Heat shock and the heat shock proteins

Stress protein synthesis by crayfish CNS tissue in vitro

Some crustacean axons remain functional for months after injury. This unusual property may require stress proteins synthesized by those neurons or provided to them by glial cells. To begin to explore this hypothesis, we examined the conditions that stimulated stress protein synthesis by crayfish CNS tissue in vitro. Incubation for 1-15 h with arsenite or at temperatures about 15 degrees C higher than the acclimation temperature of 20 degrees C induced transient expression of several stress proteins. The heat stress response was blocked by Actinomycin D, suggesting that synthesis of new mRNA was required. In addition, the major crayfish 66 kD stress protein and its mRNA had sequence identities with the 70 kD stress proteins of mammals. Since the crayfish stress response has much in common with that of other organisms, the unique advantages of the crayfish nervous system can be used to study the impact of stress proteins on glial and neuronal function.

Characterisation of missense mutations in the Act88F gene of Drosophila melanogaster

We have created missense mutations in the indirect flight muscle (IFM)-specific Act88F actin gene of Drosophila melanogaster by random in vitro mutagenesis. Following P element-mediated transformation into wild-type flies and subsequent transfer of the inserts into Act88F null strains, the effects of the actin mutants on the structure and function of the IFMs were examined. All of the mutants were antimorphic for flight ability. E316K and G368E formed muscle with only relatively small defects in structure whilst the others produced IFMs with large amounts of disruption. E334K formed filaments but lacked Z discs. V339I formed no muscle structure in null flies and did not accumulate actin. E364K and G366D both had relatively stable actin but did not form myofibrils. Using an in vitro polymerisation assay we found no significant effects on the ability of the mutant actins to polymerise. E364K and G366D also caused a strong induction of heat shock protein (hsp) synthesis at normal temperatures and accumulated large amounts of hsp22 which, together with the mutant actin, was resistant to detergent extraction. Both E316K and E334K caused a weak induction of hsp synthesis. We discuss how the stability, structure and function of the different mutant actins affects myofibril assembly and function, and the induction of hsps.

Differential adaptive response to hyperosmolarity of 3T3 and transformed SV3T3 cells

Both 3T3 and simian virus 40-transformed 3T3 (SV3T3) cells were used to investigate differences in population kinetics, protein synthesis, monovalent ion levels, and amino acid accumulations between normal and transformed cells exposed to hyperosmolarity at 0.5 Osm. Under similar culture conditions, SV3T3 cells were found to be more sensitive in their proliferative response than normal cells to the hyperosmolar treatment. In the normal 3T3 cells, the increase in transport of amino acids was less sustained and was associated with higher levels of accumulated amino acids. The equilibrium distribution of intracellular monovalent cations and the rate of protein synthesis also returned faster to baseline values in the normal cells than in the transformed cells. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) analysis revealed the induction of a 69-kDa polypeptide in the 3T3 cells but not in the SV3T3 cells after exposure to hyperosmolarity. On electrofocusing and relative mass analysis, this polypeptide closely migrated with the 70-kDa heat shock protein (hsp) family, although it was unrelated immunologically to the inducible 72-kDa hsp.

The isolated neonatal rat-cardiomyocyte used in an in vitro model for 'ischemia'. II. Induction of the 68 kDa heat shock protein

In a model system of cultured rat cardiac cells, the expression of the heat shock protein hsp68 was studied after simulating ischemia. We observed both an increase in hsp68 mRNA levels and hsp68 synthesis, while under normal conditions hsp68 and its mRNA could not be detected. Using an antibody against hsp70 and hsp68, immunofluorescence studies showed that during 'ischemia', when hsp68 is not yet synthesized, hsp70 migrated into the nucleus. These results demonstrate that the expression of hsp68 can be used as a marker for the occurrence of ischemia. Furthermore, these findings support the fact that this in vitro system is a suitable model for the study on myocardial infarction.

Ubiquitin and heat shock protein expression in amyotrophic lateral sclerosis

The expression of two heat shock proteins, HSP72 and p57, in addition to ubiquitin, has been studied immunocytochemically in nine amyotrophic lateral sclerosis (ALS) cases and 10 age-matched controls. HSP72 and p57 antibodies did not identify the characteristic ubiquitin-immunoreactive inclusions present in anterior horn cells in ALS spinal cord. Antibodies to HSP72, but not to p57 or ubiquitin, strongly labelled structures corresponding to polyglucosan bodies in spinal grey matter. Such immunoreactive profiles were more abundant in ALS cases, although they were also present in control material. They were sometimes identified by haematoxylin and eosin and periodic acid Schiff reaction, but were not labeled by phosphotungstic acid haematoxylin or by antibodies to glial fibrillary acidic protein. Although ubiquitin, HSP72 and p57 are stress-induced proteins, they are expressed differently and might therefore have different significance in neuronal degeneration.

