The relationship of the rat brain 68 kDa microtubule-associated protein with synaptosomal plasma membranes and with the Drosophila 70 kDa heat-shock protein

A plausible involvement of plasmalemmal voltage-dependent anion channel 1 in the neurotoxicity of 15-deoxy-Δ12,14 -prostaglandin J2

INTRODUCTION

15-deoxy-Δ^12,14 -prostaglandin J₂ (15d-PGJ₂ ) causes neuronal apoptosis independently of its nuclear receptor, peroxysome-proliferator activated receptor γ. Its membrane receptor, chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), did not also mediate the neurotoxicity of 15d-PGJ₂ . In the present study, we ascertained whether membrane targets beside CRTH2 were involved in the neurotoxicity of 15d-PGJ₂ .

METHODS

Neuronal membrane targets for 15d-PGJ₂ were separated by two-dimensional electrophoresis, identified by proteomic approach. Their localizations were detected by microscopic immunofluorescence study. Cell viability and apoptosis was evaluated by MTT-reducing activity and caspase-3 activity, respectively.

RESULTS

Voltage-dependent anion channel 1 (VDAC1) was identified as one of membrane targets for 15d-PGJ₂ . Modification of VDAC1 with 15d-PGJ₂ was detected by pull-down assay. VDAC1 was detected in the plasma membrane and localized on the neuronal cell surface. VDAC1 was partially colocalized with membrane targets for 15d-PGJ₂ . The anti-VDAC antibody significantly attenuated the neurotoxicity of 15d-PGJ₂ , accompanied by the suppression of the 15d-PGJ₂ -stimulated caspase-3.

CONCLUSION

These findings suggested that the plasmalemmal VDAC might be involved in the neurotoxicity of 15d-PGJ₂ .

Anti-heat Shock 70 kDa Protein Antibody Induced Neuronal Cell Death

Heat shock protein 70 (Hsp70) is not only a molecular chaperone in cytosol, but also presents in synaptic plasma membranes. To detect plasmalemmal Hsp70 (pl-Hsp70), neurons were immunostained with anti-Hsp70 antibody without permeabilization and fixation. Dotted immunofluorescent signals at neuronal cell bodies and neurites indicated the localization of Hsp70 on the neuronal cell surface. To target only pl-Hsp70, but not cytosolic Hsp70, the anti-Hsp70 antibody was applied without permeabilization in the primary culture of rat cortical neurons. The antibody induced neuronal cell death in a concentration-dependent manner. The anti-Hsp70 antibody activated ubiquitin-proteasome pathway, but inactivated caspase-3. A lag time was required for the neurotoxicity of anti-Hsp70 antibody. Hydrogen peroxide was increased in the anti-Hsp70 antibody-treated neurons during the lag time. Catalase suppressed the anti-Hsp70 antibody-reduced cell viability via the plausible inhibition of hydrogen peroxide generation. One of down-streams of hydrogen peroxide exposure is activation of the mitogen-activated protein kinase (MAPK) signaling cascade. The neurotoxicity of anti-Hsp70 antibody was partially ascribed to c-Jun N-terminal kinase among MAPKs. In conclusion, the anti-Hsp70 antibody targeted pl-Hsp70 on the neuronal cell surface and induced neuronal cell death without complement. Furthermore, hydrogen peroxide appeared to mediate the neuronal cell death, which was accompanied with the enhancement of the ubiquitin-proteasome pathway and the suppression of caspase in a different fashion from the known cell death.

Role of Membrane Components in Thermal Injury of Cells and Development of Thermotolerance

Exposure of cells to hyperthermia induces a transient resistance to subsequent heat treatment. The specific mechanisms responsible for hyperthermic cell killing and thermotolerance development are not well understood. It seems that heat may induce at least two different states of thermotolerance, of which one is dependent on protein synthesis. The expression of thermotolerance may include multiple cytoplasmic and membrane components. A number of studies have indicated that membranes play an important role in governing the thermal injury of cells. It seems, therefore, that heat denatured plasma membrane proteins may be a potential target for thermal stress and a trigger for the induction of thermotolerance. The localization of heat shock proteins in the plasma membrane and the suggestion of thermal resistance in enucleate erythrocytes support this suggestion. However, a direct relationship between the plasma membrane and hyperthermic killing or development of thermotolerance has not been found.

Loss of Hsp70-Hsp40 chaperone activity causes abnormal nuclear distribution and aberrant microtubule formation in M-phase of Saccharomyces cerevisiae

The 70-kDa heat shock proteins, hsp70, are highly conserved among both prokaryotes and eukaryotes, and function as chaperones in diverse cellular processes. To elucidate the function of the yeast cytosolic hsp70 Ssa1p in vivo, we characterized a Saccharomyces cerevisiae ssa1 temperature-sensitive mutant (ssa1-134). After shifting to the restrictive temperature (37 degreesC), ssa1-134 mutant cells showed abnormal distribution of nuclei and accumulated as large-budded cells with a 2 N DNA content. We observed more prominent mutant phenotypes using nocodazole-synchronized cells: when cells were incubated at the restrictive temperature following nocodazole treatment, viability was rapidly lost and abnormal arrays of bent microtubules were formed. Chemical cross-linking and immunoprecipitation analyses revealed that the interaction of mutant Ssa1p with Ydj1p (cytosolic DnaJ homologue in yeast) was much weaker compared with wild-type Ssa1p. These results suggest that Ssa1p and Ydj1p chaperone activities play important roles in the regulation of microtubule formation in M phase. In support of this idea, a ydj1 null mutant at the restrictive temperature was found to exhibit more prominent phenotypes than ssa1-134. Furthermore, both ssa1-134 and ydj1 null mutant cells exhibited greater sensitivity to anti-microtubule drugs. Finally, the observation that SSA1 and YDJ1 interact genetically with a gamma-tubulin, TUB4, supports the idea that they play a role in the regulation of microtubule formation.

Heat shock modulates the expression of the metastasis associated gene MTS1 and proliferation of murine and human cancer cells

Mts1 is a metastasis-associated gene of the S-100 gene family and codes for a Ca2+-binding protein. It is highly expressed in murine and human cancers of high invasive and metastatic potential. Recent work has shown that the mts1 protein might be involved in cell cycle regulation. An upregulation of its expression drives cells into the S phase, together with an enhanced expression of p53 phosphoprotein, which has led to the suggestion that mtsl protein might be sequestering p53 thereby abrogating the G1-S checkpoint control normally exerted by p53. Preliminary studies showed that expression of mts1 is downregulated by hyperthermia. We present evidence that in murine BL6 melanoma cells and human HUT cells that hyperthermia downregulates the mts1 gene. It is also downregulated in heat-resistant variants of the B16 melanoma and HUT cells. In parallel, there is a decrease in the size of the S phase fraction and an increase in the doubling time of cells. Cell subjected to hyperthermia show an 2- to 3.5-fold increase in the expression of HSP28 which has been shown to possess a proliferation inhibitory action. It is postulated that a complete regulatory loop involving mtsl, p53, and HSP28 might be involved in cell proliferation.

