compounds, known as geroprotectors, employing the power of transcriptomics to predict biological age. Using age-stratified human tissue transcriptomes and machine learning, we generated age classifiers and applied these to transcriptomic changes induced by 1,309 different compounds in human cells, ranking these compounds by their ability to induce a “youthful” transcriptional state. Testing the top candidates in C. elegans, we identified two Hsp90 inhibitors, monorden and tanespimycin, which extended the animals’ lifespan and improved their health. Hsp90 inhibition induces expression of heat shock proteins known to improve protein homeostasis. Consistently, monorden treatment improved the survival of C. elegans under proteotoxic stress, and its benefits depended on the cytosolic unfolded protein response-inducing transcription factor HSF-1. Taken together, our method represents an innovative geroprotector screening approach and was able to identify a class that acts by improving protein homeostasis.

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Transcriptome-based age classifiers can distinguish young versus old tissues

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Application of age classifiers to drug-induced transcriptomes finds geroprotectors

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Validation of geroprotectors in C. elegans highlights Hsp90 inhibitors

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Hsp90 inhibitors act through HSF-1 to improve health and extend lifespan

Analysis of Mitochondrial Proteins in the Surviving Myocardium after Ischemia Identifies Mitochondrial Pyruvate Carrier Expression as Possible Mediator of Tissue Viability

The endogenous mechanisms contributing to tissue survival following myocardial infarction are not fully understood. We investigated the alterations in the mitochondrial proteome after ischemia-reperfusion (I/R) and its possible implications on cell survival. Mitochondrial proteomic analysis of cardiac tissue from an in vivo porcine I/R model found that surviving tissue in the peri-infarct border zone showed increased expression of several proteins. Notably, these included subunits of the mitochondrial pyruvate carrier (MPC), namely MPC1 and MPC2. Western blot, immunohistochemistry, and mRNA analysis corroborated the elevated expression of MPC in the surviving tissue. Furthermore, MPC1 and MPC2 protein levels were found to be markedly elevated in the myocardium of ischemic cardiomyopathy patients. These findings led to the hypothesis that increased MPC expression is cardioprotective due to enhancement of mitochondrial pyruvate uptake in the energy-starved heart following I/R. To test this, isolated mouse hearts perfused with a modified Krebs buffer (containing glucose, pyruvate, and octanoate as metabolic substrates) were subjected to I/R with or without the MPC transport inhibitor UK5099. UK5099 increased myocardial infarction and attenuated post-ischemic recovery of left ventricular end-diastolic pressure. However, aerobically perfused control hearts that were exposed to UK5099 did not modulate contractile function, although pyruvate uptake was blocked as evidenced by increased cytosolic lactate and pyruvate levels. Our findings indicate that increased expression of MPC leads to enhanced uptake and utilization of pyruvate during I/R. We propose this as a putative endogenous mechanism that promotes myocardial survival to limit infarct size.

Dual effect of heat shock on DNA replication and genome integrity

The data presented here suggest that in an asynchronous cell culture, heat shock might affect DNA integrity both directly and via arrest of replication fork progression and that the phosphorylation of histone H2AX has a protective effect on the arrested replication forks in addition to its known DNA damage signaling function.

Heat shock (HS) is one of the better-studied exogenous stress factors. However, little is known about its effects on DNA integrity and the DNA replication process. In this study, we show that in G1 and G2 cells, HS induces a countable number of double-stranded breaks (DSBs) in the DNA that are marked by γH2AX. In contrast, in S-phase cells, HS does not induce DSBs but instead causes an arrest or deceleration of the progression of the replication forks in a temperature-dependent manner. This response also provoked phosphorylation of H2AX, which appeared at the sites of replication. Moreover, the phosphorylation of H2AX at or close to the replication fork rescued the fork from total collapse. Collectively our data suggest that in an asynchronous cell culture, HS might affect DNA integrity both directly and via arrest of replication fork progression and that the phosphorylation of H2AX has a protective effect on the arrested replication forks in addition to its known DNA damage signaling function.

