Regulation of hsp90 and hsp70 genes during antheridiol-induced hyphal branching in the oomycete Achlya ambisexualis

When mycelia of Achlya ambisexualis J. Raper strain E87 were undergoing antheridial branching, a marked increase was observed in the levels of transcript populations encoding the heat shock protein chaperone Hsp90 and transcript populations encoding three different Hsp70-family heat shock protein chaperones, respectively. Although up to 90% of hyphae in the hormone-treated thalli were undergoing antheridial branching, no similar increase in the level of transcripts encoding actin was observed. Nuclear run-on assays demonstrated that the observed antheridiol-induced increases in the levels of the chaperone RNAs resulted from increased transcription. Although not tested for function, the nucleotide sequence of the 5' flanking region of each of the two A. ambisexualis hsp90 genes revealed a diversity of sequences and motifs similar or identical to the sequences of known transcription factor response elements. Among these potential response element sequences observed in the A. ambisexualis genes were motifs observed also in animal steroid hormone response elements. Surrounding the primer-extension determined transcription start site of each A. ambisexualis hsp90 gene was a 16-nucleotide sequence that matched in 14 out of 16 nucleotides a sequence found in the transcription initiation region of many different oomycete genes.

Requirement for Hsp90 and a CyP-40-type cyclophilin in negative regulation of the heat shock response

The heat shock response is a highly conserved mechanism that allows cells to withstand a variety of stress conditions. Activation of this response is characterized by increased synthesis of heat shock proteins (HSPs), which protect cellular proteins from stress-induced denaturation. Heat shock transcription factors (HSFs) are required for increased expression of HSPs during stress conditions and can be found in complexes containing components of the Hsp90 molecular chaperone machinery, raising the possibility that Hsp90 is involved in regulation of the heat shock response. To test this, we have assessed the effects of mutations that impair activity of the Hsp90 machinery on heat shock related events in Saccharomyces cerevisiae. Mutations that either reduce the level of Hsp90 protein or eliminate Cpr7, a CyP-40-type cyclophilin required for full Hsp90 function, resulted in increased HSF-dependent activities. Genetic tests also revealed that Hsp90 and Cpr7 function synergistically to repress gene expression from HSF-dependent promoters. Conditional loss of Hsp90 activity resulted in both increased HSF-dependent gene expression and acquisition of a thermotolerant phenotype. Our results reveal that Hsp90 and Cpr7 are required for negative regulation of the heat shock response under both stress and nonstress conditions and establish a specific endogenous role for the Hsp90 machinery in S. cerevisiae.

Specific binding of tetratricopeptide repeat proteins to the C-terminal 12-kDa domain of hsp90

The molecular chaperone hsp90 in the eukaryotic cytosol interacts with a variety of protein cofactors. Several of these cofactors have protein domains containing tetratricopeptide repeat (TPR) motifs, which mediate binding to hsp90. Using a yeast two-hybrid screen, the 12-kDa C-terminal domain of human hsp90alpha (C90) was found to mediate the interaction of hsp90 with TPR-containing sequences from the hsp90 cofactors FKBP51/54 and FKBP52. In addition, the mitochondrial outer membrane protein hTOM34p was identified as a TPR-containing putative partner protein of hsp90. In experiments with purified proteins, the TPR-containing cofactor p60 (Hop) was shown to form stable complexes with hsp90. A deletion mutant of hsp90 lacking the C90 domain was unable to bind p60, whereas deletion of the approximately 25-kDa N-terminal domain of hsp90 did not affect complex formation. Both p60 and FKBP52 bound specifically to the C90 domain fused to glutathione S-transferase and competed with each other for binding. In reticulocyte lysate, the C90 fusion protein recognized the TPR proteins p60, FKBP52, and Cyp40. Thus, our results identify the C90 domain as the specific binding site for a set of hsp90 cofactors having TPR domains.