Tissue-Type-Specific Heat-Shock Response and Immunolocalization of Class I Low-Molecular-Weight Heat-Shock Proteins in Soybean

A monospecific polyclonal antibody was used to study the tissue-type specificity and intracellular localization of class I low-molecular-weight (LMW) heat-shock proteins (HSPs) in soybean (Glycine max) under different heat-shock regimes. In etiolated soybean seedlings, the root meristematic regions contained the highest levels of LMW HSP. No tissue-type-specific expression of class I LMW HSP was detected using the tissue-printing method. In immunolocalization studies of seedlings treated with HS (40[deg]C for 2 h) the class I LMW HSPs were found in the aggregated granular structures, which were distributed randomly in the cytoplasm and in the nucleus. When the heat shock was released, the granular structures disappeared and the class I LMW HSPs became distributed homogeneously in the cytoplasm. When the seedlings were then given a more severe heat shock following the initial 40[deg]C -> 28[deg]C treatment, a large proportion of the class I LMW HSPs that originally localized in the cytoplasm were translocated into the nucleus and nucleolus. Class I LMW HSPs may assist in the resolubilization of proteins denatured or aggregated by heat and may also participate in the restoration of organellar function after heat shock.

Molecular chaperones and the centrosome. A role for TCP-1 in microtubule nucleation

Molecular chaperones play an important role in facilitating the proper maturation of many newly synthesized proteins. Here we provide evidence that molecular chaperones also participate in regulating the assembly of the microtubule cytoskeleton. Via indirect immunofluorescence analysis, both hsp 73 and TCP-1 localized within the centrosome in interphase and mitotic cells. These proteins, along with the centrosome-specific protein, pericentrin, were also present within an enriched preparation of centrosomes. Because the centrosome serves as an initiation site for microtubule growth, we examined the ability of cells to regrow their microtubule network in the presence of hsp 73 or TCP-1 specific antibodies. Purified tubulin and GTP were added to cells following the depolymerization and extraction of cellular microtubules. Microtubules were observed to nucleate off the centrosome using this system, even in the presence of anti-hsp 73 antibodies. Incubation with anti-TCP-1 antibodies, however, blocked microtubule regrowth off the centrosome. Similarly, anti-TCP-1 antibodies microinjected into living cells first treated with nocodazole also inhibited the regrowth of the microtubule network following removal of the microtubule poison. Our results complement earlier genetic studies in yeast implicating a role for TCP-1 in microtubule mediated processes, and may help to explain the previously reported mitotic and meiotic abnormalities associated with TCP-1 mutations.

Rapid refolding studies on the chaperone-like alpha-crystallin. Effect of alpha-crystallin on refolding of beta- and gamma-crystallins

alpha-Crystallin, a multimeric protein present in the eye lens, is shown to have chaperone-like activity in preventing thermally induced aggregation of enzymes and other crystallins. We have studied the rapid refolding of alpha-crystallin, and compared it with other calf eye lens proteins, namely beta- and gamma-crystallins. alpha-Crystallin forms a clear solution upon rapid refolding from 8 M urea. The refolded alpha-crystallin has native-like secondary, tertiary, and quaternary structures as revealed by circular dichroism and fluorescence characteristics as well as gel filtration and sedimentation velocity measurements. On rapid refolding, beta- and gamma-crystallins aggregate and form turbid solutions. The presence of alpha-crystallin in the refolding buffer marginally increases the recovery of beta- and gamma-crystallins in the soluble form. However, unfolding of these crystallins together with alpha-crystallin using 8 M urea and subsequent refolding significantly increases the recovery of these proteins in the soluble form. These results indicate that an intermediate of alpha-crystallin formed during refolding is more effective in preventing the aggregation of beta- and gamma-crystallins. This supports our earlier hypothesis (Raman, B., and Rao, C. M. (1994) J. Biol. Chem. 269, 27264-27268) that the chaperone-like activity of alpha-crystallin is more pronounced in its structurally perturbed state.

Temperature dependent chaperone-like activity of alpha-crystallin

Alpha-crystallin, a multimeric protein present in the eye lens, is known to have chaperone-like activity in preventing the aggregation of enzymes and other crystallins. We have studied the chaperone-like activity of this protein towards the aggregation of insulin B chain, induced by reducing the interchain disulphide bond with dithiothreitol. At room temperature, there is no detectable protection (at a 1:1 (w/w) ratio of insulin: alpha-crystallin) against the aggregation of insulin B chain by alpha-crystallin, whereas it completely prevents this aggregation at 40 degrees C. We have monitored the temperature dependence of the protection of aggregation by alpha-crystallin; the protection increases sharply above 30 degrees C and reaches almost 100% by 41 degrees C. Probing the hydrophobic surfaces of alpha-crystallin with the hydrophobic fluorphore 8-anilino-1 naphthalene sulfonate suggests that the hydrophobic surfaces of alpha-crystallin are exposed to a greater extent above 30 degrees C. A complete prevention of the aggregation is achieved at 27.6 degrees C by increasing the concentration of alpha-crystallin by more than 8 fold. Similar temperature dependent chaperone-like activity of alpha-crystallin is observed towards the aggregation of zeta-crystallin, an enzyme crystallin from guinea pig. We have earlier shown that alpha-crystallin exposes hydrophobic surface(s) at temperatures above 30 degrees C. These results support our earlier hypothesis [Raman, B. and Rao, Ch.M. (1994) J. Biol. Chem. 269, 27264-27268] that the chaperone-like activity of alpha-crystallin is more pronounced in its structurally perturbed state.

Identification of an HSP70-related protein associated with the centrosome from dinoflagellates to human cells

The monoclonal antibody CTR210 raised against isolated human centrosomes strongly decorates the centrosome and more weakly a domain congruent with the Golgi apparatus in several animal cells (HeLa, 3T3, CHO, PtK2). Both decorations resist Triton extraction in conditions which totally extract the Golgi apparatus, as judged by galactosyltransferase decoration. A 67 kDa centrosomal antigen can be demonstrated in human cells with this antibody. CTR210 also decorates the centrosome or associated structures in several systems, including unicellular eukaryotes such as dinoflagellates or ciliates. A 72 kDa antigen has been identified and purified from the dinoflagellate C. cohnii and its NH2-terminal sequence partially established. It shows a close homology with HSP70 proteins. The possibility that the 72 kDa antigen belongs to this chaperone family was further supported using a mAb reacting, in most species, with HSP70. A polyclonal antibody raised against the 72 kDa antigen from C. cohnii decorates the centrosome in human cells and reacts with the CTR210 centrosomal 67 kDa antigen. These results suggest that specific chaperone proteins are associated with the centrosome in eukaryotic cells. The centrosomal chaperones could participate in the microtubule nucleation reaction or in the process of centrosome assembly.