Engineering stochasticity in gene expression

Stochastic fluctuations (noise) in gene expression can cause members of otherwise genetically identical populations to display drastically different phenotypes. An understanding of the sources of noise and the strategies cells employ to function reliably despite noise is proving to be increasingly important in describing the behavior of natural organisms and will be essential for the engineering of synthetic biological systems. Here we describe the design of synthetic constructs, termed ribosome competing RNAs (rcRNAs), as a means to rationally perturb noise in cellular gene expression. We find that noise in gene expression increases in a manner proportional to the ability of an rcRNA to compete for the cellular ribosome pool. We then demonstrate that operons significantly buffer noise between coexpressed genes in a natural cellular background and can even reduce the level of rcRNA enhanced noise. These results demonstrate that synthetic genetic constructs can significantly affect the noise profile of a living cell and, importantly, that operons are a facile genetic strategy for buffering against noise.

Oxalate exposure provokes HSP 70 response in LLC-PK1 cells, a line of renal epithelial cells: protective role of HSP 70 against oxalate toxicity

We investigated the effects of oxalate on immediate early genes (IEGs) and stress protein HSP 70, commonly induced genes in response to a variety of stresses. LLC-PK1 cells were exposed to oxalate. Gene transcription and translation were monitored by Northern and Western blot analysis. RNA and DNA synthesis were assessed by [(3)H]-uridine and [(3)H]-thymidine incorporation, respectively. Oxalate exposure selectively increased the levels of mRNA encoding IEGs c-myc and c-jun as well as stress protein HSP 70. While expression of c-myc and c-jun was rapid (within 15 min to 2 h) and transient, HSP 70 expression was delayed (approximately 8 h) and stable. Furthermore, oxalate exposure resulted in delayed induction of generalized transcription by 18 h and reinitiation of the DNA synthesis by 24 h of oxalate exposure. Moreover, we show that prior induction of HSP 70 by mild hypertonic exposure protected the cells from oxalate toxicity. To the best of our knowledge this is the first study to demonstrate rapid IEG response and delayed heat-shock response to oxalate toxicity and protective role of HSP 70 against oxalate toxicity to renal epithelial cells. Oxalate, a metabolic end product, induces IEGs c-myc and c-jun and a delayed HSP 70 expression; While IEG expression may regulate additional genetic responses to oxalate, increased HSP 70 expression would serve an early protective role during oxalate stress.

The role of immune tolerance in preventing and treating arthritis

It has become increasingly clear that the innate and adaptive arms of the immune response cooperate in generating autoimmune damage in the pathogenesis of rheumatoid arthritis and juvenile idiopathic arthritis. Treatment targets the immunologic pathophysiology of the disease and is based on regaining immune tolerance. Recently introduced biological agents neutralize or simply block cytokines and their proinflammatory pathways, with favorable clinical outcome. However, major downsides are their lack of specificity and the need of continuous administration to be effective. Possibly, more can be gained from a specific approach. Indeed, recent findings suggest that targeting antigen-specific T cells can reinstate regulatory mechanisms and thus induce immune tolerization. This improved understanding has paved the way to novel immunotherapeutic approaches, some of which will be discussed here.

Oxidative-stress-related proteome changes in Helicobacter pylori-infected human gastric mucosa