Quantification of the nucleocytoplasmic distribution of wild type and modified proteins using confocal microscopy: interaction between 90-kDa heat shock protein (Hsp90 alpha) and glucocorticosteroid receptor (GR)

The investigation of molecular interactions in whole cells by immunofluorescence was developed recently, based on the targeting of the protein partners to different cellular compartments and analysis of the modifications in their subcellular distribution resulting from their interaction. This paper describes the adaptation of the confocal microscopy to the quantification of the partitioning of transiently coexpressed proteins between nucleus and cytoplasm. We defined a nucleocytoplasmic ratio R, corresponding to the difference between nuclear and cytoplasmic fluorescence intensities divided by their sum (N - C/N + C), which does not refer to absolute fluorescence intensities. Interaction was detected by statistically comparing the distribution of R value frequencies in cell populations expressing one or both proteins. The convenience of this whole cell method was demonstrated by detecting and analyzing interaction between the human glucocorticosteroid receptor (GR) and the chick 90-kDa heat shock protein (Hsp90), using various combinations of wild-type and nuclear- or cytoplasmic-targeted GR and Hsp90. In addition, three Hsp90 deletion/ truncation mutants were tested: the C-terminal truncated mutant NC4 interacted slightly, indicating the contribution of this part of the molecule to the interaction with GR, while the shorter truncated mutant NC6 did not interact with GR, likely resulting from an incorrect folding of the molecule. No role for the first charged region (delta A') was found as shown by the strong interaction detected for the delta A'Hsp90. This method can fruitfully be applied to the delimitation of the amino-acid sequences involved in protein-protein interaction by mutational analysis, especially to seek confirmation of other methods or when other approaches have failed.

[Comparative study of expression levels of the major human heat shock proteins in cancer and normal tissues]

OBJECTIVE

To investigate and compare mRNA expression levels of the major human HSPs (including HSP90 alpha, HSP90 beta, HSP70, HSC70 and HSP27) in 25 cases of laryngeal carcinomas and normal controls.

METHODS

mRNA slot blot hybridization technique was used and cDNA probes of HSP27, HSC70 and HSP90 beta were prepared with PCR method.

RESULTS

HSP90 alpha and HSP70 expression was significantly enhanced approximately 5 fold in laryngeal cancer tissues compared to that in the normal larynx tissues while HSP27, HSC70 and HSP90 beta expression was at similar levels.

CONCLUSION

The results suggest that HSP90 alpha and HSP70 may play more important role in the carcinogenic process of laryngeal cancer. To find out mechanisms involved will pave the way for the application of HSPs on the biologic therapy of laryngeal cancer.

Cloning and sequence analysis of Hsp89alpha DeltaN, a new member of theHsp90 gene family

We have identified a novel member of the Hsp90 gene family. This new gene, Hsp89alpha DeltaN, is remarkable in that it appears to represent a recent evolutionary event. Hsp89alpha DeltaN is identical in nucleotide sequence to Hsp89alpha for codons 224 to 732 (end). However, Hsp89alpha DeltaN cDNA lacks the ATP/geldanamycin binding domain (codons 1-220), instead containing 544 nucleotides of unique DNA at its 5' end including 30 novel codons.

A chloroquine resistance locus in the rodent malaria parasite Plasmodium chabaudi

We have located a possible chloroquine resistance locus in the genome of the rodent malaria parasite Plasmodium chabaudi. Two genetically distinct clones of the parasite were grown in vivo and allowed to undergo genetic crossing. The clones differed from each other in their susceptibility to chloroquine; AS(3CQ) had been selected for a low level of resistance to the drug whereas AJ is chloroquine-sensitive. Independent recombinant progeny (20) were cloned from the products of two crosses, phenotyped for their susceptibility to chloroquine, and genotyped for their inheritance of 46 chromosome-specific markers. No association was found between chloroquine susceptibility and the inheritance of pcmdr1, the P. chabaudi homologue of the pfmdr1 multi-drug resistance gene of P. falciparum. Also, there was no association between chloroquine susceptibility and the inheritance of a marker linked to a putative chloroquine resistance locus in a P. falciparum cross. However, 16 of the progeny clones showed co-segregation of four linked markers on chromosome 11 with their resistance phenotype. This result suggests that a locus for chloroquine resistance exists on this chromosome in P. chabaudi.