Structure and modifications of the junior chaperone alpha-crystallin. From lens transparency to molecular pathology

alpha-Crystallin is a high-molecular-mass protein that for many decades was thought to be one of the rare real organ-specific proteins. This protein exists as an aggregate of about 800 kDa, but its composition is simple. Only two closely related subunits termed alpha A- and alpha B-crystallin, with molecular masses of approximately 20 kDa, form the building blocks of the aggregate. The idea of organ-specificity had to be abandoned when it was discovered that alpha-crystallin occurs in a great variety of nonlenticular tissues, notably heart, kidney, striated muscle and several tumors. Moreover alpha B-crystallin is a major component of ubiquinated inclusion bodies in human degenerative diseases. An earlier excitement arose when it was found that alpha B-crystallin, due to its very similar structural and functional properties, belongs to the heat-shock protein family. Eventually the chaperone nature of alpha-crystallin could be demonstrated unequivocally. All these unexpected findings make alpha-crystallin a subject of great interest far beyond the lens research field. A survey of structural data about alpha-crystallin is presented here. Since alpha-crystallin has resisted crystallization, only theoretical models of its three-dimensional structure are available. Due to its long life in the eye lens, alpha-crystallin is one of the best studied proteins with respect to post-translational modifications, including age-induced alterations. Because of its similarities with the small heat-shock proteins, the findings about alpha-crystallin are illuminative for the latter proteins as well. This review deals with: structural aspects, post-translational modifications (including deamidation, racemization, phosphorylation, acetylation, glycation, age-dependent truncation), the occurrence outside of the eye lens, the heat-shock relation and the chaperone activity of alpha-crystallin.

Both viral (adenovirus E1B) and cellular (hsp 70, p53) components interact with centrosomes

Human 293 cells, transformed by and expressing the early region of the adenovirus genome (i.e., E1A and E1B), contain a phase-dense cytoplasmic structure situated in close proximity to the nucleus. Via indirect immunofluorescence studies such structures have been previously shown to contain both the adenovirus E1B (55 kDa) protein as well as the tumor suppressor gene product p53. Here we show that such structures also stain positive for the cytoplasmic hsp 70 proteins. Such phase-dense structures containing hsp 70, p53, and adenovirus E1B are not unique to 293 cells but also are observed in rodent cell lines stabily transfected with the early region of the adenovirus genome. Using an antibody against a centrosomal protein, pericentrin, we show that these cytoplasmic phase-dense structures are in close proximity to the centrosome. Cell fractionation studies revealed such structures to be highly detergent insoluble. However, like the centrosome, the cytoplasmic phase-dense structures could be rendered detergent soluble following treatment of the cells with agents that disrupt the integrity of the cytoskeleton. While the phase-dense structures appear in close proximity to the centrosome in interphase cells, during mitosis the centrosome and the phase-dense bodies separate from one another. Owing to these observations we examined whether hsp70 and p53 might also co-localize with the centrosome in other cell types not expressing the adenovirus E1A/E1B proteins. We show that a portion of both hsp70 and p53 indeed are present within the centrosome in Hela, COS, and 3T3 cells. These observations raise the possibility that components like hsp70 and p53 may participate in the mechanism(s) controlling cell division in mammalian cells.

Characterisation of a vindesine-resistant human small-cell lung cancer cell line

We established a vindesine-resistant (x 11.6) human small-cell lung cancer cell line (H69/VDS) by stepwise exposure of parent line H69 to vindesine. H69/VDS showed cross-resistance to taxol (x 10.1), vincristine (x 6.9) and colchicine (x 3.4) but not to doxorubicin, cisplatin or etoposide. There was no significant difference in intracellular [3H]-vincristine and doxorubicin accumulation between H69 and H69/VDS cells. The human mdr1 mRNA was not detected in either of the cell lines. These results indicated that H69/VDS did not express a typical multidrug resistant phenotype. Addition of 20 microM verapamil enhanced the growth inhibitory effect of vindesine on both H69/VDS (x 12.0) and H69 cells (x 3.8). The amount of total tubulin in H69/VDS cells was lower than that in the H69 parental cells. No significant increase was observed in the amount of total and polymerised tubulins of H69 cells. In H69/VDS cells, however, verapamil increased the amount of total tubulin to the level of parental cells, but decreased the amount of polymerised tubulin. Modulation of tubulin may play a role in the resistance to vindesine.

Cytoskeletal thermotolerance in NRK cells

We investigated the effect of heat shock on the cytoskeletons (actin stress fibres, intermediate filaments and microtubules) and the relation between thermotolerance of cytoskeletons and thermotolerance as defined by clonogenic survival in normal rat kidney (NRK) cells. Upon heating at 45 degrees C for 15 min, almost all actin stress fibres were disrupted. During the recovery period after heat shock the stress fibres were reorganized rapidly and returned to their preheated state by 16 h. When the cells were heated again at 45 degrees C for 15 min, the disruption of stress fibres was less severe, indicating thermotolerant state of stress fibres. However, the thermotolerant state of stress fibres induced by prior treatment with sodium arsenite or by heating at 42 degrees C for 2 h was less evident than that induced by prior heat shock at 45 degrees C. The intermediate filaments in NRK cells were very heat-resistant; no apparent changes were observed even after heat shock at 45 degrees C for 60 min, and prior conditioning treatments could not induce thermotolerance of microtubules. All prior conditioning treatments could induce heat shock proteins and thermotolerance as defined by clonogenic survival. From these results it is suggested that there is no correlation between cytoskeletal thermotolerance and either heat shock protein level or thermotolerance as defined by clonogenic survival in NRK cells.

Induction of HSP70 is associated with vincristine resistance in heat-shocked 9L rat brain tumour cells

The most prominent cellular changes in heat-shock response are induction of HSPs synthesis and reorganisation of cytoskeleton. Vincristine was used as a tool to evaluate the integrity of microtubules in 9L rat brain tumour cells recovering from heat-shock treatment. Cells treated at 45 degrees C for 15 min and recovered under normal growing condition became resistant to vincristine-inflicted cytotoxicity and microtubule destruction. Among all HSPs, the level of HSP70 and the degree of vincristine resistance are best correlated. HSP70 and tubulin were found to be associated with each other as they were co-immunoprecipitated by either anti-HSP70 or anti-beta-tubulin monoclonal antibody. The current studies establish for the first time that HSP70 can complex with tubulin in cells and this association may stabilise the organisation of microtubules thus protect the heat-treated cells from vincristine damage. These findings are noteworthy in combining hyperthermia and chemotherapy in the management of malignant diseases.

