Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
Mol Endocrinol 1998 Mar
PMID:Analysis of FKBP51/FKBP52 chimeras and mutants for Hsp90 binding and association with progesterone receptor complexes. 951 52

The modulation of the chaperone activity of the heat shock cognate Hsc70 protein in mammalian cells involves cooperation with chaperone cofactors, such as Hsp40; BAG-1; the Hsc70-interacting protein, Hip; and the Hsc70-Hsp90-organizing protein, Hop. By employing the yeast two-hybrid system and in vitro interaction assays, we have provided insight into the structural basis that underlies Hsc70's cooperation with different cofactors. The carboxy-terminal domain of Hsc70, previously shown to form a lid over the peptide binding pocket of the chaperone protein, mediates the interaction of Hsc70 with Hsp40 and Hop. Remarkably, the two cofactors bind to the carboxy terminus of Hsc70 in a noncompetitive manner, revealing the existence of distinct binding sites for Hsp40 and Hop within this domain. In contrast, Hip interacts exclusively with the amino-terminal ATPase domain of Hsc70. Hence, Hsc70 possesses separate nonoverlapping binding sites for Hsp40, Hip, and Hop. This appears to enable the chaperone protein to cooperate simultaneously with multiple cofactors. On the other hand, BAG-1 and Hip have recently been shown to compete in binding to the ATPase domain. Our data thus establish the existence of a network of cooperating and competing cofactors regulating the chaperone activity of Hsc70 in the mammalian cell.
Mol Cell Biol 1998 Apr
PMID:The carboxy-terminal domain of Hsc70 provides binding sites for a distinct set of chaperone cofactors. 952 74

The ubiquitous molecular chaperone Hsp90 acts in concert with a cohort of associated proteins to facilitate the functional maturation of a number of cellular signaling proteins, such as steroid hormone receptors and oncogene tyrosine kinases. The Hsp90-associated protein p23 is required for the assembly of functional steroid aporeceptor complexes in cell lysates, and Hsp90-binding ansamycin antibiotics disrupt the activity of Hsp90-dependent signaling proteins in cultured mammalian cells and prevent the association of p23 with Hsp90-receptor heterocomplexes; these observations have led to the hypotheses that p23 is required for the maturation of Hsp90 target proteins and that ansamycin antibiotics abrogate the activity of such proteins by disrupting the interaction of p23 with Hsp90. In this study, I demonstrate that ansamycin antibiotics disrupt the function of Hsp90 target proteins expressed in yeast cells; prevent the assembly of Sba1, a yeast p23-like protein, into steroid receptor-Hsp90 complexes; and result in the assembly of receptor-Hsp90 complexes that are defective for ligand binding. To assess the role of p23 in Hsp90 target protein function, I show that the activity of Hsp90 target proteins is unaffected by deletion of SBA1. Interestingly, steroid receptor activity in cells lacking Sba1 displays increased sensitivity to ansamycin antibiotics, and this phenotype is rescued by the expression of human p23 in yeast cells. These findings indicate that Hsp90-dependent signaling proteins can achieve a functional conformation in vivo in the absence of p23. Furthermore, while the presence of p23 decreases the sensitivity of Hsp90-dependent processes to ansamycin treatment, ansamycin antibiotics disrupt signaling through some mechanism other than altering the Hsp90-p23 interaction.
Mol Cell Biol 1998 Jun
PMID:Genetic and biochemical analysis of p23 and ansamycin antibiotics in the function of Hsp90-dependent signaling proteins. 958 73

The in vivo interaction of estrogen receptor (ER) and Hsp90, demonstrated in the absence of hormone by a nuclear cotranslocation assay of the cytoplasmic Hsp90 with the karyophilic receptor, was disrupted by agonist and antagonist ligands, which, after dissociating the Hsp90, allowed the chaperone protein to be relocalized in the cytoplasm. The pure antiestrogen RU 58668 (RU), which was unable to stimulate an estrogen-dependent reporter gene and completely inhibited its estradiol-induced activity, also profoundly modified the subcellular distribution of ER in a specific time- and dose-dependent manner; ER appeared as speckled fluorescent clusters mainly located in the perinuclear region of the cytoplasm. The kinetics of appearance and reversal of the RU-dependent ER mislocalization in the presence or absence of cycloheximide demonstrated 1) that this effect was reversed by RU withdrawal or estradiol (E2) treatment, and 2) that cycloheximide with RU inhibited and reversed the ER cytoplasmic mislocalization induced by RU alone. These results point to a protein synthesis-dependent step in the mechanism of action of this antiestrogen. After RU treatment, a large portion of ER was found in the particulate fraction of the cytoplasm. However, confocal and electron microscopic analysis showed that ER clusters were not associated with specific cytoplasmic organelles or compartments. Using ER mutants, it was found that the ligand binding domain was sufficient for RU to produce receptor mislocalization, while the constitutive nuclear localization signals were dispensable. We propose that the antiestrogenic properties of RU are primarily due to the induction of an aggregation-prone receptor conformation that cannot undertake the constitutive and the ligand-induced nuclear localization function of the receptor because it is sequestered in the cytoplasm by fast turning over protein(s). We predict that antiestrogens able to block ER nuclear localization will behave as pure antihormones and will inhibit all the nuclear action of ER elicited by agonistic ligands or by ligand-independent mechanisms such as growth factor stimulation.
Mol Endocrinol 1998 Jun
PMID:Interaction and dissociation by ligands of estrogen receptor and Hsp90: the antiestrogen RU 58668 induces a protein synthesis-dependent clustering of the receptor in the cytoplasm. 962 60

