So-called Heat Shock Proteins Research Articles

Production components in transformed and untransformed ‘Micro- Tom’ tomato plants

ABSTRACT Changes to the amounts of certain proteins have resulted in several studies, among them the so-called heat shock proteins (HSP), which take many forms, most of them constitutive. However, other forms may be inducible by a particular stress factor. The ‘Micro-Tom’ tomato is considered a model for experimental studies due to having suitable characteristics, such as reduced size, short generation time, and ease of transformation. Growth and production components were therefore evaluated in ‘Micro-Tom’ tomato plants transformed for different levels of mitochondrial HSP (MT-sHSP23.6). Plants from genotypes of the ‘Micro-Tom’ tomato (untransformed, and transformed with overexpression and with expression silencing) were grown under controlled conditions of temperature, photoperiod and photon flux density. To obtain the data, successive collections were carried out at regular intervals (21 days) throughout the development cycle of the plants, starting from the 21st day after transplanting (DAT). Total dry matter, leaf area, dry-weight partitioning between the plant organs, and production components were determined in the three genotypes. From interpretation of the results, it was found that plants transformed with overexpression of MT-sHSP23.6 displayed greater production capacity, considering the fresh weight of the fruit; but in general, the data showed that genetic transformation did not bring about major changes in growth, since the three genotypes displayed similar behaviour.

Recombinant small heat shock protein from Acholeplasma laidlawii increases the Escherichia coli viability in thermal stress by selective protein rescue

In both prokaryotes and eukaryotes, the survival at temperatures considerably exceeding the optimum is supported by intense synthesis of the so-called heat shock proteins (HSPs), which act to overcome the adverse effects of heat stress. Among mycoplasmas (class Mollicutes), which have significantly reduced genomes, only some members of the Acholeplasmataceae family possess small HSPs of the α-crystallin type. Overproduction of a recombinant HSP IbpA (Hsp20) from the free-living mycoplasma Acholeplasma laidlawii was shown to increase the resistance of Escherichia coli to short-term heat shock. It has been long assumed that IbpA prevents protein aggregation and precipitation thereby increasing viability of E. coli cells. Several potential target proteins interacting with IbpA under heat stress were identified, including biosynthetic enzymes, enzymes of energy metabolism, and components of the protein synthesis machinery. Statistical analysis of physicochemical properties indicated that IbpA interaction partners significantly differ in molecular weight, charge, and isoelectric point from other members of the E. coli proteome. Upon shortterm exposure to increased temperature, IbpA was found to preferentially interact with high-molecular weight proteins having a pI of about 5.1, significantly lower than the typical values of E. coli proteins.

Chemical inducers of heat shock proteins derived from medicinal plants and cytoprotective genes response

Environmental stress induces damage that activates an adaptive response in any organism. The cellular stress response is based on the induction of cytoprotective proteins, the so-called stress or heat shock proteins (HSPs). HSPs are known to function as molecular chaperones which are involved in the therapeutic approach of many diseases. Therefore in the current study we searched nontoxic chaperone inducers in chemical compounds isolated from medicinal plants. Screening of 80 compounds for their Hsp70-inducing activity in human lymphoma U937 cells was performed by western blotting. Five compounds showed significant Hsp70 up-regulation among them shikonin was most potent. Shikonin was able to induce Hsp70 at 0.1 µM after 3 h without activation of heat shock transcription factor 1 (HSF-1). It also induces significant reactive oxygen species generation. The expression level of genes responsive to shikonin was studied using global-scale microarrays and computational gene expression analysis tools. Significant increase in the nuclear factor erythroid 2-related factor 2 (Nrf2, NFEL2L2) -mediated oxidative stress response was observed that leads to the activation of HSP. The results of gene chip analysis were further confirmed by real-time qPCR assay. In short, the detailed mechanisms of Hsp70 induction by shikonin is not fully understood, Nrf2 and its target genes might be involved in the Hsp70 up-regulation in U937 cells.

