Role of the protein chaperone YDJ1 in establishing Hsp90-mediated signal transduction pathways

The substrate-specific protein chaperone Hsp90 (heat shock protein 90) from Saccharomyces cerevisiae functions in diverse signal transduction pathways. A mutation in YDJ1, a member of the DnaJ chaperone family, was recovered in a synthetic-lethal screen with Hsp90 mutants. In an otherwise wild-type background, the ydj1 mutation exerted strong and specific effects on three Hsp90 substrates, derepressing two (the estrogen and glucocorticoid receptors) and reducing the function of the third (the tyrosine kinase p60v-src). Analysis of one of these substrates, the glucocorticoid receptor, indicated that Ydj1 exerts its effects through physical interaction with Hsp90 substrates.

Evidence for a 90 kDa heat-shock protein gene expression in the amphibian oocyte

In order to study expression of a 90-kDa heat-shock protein during amphibian oogenesis at physiological temperature, we isolated a Pleurodeles waltl hsc90 cDNA by screening an ovarian cDNA library with a chicken hsp90 cDNA probe. The cDNA thus obtained--named Pw90--shows a high homology level with the hsp90 gene in other species. RNase protection analysis led us to conclude that this sequence is part of the cognate gene hsc90 and is constitutively expressed in oocytes. Furthermore, results of quantitative Northern blot analysis, as well as in situ hybridizations on oocyte sections or lampbrush chromosome spreads, provide evidence for expression of hsc90 transcripts at every stage of oogenesis. Moreover, they point to the fact that an accumulation of transcripts occurs very early in oogenesis. Simultaneously, the expression of HSC90-related protein was analyzed on Western blots using a monoclonal antibody (AC88) and a polyclonal antibody (AP90Ct) raised against the Pleurodeles C-terminal part of HSC90. We provide evidence for a net accumulation of HSC90-related protein in oocytes. Immunolocalization shows that a nuclear transfer occurs in the course of oogenesis and leads to a concentration equilibrium between cytoplasm and nucleus in stage VI oocytes.

Expression of hsp90 beta messenger ribonucleic acid in patients with familial glucocorticoid resistance--correlation to receptor status

We have previously shown an increased specific DNA-binding of liganded unactivated glucocorticoid receptor (GR) to the LTR-region of MMTV DNA in a patient with primary cortisol resistance and receptor thermolability indicating a defective interaction of GR with hsp90. In some patients, however, no apparent receptor abnormality was found in spite of a characteristic phenotype. mRNA expression levels of hsp90 beta were analysed in cultured fibroblasts from patients with known receptor defects, such as thermolability, decreased ligand binding affinity and low receptor expression levels, and from patients with a cortisol resistant phenotype but no detected receptor alteration. Fibroblasts from patients with GR defects expressed higher hsp90 beta mRNA levels as compared to patients with no receptor defects or to healthy controls. These data indicate that GR defects are associated with increased hsp90 beta mRNA levels.

Identification of a protein with homology to hsp90 that binds the type 1 tumor necrosis factor receptor

The yeast-based two hybrid has been used to identify a novel protein that binds to the intracellular domain of the type 1 receptor for tumor necrosis factor (TNFR-1IC). The TNF receptor-associated protein, TRAP-1, shows strong homology to members of the 90-kDa family of heat shock proteins. After in vitro transcription/translation and 35S labeling, TRAP-1 was precipitated using a fusion protein consisting of glutathione S-transferase and TNFR-1IC, showing that the two proteins directly interact. The ability of deletion mutants of TNFR-1 to interact with TRAP-1 was tested using the two hybrid system. This showed that the amino acid sequences that mediate binding are diffusely distributed outside of the domain in the C terminus of TNFR-1IC that signals cytotoxicity. The 2.4-kilobase TRAP-1 mRNA was variably expressed in skeletal muscle, liver, heart, brain, kidney, pancreas, lung, and placenta. TRAP-1 mRNA was also detected in each of eight different transformed cell lines. Identification of TRAP-1 may be an important step toward defining how TNFR-1, which does not contain protein tyrosine kinase activity, transmits its message to signal transduction pathways.