Thermolability of mouse oocytes is due to the lack of expression and/or inducibility of Hsp70

Eukaryotic and prokaryotic cells have been shown to respond to physical and chemical stress by the induction of proteins called heat shock proteins. Heat shock protein 70 (Hsp70), is the most ubiquitous of these proteins. Although heat shock proteins are generally thought to protect cells from physiologically stressful stimuli, it cannot be assumed that this is so, because several cases exist in which thermotolerance is acquired without the production of heat shock proteins, and in several other cases the hyperproduction of these heat shock proteins does not produce thermotolerance. In this study we show that unfertilized mouse oocytes are sensitive to elevated temperatures, and that the synthesis of Hsp70 cannot be induced in these oocytes. Furthermore, our data demonstrate that the expression of Hsp70 in mouse oocytes is sufficient for the acquisition of thermotolerance. Mouse oocytes were injected with mRNA for Hsp70, and the viability of these oocytes was determined after heating. The number of viable oocytes was significantly higher in the group injected with Hsp70 mRNA and then heated compared with oocytes injected with Hsp70 antisense mRNA and sham-injected controls treated in an identical manner. No significant differences in the number of viable oocytes were found between the group that had been injected with Hsp70 mRNA, heated, and then allowed to recover for 3 hr and the group maintained at 37 degrees C throughout.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid expression of heat shock protein in the rabbit after brief cardiac ischemia

The effect of brief myocardial ischemia on the expression of heat shock protein (HSP 70) was examined in an in vivo rabbit model of myocardial ischemia using Northern blotting. Functional studies were carried out in the open-chested anesthetized rabbit. The large marginal branch of the left circumflex was occluded four times for 5 min. Using piezoelectric crystals implanted midwall in the ischemic zone, end-diastolic length, end-systolic length, and percent segmental shortening were assessed. Expression of HSP 70 was measured by Northern blotting. A single 5-min coronary occlusion doubled the expression of HSP 70 whereas four cycles of 5 min of ischemia/5 min of reperfusion resulted in a threefold increase in HSP 70 mRNA (P less than 0.001). Measurements with the piezoelectric crystals showed mild myocardial dysfunction concomitant with the increase in HSP 70. This increase in HSP 70 mRNA after repetitive brief ischemia was transient, occurring as early as 1 h and returning to baseline by 24 h after ischemia. Western blot analysis with a monoclonal antibody to HSP 70 was used to compare sham and postischemic myocardial HSP 70 levels. Changes in the amount of HSP 70 were evident as early as 2 h and were even more striking at 24 h.

Immunological evidence for the association between simian virus 40 115-kDa super T antigen and hsp70 proteins in rat, monkey, and human cells

Immunological evidence was provided that in subclone 7 cell line, which is derived from SV40 transformed cells, 115-kDa super T antigen, a transformation-competent, elongated form of large T antigen was physically complexed with hsp70 proteins. This conclusion was first based on the coimmunoprecipitation from unstressed or heat shocked subclone 7 cells of both super T antigen and hsp70 proteins. This was observed with any one of a set of anti-T monoclonal antibodies reacting to determinants located either in the C-terminal region or in the N terminal region. Reciprocally coimmunoprecipitation of both hsp70 and super T was also observed in the anti-hsp70 peptide serum-immunoprecipitate. The formation of complexes between hsp70 proteins and super T antigen in subclone 7 cells was also confirmed by Western blot experiments. Moreover, when expressed in cell lines originating from human (Hela cells) or monkey (CV1P cells) species following transfection with the relevant plasmid, super T antigen again displayed the ability to associate with hsp70 proteins. Considering that super T antigen was obtained in laboratory experiments as a stable evolutionary variant of SV40 large T antigen, it is suggested that the marked ability of super T antigen to associate with heat shock protein could be selectively advantageous under certain conditions.

Muscle protein changes following eccentric exercise in humans

This study characterized changes in the protein composition of human muscle tissue after eccentric exercise. Four subjects performed 70 maximum eccentric, isokinetic actions of the forearm flexors with one arm. The other arm served as control. A biopsy of the biceps muscle of each arm was taken 2 days after exercise when muscles were very sore (mean = 8.0; 1 = normal; 10 = very, very sore), and muscle damage was documented by a mean decrease of 0.2 radians in the relaxed elbow angle. Proteins from the biopsy tissue were solubilized in a high ionic strength buffer containing several proteolytic inhibitors. Protein concentrations of the extracts were determined and identical amounts loaded onto sodium dodecyl sulfate (SDS) polyacrylamide gels (7.5, 12.5, and 17.5%). Densitometric analysis of the Coomassie brilliant blue stained gels revealed alterations in the amounts of three protein bands in the exercised tissue relative to the control. These changes were in the linear portion of the graph of absorbance versus protein amount. Wilcoxon's signed rank test showed the first two of the following bands to increase significantly in amount (P less than 0.062). The average percentage changes [mean (SEM)] for these bands were 63 (21), 39 (5), and 82 (35). The corresponding molecular weights determined from known standards were 76300 (860), 33200 (310), and 12000 (80) daltons, respectively. These changes imply that the increased synthesis, decreased degradation, or some combination thereof, of these three proteins may be necessary for the repair or regeneration response to exercise-induced muscle damage.

Effects of copper and tributyltin on stress protein abundance in the rotifer Brachionus plicatilis

1. Exposure of the rotifer Brachionus plicatilis to elevated temperature resulted in the synthesis of a number of proteins, including a prominent one of 58,000 Da (SP58). 2. This protein is immunologically crossreactive with the 65,000 Da heat shock protein of the moth Heliothis virescens, which is a member of a highly conserved family of mitochondrial proteins. 3. Exposure of rotifers to sublethal doses of CuSO4 leads to a 4-5-fold increase in abundance of SP58, with maximum increase occurring at a dose that is approximately 5% of the LC50 for that compound. 4. A similar response was seen with tributyl tin (TBT). Kinetics of induction were sigmoidal, with induction occurring in the range of 20-30 micrograms/l. 5. No response was observed when rotifers were exposed to aluminum chloride, mercury chloride, pentachlorophenol, sodium arsenite, sodium azide, sodium dodecyl sulfate, or zinc chloride. 6. These results indicate that changes in stress protein abundance may prove useful as a biomarker of exposure to particular toxicants.