Mathematical modeling of heat shock protein synthesis in response to temperature change

One of the most important questions in cell biology is how cells cope with rapid changes in their environment. The range of common molecular responses includes a dramatic change in the pattern of gene expression and the elevated synthesis of so-called heat shock (or stress) proteins (HSPs). Induction of HSPs increases cell survival under stress conditions [Morimoto, R.I., 1993. Cells in stress: transcriptional activation of heat shock genes. Science 259, 1409–1410]. In this paper we propose a mathematical model of heat shock protein synthesis induced by an external temperature stimulus. Our model consists of a system of nine nonlinear ordinary differential equations describing the temporal evolution of the key variables involved in the regulation of HSP synthesis. Computational simulations of our model are carried out for different external temperature stimuli. We compare our model predictions with experimental data for three different cases—one corresponding to heat shock, the second corresponding to slow heating conditions and the third corresponding to a short heat shock (lasting about 40 min). We also present our model predictions for heat shocks carried out up to different final temperatures and finally we present a new hypothesis concerning the molecular response to stress that explains some phenomena observed in experiments.

Acting at a Distance

MOLECULAR BIOLOGY Unfolded proteins are dangerous to the cell; exposing hydrophobic amino acid side chains will promote nonspecific aggregation and interfere with intracellular processes. Chaperones are proteins that assist in the folding and unfolding of other proteins. They are found in all organisms, and among their number are the so-called heat shock proteins (Hsps), which combat heat-induced stress. In Escherichia coli , the heat shock transcription factor σ32 regulates heat-shock gene expression, and it is in turn regulated by Hsps: DnaK (the prokaryote equivalent of Hsp70) and the co-chaperone DnaJ. Rodriguez et al. show that DnaK and DnaJ bind independently to distinct domains of σ32 in its native, folded state. The DnaK binding site would normally be occluded on σ32 that is bound to RNA polymerase, suggesting that DnaJ binds σ32 first. The binding of DnaJ destabilizes σ32 at a site in the vicinity of the DnaK binding site, favoring the rapid binding of DnaK once σ32 is released from RNA polymerase. Hsp70 systems in general may act in a similar manner: promoting disassembly and folding of aggregated substrate proteins by altering their conformations from a distance. — GR Mol. Cell 32 , 347 (2008).

Conformational changes resulting from pseudophosphorylation of mammalian small heat shock proteins—a two-hybrid study

The human genome codes for 10 so-called mammalian small heat shock or stress proteins (sHsp) with the various tissues expressing characteristic sets of sHsps. Most sHsps interact with each other and form homo- and heterooligomeric complexes. Some of the sHsps are phosphoproteins in vivo, and phosphorylation has been implicated in the regulation of complex size and composition. In this study, we analyze, by the 2-hybrid method, the reporter gene activation pattern of several sHsp pairs that previously have been demonstrated to interact. We show that pseudophosphorylation (mimicry of phosphorylation) of the homologous phosphorylation sites Ser15 and Ser16 in Hsp27 and Hsp20, respectively, modulates characteristics of these sHsps that can be detected by their ability to activate reporter genes in suitable 2-hybrid assays. Pseudophosphorylation of the separated N-terminus of Hsp27 alone is not sufficient for the activation of the reporter genes, whereas the separated C-terminus is sufficient. We conclude that pseudophosphorylation of Hsp27 and Hsp20 at their N-termini results in conformational changes that can be detected by their interaction with other sHsps. Pseudophosphorylation of alphaB-crystallin at Ser19, in contrast, had no detectable consequences.