Stress-response (heat-shock) protein 90 expression in tumors of the central nervous system: an immunohistochemical study

This retrospective study deals with the expression of stress-response (heat-shock) protein 90 (srp 90) in a series of 148 human brain tumors. Immunohistochemical procedures were employed; cells of the human breast cancer line MCF7 exposed to hyperosmolar stress served as positive controls. Deposits of reaction products were found in the cytoplasm and they displayed a granular pattern. srp 90 was detected in 14/31 meningiomas and 5/10 breast cancer metastases to the brain. The protein was also present in 6/13 glioblastomas and 7/18 astrocytomas. In addition, a positive reaction was found in 2/10 medulloblastomas, 2/14 primitive neuroectodermal tumors, 1/11 pituitary tumor, 2/21 schwannomas and 2/11 lung tumor metastases; however, oligodendrogliomas and primary malignant lymphomas were not stained. The srp 90 was detected in Western blots of meningioma tissue homogenates. No significant immunohistochemical reaction was seen with sections of normal human cerebra, brain stem, cerebella, pituitary glands and spinal cords. These results document the expression of srp 90 by a variety of primary and metastatic intracranial tumors.

Isolation of chicken hsp90 beta gene promoter

In order to define the mechanisms responsible for the differential expression of chicken hsp90 alpha and beta genes, a portion of the chicken hsp90 beta genomic sequence, including 3081 bp upstream from the transcription initiation site and 2718 bp of structural gene sequence which covers 7 exons and 6 introns was investigated. The transcriptional initiation site was determined by primer extension, RNAase and S1 nuclease mapping, Northern blot and cloning of 5' end of cDNA. The first intron, as in other hsp90 genes, is located just before the ATG initiation codon. Three Sp1 sites are located near the TATA box. The apparent major divergence with the hsp90 alpha promoter is that, in the hsp90 beta promoter, the only CAAT box and HSE element are located at about 3 and 2 kb upstream the TATA box, respectively. These features may explain why chicken hsp90 beta mRNA is generally less abundant than alpha and is not inducible by heat shock or serum/growth factor stimulation.

Sequence, transcript characterization and polymorphisms of a Plasmodium falciparum gene belonging to the heat-shock protein (HSP) 90 family

A gene (pfhsp86) encoding a member of the heat-shock protein 90 (HSP90) family has been isolated from Plasmodium falciparum (Pf). The pfhsp86 coding region comprises two exons separated by an 0.8-kb intron with consensus splice junction sequences. The transcript itself is 3.4-kb long and includes a 0.65-kb 5'-untranslated region (UTR) and a 0.54-kb 3'-UTR. Upstream of the transcription start point (tsp) are putative promoter modules: an inverted CCAAT box, a G + C-rich sequence and several TATA sequences. Transcription is enhanced in in erythrocyte-stage parasites cultivated at elevated temperatures (2-3-fold at 39 degrees C and 3-4-fold at 41 degrees C). The pfhsp86 gene maps within a chromosome 7 segment that is linked to chloroquine (Cq) response in a Pf cross. The parents of this cross (Dd2, HB3) differ in the first exon by two trinucleotide repeats, while more divergence is apparent between the introns. These trinucleotide repeat differences are linked to Cq response in the HB3 x Dd2 cross, but they did not predict Cq response in nine Pf lines from different locations.