Estradiol increases phosphorylation of the 90 kDa heat shock protein not associated with estradiol receptor in MCF-7 cells in culture

MCF-7 cells in monolayer culture were incubated with [32P]orthophosphate for 18 h followed by covalent whole cell labelling of the estradiol receptor with tritiated tamoxifen aziridine [( 3H]TA). The heat shock protein (hsp-90) bound to receptor was precipitated with monoclonal antibodies H222 or JS 34/32, coupled to protein A-Sepharose and purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions. Hsp-90 not associated with receptor was similarly purified after isolation with the monoclonal antibody AC88. It was found that estradiol treatment of the cells markedly increased phosphate incorporation in the free hsp-90, without affecting heat shock protein bound to receptor. A 6-fold increase in phosphate content was observed after 10 min incubation of the cells with estradiol. A similar effect was seen after treatment of the cells with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). The calcium ionophore A23187 had no influence on hsp-90 phosphorylation, and treatment of the cells with forskolin to increase the cellular content of cAMP had a reverse effect. A 50% reduction of the phosphate content in the free hsp-90 was observed after 15 min treatment. The observation that estradiol, TPA and forskolin had effect only on hsp-90 not bound to receptor is an indication that the receptor-hsp-90 complex exists in vivo. Time course studies show that the effect of estradiol is non-genomic. Two possible explanations of the results seem to exist. Either estradiol induces an increase in the degree of phosphorylation of hsp-90, or hsp-90 is translocated to the cytosol from a different cellular compartment.

The pattern of 72-kDa heat shock protein-like immunoreactivity in the rat brain following flurothyl-induced status epilepticus

The inducible 72-kDa heat shock protein (HSP72) is a highly conserved stress protein that is expressed in CNS cells and may play a role in protection from neural injury. We used a monoclonal antibody to HSP72 and immunocytochemistry to localize HSP72 in the rat brain 24 h following either 30 or 60 min of flurothyl-induced status epilepticus. Sprague-Dawley rats were anesthetized with halothane, paralyzed, and ventilated, and remained normotensive and well oxygenated for the duration of the seizures. Seizure activity was quantified via analysis of the scalp EEG pattern. HSP72-like immunoreactivity (HSP72-LI) was induced in specific brain regions in a graded fashion that correlated, in part, with the duration and degree of seizure activity. Milder seizures produced HSP72-LI limited to layers 2 and 3 of frontoparietal cortex, dentate hilus cells, and CA3 pyramidal neurons. More extensive seizures led to HSP72-LI in layers 2, 3 and 5 of frontoparietal and visual cortex, dentate hilus cells, CA1 and CA3 pyramidal neurons, and certain thalamic and amygdaloid nuclei. These are similar to many, but not all, of the brain regions known to be injured with this model. No HSP72-LI was observed in sham-treated controls or flurothyl-treated animals whose seizures were controlled with pentobarbital. HSP72-LI thus localizes to certain regions of seizure-induced injury, and may provide a sensitive method of detecting neuronal 'stress' or injury relatively soon after status epilepticus. Whether or not HSP72 synthesis plays a protective role in the pathogenesis of seizures, or is only a marker for cell injury, remains to be determined.

Protein phosphorylation and kinase activities in tumour cells after hyperthermia

Phosphorylation of various proteins and the activities of specific kinases were studied in tumour cells after hyperthermia. P388 lymphoid tumour cells were treated at 40-45 degrees C for 1 h in vitro. Immediately after heat treatment, particulate and cytosol cell fractions were isolated, phosphorylated proteins separated and various kinase activities were measured. Hyperthermic treatment of the cells caused a significant decrease in protein kinase C activity while the activity of calcium-ion and phospholipid-independent protein kinases increased. Phosphorylation of cytosol proteins of 120, 80, 33, 25 and 14 kDa increased significantly after hyperthermia, and protein kinase C selectively phosphorylated the last three of these proteins. The phosphorylation of three heat shock proteins (44, 70 and 85 kDa) was not changed after hyperthermic treatment. Four tyrosine kinase activities were separated. The protein tyrosine kinase activity decreased to one-tenth of the control value after 45 degrees C for 1 h hyperthermia. The changes in kinase activities and protein phosphorylation induced by hyperthermia proved to be temperature- and time-dependent.