Altered Hsp90 function in cancer: A unique therapeutic opportunity

Molecular chaperones or so-called heat shock proteins serve as central integrators of protein homeostasis within cells. In performing this function, they guide the folding, intracellular disposition, and proteolytic turnover of many key regulators of cell growth, differentiation, and survival. Recent data show essential roles for the chaperones in facilitating malignant transformation at the molecular level and support the concept that their altered utilization during oncogenesis is critical to the development of human cancers. The field is evolving rapidly, but it has become apparent that chaperones can serve as biochemical buffers at the phenotypic level for the genetic instability that is characteristic of many human cancers. Chaperone proteins thus allow tumor cells to tolerate the mutation of multiple critical signaling molecules that would otherwise be lethal. Much of the recent progress in understanding the complex role of heat shock proteins in tumorigenesis has been made possible by the discovery of several natural product antitumor antibiotics that selectively inhibit the function of the chaperone Hsp90. These agents have been used as probes to define the biological functions of Hsp90 at the molecular level and to validate it as a novel target for anticancer drug action. One of these agents, 17-allylamino,17-demethoxygeldanamycin (NSC 330507) has begun phase II clinical trials, and several second-generation compounds are now in late preclinical development. The best way to use Hsp90 inhibitors as anticancer agents remains to be defined. Trials accomplished to date, however, serve as proof of principle that Hsp90 function can be modulated pharmacologically without undue toxicity in humans. Given the redundancy and complexity of the signaling pathway abnormalities present in most cancers, the ability of Hsp90 inhibitors to alter the activity of multiple aberrant signaling molecules instead of just one or two (as most current-generation molecular therapeutics have been designed to do) may prove of unique therapeutic benefit.

Gut function and dysfunction in young pigs: physiology

The post-weaning period in pigs is characterized by an immediate but transient drop in feed intake resulting in severe undernutrition and growth check. This in turn affects various aspects of small intestinal architecture and function leading to gut-associated disorders and often diarrhea. Among these, villus atrophy and digestive enzyme activity depression have been documented. More recent investigations clearly demonstrate early signs of local inflammation including immune cell infiltration and increased pro-inflammatory cytokine gene expression, signs of cytoprotection through up-regulation of so-called heat shock proteins, indications of tissue alterations by proteases (stromelysin) and finally epithelial functional disorders in mineral absorption/secretion and perme- ability. This is followed by a regenerative phase, probably stimulated by feed intake resumption, resulting in down-regulation of many intestinal indicators. However, some of them then display new spatio-temporal adult-type adaptive patterns of maturation. A limited number of substances, partic- ularly nitrogenous compounds and complex preparations of animal origin (colostrum, plasma) have proven to be successful, at least partly, in minimizing post-weaning intestinal disturbances. Thus further research in intestinal physiology, in association with microbiology and immunology, is war- ranted to strengthen our understanding of the mechanisms of gut disorders in order to provide a better rational basis for designing suitable alternatives to in-feed antibiotics for pigs.

Heat shock proteins and cardiovascular pathophysiology.

In the eukaryotic cell an intrinsic mechanism is present providing the ability to defend itself against external stressors from various sources. This defense mechanism probably evolved from the presence of a group of chaperones, playing a crucial role in governing proper protein assembly, folding, and transport. Upregulation of the synthesis of a number of these proteins upon environmental stress establishes a unique defense system to maintain cellular protein homeostasis and to ensure survival of the cell. In the cardiovascular system this enhanced protein synthesis leads to a transient but powerful increase in tolerance to such endangering situations as ischemia, hypoxia, oxidative injury, and endotoxemia. These so-called heat shock proteins interfere with several physiological processes within several cell organelles and, for proper functioning, are translocated to different compartments following stress-induced synthesis. In this review we describe the physiological role of heat shock proteins and discuss their protective potential against various stress agents in the cardiovascular system.

Modulating cellular aging in vitro: hormetic effects of repeated mild heat stress on protein oxidation and glycation.

Intracellular and extracellular proteins are subject to a variety of spontaneous non-enzymatic modifications which affect their structure, function and stability. Protein oxidation and glycation are tightly linked and are implicated in the development of many pathological consequences of aging. Although multiple endogenous pathways in the cell can prevent the formation of oxidized and glycated proteins, and repair and degrade abnormal proteins, such abnormal proteins do accumulate during aging. The heat shock response involving the family of stress-proteins or the so-called heat shock proteins (HSP), represents the quickest and highly conserved response to proteotoxic insults. Since repeated mild heat stress is able to prevent the onset of various age-related changes during cellular aging in vitro, we suggest that treatments which increase HSP expression should reduce the extent of accumulation of abnormal proteins during aging. Such modulation of aging is an example of hormesis, which is characterized by the beneficial effects resulting from the cellular responses to mild repeated stress.