Transforming growth factor-beta 1 rapidly induces Hsp70 and Hsp90 molecular chaperones in cultured chicken embryo cells

In this report we show that: (1) molecular chaperones in the heat shock protein (hsp) family are a new class of cellular proteins induced by Transforming Growth Factor-beta 1 (TGF beta), a cytokine present in serum, (2) rapid induction of Hsc70 precedes a general increase in protein synthesis and may be a preparatory event, (3) TGF beta is a potent regulator of overall protein synthesis in chicken embryo cells (CEC), and (4) isoforms of Hsp90 with different biochemical properties exist, raising the possibility that they may have different functions. TGF beta can substitute for serum in stimulating synthesis of members of the Hsp90 and Hsp70 families of stress proteins, whereas other cytokines, including PDGF, FGF, and EGF, were not effective nor did they enhance the stimulatory effect of TGF beta on the hsp's. Analysis of the induction of hsp's using one- and two-dimensional polyacrylamide gel electrophoresis indicated that members of the Hsp70 family of molecular chaperones were induced rapidly by TGF beta, reaching maximum rates of accumulation by 5 hours of treatment. Total protein synthesis increased more slowly, undergoing an approximately twofold increase in 24 hours. Using a modified protocol for two-dimensional gel electrophoresis, the Hsp90 protein family was separated into four isoelectric forms, two of which were phosphorylated (Hsp90-2 and -4). These phosphorylated isoforms turned over faster than the unphosphorylated forms of Hsp90. All four isoforms were heat inducible, but only Hsp90-2 and -3 were induced rapidly by TGF beta, again within 5 hours of treatment. The effects of serum on these protein families were similar to those of TGF beta, suggesting that this cytokine may be the serum component primarily responsible for up-regulating members of the Hsp90 and Hsp70 families. We hypothesize that cells rapidly increase their chaperoning capacity for newly synthesized polypeptides in preparation for an increase in the rate of synthesis of proteins up-regulated by TGF beta.

Evidence for the localization of the nuclear-coded 22-kDa heat-shock protein in a subfraction of thylakoid membranes

The precursor to the nuclear-coded 22-kDa heat-shock protein of chloroplasts (HSP 22) has been transported into isolated intact chloroplasts from heat-shocked plants. The localization of the mature protein in the chloroplast membrane was investigated. We have shown that the processed HSP 22 of pea was not bound to envelopes and found predominantly in thylakoid membranes. The binding of HSP 22 was stable in the presence of high salt concentrations. Solubilization of thylakoid membranes with Triton X-100 and phase partitioning with Triton X-114 indicate an intrinsic localization of HSP 22 or, alternatively, a non-covalent association with integral membrane protein(s). After fractionation into grana and stroma lamellae, HSP 22 was found mostly in the grana-membrane subfraction.

Two 68-kDa proteins in slow axonal transport belong to the 70-kDa heat shock protein family and the annexin family

The major 68-kDa protein found selectively in the faster of the two subcomponents of slow axonal transport [group IV or slow component b (SCb)] in the rat sciatic nerve has been characterized. It was found to contain two distinct classes of proteins, S1 and S2, both of which have isoelectric points of 5.7, but differ in their solubility in the presence of calcium. The S1 protein, which contributes up to 70% of the 68-kDa component, was soluble in the presence or absence of calcium, whereas the S2 protein was bound to the cytoskeleton in a calcium-dependent manner. Further characterization of the two proteins by peptide mapping and immunological methods revealed that the S1 protein belonged to a family of proteins related to the 70-kDa heat shock protein, whereas the S2 protein was identical to 68-kDa calelectrin (annexin VI). Selective occurrence in SCb of these proteins with potential abilities to regulate protein-protein or protein-membrane interactions suggests that they may play important roles in the control of cytoskeletal organization in the axon, because SCb contains mainly cytoskeletal proteins in a more dynamic form compared with the slowest rate component, slow component a, which is enriched in the stably polymerized form of these proteins.

Stress proteins, autoimmunity, and autoimmune disease

At birth, the immune system is biased toward recognition of microbial antigens in order to protect the host from infection. Recent data suggest that an important initial line of defense in this regard involves autologous stress proteins, especially conserved peptides of hsp60, which are presented to T cells bearing gamma delta receptors by relatively nonpolymorphic class lb molecules. Natural antibodies may represent a parallel B cell mechanism. Through an evolving process of "physiological" autoreactivity and selection by immunodominant stress proteins common to all prokaryotes, B and T cell repertoires expand during life to meet the continuing challenge of infection. Because stress proteins of bacteria are homologous with stress proteins of the host, there exists in genetically susceptible individuals a constant risk of autoimmune disease due to failure of mechanisms for self-nonself discrimination. That stress proteins actually play a role in autoimmune processes is supported by a growing body of evidence which, collectively, suggests that autoreactivity in chronic inflammatory arthritis involves, at least initially, gamma delta cells which recognize epitopes of the stress protein hsp60. Alternate mechanisms for T cell stimulation by stress proteins undoubtedly also exist, e.g., molecular mimicry of the DR beta third hypervariable region susceptibility locus for rheumatoid arthritis by a DnaJ stress protein epitope in gram-negative bacteria. While there still is confusion with respect to the most relevant stress protein epitopes, a central role for stress proteins in the etiology of arthritis appears likely. Furthermore, insight derived from the work thus far in adjuvant-induced arthritis already is stimulating analyses of related phenomena in autoimmune diseases other than those involving joints. Only limited data are available in the area of humoral autoimmunity to stress proteins. Autoantibodies to a number of stress proteins have been identified in SLE and rheumatoid arthritis, but their pathogenetic significance remains to be established. Nevertheless, the capacity of certain stress proteins to bind to multiple proteins in the nucleus and cytoplasm both physiologically and during stress or injury to cells, suggests that stress proteins may be important elements in the "immunogenic particle" concept of the origin of antinuclear and other autoantibodies. In short, this fascinating group of proteins, so mysterious only a few years ago, has impelled truly extraordinary new lines of investigation into the nature of autoimmunity and autoimmune disease.

Induction of heat shock (stress) genes in the mammalian brain by hyperthermia and other traumatic events: a current perspective

Is the heat shock response physiologically relevant? For example, following hyperthermia or ischemia, what neural cell types show induction of heat shock genes and what is the time course of the effect? Initial experiments in this area demonstrated the prominent induction of a 70 kDa heat shock protein (hsp70) when labeled brain proteins isolated from hyperthermic animals were analyzed. Recently, in situ hybridization and immunocytochemistry have been utilized to map out the pattern of expression of both constitutively expressed and stress-inducible members of the hsp70 multigene family. Different types of neural trauma have been found to induce characteristic cellular responses in the mammalian brain with regard to the type of brain cell that responds by inducing hsp70 and the timing of the induction response. Fever-like temperature causes a dramatic induction of hsp70 mRNA within 1 hr in fiber tracts of the forebrain and cerebellum, a pattern consistent with a strong glial response to heat shock. Tissue injury, namely, a small surgical cut in the cerebral cortex, induces a rapid and highly localized induction of hsp70 mRNA in cells proximal to the injury site. Using an immunocytochemical approach, a neuronal pattern of induction of hsp70 has been demonstrated following ischemia or kainic acid-induced seizures. It is apparent that the pattern of induction of hsp70 may be a useful early marker of cellular injury and may identify previously unrecognized areas of vulnerability in the nervous system.