Cultured skin fibroblasts isolated from mice devoid of the prion protein gene express major heat shock proteins in response to heat stress

Recent evidence has suggested that molecular chaperones participate in the conformational change between the normal cellular prion protein (PrPC) and its scrapie isoform (PrPSc). To study a role of PrPC in the regulation of expression of heat shock proteins (HSPs), a group of molecular chaperones, heat-induced expression of major HSPs (HSP105, HSP90alpha, HSP72, HSC70, HSP60, and HSP25) was investigated in cultured skin fibroblasts isolated from the mice homogeneous for a disrupted PrP gene (PrP-/- mice) by Western blot analysis and immunocytochemistry. Two lines of fibroblasts were established and designated SFK derived from the PrP-/- mice and SFH derived from the PrP+/+ mice, respectively. In both SFK and SFH cells, HSP105, HSP72, and HSP25 were expressed at low levels under unstressed conditions but they were induced markedly following exposure to heat stress (43 degreesC/20 min) at 3-72 h postrecovery. In both cell types, HSC70 and HSP60 were expressed at high levels under unstressed conditions and their levels remained unchanged after heat shock treatment. HSP90alpha was undetectable in both cell types under any conditions examined. The pattern of expression, induction, and subcellular location of HSP105, HSP72, HSC70, HSP60, and HSP25 was not significantly different between SFK and SFH cells under unstressed and heat-stressed conditions. Furthermore, the levels of constitutive expression of HSP105, HSC70, HSP60, and HSP25 were similar between the brain tissues isolated from the PrP-/- and PrP+/+ mice. These results indicate that HSP induction is not affected by either the existence or the absence of PrPC in the cells.

[Study on HSP70, 90 mRNA gene expression in peripheral blood mononuclear cells with steroid-resistant asthmatics]

OBJECTIVE

To investigate the role of heat shock protein(HSP) 70, 90 alpha, 90 beta mRNA on the pathogenesis of steroid-resistant(SR) asthma.

METHOD

9 SR asthmadics 16 steroid sensitive (SS) asthmatics and 10 normal healthy volunteers were studied. With reverse transcription-polymerase chain reaction(RT-PCR), the expression of hsp70, 90 alpha, 90 beta mRNA were detected in peripheral blood mononuclear cell(PMBC) from normal volunteers and SR. steroid-sensitive(SS) asthmatics. Inhibition of PHA-induced lymphocyte proliferation by dexamethasones (Dex) was investigated using lymphocyte proliferation assay.

RESULT

There were no expression of hsp70mRNA in PMBC of normal volunteers; the levels of expression of hsp70, 90 alpha, 90 beta mRNA in PBMC of SR asthmatics (70 = 2.95 +/- 1.12, 90 alpha = 2.17 +/- 0.89, 90 beta = 2.22 +/- 0.83) were significantly higher than SS asthmatics (70 = 0.23 +/- 0.09, 90 alpha = 1.07 +/- 0.39, 90 beta = 0.94 +/- 0.32) (P < 0.01) and normal volunteers (70 = 0, 90 alpha = 0.45 +/- 0.19, 90 beta = 0.32 +/- 0.15) (P < 0.01); There were significantly positive correlation between the degree of inhibition by Dex(10(-7) mol/L) of SR, SS asthmatics of proliferation of T lymphocytes and the expression of hsp70, 90 alpha, 90 beta mRNA in PMBC(P < 0.01).

CONCLUSION

There were expression of hsp70, 90 alpha, 90 beta gene in PMBC from SR asthmatics, but increased with worsening of inflammation and prolonging of the duration of disease. The more hsp 90 gene expression, the less T lymphocytes were inhibited by Dex.

Molecular chaperones as HSF1-specific transcriptional repressors

The rapid yet transient transcriptional activation of heat shock genes is mediated by the reversible conversion of HSF1 from an inert negatively regulated monomer to a transcriptionally active DNA-binding trimer. During attenuation of the heat shock response, transcription of heat shock genes returns to basal levels and HSF1 reverts to an inert monomer. These events coincide with elevated levels of Hsp70 and other heat shock proteins (molecular chaperones). Here, we show that the molecular chaperone Hsp70 and the cochaperone Hdj1 interact directly with the transactivation domain of HSF1 and repress heat shock gene transcription. Overexpression of either chaperone represses the transcriptional activity of a transfected GAL4-HSF1 activation domain fusion protein and endogenous HSF1. As neither the activation of HSF1 DNA binding nor inducible phosphorylation of HSF1 was affected, the primary autoregulatory role of Hsp70 is to negatively regulate HSF1 transcriptional activity. These results reveal that the repression of heat shock gene transcription, which occurs during attenuation, is due to the association of Hsp70 with the HSF1 transactivation domain, thus providing a plausible explanation for the role of molecular chaperones in at least one key step in the autoregulation of the heat shock response.