Hsp72 induction: a potential molecular mediator of the delay phenomenon.

The molecular basis of enhanced ischemic tissue survival in flaps preconditioned by surgical delay is poorly understood. Because elevated expression of so-called heat shock or stress proteins has been shown to protect tissues/organs against ischemic injury, the authors examined whether the levels of the most highly induced stress protein-hsp72-were elevated in delayed muscle flaps using a rat muscle flap model. Bilateral latissimus dorsi muscle flaps based on the thoracodorsal vessels were elevated in 16 male Sprague-Dawley rats. For each animal, one side was selected randomly to undergo preconditioning by surgical delay for a 7-day period prior to elevation. Delay was accomplished by preserving the thoracodorsal pedicle and a single large distal intercostal perforating vessel. After bilateral flap elevation, latissimus dorsi tissue was harvested from proximal, central, and distal flap segments 0, 1, 3, and 7 days postoperatively (N = 4 for each group), and was analyzed for the expression of hsp72 via Western blot analysis. At the time of harvest, flap viability was assessed by staining with nitroblue tetrazolium. Flap perfusion was measured prior to muscle elevation and harvest using laser Doppler flowmetry. The results demonstrate that delayed muscle flaps had significantly greater total perfusion (p < 0.05) and survival (p < 0.03) 1, 3, and 7 days after elevation compared with the acutely elevated control tissue. Western blot analysis revealed that tissues harvested from the delayed flaps expressed substantially higher levels of hsp72 compared with the acutely elevated control samples. Segmental analysis also revealed a proximal > middle > distal expression of hsp72 in the delayed flaps (p < 0.05). Flap preconditioning by surgical delay increases the expression of hsp72. Moreover, regional differences in hsp72 gene expression are associated with differences in perfusion and survival of delayed muscle flaps. These results indicate that hsp72 may play a substantial role in mediating the delay phenomenon.

Expression of heat shock genes inClostridium acetobutylicum

Characterization of the heat shock response in Clostridium acetobutylicum has indicated that at least 15 proteins are induced by a temperature upshift from 30 to 42 degrees C. These so-called heat shock proteins include DnaK and GroEL, two highly conserved molecular chaperones. Several genes encoding heat shock proteins of C. acetobutylicum have been cloned and analysed. The dnaK operon includes the genes orfA (a heat shock gene with an unknown function), grpE, dnaK, and dnaJ; and the groE operon the genes groES and groEL. The hsp18 gene coding for a member of the small heat shock protein family constitutes a monocistronic operon. Interestingly, the heat shock response in this bacterium is regulated by a mechanism, which is obviously different from that found in Escherichia coli. So far, no evidence for a heat shock-specific sigma factor of the RNA polymerase in C. acetobutylicum has been found. In this bacterium, like in many Gram-positive and several Gram-negative bacteria, a conserved inverted repeat is located upstream of chaperone/chaperonin-encoding stress genes such as dnaK and groEL and may be implicated as a cis-acting regulatory site. The inverted repeat is not present in the promoter region of hsp18. Therefore, in C. acetobutylicum there are at least two classes of heat shock genes with respect to the type of regulation. Evidence has been found that a repressor is involved in the regulation of the heat shock response in C. acetobutylicum. However, this regulation seems to be independent of the inverted repeat motif, and the mechanism by which the inverted repeat motif mediates regulation remains to be elucidated.(ABSTRACT TRUNCATED AT 250 WORDS)

Stress proteins: the exercise response.