The human heat-shock protein family. Expression of a novel heat-inducible HSP70 (HSP70B') and isolation of its cDNA and genomic DNA

The human heat-shock protein multigene family comprises several highly conserved proteins with structural and functional properties in common, but which vary in the extent of their inducibility in response to metabolic stress. We have isolated and characterized a novel human HSP70 cDNA, HSP70B' cDNA, and its corresponding gene sequence. HSP70B' cDNA hybrid-selected an mRNA encoding a more basic 70 kDa heat-shock protein that both the major stress-inducible HSP70 and constitutively expressed HSC70 heat-shock proteins, which in common with other heat-shock 70 kDa proteins bound ATP. The complete HSP70B' gene was sequenced and, like the major inducible HSP70 gene, is devoid of introns. The HSP70B' gene has 77% sequence similarity to the HSP70 gene and 70% similarity to HSC70 cDNA, with greatest sequence divergence towards the 3'-terminus. The HSP70B' gene represents a functional gene, as indicated by Northern-blot analysis with specific oligonucleotides, hybrid-selected translation with a specific 3' cDNA sequence and S1 nuclease protection experiments. In contrast with HSP70 mRNA, which is present at low concentrations in HeLa cells and readily induced by heat or CdCl2 treatment in both fibroblasts and HeLa cells, HSP70B' mRNA was induced only at higher temperature and showed no basal expression. The differences in patterns of induction may be due to the special features of the promoter region of the HSP70B' gene.

Altered synthesis of the 26-kDa heat stress protein family and thermotolerance in cell lines with elevated levels of calcium-binding proteins

Using a bovine papilloma virus-based vector, mouse mammary adenocarcinoma cells have been transformed to express elevated amounts of functional calmodulin (CaM) (Rasmussen and Means, 1987) and another Ca2(+)-binding protein, parvalbumin (PV) (Rasmussen and Means, 1989) that is not normally synthesized in these cells. Parental cells (C127) and cells transformed by the vector alone (BPV-1), the vector containing a CaM gene (CM-1), or the vector containing parvalbumin (PV-1) were used to study the effect of increased synthesis of Ca2(+)-binding proteins on heat-stress protein (HSP) synthesis and cell survival following heating at 43 degrees C. The induction, stability, and repression of the synthesis of most HSPs after 43 degrees C heating was not significantly affected by increased amounts of Ca2(+)-binding proteins, but the rate of synthesis of all three isoforms of the 26-kDa HSP (HSP26) was greatly reduced. C127 cells, which have about one half as much CaM as do BPV-1 cells, synthesized the most HSP26. CM-1 cells, which have more than fourfold higher levels of CaM than do BPV-1 cells, had a rate of synthesis of HSP26 approaching that of unheated cells. BPV-1 cells, with a two-fold increase in CaM, were intermediate in HSP26 synthesis. This effect on HSP26 synthesis may be largely related to the Ca2(+)-binding capacity of CaM rather than to a specific CaM-regulated function, since PV-1 cells also showed reduced rates of HSP26 synthesis. Survival experiments showed that reduced HSP26 synthesis in cells with increased amounts of Ca2(+)-binding proteins did not significantly alter intrinsic resistance to continuous 43 degrees C heating. Thermotolerance was not reduced and appeared to develop more rapidly in CM-1 and PV-1 cells. These results suggest that (1) the signal for HSP26 synthesis can be largely abrogated by elevated Ca2+ binding protein levels, and (2) if these HSPs are involved in thermotolerance development, that function may be associated with intracellular Ca2+ homeostasis.

The effect of calmodulin antagonists on hyperthermic cell killing and the development of thermotolerance

The role of calmodulin (CaM) in hyperthermic cell killing, and the development of thermotolerance in rat 13762NF mammary adenocarcinoma cells, was investigated by using the CaM antagonists W-7 [N-(6-aminohexyl)-5-chloro-1-naphthalene sulphonamide] and W-13 [N-(4-aminobutyl)-2-chloro-naphthalenesulphonamide] and their less active analogues W-5 [N-(6-aminohexyl)-1-naphthalenesulphonamide] and W-12 [N-(4-aminobutyl)-2-naphthalenesulphonamide]. The CaM antagonists W-7 and W-13 potentiated 43 degrees C cell killing (and the less active analogues did not) at a concentration compatible with CaM inhibition, thus hyperthermic perturbation of CaM-regulated processes may contribute to cellular lethality. The potentiation of hyperthermic killing by antagonists appeared to be temperature-dependent, sensitizing much more effectively to 43 degrees C than to 42 degrees C killing. The effect may be related to differing primary mechanisms of hyperthermic killing activated at the two temperatures, or simply to differences in incorporation or localization of the antagonists. The presence of the CaM antagonists throughout fractionated 42 degrees C or 43 degrees C heating, or during continuous 42 degrees C heating, did not significantly inhibit or potentiate the triggering and development of thermotolerance or alter the rates of heat stress protein (HSP) synthesis. Studies using CaM-agarose isolation of CaM-binding proteins indicated that binding of some HSP to CaM-agarose occurred and was Ca2+-dependent. The specificity and physiological relevance of these HSP binding to CaM was not clear, since their affinity was not high in these cells. Presumably W-7 would perturb any physiologically relevant CaM-protein interactions in cells but W-7 concentrations that reduced HSP and other protein binding to CaM-agarose columns by 50 per cent or more, had no effect on thermotolerance development in cells. These observations, combined with the studies that showed little effect of CaM antagonists on HSP synthesis at concentrations which potentiated cell killing, suggested that events leading to triggering or developing thermotolerance were not strongly dependent on any putative HSP binding to CaM. These studies also suggest some targets of hyperthermic cell killing at 43 degrees C are different from those that lead to the triggering and development of thermotolerance.