Analysis of FKBP51/FKBP52 chimeras and mutants for Hsp90 binding and association with progesterone receptor complexes

FKBP51, FKBP52, and Cyp40 bind competitively to Hsp90 through their respective tetratricopeptide repeat (TPR) domains, and any one of the three immunophilins can be isolated in mature steroid receptor complexes. During cell-free assembly reactions, FKBP51 associates preferentially with progesterone and glucocorticoid receptors, but less preference is observed in FKBP51 association with estrogen receptor. A number of mutant FKBP forms were generated to map sequences responsible for FKBP51's preferred association with progesterone receptor. A double-point mutation in the peptidyl prolyl isomerase domain of FKBP51 that reduces enzymatic activity by greater than 90% had no observed effect on FKBP51 interactions with progesterone receptor or Hsp90. Coprecipitation of FKBP51 and FKBP52 truncation mutants with Hsp90 indicated that sequences both upstream and downstream of the TPR domain are necessary for Hsp90 binding. FKBP chimeric constructs were also generated and tested for Hsp90 binding and receptor association. The TPR domain of FKBP51 required appropriate downstream sequences for Hsp90 binding, but FKBP52's TPR domain did not. The C-terminal region of FKBP51 that functionally interacts with the TPR domain to permit Hsp90 binding also conferred preferential association with PR. In conclusion, despite the overall similarity of FKBP51 and FKBP52, these two immunophilins associate differentially with steroid receptors, and the difference relates to both the Hsp90-binding TPR domain and to poorly conserved C-terminal sequences.

The nuclear factor interleukin-6 (NF-IL6) and signal transducer and activator of transcription-3 (STAT-3) signalling pathways co-operate to mediate the activation of the hsp90beta gene by interleukin-6 but have opposite effects on its inducibility by heat shock

The levels of the 90 kDa heat-shock protein (hsp90) and the activity of the hsp90beta gene promoter are increased in response to treatment by interleukin (IL)-6. The hsp90beta gene promoter contains binding sites for the transcription factors nuclear factor IL-6 (NF-IL6) and signal transducer and activator of transcription 3 (STAT-3), which are activated respectively by the mitogen-activated-protein-kinase and Jak-kinase pathways following IL-6 treatment. Both these factors can activate the hsp90 promoter and have a strong synergistic effect on its activity, which appears to be critical for IL-6-mediated activation of the promoter. Interestingly, the two factors interact differently with the heat-shock factor (HSF) and a heat-shock stress. Thus STAT-3 reduces the stimulatory effect of heat shock whereas NF-IL6 enhances it. When applied together, heat shock and IL-6 produce only weak activation of the hsp90 promoter compared with either stimulus alone, indicating that the inhibitory effect of STAT-3 on HSF predominates under these conditions. In contrast, IL-1, which activates only the NF-IL6 pathway, synergizes with heat shock to produce strong activation of hsp90. These effects are discussed in terms of the multiple stimuli that may regulate the hsp90 promoter in unstressed cells and their interaction with its stress-mediated activation.

[The role of the heat shock protein in human breast cancer]

OBJECTIVE

To study the role of heat shock proteins (HSP) in the cell cycle and various processes of carcinogenesis.

METHODS

Immunohistochemical SP methods, electron microscopy, in situ hybridization and RT-PCR were used to evaluate the expression of HSP, mainly HSP90, ubiquitin and HSP70 in breast cancer tissues.