Helicobacter pylori infection leads to gastroduodenal inflammation, peptic ulceration and gastric carcinoma. Proteomic analysis of the human gastric mucosa from the patients with erosive gastritis, peptic ulcer or gastric cancer, which were either infected or not with H. pylori, was used to determine the differentially expressed proteins by H. pylori in the human gastric mucosa in order to investigate the pathogenic mechanism of H. pylori -induced gastric diseases. Prior to the experiment, the expression of the main 18 proteins were identified in the gastric mucosa and used for a proteome map of the human gastric mucosa. Using two-dimensional electrophoresis of the protein isolated from the H. pylori -infected tissues, Coomassie Brilliant Blue staining and computerized analysis of the stained gel, the expression of eight proteins were altered in the H. pylori -infected tissues compared with the non-infected tissues. MS analysis (matrix-assisted laser desorption/ionization-time of flight MS) of the tryptic fragment and a data search allowed the the identification of the four increased proteins (78 kDa glucose-regulated protein precursor, endoplasmin precursor, aldehyde dehydrogenase 2 and L-lactate dehydrogenase B chain) and the four decreased proteins (intracellular chloride channel protein 1, glutathione S-transferase, heat-shock protein 60 and cytokeratin 8) caused by H. pylori infection in the gastric mucosa. These proteins are related to cell proliferation, carcinogenesis, cytoskeletal function and cellular defence mechanism. The common feature is that these proteins are related to oxidative-stress-mediated cell damage. In conclusion, the established gastric mucosal proteome map might be useful for detecting the disease-related protein changes. The H. pylori -induced alterations in protein expression demonstrate the involvement of oxidative stress in the pathogenesis of H. pylori -induced gastric diseases, including inflammation, ulceration and carcinogenesis.

Chronic hypoxia preconditioning increases survival in rats suffering from heatstroke

1. In the present study, we assessed the protective effects of chronic hypoxia preconditioning against heatstroke-induced injury in urethane-anaesthetized rats. Heatstroke was induced by exposing the animals to an ambient temperature of 42 degrees C. The time at which both the mean arterial pressure (MAP) and local cerebral blood flow (CBF) in the striatum began to decrease from peak levels was taken as the onset of heatstroke. Control rats were exposed to a temperature of 24 degrees C. 2. Mean arterial pressure, CBF, blood pH, PaO2, PaCO2 and survival time (the interval between onset of heatstroke and cardiac arrest) after heat stress were all lower than in control rats (in which 'survival time' was defined as > 360 min). However, blood lactate concentrations were greater in rats exposed to heat. Rats placed at high altitude (HA), when exposed to the same heat stress (42 degrees C) survived much longer (113 +/- 26 min; n = 8) than rats maintained at sea level (SL; 20 +/- 2 min; n = 8). 3. After the onset of heatstroke, blood pH and lactate concentrations were found to be significantly higher and lower, respectively, in HA rats than in SL rats. 4. Western blot assay revealed that chronic hypoxia preconditioning induced heat shock protein (HSP) 72 expression in both the kidneys and lungs. 5. Thus, it appears that the observed benefit of chronic hypoxia preconditioning is related to attenuation of tissue acidification and elevations of HSP72 expression in both kidneys and lungs during heatstroke.

Antibodies to 70 kD and 90 kD heat shock proteins are associated with graft-versus-host disease in peripheral blood stem cell transplant recipients

The development of graft-versus-host disease (GVHD) can be modified by non-MHC factors. Based on our previous studies that showed an involvement of 70kD heat shock protein (hsp70) in the pathology of acute GVHD in a rat model, we determined serum levels of antibodies to hsp70, hsp90 and hsp60 in human recipients after allogeneic peripheral blood stem cell transplantation (PBSCT). Serum levels of these antibodies were correlated with GVHD status in the recipients. Twenty-nine recipients with high-risk haematological malignances, who received G-CSF mobilized allogeneic PBSCT from HLA matched family donors, were evaluated between 30 and 960 days after transplantation. Two recipients had no GVHD, 18 developed acute followed by chronic GVHD and nine developed only chronic GVHD. Patients with acute GVHD had a significant increase in IgM anti-hsp70 and/or anti-hsp90 early (30-90 days) after transplantation. In addition, an increase in IgM anti-hsp70 and/or anti-hsp90 antibodies preceded or accompanied chronic GVHD. Antibody levels returned to normal within the next 400 days in the majority of patients. Anti-hsp60 antibody levels were not different from control levels regardless of GVHD status. This study implies that the development of acute and/or chronic GVHD in humans is accompanied by an increase in anti-hsp70 and anti-hsp90 antibodies. Monitoring levels of anti-hsp70 and anti-hsp90 antibodies in stem cell transplant recipients may serve as a diagnostic tool and help to predict the onset of GVHD.