Effects of pulsed ultrasound and temperature on the development of rat embryos in culture

Rat embryos in culture were exposed to pulsed ultrasound at SPTA intensity of 1.2 W/cm2 for 5, 15, and 30 min on day 9.5 of development. The whole embryo culture system allowed precise temperature control for directly examining the effects of ultrasound on the developing neural plate. After exposure, embryos were maintained in culture for a further 48 hr. No major morphological abnormalities were observed but a reduction in somite number occurred in the group insonated for 30 min, which was equivalent to a 2 hr delay in embryonic development. Similar delay in growth and "blistering" in the prosencephalon region of some embryos were observed after insonation for 15 min at 40.0 degrees C, an elevation of 1.5 degrees C over the temperature used for controls. Exposure to ultrasound for 15 min at 40 degrees C caused significant reduction in the growth of the head compared with that of control embryos. Heat shock genes for hsps 71/73 and 88 kD were induced after insonation for 30 min at 38.5 degrees C. Insonation did not cause any temperature changes in the culture medium. However, when the temperature of the culture medium was increased during insonation, defective development occurred. The results of these in vitro experiments suggest that ultrasound if resulting in significant hyperthermia could affect the development during early organogenesis of the neural plate and in particular they suggest that the embryo is at greater risk of damage during hyperthermic conditions. These results should provoke discussion of the concept that ultrasound in the febrile patient may present an increased embryonic risk which should be considered when deliberating on the use of diagnostic ultrasound procedures in the pregnant patient.

The heat shock protein hsp70 binds in vivo to subregions 2-48BC and 3-58D of the polytene chromosomes of Drosophila hydei

Multiple interactions of members of the hsp70 family with cellular components have already been described. We present, however, the first evidence that upon heat shock treatment hsp70 molecules interact with specific chromosomal subdivisions of the polytene chromosomes of Drosophila hydei. After a heat shock treatment of 20 min the protein binds to subdivision 3-58D1 and to the heat shock inducible subdivisions 2-48B3-6 and 2-48C1-2. Hsp70 molecules were also observed in subdivision 3-58D1 during recovery at 25 degrees C but not in subdivisions 2-48B3-6 and 2-48C1-2. Our data suggest that this interaction is stress specific. DNase and RNase experiments suggest, moreover, that the hsp70 molecules bind to RNA from ribonucleoproteins (RNPs) in subdivisions 2-48B3-6 and 2-48C1-2 and to DNA in subdivision 3-58D1. The DNA sequences in subdivision 3-58D1 seem to have the potential to adopt the Z-DNA conformation.

Ubiquitin, cell stress and diseases of the nervous system

Cells, including those of the nervous system, respond to damage by an increase in the synthesis of a family of proteins called 'stress proteins' which are amongst the most conserved gene products in evolution suggesting fundamental roles in cell metabolism. Stress-induced proteins have functions in normal cells, particularly for the importation of protein into membrane-limited organelles, and their up-regulation following stress is thought to be cytoprotective, by protecting proteins and organelles from damage. Ubiquitin is an important protein induced by cell stress. It is only found in nucleated cells and has several known functions; the most investigated being as a co-factor for the non-lysosomal intracellular degradation of abnormal or short lived proteins. Morphological studies using immunohistochemistry to localize ubiquitin protein conjugates have revealed that ubiquitin is a component of many of the filamentous inclusion bodies characteristic of neurodegenerative diseases, suggesting activation of a common neuronal response in this type of disease process. Immunohistochemical localization of ubiquitin conjugates has provided a new tool for the sensitive detection of such inclusions and has resulted in the identification of novel inclusion bodies in all cases of motor neuron disease. Preliminary work on enzymes involved in ubiquitin metabolism suggest that there are several possible mechanisms for the formation of inclusion bodies and may provide indirect evidence for the dynamics of inclusion body formation. Work in other areas of pathology indicate important roles for the stress proteins in immune surveillance and autoimmunity and it is likely that the general principles which are currently evolving will also have an impact in neuropathology.

Functions of maternal mRNA in early development

In this review, the types of mRNAs found in oocytes and eggs of several animal species, particularly Drosophila, marine invertebrates, frogs, and mice, are described. The roles that proteins derived from these mRNAs play in early development are discussed, and connections between maternally inherited information and embryonic pattern are sought. Comparisons between genetically identified maternally expressed genes in Drosophila and maternal mRNAs biochemically characterized in other species are made when possible. Regulation of the meiotic and early embryonic cell cycles is reviewed, and translational control of maternal mRNA following maturation and/or fertilization is discussed with regard to specific mRNAs.

Genetic assessment of stationary phase for cells of the yeast Saccharomyces cerevisiae

Starvation of cells of the yeast Saccharomyces cerevisiae causes cessation of proliferation and acquisition of characteristic physiological properties. The stationary-phase state that results represents a unique developmental state, as shown by a novel conditional phenotype (M. A. Drebot, G. C. Johnston, and R. A. Singer, Proc. Natl. Acad. Sci. USA 84:7948-7952, 1987): mutant cells cannot proliferate at the restrictive temperature when stimulated to reenter the mitotic cell cycle from stationary phase but are unaffected and continue proliferation indefinitely if transferred to the restrictive temperature during exponential growth. We have exploited this reentry mutant phenotype to demonstrate that the same stationary-phase state is generated by nitrogen, sulfur, or carbon starvation and by the cdc25-1 mutation, which conditionally impairs the cyclic AMP-mediated signal transduction pathway. We also show that heat shock, a treatment that elicits physiological perturbations associated with stationary phase, does not cause cells to enter stationary phase. The physiological properties associated with stationary phase therefore do not result from residence in stationary phase but from the stress conditions that bring about stationary phase.