Association of a cellular heat shock protein with simian virus 40 large T antigen in transformed cells

The viral oncoprotein of simian virus 40, large T antigen (T-ag), is essential for viral replication and cellular transformation. To understand the mechanisms by which T-ag mediates its multifunctional properties, it is important to identify the cellular targets with which it interacts. A cellular protein of 73 kilodaltons (p73) which specifically associates with T-ag in simian virus 40-transformed BALB/c 3T3E cells has been identified. The binding of p73 to T-ag was demonstrated by coimmunoprecipitation analyses using polyclonal and monoclonal antibodies specific for T-ag. The interaction of p73 with T-ag was independent of T-ag complex formation with the cellular protein p53. Partial V8 protease cleavage maps for p73 and the cellular heat shock protein hsp70 were identical. Immunoblot analyses indicated that p73 complexed to T-ag was antigenically related to hsp70. T-ag deletion mutants were constructed that remove internal, amino-terminal, and carboxy-terminal sequences. These mutants mapped the p73 binding domain to the amino terminus of T-ag. The specific dissociation of p73 from the p73/T-ag complex was mediated by ATP; GTP, CTP, and UTP were also utilized as substrates. These characteristics suggest that p73 may be a member of the hsp70 family of heat shock proteins. The biologic significance of p73/T-ag complex formation has yet to be determined.

The nuclear-coded chloroplast 22-kDa heat-shock protein of Chlamydomonas. Evidence for translocation into the organelle without a processing step

A cDNA clone, pCHS62, was isolated using poly(A)-rich RNA from heat-shocked Chlamydomonas reinhardtii cells. The clone has a length of 1.1 kb and codes for the complete heat-shock protein which was reported to be associated with the grana region of the thylakoid membranes and ascribes protection against photoinhibition during heat-shock. An expression vector prepared in the pUC19 plasmid was used to obtain a fusion protein against which rabbit polyclonal antibodies have been raised. The antibodies react specifically with the heat-shock protein of 22 kDa synthesized in vivo during heat-shock, which is localized in the grana thylakoids, with the in vitro translated product using poly(A)-rich RNA from heat-treated cells as well as with the hybrid release translation product of the pCHS62 clone. The clone was sequenced. It contains a 5' region consisting of 85 nucleotides, an open reading frame of 471 nucleotides and a non-coding 3' region of 600 nucleotides. Northern hybridization indicates a length of 1.7 kb for the messenger RNA of heat-shock protein 22. Analysis of similarity between the derived amino acid sequence of this protein and other heat-shock proteins demonstrates that this protein belongs to the small-molecular-mass plant heat-shock protein family and also shows similarities with animal heat-shock proteins including the presence of a short region possessing similarity with bovine alpha-crystalline as reported for other heat-shock proteins. The molecular mass of the protein as determined from the sequence is 16.8 kDa. Despite its localization in the chloroplast membranes, it does not seem to include a transit peptide sequence, in agreement with previous data. The sequence contains only a short hydrophobic region compatible with its previously reported localization as a thylakoid extrinsic protein.

The major inducible heat shock protein hsp68 is not required for acquisition of thermal resistance in mouse plasmacytoma cell lines

In mouse cells, the major inducible heat shock protein is a protein of 68,000 daltons (hsp68). We have previously shown that mouse plasmacytomas do not express hsp68. We have now made use of these natural mutants to assess the contribution of hsp68 to acquired thermotolerance. An endpoint limiting dilution assay was used to quantify cell survival to lethal stresses. Two test plasmacytoma cell lines (C1.18.1 and J558) and an hsp68-positive myeloma, XC1.1/51, used as a control, were examined. All showed recovery when pretreated for 10 min at 44 degrees C 2 h before exposure to otherwise lethal stresses of 1 to 4 h at 43 degrees C. Similar results were obtained with the Friend erythroleukemia line D1B, which we have also shown not to express hsp68. These results indicate that hsp68 is not required for protection against thermal stresses in mouse cells.

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.

Response of cultured Müller cells to heat shock--an immunocytochemical study of heat shock and intermediate filament proteins in response to temperature elevation

Müller cells from adult rabbit retina were cultured at normal (37 degrees C) temperature and under heat shock conditions (42-43 degrees C) for either 1.5 hr or 4 hr. The presence of heat shock proteins of three different molecular weights, and of vimentin, was identified by the use of monoclonal antibodies and of GFAP by a suitable polyclonal antibody coupled in each instance with immunofluorescence microscopy or immuno-electron microscopy. Heat shock conditions resulted in the expression of HSP of molecular weights in the ranges 57-61 kD, 68 kD and 90 kD. The high level of expression of GFAP in unshocked Müller cell cultures (80-90% of cells) was reduced after 1.5 hr of heat shock to 20-30% of cells, and after 4 hr to only 5%. Although the expression of vimentin (90% of untreated cells) was only slightly reduced by heat shock (60-80% of cells) the intracellular staining pattern of vimentin was greatly altered by heat shock. Changes in the expression of HSP, GFAP and vimentin can all be regarded as part of the Müller cell response to heat shock conditions.

Selective release from cultured mammalian cells of heat-shock (stress) proteins that resemble glia-axon transfer proteins

Cultured rat embryo cells were stimulated to rapidly release a small group of proteins that included several heat-shock proteins (hsp110, hsp71, hscp73) and nonmuscle actin. The extracellular proteins were analyzed by two-dimensional polyacrylamide gel electrophoresis. Heat-shocked cells released the same set of proteins as control cells with the addition of the stress-inducible hsp110 and hsp71. Release of these proteins was not blocked by either monensin or colchicine, inhibitors of the common secretory pathway. A small amount of the glucose-regulated protein grp78 was externalized by this pathway. The extracellular accumulation of these proteins was inhibited after they were synthesized in the presence of the lysine analogue aminoethyl cysteine. It is likely that the analogue-substituted proteins were misfolded and could not be released from cells, supporting our conclusion that a selective release mechanism is involved. Remarkably, actin and the squid heat-shock proteins homologous to rat hsp71 and hsp110 are also among a select group of proteins transferred from glial cells to the squid giant axon, where they have been implicated in neuronal stress responses (Tytell et al.: Brain Res., 363:161-164, 1986). Based in part on the similarities between these two sets of proteins, we hypothesized that these proteins were released from labile cortical regions of animal cells in response to perturbations of homeostasis in cells as evolutionarily distinct as cultured rat embryo cells and squid glial cells.

The major inducible heat shock protein hsp68 is not required for acquisition of thermal resistance in mouse plasmacytoma cell lines

In mouse cells, the major inducible heat shock protein is a protein of 68,000 daltons (hsp68). We have previously shown that mouse plasmacytomas do not express hsp68. We have now made use of these natural mutants to assess the contribution of hsp68 to acquired thermotolerance. An endpoint limiting dilution assay was used to quantify cell survival to lethal stresses. Two test plasmacytoma cell lines (C1.18.1 and J558) and an hsp68-positive myeloma, XC1.1/51, used as a control, were examined. All showed recovery when pretreated for 10 min at 44 degrees C 2 h before exposure to otherwise lethal stresses of 1 to 4 h at 43 degrees C. Similar results were obtained with the Friend erythroleukemia line D1B, which we have also shown not to express hsp68. These results indicate that hsp68 is not required for protection against thermal stresses in mouse cells.