Heat shock and stress response of Taenia solium and T. crassiceps (Cestoda)

Heat shock and stress responses are documented for the first time in larval stages of the cestodes Taenia solium and Taenia crassiceps. Radioactive metabolic labelling after in vitro incubation of cysts at 43 degrees C, revealed the induction of heat shock proteins. In T. crassiceps, the major heat shock proteins were 80, 70 and 60 kDa. After prolonged incubation, a set of low molecular weight heat shock proteins (27, 31, 33 and 38 kDa), were also induced. In vitro incubation of cysts at 4 degrees C, induced the synthesis of stress proteins ranging from 31 to 80 kDa, indicating the parasite is also able to respond to cold shock. T. solium cysts exposure to temperature stress also resulted in an increased synthesis of 2 major heat shock proteins of 80 and 70 kDa. Western blots using the excretory-secretory products of T. solium showed that 2 heat shock proteins were recognized by antibodies in the sera of cysticercotic patients: one of 66 kDa and another migrating close to the run front. The T. solium 66 kDa protein was also recognized by specific antibodies directed to a 60 kDa bacterial heat shock protein, suggesting that it belongs to this family of proteins.

Heat shock proteins, tumor immunogenicity and antigen presentation: an integrated view

A broad range of studies has established that heat shock proteins (Hsps) potentially play a role in tumor immunosurveillance. Here, Andrew Wells and Miroslav Malkovsky highlight recent data that demonstrate a causal relationship between the expression of Hsps and tumor immunogenicity, and suggest several mechanisms by which Hsps might influence the capacity of a tumor to induce an immune response.

The multiple sclerosis lesion: initiated by a localized hypoperfusion in a central nervous system where mechanisms allowing leukocyte infiltration are readily upregulated?

A mechanism is proposed that may explain the factors that initiate a multiple sclerosis (MS) lesion. It is based upon the following two hypotheses: (i) there is a lower stimulus threshold for upregulating the mechanisms that result in leukocyte infiltration in individuals predisposed to developing MS; (ii) the MS lesion is initiated as a reduction in blood flow to a localized region of white matter. This reduction in blood flow leads to: (a) degenerative white matter changes affecting oligodendrocytes; (b) upregulation of chemokines in the endothelial cells and/or glial cells; and (c) upregulation of cell adhesion molecules on endothelial cells. Signals from the hypoxemic and hypoglycemic glial cells, likely involving myelin molecules and cytokines, result in an inflammatory immune response that results in rampant demyelination. Evidence supporting the proposed mechanism is presented, as well as suggestions on how to test the validity of the proposal.

Calreticulin associates with stress proteins: implications for chaperone function during heat stress

Acute heat stress leads to the glycosylation of a "prompt" stress glycoprotein, P-SG67/64, identified as calreticulin. In the present study, we used immunoprecipitation to investigate the interactions of P-SG/calreticulin with other proteins during cellular recovery from heat stress. In heat-stressed CHO and M21 cells, both glycosylated and unglycosylated P-SGs interact with HSP90, GRP94, GRP78, and the other prompt stress glycoprotein, P-SG50, in an ATP-independent manner. Specificity of HSP-P-SG interactions was determined by chemical cross-linking with the homo-bifunctional agent DSP (3,3'-dithiobis[succinimidyl propionate]). Characterization of the cross-linked complexes involving calreticulin and heat shock proteins (HSPs) showed an average mass of 400-600 kDa by gel filtration chromatography. Overall, the consistent association of glycosylated and unglycosylated calreticulin with P-SG50 and unglycosylated HSPs suggests that P-SG/calreticulin is an active member of the cast of glycone/aglycone chaperones that cooperate to achieve cellular recovery from acute heat stress.