Induction of cellular hsp70 expression by human cytomegalovirus

Expression of the cellular heat shock protein 70 gene (hsp70) is transiently induced by human cytomegalovirus (HCMV) infection of permissive human diploid fibroblasts. Induction of the cellular heat shock response during critical times of infection had previously been reported to alter the growth of HCMV in vitro. Thus, a potential interaction between heat shock proteins and HCMV expression was indicated. HCMV dramatically increased expression of hsp70 RNA within 8 h of infection. hsp70 RNA remained elevated at 24 and 48 h postinfection and decreased to low levels of 72 h postinfection. Induction of HSP70 protein occurred more slowly; inducible HSP70 protein encoded by this RNA increased within 16 h postinfection and continued to increase throughout infection until 72 h postinfection, when the highest abundance of inducible HSP70 protein was observed. Cells that received both heat (43 degrees C for 70 min) treatment and HCMV infection expressed hsp70 RNA to levels above the sum of levels present in cells given either treatment alone. Furthermore, hsp70 RNA induction occurred earlier and remained elevated longer than in cells infected with HCMV alone or in cells treated with heat alone, respectively. Nevertheless, the pattern of HCMV immediate-early transcript expression at 2, 4, and 6 h postinfection appeared to be unchanged by this prior heat treatment. Our results suggest that heat shock treatment and HCMV infection can act additively in stimulating hsp70 RNA expression. The previously reported stimulation of HCMV growth in vitro following the heat shock response apparently does not result from alterations in the steady-state expression of HCMV immediate-early transcripts.

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.

Reprogramming of gene expression in postischemic rat liver: induction of proto-oncogenes and hsp 70 gene family

Steady-state levels of messenger RNA (mRNA) for different members of the heat-shock protein 70 gene family were studied in rat livers reperfused after non-necrogenic ischemia. The expression of constitutive hsc 73 gene decreases during ischemia, returns to normal upon reperfusion, and increases 4 hr after restoration of blood flow. Reperfusion induces the expression of another hsp 70 gene family member (the so-called inducible hsp 70 gene), which remains at high levels for at least 7 hr. The induction of hsp 70 family genes is preceded by activation of the cellular oncogene c-fos, the most prompt change in gene expression detected in reperfused liver. Run-on experiments demonstrate that the increased expression of these genes is largely dependent on activation of transcription. Changes in the amount of c-myc and ornithine decarboxylase mRNA are not evident, while the level of the mRNA for glucose-regulated protein GRP 78 increases later, concurrent with the onset of the acute phase response to surgical trauma. Analysis of polysomal and nonpolysomal fractions from sucrose gradients indicates that in postischemic liver, hsp 70 and hsc 73 mRNA are rapidly engaged on light polysomal or nonpolysomal complexes and are later shifted to polysomes. Albumin mRNA displays the same behavior, indicating that hsp 70 mRNA are not preferentially translated and that increased transcription is the major mechanism for enhanced hsp synthesis in postischemic liver. Damage by active oxygen species, pressure overload, and derangements of protein synthesis is likely to include the causative factors of increased expression of c-fos and the hsp 70 gene family in postischemic reperfused liver.

Increased thermostability of thermotolerant CHL V79 cells as determined by differential scanning calorimetry

Heat shock denatures cellular protein and induces both a state of acquired thermotolerance, defined as resistance to a subsequent heat shock, and the synthesis of a category of proteins referred to as heat-shock proteins (HSPs). Thermotolerance may be due to the stabilization of thermolabile proteins that would ordinarily denature during heat shock, either by HSPs or some other factors. We show by differential scanning calorimetry (DSC) that mild heat shock irreversibly denatures a small fraction of Chinese hamster lung V79-WNRE cell protein (i.e., the enthalpy change, which is proportional to denaturation, on scanning to 45 degrees C at 1 degree C/min is approximately 2.3% of the total calorimetric enthalpy). Thermostability, defined by the extent of denaturation during heat shock and determined from DSC scans of whole cells, increases as the V79 cells become thermotolerant. Cellular stabilization appears to be due to an increase in the denaturation temperature of the most thermolabile proteins; there is no increase in the denaturation temperatures of the most thermally resistant proteins, i.e., those denaturing above 65 degrees C. Cellular stabilization is also observed in the presence of glycerol, which is known to increase resistance to heat shock and to stabilize proteins in vitro. A model is presented, based on a direct relationship between the extent of hyperthermic killing and the denaturation or inactivation of a critical target that defines the rate-limiting step in killing, which predicts a transition temperature (Tm) of the critical target for control V79-WNRE cells of 46.0 degrees C and a Tm of 47.3 degrees C for thermotolerant cells. This shift of 1.3 degrees C is consistent with the degree of stabilization detected by DSC.

Isolation and identification of a polypeptide in the Hsp 70 family that binds substance P

During the course of an attempt to purify the substance P (SP) receptor from horse salivary glands by substance P-affinity chromatography, a polypeptide of Mr = 78,000 was isolated. The first fifteen amino acid residues at the amino terminus were determined and, unexpectedly, were found to be identical with the amino terminus of a glucose-regulated protein (GRP) of the same molecular weight, a protein that has been identified as a member of the heat shock protein family. This finding raises the intriguing possibility that SP may interact in vivo with GRPs and other members of the heat shock protein family and play a role in modulating their biological activities.