RESULTS

HSP90 mRNA was expressed at much higher levels in cancerous tissue than in non-cancerous tissues. In addition, a close relation between HSP90 mRNA expression and proliferating cell nuclear antigen labelling index (PCNA L. I.) was observed in cancerous tissue. These findings suggest that increased expression of HPS90 isoform may play a role in cell proliferation. On the other hand, HSP90 mRNA was expressed in the more poorly differentiated carcinomas of the breast. The intracellular localization of HSP70 was consistent with that of ubiquitin. The PCNA L. I. was significantly higher in specimens showing HSP70 in nucleus. HSP73 mRNA, a member of HSP70 family, was also expressed at higher levels in cancerous tissues associated with a high PCNA L. I. than in non-cancerous tissues.

CONCLUSION

These results suggest that HSP90 may play a role in cancer cell proliferation and that HSP90 may contribute to cell differentiation and structural constitution. In addition, HSP70, especially HSP73, is related to ubiquetin and seems to be a marker for cancer proliferation.

Genomic organization of hsp90 gene family in Arabidopsis

We have isolated six members of the hsp90 gene family from Arabidopsis thaliana. Three genes designated hsp81.2, 81.3 and 81.4 are clustered within a 15 kb genomic region while two of these are 1.5 kb apart in a head-to-head orientation. The deduced amino acid sequence shows that the members can be divided into two types. The hsp81.1, 81.2, 81.3 and 81.4 genes comprise the cytosolic hsp90 type having few introns. However, the hsp88.1 and 89.1 genes comprising the organelle type are composed of 18 or 19 introns. Sequence comparison showed there is high homology among the cytosolic members while there is less homology among the organelle members. The expression of the hsp90 genes and mRNA accumulation in plants and calli is very low at control temperatures and is strongly induced by heat-shock. Arsenite stress strongly stimulates the expression of this gene family.

In vivo functions of the Saccharomyces cerevisiae Hsp90 chaperone

In the highly concentrated environment of the cell, polypeptide chains are prone to aggregation during synthesis (as nascent chains await the emergence of the remainder of their folding domain), translocation, assembly, and exposure to stresses that cause previously folded proteins to unfold. A large and diverse group of proteins, known as chaperones, transiently associate with such folding intermediates to prevent aggregation, but in many cases the specific functions of individual chaperones are still not clear. In vivo, Hsp90 (heat shock protein 90) plays a role in the maturation of components of signal transduction pathways but also exhibits chaperone activity with diverse proteins in vitro, suggesting a more general function. We used a unique temperature-sensitive mutant of Hsp90 in Saccharomyces cerevisiae, which rapidly and completely loses activity on shift to high temperatures, to examine the breadth of Hsp90 functions in vivo. The data suggest that Hsp90 is not required for the de novo folding of most proteins, but it is required for a specific subset of proteins that have greater difficulty reaching their native conformations. Under conditions of stress, Hsp90 does not generally protect proteins from thermal inactivation but does enhance the rate at which a heat-damaged protein is reactivated. Thus, although Hsp90 is one of the most abundant chaperones in the cell, its in vivo functions are highly restricted.

Analysis of the transcriptional activity of amplified genes in tumour cells by fluorescence in situ hybridization

In this paper we present a new application of the detection of nuclear transcripts by fluorescence in situ hybridization (FISH) for studying the transcriptional activity of amplified genes in tumour cells. As a model, we have used the A431 cell line in which several amplification sites have been identified. We focused on two amplified regions: (1) the 6p12 region, which was found amplified by using comparative genomic hybridization, and which contains an amplification of the hsp90 beta gene; (2) the 7p12-p13 region, which displays a 20- to 30-fold amplification of the gene encoding the epidermal growth factor receptor (EGFr). By using FISH to detect nuclear transcripts, we show that the extra-copies of the hsp90 beta and EGFr genes are actively transcribed within the sites of amplification. This work illustrates the potential of this method as a tool for functional in situ cytogenetic analyses.

A mutation in an HSP90 gene affects the sexual cycle and suppresses vegetative incompatibility in the fungus Podospora anserina

Vegetative incompatibility is widespread in fungi but its molecular mechanism and biological function are still poorly understood. A way to study vegetative incompatibility is to investigate the function of genes whose mutations suppress this phenomenon. In Podospora anserina, these genes are known as mod genes. In addition to suppressing vegetative incompatibility, mod mutations cause some developmental defects. This suggests that the molecular mechanisms of vegetative incompatibility and development pathway are interconnected. The mod-E1 mutation was isolated as a suppressor of the developmental defects of the mod-D2 strain. We show here that mod-E1 also partially suppresses vegetative incompatibility, strengthening the link between development and vegetative incompatibility. mod-E1 is the first suppressor of vegetative incompatibility characterized at the molecular level. It encodes a member of the Hsp90 family, suggesting that development and vegetative incompatibility use common steps of a signal transduction pathway. The involvement of mod-E in the sexual cycle has also been further investigated.