T-cell epitopes recognized within the 65,000 MW hsp in patients with IgA nephropathy

IgA nephropathy (IgAN) is the commonest cause of glomerulonephritis and clinical exacerbation of IgAN is frequently associated with mucosal infection. T-cell receptor gamma delta (TCR gamma delta+) cells are increased in both the circulation and in renal biopsies of patients with progressive IgAN. We examined the hypothesis that specific peptides within the 65,000 MW heat-shock protein (hsp) might stimulate TCR gamma delta cells and play a part in the immunopathogenesis of IgAN. We studied T-cell proliferative responses stimulated by overlapping peptides derived from the sequence of mycobacterial 65,000 MW hsp. Three T-cell epitopes have been identified (peptides 51-65, 71-85 and 281-295). The three peptides have a synergistic effect and they stimulate significantly higher proliferation of T cells in patients with IgAN than in disease or healthy controls. This response was inhibited by monoclonal antibodies (mAb) to TCR gamma delta+ and human leucocyte antigen (HLA) class I, but not by mAb to HLA class II. The involvement of TCR gamma delta+ cells was confirmed by up-regulation of the proportion of TCR gamma delta+ cells when stimulated with the three specific peptides. We suggest that IgAN might be associated with mucosal infection by a variety of micro-organisms and that peptides within the microbial hsp cross-react with the homologous human hsp which may stimulate TCR gamma delta+ cells and play a part in the pathogenesis of IgAN.

Transcriptional modulation of viral reporter gene constructs following induction of the cellular stress response

In this study, we report that commonly used methods of transient transfection induce the cellular stress response and a recovery period is required following transfection when analyzing cellular stress responsive genes. Four transfection methods were examined for their ability to induce the stress response by measuring the expression of heat shock protein (hsp) 72. We demonstrate that electroporation increases expression of hsp 72 in HUT 78 cells. Additionally, DEAE-dextran and liposome-mediated transfection resulted in increased hsp 72 expression in an adherent cell line (HeLa). Liposome-mediated transfection differentially induced cell stress, dependent on the transfection time in serum-free culture conditions. The stress responsiveness of two viral promoters, the HTLV-1 long terminal repeat and CMV immediate early transcriptional unit were examined. We found the maximal stress-mediated enhancement of transcription with both promoters did not occur until the cells recovered for 24 h following transfection.

The cellular stress response enhances human T-cell lymphotropic virus type 1 basal gene expression through the core promoter region of the long terminal repeat

Viral protein expression is postulated to play a critical role in the pathogenesis of human T-cell lymphotropic virus type 1 (HTLV-1)-associated diseases. Therefore, knowledge of the cellular events which initiate or enhance viral gene expression is important in understanding the mechanism of HTLV-1-induced disease. In this report, we examined the modulation of transcription of the HTLV-1 long terminal repeat (LTR) following induction of the cellular stress response. We demonstrate by both in vitro transcription assays and transient transfections that induction of the stress response increases basal transcription from the LTR. Transient cotransfection assays indicate that stress induction of viral transcription is Tax independent. In addition, we provide evidence that the sequences responsible for the enhanced transcription are -52 through +157 of the U3/R region of the HTLV-1 LTR. Finally, our data suggest that the increase in transcription is mediated through an intermediate polymerase II/polymerase III transcriptional complex, demonstrated by the inability to abolish the effect with low concentrations of alpha-amanitin.