A class of proteins that undergoes preferential synthesis following a variety of stressors has been demonstrated to carry out important cellular functions under both stressed and nonstressed conditions. These so-called heat shock (HSP) or stress (SP) proteins have been termed "molecular chaperones" and play important roles in cellular transportation, assembly/degradation, and cell survival. This review provides a basic introduction to the function and regulation of these proteins. Emphasis is placed on members of the HSP 70 family of proteins (especially HSP 72) and their role in cellular protection, their pattern of distribution in skeletal muscle, and changes in their expression following exercise and exercise training.

Expression of heat shock genes in Clostridium acetobutylicum

Characterization of the heat shock response in Clostridium acetobutylicum has indicated that at least 15 proteins are induced by a temperature upshift from 30 to 42°C. These so-called heat shock proteins include DnaK and GroEL, two highly conserved molecular chaperones. Several genes encoding heat shock proteins of C. acetobutylicum have been cloned and analysed. The dnaK operon includes the genes orfA (a heat shock gene with an unknown function), grpE, dnaK, and dnaJ; and the groE operon the genes groES and groEL. The hsp18 gene coding for a cell member of the small heat shock protein family constitutes a monocistronic operon. Interestingly, the heat shock response in this bacterium is regulated by a mechanism, which is obviously different from that found in Escherichia coli. So far, no evidence for a heat shock-specific sigma factor for the RNA polymerase in C. acetobutylicum has been found. In this bacterium, like in many Gram-positive and several Gram-negative bacteria, a conserved inverted repeat is located upstream of chaperone/chaperonin-encoding stress genes such as dnaK and groEL and may be implicated as a cis-acting regulatory site. The inverted repeat is not present in the promoter region of hsp18. Therefore, in C. acetobutylicum there are at least two classes of heat shock genes with respect to the type of regulation. Evidence has been found that a repressor is involved in the regulation of the heat shock response in C. acetobutylicum. However, this regulation seems to be independent of the inverted repeat motif, and the mechanism by which the inverted repeat motif mediates regulation remains to be elucidated. Another protein with a potential regulatory function might be the 21-kDa heat shock protein, which is induced significantly earlier than the majority of heat shock proteins. This protein has similarity to the redox carrier rubredoxin. Interestingly, heat shock genes are expressed in C. acetobutylicum at an increased rate not only after heat stress but also during the initiation of solvent formation. The mRNA level of some heat shock genes, e.g. dnaK, reached a maximum at the same time during the metabolic shift as the mRNA levels of genes necessary for solvent production. Therefore, the heat shock response in C. acetobutylicum might be part of a global regulatory network including different stress responses like heat shock, metabolic switch, and also sporulation.

Heat shock proteins and protection against myocardial ischemia

The incidence of myocardial infarcts has significantly decreased in the past decade. Research aimed at identifying the cause of atherosclerosis and efforts to prevent it have contributed to this decrease in myocardial infarction, tIowever in spite of early reperfusion, loss of functional myocardium leading to subsequent severe cardiac failure still remains a significant medical problem (American tteart Association, 1990). The salvage of additional myocardinm is, therefore, a highly desirable aim. Recent evidence indicates that endogenous protective mechanisms are activated in the ischemic cardiomyocyte. A better understanding of these endogenous protective mechanisms will most likely lead to additional myocardial salvage in the reperfused myocardium. Ischemia is known to produce a number of intracellular changes within the cardiomyocyte. These changes include among others increased cel-lular calcium levels, altered osmotic control, membrane damage, free radical production, decreased intracellular pit, depressed ATP levels, oxygen depletion, decreased intracellular glucose levels, etc. (Bonventre, 1988). These events represent a form of metabolic or hypoxic stress which is known to produce protein denaturation within the cell. Interestingly, an increase in denatured proteins in the cell has been reported to result in the onset of the heat shock response which increased the synthesis of the so-called heat shock proteins (HSPs) (Ananthan et al., 1986). The heat shock response has been shown to occur in all organisms examined to date. This heat shock response consists of a transient rearrangement of cellular activities to cope with the stress period by protecting essential components within the cell so as to permit it lo resume normal activity during recovery /i'om the slress (Lindquist, 1986). This ability of the cell for self-preservation has attracted the attention of several investigators in the field. Several studies have shown that a hyperthermic treatment of experimental animals can result in a signitlcantly improved myocardial salvage lbllowing c(~ronary occlusion and reperfusion in vhTo (Donnelty et al., 1992; Currie et aL, 1993) as well as in an isolated perfused heart model (Walker et al., 1993). Interestingly, recent studies have now demonstrated a direct correlation between the amount of one of tlhese iheat shock proteins (HSP70) and the degree of myocardkd protection following a hyperthermic treatment in experimental animals ( t tu t te re t al., 1994; Marber et aL, 1994). A closer examination of this group of proteins (liSPs) and their involvement in cardioprotection during myocardial infarction is then extremely important as a means to understand the cardiac cell's ability to protect itself against ischemic injury. The present review will attempt to cover what is known about these proteins and the more recent studies related to their expression and myocardial protection.