The Saccharomyces cerevisiae SBA1 gene was cloned by PCR amplification from yeast genomic DNA following its identification as encoding an ortholog of human p23, an Hsp90 cochaperone. The SBA1 gene product is constitutively expressed and nonessential, although a disruption mutant grew more slowly than the wild type at both 18 and 37 degreesC. A double deletion of SBA1 and STI1, encoding an Hsp90 cochaperone, displayed synthetic growth defects. Affinity isolation of histidine-tagged Sba1p (Sba1(His6)) after expression in yeast led to coisolation of Hsp90 and the cyclophilin homolog Cpr6. Using an in vitro assembly assay, purified Sba1(His6) bound to Hsp90 only in the presence of adenosine 5'-O-(3-thiotriphosphate) or adenyl-imidodiphosphate. Furthermore, interaction between purified Sba1(His6) and Hsp90 in yeast extracts was inhibited by the benzoquinoid ansamycins geldanamycin and macbecin. The in vitro assay was also used to identify residues in Hsp90 that are important for complex formation with Sba1(His6), and residues in both the N-terminal nucleotide binding domain and C-terminal half were characterized. In vivo analysis of known Hsp90 substrate proteins revealed that Sba1 loss of function had only a mild effect on the activity of the tyrosine kinase v-Src and steroid hormone receptors.
Mol Cell Biol 1998 Jul
PMID:SBA1 encodes a yeast hsp90 cochaperone that is homologous to vertebrate p23 proteins. 963 55

Cyclophilins are cis-trans-peptidyl-prolyl isomerases that bind to and are inhibited by the immunosuppressant cyclosporin A (CsA). The toxic effects of CsA are mediated by the 18-kDa cyclophilin A protein. A larger cyclophilin of 40 kDa, cyclophilin 40, is a component of Hsp90-steroid receptor complexes and contains two domains, an amino-terminal prolyl isomerase domain and a carboxy-terminal tetratricopeptide repeat (TPR) domain. There are two cyclophilin 40 homologs in the yeast Saccharomyces cerevisiae, encoded by the CPR6 and CPR7 genes. Yeast strains lacking the Cpr7 enzyme are viable but exhibit a slow-growth phenotype. In addition, we show here that cpr7 mutant strains are hypersensitive to the Hsp90 inhibitor geldanamycin. When overexpressed, the TPR domain of Cpr7 alone complements both cpr7 mutant phenotypes, while overexpression of the cyclophilin domain of Cpr7, full-length Cpr6, or human cyclophilin 40 does not. The open reading frame YBR155w, which has moderate identity to the yeast p60 homolog STI1, was isolated as a high-copy-number suppressor of the cpr7 slow-growth phenotype. We show that this Sti1 homolog Cns1 (cyclophilin seven suppressor) is constitutively expressed, essential, and found in protein complexes with both yeast Hsp90 and Cpr7 but not with Cpr6. Cyclosporin A inhibited Cpr7 interactions with Cns1 but not with Hsp90. In summary, our findings identify a novel component of the Hsp90 chaperone complex that shares function with cyclophilin 40 and provide evidence that there are functional differences between two conserved sets of Hsp90 binding proteins in yeast.
Mol Cell Biol 1998 Dec
PMID:CNS1 encodes an essential p60/Sti1 homolog in Saccharomyces cerevisiae that suppresses cyclophilin 40 mutations and interacts with Hsp90. 981 21

Saccharomyces cerevisiae harbors two cyclophilin 40-type enzymes, Cpr6 and Cpr7, which are components of the Hsp90 molecular chaperone machinery. Cpr7 is required for normal growth and is required for maximal activity of heterologous Hsp90-dependent substrates, including glucocorticoid receptor (GR) and the oncogenic tyrosine kinase pp60(v-src). In addition, it has recently been shown that Cpr7 plays a major role in negative regulation of the S. cerevisiae heat shock transcription factor (HSF). To better understand functions associated with Cpr7, a search was undertaken for multicopy suppressors of the cpr7Delta slow-growth phenotype. The screen identified a single gene, designated CNS1 (for cyclophilin seven suppressor), capable of suppressing the cpr7Delta growth defect. Overexpression of CNS1 in cpr7Delta cells also largely restored GR activity and negative regulation of HSF. In vitro protein retention experiments in which Hsp90 heterocomplexes were precipitated resulted in coprecipitation of Cns1. Interaction between Cns1 and the carboxy terminus of Hsp90 was also shown by two-hybrid analysis. The functional consequences of CNS1 overexpression and its physical association with the Hsp90 machinery indicate that Cns1 is a previously unidentified component of molecular chaperone complexes. Thus far, Cns1 is the only tetratricopeptide repeat-containing component of Hsp90 heterocomplexes found to be essential for cell viability under all conditions tested.
Mol Cell Biol 1998 Dec
PMID:Cns1 is an essential protein associated with the hsp90 chaperone complex in Saccharomyces cerevisiae that can restore cyclophilin 40-dependent functions in cpr7Delta cells. 981 22