A role for Hsp90 in cell cycle control: Wee1 tyrosine kinase activity requires interaction with Hsp90

Wee1 protein kinase regulates the length of G2 phase by carrying out the inhibitory tyrosyl phosphorylation of Cdc2-cyclin B kinase. Mutations were isolated that suppressed the G2 cell cycle arrest caused by overproduction of Wee1. One class of swo (suppressor of wee1 overproduction) mutation, exemplified by swo1-26, also caused a temperature sensitive lethal phenotype in a wee1+ background. The swo1+ gene encodes a member of the Hsp90 family of stress proteins. Swo1 is essential for viability at all temperatures. Swo1 coimmunoprecipitates with Wee1, showing that the two proteins interact. The swo1-26 mutant undergoes premature mitosis when grown at a semi-permissive temperature. These data strongly indicate that formation of active Wee1 tyrosine kinase requires interaction with Swo1, perhaps in a manner analogous to the previously demonstrated interaction between Hsp90 and v-src tyrosine kinase. These observations demonstrate a unexpected role for Hsp90 in cell cycle control.

Constitutive expression of heat shock protein 90 (HSP90) in neurons of the rat brain

Immunoblot analysis, immunocytochemistry and immuno-electron microscopy were employed to study the expression of HSP90 protein in the adult rat brain, using a specific polyclonal antiserum. Immunoblot analysis demonstrated equal levels of HSP90 in microdissected extracts from hippocampus, cortex, striatum and cerebellum. Immunocytochemistry and immuno-electron microscopy provided evidence that HSP90 is markedly expressed throughout all neuronal subpopulations of the CNS but not in non-neuronal cells except ependyma and choroid plexus. At the ultrastructural level, HSP90 immunoreactivity was predominantly found in perikarya but to a lesser extent also in dendrites and nuclei. The constitutive expression of HSP90 in widespread neuronal cell populations suggests a functional role in the physiological molecular program of CNS neurons.

Sequence and expression of a 90-kilodalton heat-shock protein family member of Theileria parva

A Theileria parva specific full-length cDNA clone, T7, which encodes a protein with more than 60% homology to heat shock protein 90 (hsp90) of other organisms, has been identified. T7 appears to be a single copy gene. The gene is expressed as a protein of 87 kDa in both the sporozoite and schizont stages of T. parva. The protein was not found in the piroplasm stage, although the corresponding transcript was detected, suggesting post-transcriptional regulation of the gene. In the schizont stage the T7 protein is upregulated upon heat shock and localized in the cytoplasm.

Analysis of tissue-specific expression of Arabidopsis thaliana HSP90-family gene HSP81

We have isolated three HSP90-family genes from Arabidopsis: HSP81-1 which is heat-inducible, and HSP81-2 and -3 which are highly expressed under normal growth temperatures. Northern blot analysis and RNase protection analysis, using gene specific probes, showed that HSP81-2 and -3 mRNA were present in all tissues and abundant in roots, floral bud clusters, and flowers at 22 degrees C. A small amount of HSP81-1 mRNA was detected only in roots. In situ hybridization and histochemical analysis using transgenic plants carrying chimeric gene fusions, with an HSP81 promoter region fused to a beta-glucuronidase (GUS) gene, confirmed these results. At 22 degrees C, high GUS activity was observed in the root apical meristems, pollen and tapeta in HSP81-2::GUS and HSP81-3::GUS transgenic plants, while only branches of the root in HSP81-1::GUS transgenic plants expressed high GUS activity. After 2 hours of 35 degrees C treatment, extensively high GUS activity was observed in all tissues in HSP81-1::GUS transgenic plants, while elevated but tissue specific expression was observed in HSP81-2 and -3 transgenic plants. Exogenous application of various chemicals such as ABA, GA3, kinetin, IAA, NaCl, and mannitol revealed that 10 mM IAA and 0.1 M NaCl significantly enhanced the accumulation of HSP81-2 and -3 transcripts. Only a slight response to IAA was observed in HSP81-1 mRNA accumulation at 22 degrees C; the increase was possibly caused by a novel pathway other than heat-shock-response pathway.