Acclimatization, preconditioning and heat shock proteins

During prior acclimatization, mineworkers acquire tolerance against the adverse effects of working in a warm environment. In this article, the possible involvement of heat shock proteins as mediators of acclimatization is proposed. Acclimatization is compared with preconditioning. Preconditioning of isolated cells or organs by prior exposure to a temperature higher than normal or exposure to an ischaemic insult endow tolerance on them when later confronted with a severe ischaemic stress. This tolerance is possibly mediated by heat shock proteins induced by the heating or ischaemic preconditioning episode. Functioning of the induced heat shock proteins may therefore underlie the protective mechanisms in both acclimatization and preconditioning.

Heat shock proteins are differentially expressed in human gastrointestinal cancers

The heat shock proteins (Hsp) are stress-responsive genes present in all species; increases of Hsp can confer chemotherapeutic resistance to certain cancers. The purpose of this study was to determine Hsp expression in human gastric, pancreatic and colon cancers. Gastric (n = 3), pancreatic (n = 6) and colon (n = 8) cancers were extracted for RNA and protein, and Northern and Western blots performed. We found that hsp70 and hsp27 mRNA levels were differentially expressed in the gastrointestinal cancers; mRNA expression closely correlated with protein levels suggesting regulation at the level of transcription. In addition, Hsp90 and BiP proteins were constitutively expressed in the gastrointestinal cancers. We conclude that the Hsp are differentially expressed in human gastric, pancreatic and colon cancers; these increases in Hsp occur constitutively and are not the result of physiological or environmental stresses. Increases of Hsp expression in cancer cells may enhance resistance and account for the altered sensitivity of certain gastrointestinal cancers to chemotherapeutic agents.

Peptide transporter-independent, stress protein-mediated endosomal processing of endogenous protein antigens for major histocompatibility complex class I presentation

The peptide transporter-defective cell line RMA-S expressing the wild-type simian virus 40 large T antigen (wtT-Ag) from a transfected gene did not present two well-defined, H-2 class I (Db)-restricted epitopes of T-Ag to cytotoxic T lymphocytes (CTL). Hence, "endogenous" processing and presentation of the wtT-Ag depended on a functional peptide transporter heterodimer. In contrast, both T-Ag epitopes were efficiently presented to CTL by transfected RMA-S cells expressing a truncated, cytoplasmic T-Ag variant (cT-Ag) or a karyophilic, amino-terminal 272-amino acid T-Ag fragment. Transporter-independent "endogenous" processing of mutant T-Ag molecules correlated with their association with the constitutively expressed heat shock protein 73 (hsp73). Class I-restricted presentation of both epitopes processed from these hsp73-associated protein antigens was sensitive to NH4Cl and chloroquine. These data indicate that selected intracellular proteins access an alternative, hsp73-mediated pathway for class I-restricted presentation that operates independent of peptide transporters in an endosomal compartment.

Sendai virus pneumonia: evidence for the early recruitment of gamma delta T cells during the disease course

We previously reported that gamma delta T cells appeared and could play a protective role early in infections with intracellular bacteria such as Listeria monocytogenes, Mycobacterium bovis BCG, and Salmonella choleraesuis. To extend these findings to virus infection, we examined the developmental sequence of gamma delta T cells in bronchoalveolar lavage during the course of Sendai virus infection in C57BL/6 mice. To produce a natural but nonlethal infection course as far as possible, we used a sublethal dose of a wild-type virus which had not been subjected to serial passages in a chicken embryo, hence retaining full virulence for mice. Virus titers in lungs reached a peak on day 6 and then decreased to an undetectable level by day 10. This time course of virus reproduction was immediately and coincidentally followed by the developmental course of gamma delta T cells, in which the cell number peaked on day 7 and then decreased to a marginal level by day 10. On the other hand, the alpha beta T-cell number continued to increase until day 10 and remained at a high level thereafter. The early-appearing gamma delta T cells were CD4-, CD8-, IL-2R alpha- beta+, CD44+, Mel-14-, and LFA-1 alpha/beta+ in phenotype and used V gamma 1/2 and V gamma 4 and V delta 3, V delta 4, V delta 5, and V delta 6. The gamma delta T cells were responding to macrophages from infected mice when the cells were cultured in vitro. Furthermore, the expression of endogenous heat shock protein (hsp) was infection specific, and its level appeared to correlate with the gamma delta T-cell development. These results suggest that the early recruitment of gamma delta T cells, which proliferate in response to endogenous hsp+ cells, is also characteristic of this virus infection, although this view appears to be contradictory to earlier reports.