Intratumoral heterogeneity for hsp90beta mRNA levels in a breast cancer cell line

BC-3A and BC-61 are two breast cancer cell lines that have been cloned from parental 8701-BC cells and exhibit different biosynthetic, proliferative, and invasive properties in vitro. In the attempt to search whether alterations in the profiles of gene expression could be detected, we have submitted both cytotypes to identification of differentially expressed cDNAs. In addition, steroid hormone receptor mRNA arrays and in vivo tumorigenesis of the two lines have been checked. The technique used allowed identification of changes in the expression of the 90-kD heat shock protein-beta (hsp90beta) which is prominently down-regulated in BC-61 cells. Because we have also found that these cells, which lack estrogen receptor mRNA synthesis, display a more invasive behavior in vitro and increased tumorigenesis in vivo, we propose that evaluation of hsp903 transcript levels may be taken into consideration for screening as a novel molecular marker of breast cancer progression.

The amino-terminal domain of heat shock protein 90 (hsp90) that binds geldanamycin is an ATP/ADP switch domain that regulates hsp90 conformation

Many functions of the chaperone, heat shock protein 90 (hsp90), are inhibited by the drug geldanamycin that specifically binds hsp90. We have studied an amino-terminal domain of hsp90 whose crystal structure has recently been solved and determined to contain a geldanamycin-binding site. We demonstrate that, in solution, drug binding is exclusive to this domain. This domain also binds ATP linked to Sepharose through the gamma-phosphate. Binding is specific for ATP and ADP and is inhibited by geldanamycin. Mutation of four glycine residues within two proposed ATP binding motifs diminishes both geldanamycin binding and the ATP-dependent conversion of hsp90 to a conformation capable of binding the co-chaperone p23. Since p23 binding requires regions outside the 1-221 domain of hsp90, these results indicate a common site for nucleotides and geldanamycin that regulates the conformation of other hsp90 domains.

Essential role of the first intron in the transcription of hsp90beta gene

The human HSP90 gene family contains introns. There are two typical heat shock elements (HSE) in the first intron of human hsp90beta gene. As detected by chloramphenicol acetyl transferase (CAT) reporter activity assays, the HSE-containing intron is essential in maintaining high constitutive expression and is critical for heat shock inducibility of the human hsp90beta gene. Cellular heat shock factor 1 (HSF 1) shows much higher binding affinity toward the intronic HSEs in comparison to an atypical HSE in the 5' flanking sequence. Novel initiation sites found in the first intron probably also contribute to constitutive and heat-inducible expression of the hsp90beta gene in Jurkat cells.

Cdc37 is a molecular chaperone with specific functions in signal transduction

Cdc37 is required for cyclin-dependent kinase activation and is genetically linked with the activity of several other kinases, including oncogenic v-Src, casein kinase II, MPS-1 kinase, and sevenless. Strikingly, many pathways involving Cdc37 also involve the protein chaperone Hsp90. The identification of Cdc37 as the 50-kD protein in several Hsp90-kinase complexes, together with other data, led to the recent suggestion that Cdc37 is a kinase-targeting "subunit" of Hsp90. We directly examined the effect of Cdc37 on Hsp90 functions. Rather than simply acting as an accessory factor for Hsp90, Cdc37 is itself a protein chaperone with properties remarkably similar to those of Hsp90. In vitro, Cdc37 maintains denatured beta-galactosidase in an activation-competent state without reactivating it and stabilizes mature, but unstable, casein kinase II. In vivo, Cdc37 overexpression can compensate for decreased Hsp90 function, but the proteins are not interchangeable. Cdc37 can compensate for Hsp90 in maintaining the activity of v-Src kinase but does not maintain the activity of the glucocorticoid receptor. Thus, the very similar chaperone activities of the two proteins, uncovered through in vitro analysis, diverge in vivo in specific signal transduction pathways.