Nucleotide sequence of a cDNA encoding a heat-shock protein (HSP70) from barley (Hordeum vulgare L.).

Among various so-called heat-shock proteins is a highly conserved family that has an average molecular mass of 70 kD and is known as the HSP70 proteins. Some HSP70s are heat inducible but others are constitutive. HSP70s have been identified in many cellular compartments and function as molecular chaperones with diverse roles in protein metabolism (for review, see Hendrick and Hartl, 1993). A cDNA library of poly(A)+ RNA from 3-d-old pollinated barley ovaries in Uni-ZAP XR was screened with first-strand cDNA probes of poly(A)+ RNA from unpollinated and pollinated ovaries, respectively. A 2028-bp cDNA was identified for its elevated leve1 after pollination and converted to Bluescript SKby in vivo excision. DNA sequence was determined by the dideoxy method of Sanger (Sanger et al., 1977) using an autosequencer (Applied Biosystems, Foster City, CA, model 373A, version 1.2.0). Sequence homology analysis showed that the cDNA clone belongs to the HSP70 family. The predicted amino acid sequence was 87% identical to that of the heat-shock protein from spinach (Anderson et al., 1994). Characteristics pertaining to the barley HSP70 clone are described in Table I. Elevated mRNA levels were observed after pollination and during early embryogenesis as compared to levels in unpollinated ovaries. Moderate restriction fragment-length polymorphisms were detected for the HSP7O locus in the genomic DNA blots of five barley cultivars (Dicktoo, Morex, Steptoe, Harrington, and TR306). Using the barley genome mapping population of Steptoe X Morex (Kleinhofs et al., 1993), the HSP70 locus was mapped to the plus arm of barley chromosome 6,3.8 centimorgans from the carboxypeptidase locus (Kleinhofs et al., 1993).

Heat shock proteins functioning as molecular chaperones: their roles in normal and stressed cells.

In response to either elevated temperatures or several other metabolic insults, cells from all organisms respond by increasing the expression of so-called heat shock proteins (hsp or stress proteins). In general, the stress response appears to represent a universal cellular defence mechanism. The increased expression and accumulation of the stress proteins provides the cell with an added degree of protection. Studies over the past few years have revealed a role for some of the stress proteins as being intimately involved in protein maturation. Members of the hsp 70 family, distributed throughout various intracellular compartments, interact transiently with other proteins undergoing synthesis, translocation, or higher ordered assembly. Although not yet proven, it has been suggested that members of the hsp 70 family function to slow down or retard the premature folding of proteins in the course of synthesis and translocation. Yet another family of stress proteins, the hsp 60 or GroEL proteins (chaperonins), appear to function as catalysts of protein folding. Here I discuss the role of those stress proteins functioning as molecular chaperones, both within the normal cell and in the cell subjected to metabolic stress.

The two mammalian mitochondrial stress proteins, grp 75 and hsp 58, transiently interact with newly synthesized mitochondrial proteins.