Early activation of heat shock genes in H2O2-treated Drosophila cells

Drosophila cells of a diploid clone derived from line Kc were treated with 1 mM H2O2 for 1 to 20 minutes. Dot blot and Northern blot analysis of RNAs extracted from control and treated cells showed that the transcriptional activation of the 6 heat-shock genes tested was early, and maximal within 5 minutes of H2O2 treatment. Analysis of the kinetics of induction of the heat-shock proteins (hsps) after an exposure to H2O2 of 2 or 5 minutes, followed by removal, suggests that this brief treatment was sufficient to trigger the synthesis of all the hsps, which was maximal 1.5 to 3h after this short H2O2 treatment.

Microbial stress proteins

There is general agreement that a function, perhaps the major function, of stress proteins under normal physiological conditions is to help assembly and disassembly of protein complexes and to catalyse protein-translocation processes. It remains unclear, however, as to what role these processes play in stressed cells. It could be that cells under stress produce abnormal, misfolded or otherwise damaged proteins and that increased synthesis of stress proteins is required to counter protein modifications. A role for stress proteins in recovery of cells from stress, as opposed to a role in helping cells to withstand a lethal stress, is thus suggested. The intracellular location of stress proteins, in the unstressed and stressed cell, is worthy of further studies. Members of the hsp70 family are associated with the cytosol, mitochondria and endoplasmic reticulum. There is evidence, particularly from studies on mammalian cells (Tanguay, 1985; Welch and Mizzen, 1988; Arrigo et al., 1988), that following stress hsps migrate to various cellular compartments and subsequently delocalize after stress. However, there is little comparable data from microbial systems for this phenomenon (e.g. Rossi and Lindquist, 1989). The question as to the role of stress proteins in the transient acquisition of thermotolerance remains to be answered. It is insufficient to equate the kinetics of stress-protein synthesis with acquisition of thermotolerance. Quantitative data on the amount of stress protein present at various times, including the recovery period, is required. The demonstration that microbial stress proteins are important antigenic determinants of micro-organisms causing major debilitating diseases in the world is an exciting observation. Studies on the interplay of pathogen and host, both carrying similar antigenic hsp determinants, will be a challenging area for future research. It is likely that E. coli and Sacch. cerevisiae, with their well-established biochemical and genetic properties, will continue to be the experimental systems of choice for studies on stress proteins. On the other hand, it is encouraging that studies on other micro-organisms have expanded in the past few years and have made substantial contributions towards our understanding of the stress response. The ubiquitous nature of the stress response and the remarkable evolutionary conservation of the stress proteins continue to be attractive areas for research.

Heat stress increases delivery of a unique sub-population of proteins conveyed by fast axonal transport

The effect of heat stress on protein synthesis and fast axonal transport was examined in vitro in bullfrog dorsal root ganglion (DRG) and associated spinal/sciatic nerve. Qualitative and quantitative changes of individual 35S-methionine-labelled proteins were determined following DRG labelling and fast transport in respective nerves via two-dimensional gel electrophoresis/autoradiography. Elevation of temperature from 18 degrees C to 33 degrees C for up to 6 hr resulted in a marked increase in synthesis of five individual DRG species of approximately 74,000 daltons that comigrate with heat shock proteins (HSPs). A quantitative comparison of species within this subset revealed two subgroups differentially affected by stress. The three most basic proteins were induced to approximately 1300% of unstressed controls after 6 hr of stress, while the two most acidic species demonstrated an increase to only 300% of controls over the same period. The relative abundance of 25 additional DRG proteins were uneffected by heat stress. Of 70 35S-labelled fast-transported proteins similarly analyzed, 15, comprising 5 families, were consistently transported at greater than 150% of controls following up to 6 hr of heat stress. Over this period all 15 proteins shared a similar profile of abundance relative to non-induced proteins. Transport was elevated to the greatest extent after 2 hr of stress, declined after 3 hr, and tended to rebound at later times. The remaining 55 fast-transported protein spots analyzed were unaffected. An increased delivery of this unique sub-population of 15 fast-transported proteins suggests a possible involvement in early cellular events that mediate heat stress in the nervous system.

Estrogenic regulation of murine uterine 90-kilodalton heat shock protein gene expression

Murine uterine steady-state protein levels of the 90-kilodalton heat shock protein (HSP90) have been demonstrated recently to be increased by estrogen in a target tissue- and steroid-specific manner (C. Ramachandran, M.G. Catelli, W. Schneider, and G. Shyamala, Endocrinology 123:956-961, 1988). We now report that this regulation occurred with both the HSP86 and HSP84 forms of HSP90 as well as with the 94-kilodalton glucose-regulated protein. At the mRNA level, this response was greatest for HSP86 (15-fold). In contrast, estradiol had no significant effect on HSP70.

Prostaglandins with antiproliferative activity induce the synthesis of a heat shock protein in human cells

Prostaglandins (PGs) A1 and J2 were found to potently suppress the proliferation of human K562 erythroleukemia cells and to induce the synthesis of a 74-kDa protein (p74) that was identified as a heat shock protein related to the major 70-kDa heat shock protein group. p74 synthesis was stimulated at doses of PGA1 and PGJ2 that inhibited cell replication, and its accumulation ceased upon removal of the PG-induced proliferation block. PGs that did not affect K562 cell replication did not induce p74 synthesis. p74 was found to be localized mainly in the cytoplasm of PG-treated cells, but moderate amounts were found also in dense areas of the nucleus after PGJ2 treatment. p74 synthesis was not necessarily associated with cytotoxicity or with inhibition of cell protein synthesis. The results described support the hypothesis that synthesis of the 70-kDa heat shock proteins is associated with changes in cell proliferation. The observation that PGs can induce the synthesis of heat shock proteins expands our understanding of the mechanism of action of these compounds whose regulatory role is well known in many physiological phenomena, including the control of fever production.