HSP 90 alpha and HSP 90 beta genes are present in the zebrafish and are differentially regulated in developing embryos

We have employed a polymerase chain reaction-based cloning strategy to demonstrate that both hsp 90 alpha and hsp 90 beta genes are present in the zebrafish. The fact that zebrafish represents the most primitive vertebrate in which hsp 90 genes have been isolated to date has allowed us to determine that the duplication event which generated the hsp 90 alpha and hsp 90 beta genes occurred shortly before the emergence of the teleosts from the rest of the vertebrate lineage. In expression studies using Northern blot analysis, hsp 90 beta mRNA was found to be present at control temperatures throughout normal embryonic development whereas hsp 90 alpha mRNA was barely detectable. Upon heat shock, hsp 90 alpha mRNA levels increased dramatically in all developmental stages examined. The levels of hsp 90 beta mRNA increased 2-3 fold during heat shock of early stage embryos. Thus, the hsp 90 alpha gene is strongly upregulated during heat shock in zebrafish embryos whereas expression of the hsp 90 beta gene appears to be weakly induced.

Molecular characterization of the heat shock protein 90 gene of the human malaria parasite Plasmodium falciparum

We report here the nucleotide sequence of hsp90 (heat shock protein 90) of Plasmodium falciparum. Computer analysis of the deduced protein sequence revealed an unusually large region of charged amino acids when compared to hsp90 from other species. This region shows striking homology to the calcium binding domain of calreticulin, the major calcium binding protein of endoplasmic reticulum. Phylogenetic tree analysis indicates that P. falciparum hsp90 is more closely related to hsp90 from plants than to hsp90 from vertebrates or other parasites. The malaria hsp90 is an ATP binding protein encoded by a single gene constitutively expressed in both asexual (trophozoite) and sexual (gametocyte) stage parasites. The hsp90 protein is homologous to a previously identified 90-kDa antigen strongly recognised by both sera from vaccinated monkeys and monoclonal antibody XIV/7.

Regulation of HSP90 and corticosteroid receptor mRNA by corticosterone levels in vivo

The non-activated 9S forms of several steroid hormone receptors are heterooligomeric complexes consisting of the aporeceptor and three heat shock proteins, hsp90, hsp70 and hsp56. Hsp90 appears to play a facilitatory role in high-affinity steroid binding and to promote the efficacy of steroid actions on target tissues. Circulating glucocorticoid levels have a major regulatory impact on the binding capacity of hippocampal and hypothalamic corticosteroid receptors, a phenomenon that affects the activity of the hypothalamic-pituitary-adrenal axis and neuronal excitability in general. This study demonstrates that hsp90 mRNA is present in substantial amounts in hippocampal and hypothalamic areas characterized by high densities of corticosteroid receptors, and in the thymus. Steady-state levels of hsp90 mRNA in these regions were altered by chronic changes of circulating glucocorticoid concentrations in a site-specific fashion. In the hippocampus, mRNAs coding for hsp90 and both types of corticosteroid receptors (type I, MR and type II, GR) displayed a coordinate increase following adrenalectomy and castration (ADX/GX); in the hypothalamus only hsp90 mRNA levels were elevated, and none of the parameters studied was affected in the thymus by steroid hormone deprivation. Supplementation of ADX/GX rats with various doses of corticosterone in vivo elicited differential responses. Moderate elevation of circulating corticosterone levels normalized ADX/GX-increased hsp90 mRNA concentrations in the hippocampus and the hypothalamic paraventricular nucleus (PVN); this was associated with similar changes in GR and MR mRNA levels in the hippocampus, while GR mRNA concentrations in the PVN were not altered.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of hsp90 in SLE

The heat shock proteins are a group of evolutionarily conserved proteins with important physiological functions, whose synthesis is enhanced by elevated temperature or other stresses. A role for one or more of these proteins in human autoimmune disease has been extensively discussed. This review considers the evidence of a role for hsp90 in systemic lupus erythematosus (SLE) where overexpression of this protein, its surface localization and auto-antibodies to it have been observed in both human patients and in the MRL/lpr mouse model of SLE.