HSP90 associates with specific heat shock puffs (hsr omega) in polytene chromosomes of Drosophila and Chironomus

The heat shock protein HSP90, which is mainly cytoplasmic, has recently been reported to be present in the nucleus. We have found a specific chromosomal localization of HSP90 in different species of Drosophila and Chironomus using immunocytochemical techniques with different mono- and polyclonal antibodies for this hsp. HSP90 was found associated with heat shock-induced puffs at 93D and 48B in salivary gland chromosomes of Drosophila melanogaster and Drosophila hydei, respectively. The localization of HSP90 to locus 93D occurred rapidly after the onset of heat shock and disappeared during recovery, concomitant with puff regression. The association of HSP90 with the 93D locus was strictly heat shock dependent as shown by the absence of HSP90 in puff 93D induced by either benzamide or colchicine. No specific nuclear staining was observed in unstressed control cells. HSP90 was also found in the temperature-induced telomeric Balbiani ring puffs (T-BRs) in Chironomus thummi and in one heat shock puff at I-1C in Chironomus tentans. Other heat shock puffs also appeared lightly stained with the HSP90 polyclonal antibody in both species of Chironomus. HSP90 was absent from the T-BRs when RNA synthesis was inhibited with Actinomycin D suggesting that the localization of HSP90 is dependent on transcription. Inhibition of protein synthesis did not prevent association of this hsp with the T-BRs, indicating that pre-existing HSP90 can associate with this locus. HSP90 did not associate with any telomeric chromosomal regions of unstressed cells. The present observations suggest that heat shock gene products such as HSP90 may somehow be involved in the regulation at the chromosomal level of other members of the heat shock gene family. Puffs 93D (D. melanogaster) and 48B (D. hydei) are equivalent and correspond to homologous gene loci (hsr omega) that have unusual features that distinguish them from other heat shock puffs. The binding of HSP90 at T-BRs and at puff I-1C in the genus Chironomus is the first demonstration, albeit indirect, of the existence of hsr omega analogous loci in species other than Drosophila.

Stress protein expression in murine tumor cells following photodynamic therapy with benzoporphyrin derivative

Photodynamic therapy (PDT) has been proven as a method of tumor eradication and is currently being used clinically to treat a wide variety of malignancies. Although it is understood that the interaction of light and sensitizer results in the production of potentially damaging oxygen species, the mechanism by which tumors are destroyed has yet to be defined fully. Using a new porphyrin sensitizer, benzoporphyrin derivative (BPD), we examined protein expression in murine tumor cells following treatment as an indication of molecular changes to target tissue concurrent with PDT-mediated damage. In order to assess the relevance of the results obtained using an in vitro PDT model, metabolic labeling of proteins synthesized subsequent to PDT was performed both in tumor cells grown and treated in tissue culture dishes and in cells explanted from PDT-treated solid tumors. We observed that the oxidative stress associated with PDT-resulted in the induction of a number of proteins corresponding to a set of heat-shock or stress proteins, and that the pattern of expression was similar when tumor cells were treated in vitro and in vivo. These results support the use of in vitro models in the dissection of the molecular effects of PDT and provide the foundation for future experiments that will examine the role of the immune system in tumor eradication by PDT.