Characterization of the thermotolerant cell. II. Effects on the intracellular distribution of heat-shock protein 70, intermediate filaments, and small nuclear ribonucleoprotein complexes

Here we further characterize a number of properties inherent to the thermotolerant cell. In the preceding paper, we showed that the acquisition of the thermotolerant state (by a prior induction of the heat-shock proteins) renders cells translationally tolerant to a subsequent severe heat-shock treatment and thereby results in faster kinetics of both the synthesis and subsequent repression of the stress proteins. Because of the apparent integral role of the 70-kD stress proteins in the acquisition of tolerance, we compared the intracellular distribution of these proteins in both tolerant and nontolerant cells before and after a severe 45 degrees C/30-min shock. In both HeLa and rat embryo fibroblasts, the synthesis and migration of the major stress-induced 72-kD protein into the nucleolus and its subsequent exit was markedly faster in the tolerant cells as compared with the nontolerant cells. Migration of preexisting 72-kD into the nucleolus was shown to be dependent upon heat-shock treatment and independent of active heat-shock protein synthesis. Using both microinjection and immunological techniques, we observed that the constitutive and abundant 73-kD stress protein similarly showed a redistribution from the cytoplasm and nucleus into the nucleolus as a function of heat-shock treatment. We show also that other lesions that occur in cells after heat shock can be prevented or at least minimized if the cells are first made tolerant. Specifically, the heat-induced collapse of the intermediate filament cytoskeleton did not occur in cells rendered thermotolerant. Similarly, the disruption of intranuclear staining patterns of the small nuclear ribonucleoprotein complexes after heat-shock treatment was less apparent in tolerant cells exposed to a subsequent heat-shock treatment.

Localization of 70-kDa stress protein induction in gerbil brain after ischemia

Induction of the 70-kDa heat shock protein, hsp70, has been demonstrated in brain following experimental stroke. In the present study, hsp70 was localized in gerbil brain at intervals after transient ischemia using a monoclonal antibody specific for stress-inducible forms of hsp70-related proteins. Induced immunoreactivity was found only in neurons, primarily in hippocampus, striatum, entorhinal cortex and some neocortical regions. Notably hsp70 accumulation was minimal in hippocampal CA1 neurons which die after brief ischemic episodes, but was most pronounced in dentate granule cells and CA3 neurons which are spared. The peak of CA3 immunoreactivity occurred at 48-h recirculation, at the onset of CA1 neuron loss at 2-4 days, demonstrating that hsp70 induction is also a component of this delayed hippocampal pathophysiology rather than a direct response to the metabolic disruption of the initial ischemic episode. These results suggest that hsp70 immunocytochemistry may serve as a marker for neuronal circuitry involved in proposed excitotoxic mechanisms after ischemia and other stresses. Control animals showed immunoreactivity in ependymal cells lining the ventricles, indicating a role for hsp70 in normal functioning of these specialized cells.

Heat shock gene expression and cytoskeletal alterations in mouse neuroblastoma cells

The cytoskeleton of neuroblastoma cells, clone Neuro 2A, is altered by two stress conditions: heat shock and arsenite treatment. Microtubules are reorganized, intermediate filaments are aggregated around the nucleus, and the number of stress fibers is reduced. Since both stress modalities induce similar cytoskeletal alterations, no thermic denaturation of one or more cytoskeletal components can be involved in this process. Heat shock proteins are induced both by heat and by arsenite. However, cells treated with arsenite synthesize hsp28 which is not detected in heat-treated cells. Synthesis of all hsps is prevented by addition of actinomycin D or cycloheximide. Under these conditions no alterations are observed in the organization of microtubules and intermediate filaments during heat or arsenite treatment. However, these drugs are not able to prevent the rapid loss of stress fibers. A re-formation of the cytoskeleton during the recovery period proceeds within 3 h and is also found to occur in the presence of a protein synthesis inhibitor. These data suggest that reorganization of microtubules and intermediate filaments during a stress treatment requires the synthesis of a new protein(s), probably hsp(s).

Trifluoperazine activates and releases latent ATP-generating enzymes associated with the synaptic plasma membrane

Neurone-specific enolase (NSE) and the brain form of creatine phosphokinase (CPK-BB) were previously found to be present in rat synaptosomal plasma membranes (SPM) using two-dimensional gel (2-D gel) and peptide analysis; enzymatic activities of these and of pyruvate kinase (PK), all involved in ATP generation, were shown to be "cryptic" unless the SPM were treated with Triton X-100. We now show that enzymatic activation also occurs when the SPM are treated with trifluoperazine (TFP). TFP activation occurred even when the enzymes were membrane associated, showing that solubilization was not responsible for "unmasking" the enzyme activities. When TFP treatment was performed at alkaline instead of neutral pH, NSE and CPK-BB were released as well as PK, nonneuronal enolase, and aldolase which were identified by 2-D gel and tryptic peptide analysis. Other proteins released included calmodulin, actin, and the 70-kilodalton heat-shock cognate protein. Tubulin, synapsin I, and a 35-kilodalton basic protein were largely unaffected. The latter was identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase on the basis of 2-D gel and peptide analyses and subsequent partial sequencing of a rat brain cDNA coding for the same protein. TFP treatment is thus useful for activating latent enzymes as well as for distinguishing enzymes that have a different disposition on the membrane.

Expression and developmental regulation of two unique mRNAs specific to brain membrane-bound polyribosomes

Translation in vitro of membrane-bound polyribosomal mRNAs from rat brain has shown several to be developmentally regulated [Hall & Lim (1981) Biochem. J. 196, 327-336]. Here we describe the isolation and characterization of cDNAs corresponding to two such brain mRNAs. One cDNA (M444) hybrid-selected a 0.95 kb mRNA directing the synthesis in vitro of a 21 kDa pI-6.3 polypeptide, which was processed in vitro by microsomal membranes. A second cDNA (M1622) hybridized to a 2.2 kb mRNA directing the synthesis of a 55 kDa pI-5.8 polypeptide. Both mRNAs were specific to membrane-bound polyribosomes. Restriction maps of the corresponding genomic DNA sequences are consistent with both being single copy. The two mRNAs were present in astrocytic and neuronal cultures, but not in liver or spleen or in neuroblastoma or glioma cells. The two mRNAs were differently regulated during brain development. In the developing forebrain there was a gradual and sustained increase in M444 mRNA during the first 3 weeks post partum, whereas M1622 mRNA appeared earlier and showed no further increase after day 10. In the cerebellum the developmental increase in M444 mRNA was biphasic. After a small initial increase there was a decrease in this mRNA at day 10, coincident with high amounts of M1622 mRNA. This was followed by a second, larger, increase in M444 mRNA, when amounts of M1622 mRNA were constant. The contrasting changes in these two mRNAs in the developing cerebellum are of particular interest, since they occur during an intensive period of cell proliferation, migration and altering neural connectivity. As these mRNAs are specific to differentiated neural tissue, they represent useful molecular markers for studying brain differentiation.