HSP90alpha gene expression may be a conserved feature of vertebrate somitogenesis

We have previously demonstrated that the hsp90alpha and hsp90beta genes in zebrafish are expressed in dramatically different spatial and temporal patterns in early embryos. In the case of hsp90alpha, expression is spatially restricted within the somites to putative myogenic cells which also express mRNA encoding the myogenic bHLH transcription factor myoD and is downregulated along with myoD following myogenesis. In the present study, we have examined hsp90alpha gene expression in developing chicken embryos using a gene-specific probe. We show that hsp90alpha gene expression is also localized to a subset of cells within the somites of chicken embryos and that the expression pattern correlates closely to that observed for myoD. Furthermore, expression of the hsp90alpha gene is strongly upregulated throughout the embryo following heat shock in a manner similar to that observed in heat-shocked zebrafish embryos. The data suggest that the hsp90alpha gene may play an evolutionarily conserved role during somitogenesis in vertebrates in addition to providing protection to all cells of the embryo following stress.

Murine 86-kDa heat shock protein gene and promoter

The class of 90 kDa heat shock proteins (Hsp90) is among the most abundant heat shock proteins (Hsps) in eukaryotic cells. In vertebrates, Hsp90 is encoded by two distinct gene families giving rise to products of 84 and 86 kDa. In mice the expression of these two genes, hsp84 and hsp86, vary with respect to each other in responses to stress, and also in response to signals for growth and development. Therefore, as a step towards understanding the molecular basis for the differential regulation of these two genes, we have isolated and characterized genomic clones of the murine hsp86 gene and its 5' flanking region. The gene is composed of eleven exons interrupted by 10 introns. The 5' region contains consensus TATA, several stimulatory protein-1 binding site (SP1) elements as well as six consensus heat shock elements (HSE) 5' of the transcription start site. An 806 bp fragment of the 5' promoter region conferred constitutive expression upon a reporter gene and this expression was increased upon heat shock.

A molecular clamp in the crystal structure of the N-terminal domain of the yeast Hsp90 chaperone

Hsp90 is a highly specific chaperone for many signal transduction proteins, including steroid hormone receptors and a broad range of protein kinases. The crystal structure of the N-terminal domain of the yeast Hsp90 reveals a dimeric structure based on a highly twisted sixteen stranded beta-sheet, whose topology suggests a possible 30-domain-swapped structure for the intact Hsp90 dimer. The opposing faces of the beta-sheets in the dimer define a potential peptide-binding cleft, suggesting that the N-domain may serve as a molecular 'clamp' in the binding of ligand proteins to Hsp90.

Disruption of the glucocorticoid receptor assembly with heat shock protein 90 by a peptidic antiglucocorticoid

Association of glucocorticoid (GR) and progesterone (PR) receptors with a set of molecular chaperones, including the 90-kDa heat shock protein (hsp90), is a dynamic process required for proper folding and maintaining these nuclear receptors under a transcriptionally inactive, ligand-responsive state. Mutational studies of the chicken hsp90 complementary DNA suggested that three regions of this protein (A, B, and Z) interact with the hormone-binding domain of GR, whereas region A is dispensable for hsp90 binding to PR. We found that this 69-amino acid region can be narrowed down to a 35-mer alpha-helical, acidic peptide, which is by itself able to inhibit hsp90 association to GR translated in vitro. The hsp90-free GR did not bind ligand, but was devoid of any specific DNA-binding activity, and higher peptide concentrations specifically inhibited the binding of activated GR to DNA. When overexpressed in cultured cells, this peptide acted as an antiglucocorticoid and inhibited the antiactivating protein-1 activity and the ligand-dependent nuclear transfer of GR. None of these effects, either in vivo and in vitro, was observed for PR. The region from residue 232 to residue 265 of hsp90 is, therefore, a domain critical for its association to GR, an association that is a prerequisite for receptor transcriptional activity. More importantly, these results demonstrate that targeting specific protein/protein interaction interfaces is a powerful means to specifically modulate nuclear receptor signaling pathways in a ligand-independent manner.