Heat-induced morphological and biochemical changes in the nuclear lamina from Ehrlich ascites tumor cells in vivo

Membrane-depleted nuclei from Ehrlich ascites tumor (EAT) cells isolated at low ionic strength in the presence of EDTA exhibit highly decondensed chromatin fibers and a loss of morphologically identifiable nucleoli. Treatment of these nuclei with nucleases and 2 M NaCl followed by low-speed centrifugation permitted the facile isolation of the nuclear lamina layer. Under the same conditions, but after heat-shock treatment of the living cells, the chromatin appears in a more condensed state, the nucleoli are well-defined, and the nuclear lamina layer was destabilized in concert with the appearance of an internal nuclear matrix and nucleolar skeleton. Furthermore, we also found both an increase in the protein mass as well as the appearance of a relatively large number of new proteins in this fraction, which are phosphorylated. The major proteins of the nuclear lamina, the lamins, and the residual vimentin remained insoluble. These heat-shock-induced changes were also accompanied by a dephosphorylation of lamins A and C but not of lamin B.

Molecular and biochemical reprogramming of oncogenesis through the activity of prooxidants and antioxidants

The antioxidant alpha-tocopherol and the weaker antioxidant and prooxidant chemopreventative, beta-carotene have been shown to inhibit tumor cell growth in vivo and in vitro. In some epidemiologic studies their serum levels were demonstrated to be inversely related to the incidence of malignant tumor. We hypothesized two basic pathways triggered by antioxidants and prooxidants, which resulted in the control of tumor cell growth. These included changes in phosphorylation and ultimately transcription. Specifically, the prooxidant beta-carotene treatment produced an oxidative stress resulting in the selective induction of heat shock proteins (hsps). These proteins and other proteins that were possibly oxidized were associated with the increased expression of cyclins (A and D) and increased cdc2 kinase expression. An increase in expression of phosphoproteins, such as p53 (tumor suppressor form) was also discerned. The level of expression for the transcription factor c-fos was reduced. Growth factors that contribute to tumor cell growth were also reduced. Increased DNA fragmentation, depression of proliferation and intracellular calcium levels, the accumulation of tumor cells in G0-->G1, and morphologic changes, were consistent with programmed cell death. Antioxidants such as alpha-tocopherol bound to membrane-associated proteins could inhibit the development of peroxidation products (hydroxyl radicals (.OH)), which attack proteins and modify their function and promote their degradation. Some kinases such as, cdc2 may be increased in activity, which would explain the observed increased expression of tumor suppressor p53, the accumulation of the tumor cells in G1 of the cell cycle and the inhibition of tumor cell proliferation. A reduction in oxidant radicals could also reduce transcription factor products, such as c-myb. Indirectly this result may occur through changes in nuclear translocation (signaling) NF-AT or the Rel-related family of transcription factors, including NF-kB (p50 or p65) or inhibition of immunophilin-calmodulin activity. Although the data remains fragmentary there are common points for control for tumor cell growth resulting from the effects of alpha-tocopherol or beta-carotene treatment. These changes involve phosphorylation and protein expression. Ultimately there is a reduction of important transcription factor protein products, a reduction in response to growth factors, and suppression of cell proliferation, resulting in increased control of the cell cycle.

Effect of heat shock on susceptibility of normal lymphoblasts and of a heat shock protein 70-defective tumour cell line to cytotoxic T lymphocytes in vitro

The effect of heat shock pretreatment of target cells on their lysability by cytotoxic T lymphocytes was analysed. Killing of Concanavalin A-stimulated normal lymphocytes by minor or major histocompatibility antigen-specific cytotoxic T lymphocytes is unchanged or even slightly enhanced after heat shock, whereas cells of the myeloma line Y3, which is derived from one of the lymphocyte donor strains, become nearly resistant to killing after the same pretreatment. Cold target inhibition experiments show that heat-shocked cells are recognized specifically and that untreated and heat-shocked target cells possess similar inhibitory potential. Y3 cells are unable to express the strongly heat-inducible heat shock protein of 70 kDa (hsp70) after heat shock; the acquired resistance is thus independent of hsp70 induction. Possible mechanisms of the different lysability seen in lymphoblasts and tumour cells after heat shock are discussed.