Chromosomal location of human genes encoding major heat-shock protein HSP70

The HSP70 family of heat-shock proteins constitutes the major proteins synthesized in response to elevated temperatures and other forms of stress. In eukaryotes members of the HSP70 family also include a protein similar if not identical to bovine brain uncoating ATPase and glucose-regulated proteins. An intriguing relation has been established between expression of heat-shock proteins and transformation in mammalian cells. Elevated levels of HSP70 are found in some transformed cell lines, and viral and cellular gene products that are capable of transforming cells in vitro can also stimulate transcription of HSP70 genes. To determine the organization of this complex multigene family in the human genome, we used complementary approaches: Southern analysis and protein gels of Chinese hamster-human somatic cell hybrids, and in situ hybridization to human chromosomes. We demonstrate that functional genes encoding HSP70 proteins map to human chromosomes 6, 14, 21, and at least one other chromosome.

A hsp70-related gene is constitutively highly expressed in testis of rat and mouse

The expression pattern of major heat shock related genes (hsp70 gene family) in various organs of mouse and rat was investigated using Northern blot analysis. Heat shock gene related transcripts were detected in total RNA by hybridization with cloned mouse hsp70 gene sequences. Cells of various organs of intact mouse and rat constitutively synthesize a 2.2 kb and a 2.5 kb RNA. Exceptionally high levels of the 2.5 kb RNA, 50-250 fold higher than in other tissues are found in testis of both rodents. The 2.5 kb RNA hybridizes strongly to an extended region of mouse hsp70 gene; it also hybridizes poorly to the Drosophila hsp70 gene. The data suggest that the 2.5 kb RNA is transcribed from a hsp70-related gene in mouse and rat.

Expression of hsp70-related gene in developing and degenerating rat testis

Rat testes contain highly elevated levels of 2.5 kb RNA transcribed from a heat shock (hsp70) related gene. In the present paper northern blot analysis was used to follow the changes in the 2.5 kb transcript level during the postnatal development of rat testis and during the degeneration of the seminiferous epithelium in adult rats caused by experimental cryptorchidism. The 2.5 kb transcript was undetectable in newborn rats until the 3rd week of life. The level of the transcript reached a maximum at the 4th week and remained unchanged from that point on. Two days after the surgical translocation of the testes from the scrotum into the abdominal cavity the level of 2.5 kb transcript rapidly declined. Presented results strongly suggest that the hsp 70-like gene coding for the 2.5 kb RNA is specifically expressed in germinal cells, most probably in the spermatocytes.

Localization of a human heat-shock HSP 70 gene sequence to chromosome 6 and detection of two other loci by somatic-cell hybrid and restriction fragment length polymorphism analysis

The human 70 kdalton heat-shock protein (HSP 70) is a member of a multigene family which is expressed in response to various physiological stresses including elevated temperatures. Using a cloned genomic HSP 70 DNA sequence we demonstrate by somatic cell hybrid and restriction fragment length polymorphism (RFLP) analyses that there are a minimum of three distinct HSP 70 loci in the human genome, one of which is located on chromosome 6.

Isolation of a mouse heat-shock gene (hsp68) by recombinational screening

We have used cloned fragments from a Drosophila melanogaster hsp70 gene and a mouse hsp68 cDNA in recombinational screens of mouse genomic libraries. Using the mouse probe we have isolated two overlapping recombinant lambda phages comprising 22 kb of cloned DNA. Southern analysis has localized the homology with the Drosophila hsp70 coding region to a 2.2-kb fragment containing the mouse heat-shock gene. Insertion accompanying recombinational screening can disrupt interesting sequences; we have overcome this inconvenience by developing a simple one-step genetic selection for phage which have precisely excised the microplasmid probe.

The brain 68-kilodalton microtubule-associated protein is a cognate form of the 70-kilodalton mammalian heat-shock protein and is present as a specific isoform in synaptosomal membranes

The relationship between the 68-kilodalton microtubule-associated protein (68KMAP) and the major heat-induced protein (HSP70) in rat and human cells was investigated by comparison of their heat induction properties and by tryptic and Cleveland peptide mapping procedures. HSP70 synthesis was induced by heat shock of rat and human cells, whereas 68KMAP was a major synthesised protein in the absence of heat shock, with its synthesis being only slightly increased on heat shock. Tryptic peptide mapping, however, indicated strong peptide homology between the two proteins. These data, therefore, confirm that 68KMAP represents a constitutively expressed, heat-shock cognate gene. Two-dimensional gel electrophoretic analysis of subcellular fractions of rat brain, combined with peptide mapping procedures, indicated that 68KMAP exists as at least two isoforms separable by isofocussing, the more acidic of which (alpha 68KMAP) is present in fractions enriched in microtubules, cytosol, microsomes, synaptosomal plasma membranes, and synaptic vesicles, and the more basic of which (beta 68KMAP) is present predominantly in fractions enriched in synaptic vesicles and synaptosomal plasma membranes. These two forms are distinguishable in terms of changes in Cleveland peptide maps, and we conclude that alpha- and beta 68KMAP, therefore, represent distinct forms. The significance of these findings to the molecular pathogenesis of Down's syndrome in the human brain is discussed.

The dynamic state of heat shock proteins in chicken embryo fibroblasts

Subcellular fractionation and immunofluorescence microscopy have been used to study the intracellular distributions of the major heat shock proteins, hsp 89, hsp 70, and hsp 24, in chicken embryo fibroblasts stressed by heat shock, allowed to recover and then restressed. Hsp 89 was localized primarily to the cytoplasm except during the restress when a portion of this protein concentrated in the nuclear region. Under all conditions, hsp 89 was readily extracted from cells by detergent. During stress and restress, significant amounts of hsp 70 moved to the nucleus and became resistant to detergent extraction. Some of this hsp 70 was released from the insoluble form in an ATP-dependent reaction. Hsp 24 was confined to the cytoplasm and, during restress, aggregated to detergent-insoluble perinuclear phase-dense granules. These granules dissociated during recovery and hsp 24 could be solubilized by detergent. The nuclear hsps reappeared in the cytoplasm in cells allowed to recover at normal temperatures. Sodium arsenite also induces hsps and their distributions were similar to that observed after a heat shock, except for hsp 89, which remained cytoplasmic. We also examined by immunofluorescence the cytoskeletal systems of chicken embryo fibroblasts subjected to heat shock and found no gross morphological changes in cytoplasmic microfilaments or microtubules. However, the intermediate filament network was very sensitive and collapsed around the nucleus very shortly after a heat shock. The normal intermediate filament morphology reformed when cells were allowed to recover from the stress. Inclusion of actinomycin D during the heat shock--a condition that prevents synthesis of the hsps--did not affect the intermediate filament collapse, but recovery of the normal morphology did not occur. We suggest that an hsp(s) may aid in the formation of the intermediate filament network after stress.