In mammalian cells, two of the so-called heat shock (hsp) or stress proteins are components of the mitochondria. One of these, hsp 58, is a member of the bacterial GroEL family, whereas the other, glucose-regulated protein (grp) 75, represents a member of the hsp 70 family of stress proteins. Owing to previous studies implicating a role for both the hsp 70 and GroEL families in facilitating protein maturation events, we used the method of native immunoprecipitation to examine whether hsp 58 and grp 75 might interact with other proteins of the mitochondria. In cells pulse-labeled with [35S]-methionine, a significant number of newly synthesized mitochondrial proteins co-precipitated with either hsp 58 or grp 75. Such interactions appeared transient. For example, providing the pulse-labeled cells a subsequent chase period in the absence of radiolabel resulted in a reduction of co-precipitating proteins. If the pulse-chase labeling experiments were performed in the presence of an amino acid analogue, somewhat different results were obtained. Specifically, although many of the newly synthesized and analogue-containing proteins again were observed to co-precipitate with grp 75, the interactions did not appear transient, but instead were stable. Under steady-state labeling conditions, we also observed a portion of hsp 58 and grp 75 in an apparent complex with one another. On addition of ATP, the complex was dissociated. Accompanying this dissociation was the concomitant autophosphorylation of grp 75. On the basis of these observations, as well as previous studies examining the structure/function of the hsp 70 and GroEL proteins, we suspect that both hsp 58 and grp 75 interact with and facilitate the folding and assembly of proteins as they enter into the mitochondria.

Exercising mammals synthesize stress proteins

Spleen cells, peripheral lymphocytes, and soleus muscles were removed from male Sprague-Dawley rats that had been run on a treadmill (24 m/min) for either 20, 40, or 60 min or to exhaustion (86 +/- 41 min) and were labeled in vitro with [35S]methionine at 37 degrees C. Similar tissues from nonrunning control rats were labeled in vitro at either 37 or 43 degrees C (heat shock). Fluorographic analyses of one- and two-dimensional polyacrylamide gel electrophoretic separations of the proteins from cells and tissues of exercised rats demonstrate the new or enhanced synthesis of proteins of approximately 65, 72, 90, and 100 kDa. Although synthesis of these proteins is low or not detectable in tissues from control rats labeled at 37 degrees C, they are prominent products of similar tissues labeled under heat-shock conditions (43 degrees C) and, in fact, correspond in Mr and pI with the so-called heat-shock proteins. These results suggest that exercise is a sufficient stimulus to induce or enhance the synthesis of heat shock and/or stress proteins in mammalian cells and tissues.

Erythrophagocytosis induces heat shock protein synthesis by human monocytes-macrophages.

Exposure of cells to elevated temperatures and other environmental stresses results in the expression of specific genes encoding the so-called heat shock proteins (HSPs). Since exogenous H2O2 induces in human monocytes the synthesis of HSPs, and previous induction of HSPs protects these cells from oxidative injury, we investigated whether HSP synthesis was also induced during generation of reactive oxygen species by the phagocyte itself during phagocytosis. As a model system, we analyzed the effects of erythrophagocytosis on protein synthesis by the human premonocytic line U937, in which phagocytosis is induced during differentiation with 1,25-dihydroxyvitamin D3. Exposure to whole erythrocytes, but not to erythrocyte ghosts, induced in the phagocytic cells only the synthesis of the 70- and 83- to 90-kDa HSPs and a 32-kDa oxidation-related stress protein identical by partial peptide mapping to heme oxygenase. The radioprotective aminothiol N-(2'-mercaptoethyl)-1,3-propanediamine (WR-1065), which can substitute for glutathione as hydrogen donor, prevented this induction. These results suggest that oxygen free radicals generated in the presence of hemoglobin-derived iron and consecutive glutathione depletion are involved in induction of stress protein synthesis during erythrophagocytosis. HSPs synthesized during phagocytosis may play a role in the phagocyte's defense mechanisms and in protective immunity.