Gene expression in response to heat shock is mediated by the heat shock transcription factor (HSF), which in yeast harbors both amino- and carboxyl-terminal transcriptional activation domains. Yeast cells bearing a truncated form of HSF in which the carboxyl-terminal transcriptional activation domain has been deleted [HSF(1-583)] are temperature sensitive for growth at 37 degreesC, demonstrating a requirement for this domain for sustained viability during thermal stress. Here we demonstrate that HSF(1-583) cells undergo reversible cell cycle arrest at 37 degreesC in the G2/M phase of the cell cycle and exhibit marked reduction in levels of the molecular chaperone Hsp90. As in higher eukaryotes, yeast possesses two nearly identical isoforms of Hsp90: one constitutively expressed and one highly heat inducible. When expressed at physiological levels in HSF(1-583) cells, the inducible Hsp90 isoform encoded by HSP82 more efficiently suppressed the temperature sensitivity of this strain than the constitutively expressed gene HSC82, suggesting that different functional roles may exist for these chaperones. Consistent with a defect in Hsp90 production, HSF(1-583) cells also exhibited hypersensitivity to the Hsp90-binding ansamycin antibiotic geldanamycin. Depletion of Hsp90 from yeast cells wild type for HSF results in cell cycle arrest in both G1/S and G2/M phases, suggesting a complex requirement for chaperone function in mitotic division during stress.
Mol Cell Biol 1999 Jan
PMID:A trans-activation domain in yeast heat shock transcription factor is essential for cell cycle progression during stress. 985 64

The influence of whole body hyperthermic stress (41 degrees C, 15 min) on association of the glucocorticoid receptor (GR) with heat shock proteins Hsp90 and Hsp70 was followed in rat liver cytosol during a 24 h period after the stress. Total cytosolic concentration of the GR, Hsp90 and Hsp70 and the amounts of Hsp90 and Hsp70 co-immunopurified with the GR were determined by a quantitative Western blotting using appropriate monoclonal antibodies. A significant decrease in the cytosolic GR level in response to the stress was noticed. The ratio of the amount of the GR to Hsp90 recruited by the GR was found to be unaltered by hyperthermia, in spite of the stress-induced increase in the total Hsp90 concentration in the cytosol. Hsp70 was also found in association with the GR and its 2.5-fold induction by the stress was accompanied by about 3-fold increase in its relative amount that co-immunopurified with the GR. The results suggest that heat stress influences the interaction of the GR with Hsp70 through the mechanisms controlling the untransformed rat liver GR heterocomplexes assembly process.
J Steroid Biochem Mol Biol 1998 Nov
PMID:Association of the rat liver glucocorticoid receptor with Hsp90 and Hsp70 upon whole body hyperthermic stress. 988 88

The maintenance of [PSI], a prion-like form of the yeast release factor Sup35, requires a specific concentration of the chaperone protein Hsp104: either deletion or overexpression of Hsp104 will cure cells of [PSI]. A major puzzle of these studies was that overexpression of Hsp104 alone, from a heterologous promoter, cures cells of [PSI] very efficiently, yet the natural induction of Hsp104 with heat shock, stationary-phase growth, or sporulation does not. These observations pointed to a mechanism for protecting the genetic information carried by the [PSI] element from vicissitudes of the environment. Here, we show that simultaneous overexpression of Ssa1, a protein of the Hsp70 family, protects [PSI] from curing by overexpression of Hsp104. Ssa1 protein belongs to the Ssa subfamily, members of which are normally induced with Hsp104 during heat shock, stationary-phase growth, and sporulation. At the molecular level, excess Ssa1 prevents a shift of Sup35 protein from the insoluble (prion) to the soluble (cellular) state in the presence of excess Hsp104. Overexpression of Ssa1 also increases nonsense suppression by [PSI] when Hsp104 is expressed at its normal level. In contrast, hsp104 deletion strains lose [PSI] even in the presence of overproduced Ssa1. Overproduction of the unrelated chaperone protein Hsp82 (Hsp90) neither cured [PSI] nor antagonized the [PSI]-curing effect of overproduced Hsp104. Our results suggest it is the interplay between Hsp104 and Hsp70 that allows the maintenance of [PSI] under natural growth conditions.
Mol Cell Biol 1999 Feb
PMID:Antagonistic interactions between yeast chaperones Hsp104 and Hsp70 in prion curing. 989 Oct 66


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