Effect of hyperthermia and X-irradiation on survival and occurrence of metastases in mice bearing P388 tumor

Survival of P388 lymphoid tumor-bearing mice and the occurrence of metastasis was studied after combined modality treatment with hyperthermia and X-irradiation. P388 ascites tumor cells were treated at 42 degrees C or 43.5 degrees C for 1 hr in vitro and transplanted on B6D2F1 mice intraperitoneally (i.p.) or intramuscularly (i.m.). Hyperthermic treatment at 43.5 degrees C increased the median survival time (MST). Increased life-span (ILS) was found after i.p. transplantation (54%) and after i.m. transplantation (30%). During the life-span of tumor-bearing animals, significantly fewer metastases were observed in liver and spleen after hyperthermia and 5-10% metastasis occurred after transplantation of ascites tumor cells treated at 43.5 degrees C in vitro compared with 90% in the untreated control animals. The lower occurrence of metastasis could not be ascribed to the higher cell-killing effect of hyperthermia. When both modalities were combined the best tumor growth retardation effect was obtained when ascites tumor cells were treated at 43.5 degrees C for 1 hr before being transplanted i.m. and 1 day later locally X-irradiated with 6 Gy. In this case, 77% ILS was found demonstrating a synergistic effect of the two modalities. While X-irradiation alone did not change the occurrence of metastasis, after combined modality treatment it was as low as with hyperthermia alone (5-10%). In connection with the significantly lower occurrence of metastasis, the possible alterations of P388 tumor cell membrane and surface proteins induced by in vitro hyperthermic treatment are discussed.

Estrogenic regulation of murine uterine 90-kilodalton heat shock protein gene expression

Murine uterine steady-state protein levels of the 90-kilodalton heat shock protein (HSP90) have been demonstrated recently to be increased by estrogen in a target tissue- and steroid-specific manner (C. Ramachandran, M.G. Catelli, W. Schneider, and G. Shyamala, Endocrinology 123:956-961, 1988). We now report that this regulation occurred with both the HSP86 and HSP84 forms of HSP90 as well as with the 94-kilodalton glucose-regulated protein. At the mRNA level, this response was greatest for HSP86 (15-fold). In contrast, estradiol had no significant effect on HSP70.

The influence of temperature and serum deprivation on the synthesis of heat-shock proteins and alpha and beta tubulin in promastigotes of Leishmania major

We have examined changes in the relative synthesis of individual proteins in promastigotes of Leishmania major subjected to decreasing serum levels in vitro. We observed increases in the relative synthesis of the putative heat-shock proteins of 82 and 70 kDa and of proteins of 79 and 41 kDa but decreases in the synthesis of proteins of 38 and 28 kDa. The relative synthesis of alpha-tubulin increased, whereas that of beta-tubulin decreased, in promastigotes subjected to decreased serum concentrations. This uncoordinated regulation of the synthesis of the tubulin proteins was not reflected as an alteration in the relative levels of the messenger RNA of the respective proteins. We have also studied changes in the synthesis of proteins in L. major promastigotes subjected to a temperature change from 26 degrees C to 34 degrees C. The results indicate that the synthesis of putative heat-shock proteins of 82, 70, 65, 41, 23 and 22 kDa increased when the parasites were incubated at the higher temperature, although these proteins were synthesised in detectable amounts at 26 degrees C. We could not detect differences between infective and non-infective promastigotes, separated by binding to peanut agglutinin, in the synthesis of individual proteins in response to increased temperature. These results were confirmed by densitometer analysis of autoradiographs of labelled promastigote proteins, and the relative changes in the synthesis of the two major heat-shock proteins, as well as alpha- and beta-tubulin, were estimated.

Induction of stress proteins in cultured human RPE-derived cells

The expression and induction of stress protein families were examined in cultured human fetal retinal pigment epithelial (RPE)-derived cells. These stress proteins (SPs) include the heat-shock proteins (HSPs) that have been shown to be highly inducible following treatment by heat, amino acid analogues, and various chemical oxidants. Three sets of proteins with molecular weights of 70, 84, and 110 kilodaltons were elevated simultaneously from constitutive levels after treatment with azetidine-2-carboxylic acid (AzC), an amino acid analogue of proline. Further experiments demonstrated that incubation of cultured human fetal RPE-derived cells with hydrogen peroxide (H2O2) at concentrations ranging from 10(-5) M to 10(-3) M for 30 minutes to 60 minutes did not elevate the levels of the common families of HSPs as with AzC. These results indicate that cultured human fetal RPE-derived cells are capable of elevated HSP biosynthesis after AzC exposure but appear resistant to H2O2 treatment.

UbiA, the major polyubiquitin locus in Caenorhabditis elegans, has unusual structural features and is constitutively expressed

Ubiquitin is a multifunctional 76-amino-acid protein which plays critical roles in many aspects of cellular metabolism. In Caenorhabditis elegans, the major source of ubiquitin RNA is the polyubiquitin locus, UbiA. UbiA is transcribed as a polycistronic mRNA which contains 11 tandem repeats of ubiquitin sequence and possesses a 2-amino-acid carboxy-terminal extension on the final repeat. The UbiA locus possesses several unusual features not seen in the ubiquitin genes of other organisms studied to date. Mature UbiA mRNA acquires a 22-nucleotide leader sequence via a trans-splicing reaction involving a 100-nucleotide splice leader RNA derived from a different chromosome. UbiA is also unique among known polyubiquitin genes in containing four cis-spliced introns within its coding sequence. Thus, UbiA is one of a small class of genes found in higher eucaryotes whose heterogeneous nuclear RNA undergoes both cis and trans splicing. The putative promoter region of UbiA contains a number of potential regulatory elements: (i) a cytosine-rich block, (ii) two sequences resembling the heat shock regulatory element, and (iii) a palindromic sequence with homology to the DNA-binding site of the mammalian steroid hormone receptor. The expression of the UbiA gene has been studied under various heat shock conditions and has been monitored during larval moulting and throughout the major stages of development. These studies indicate that the expression of the UbiA gene is not inducible by acute or chronic heat shock and does not appear to be under nutritional or developmental regulation in C. elegans.

Heat shock proteins in normal and leukemic blood cells

Heat shock proteins (HSPs) are though to represent a ubiquitous cellular response to heat or stress. We tested whether HSPs can be induced in hairy cells, other human leukemic cells, and normal lymphocytes, and whether there are additive or synergistic effects between heat shock and interferon-alpha 2b (IFN-alpha 2b) on these cells. We analyzed lysates of cells from 22 patients (6 with hairy cell leukemia, 12 with other acute and chronic leukemias and lymphocytes of 4 normals) after exposure to a heat shock and/or IFN-alpha 2b by one-dimensional polyacrylamide gel electrophoresis. In all cells a pattern of HSPs was readily induced with prominent bands identified at approximately 115, 90, and 65 kD. None of these major proteins appeared to represent the previously described IFN-alpha 2b induced band at 80 kD. IFN-alpha 2b by itself was not found to induce HSPs. We conclude that a pattern of HSPs can readily be induced in a variety of normal and leukemic human blood cells. IFN-alpha 2b is not a HSP inducer in these cells. The previously described IFN-induced p80 is apparently not a HSP.

Co-isolation of heat stress and cytoskeletal proteins with plasma membrane proteins

Previous reports have suggested the possible existence of a plasma-cell-membrane function associated with some heat stress proteins (HSPs). To investigate the effect of hyperthermia on plasma membrane proteins, rat mammary tumour clone C (MTC) cells were heated at 42 degrees C for 1 h. Their surface proteins were (1) labelled with [3H]leucine, (2) biotinylated, (3) affinity isolated with streptavidin-agarose beads under denaturing or non-denaturing conditions, and (4) analysed by one- and two-dimensional polyacrylamide-gel electrophoresis and protein blotting under denaturing conditions. Affinity isolation of biotinylated proteins enriched for a protein subfraction believed to be membrane-associated. Several proteins analogous to HSP or their heat-stress cognates (HSC) were present with these biotinylated protein subfractions in control or heated cells. The major and most consistent feature of affinity isolates from heated cells was the presence of a small fraction of the induced 68-kD HSP. The 112-, 90-, 70- and 22-kD HSC/HSP were also present in small amounts in affinity isolates of control cells, and the fraction increased in heated cells. Several structural proteins, including actin and the tubulins were present in the same affinity isolates. Protein blotting experiments indicated that none were exposed on the exterior of the plasma-cell membrane or biotinylated and thus none were exposed on the exterior of the plasma-cell membrane or biotinylated intracellularly through membrane damage. These results suggest that small fractions of several HSC are located at or near the cytoplasmic face of the plasma membrane along with cytoskeletal proteins, and that additional submembranous localization of HSP occurs after heat stress and may be part of the processes associated with membrane damage or cellular responses to heat. Further studies will be directed at establishing the relationships between these proteins and the role, if any, of the changes associated with heat stress.

Expression of heat shock proteins by isolated mouse spermatogenic cells

Proteins of the hsp70 family are abundant in mouse spermatogenic cells. These cells also synthesize relatively large amounts of a 70,000-molecular-weight protein (P70) that appears to be a cell-specific isoform of hsp70, the major heat-inducible protein (R.L. Allen, D.A. O'Brien, and E.M. Eddy, Mol. Cell. Biol. 8:828-832, 1988). In this study, proteins of unstressed and heat-stressed spermatogenic cells consisting of purified preparations of preleptotene, leptotene-zygotene, pachytene spermatocytes, and round spermatids were analyzed by two-dimensional polyacrylamide gel electrophoresis. Unstressed preleptotene and leptotene-zygotene spermatocytes contained little P70, whereas relatively large amounts of P70 were present in pachytene spermatocytes and round spermatids. Labeling studies showed that P70 was synthesized primarily in pachytene spermatocytes and that little synthesis occurred in round spermatids or in preleptotene and leptotene-zygotene stages of spermatogenesis. Synthesis of hsp70 was not detectable in unstressed cells but was induced in all stages of isolated germ cells following heat stress. These results indicate that P70 is expressed in a stage-specific manner during cell differentiation, whereas hsp70 is synthesized in response to stress in all populations of isolated spermatogenic cells examined.