Association of the transforming proteins of Rous, Fujinami, and Y73 avian sarcoma viruses with the same two cellular proteins

The Chemical Biology of Molecular Chaperones--Implications for Modulation of Proteostasis

Protein homeostasis (proteostasis) is inextricably tied to cellular health and organismal lifespan. Aging, exposure to physiological and environmental stress, and expression of mutant and metastable proteins can cause an imbalance in the protein-folding landscape, which results in the formation of non-native protein aggregates that challenge the capacity of the proteostasis network (PN), increasing the risk for diseases associated with misfolding, aggregation, and aberrant regulation of cell stress responses. Molecular chaperones have central roles in each of the arms of the PN (protein synthesis, folding, disaggregation, and degradation), leading to the proposal that modulation of chaperone function could have therapeutic benefits for the large and growing family of diseases of protein conformation including neurodegeneration, metabolic diseases, and cancer. In this review, we will discuss the current strategies used to tune the PN through targeting molecular chaperones and assess the potential of the chemical biology of proteostasis.

Hsp90 rescues PTK6 from proteasomal degradation in breast cancer cells

PTK6 [protein tyrosine kinase 6; also known as Brk (breast tumour kinase)] is a non-receptor tyrosine kinase, closely related to Src, but evolutionarily distinct, that is up-regulated in various cancers, including breast cancer. Hsp90 (heat-shock protein 90) was identified as a PTK6-interacting protein in HEK (human embryonic kidney)-293 cells overexpressing PTK6. Hsp90 interacted with the PTK6 tyrosine kinase catalytic domain, but catalytic activity was not required for the interaction. Geldanamycin, an Hsp90 inhibitor, significantly decreased the PTK6 protein level through proteasome-dependent degradation, but did not affect the level of Src. Geldanamycin treatment also decreased phosphorylation of PTK6 substrates due to reduced amounts of PTK6. Moreover, overexpression of CHIP [C-terminus of Hsc70 (heat-shock cognate 70)-interacting protein], a chaperone-dependent E3 ligase, enhanced proteosomal degradation of PTK6. Geldanamycin increased the interaction of PTK6 with CHIP, but decreased the interaction of PTK6 with Hsp90. We also found that endogenous PTK6 associated with Hsp90 and geldanamycin decreased expression of endogenous PTK6 in breast carcinoma cells. Finally, we report that silencing endogenous CHIP expression in breast carcinoma cells inhibited geldanamycin-induced PTK6 reduction. These results demonstrate that Hsp90 plays an essential role in regulating PTK6 stability and suggest that Hsp90 inhibitors may be useful as therapeutic drugs for PTK6-positive cancers, including breast cancer.

HSP90 at the hub of protein homeostasis: emerging mechanistic insights

Heat shock protein 90 (HSP90) is a highly conserved molecular chaperone that facilitates the maturation of a wide range of proteins (known as clients). Clients are enriched in signal transducers, including kinases and transcription factors. Therefore, HSP90 regulates diverse cellular functions and exerts marked effects on normal biology, disease and evolutionary processes. Recent structural and functional analyses have provided new insights on the transcriptional and biochemical regulation of HSP90 and the structural dynamics it uses to act on a diverse client repertoire. Comprehensive understanding of how HSP90 functions promises not only to provide new avenues for therapeutic intervention, but to shed light on fundamental biological questions.

Chaperones in cell cycle regulation and mitogenic signal transduction: a review

Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).

Hsp70 and Hsp90--a relay team for protein folding

Molecular chaperones are a functionally defined set of proteins which assist the structure formation of proteins in vivo. Without certain protective mechanisms, such as binding nascent polypeptide chains by molecular chaperones, cellular protein concentrations would lead to misfolding and aggregation. In the mammalian system, the molecular chaperones Hsp70 and Hsp90 are involved in the folding and maturation of key regulatory proteins, like steroid hormone receptors, transcription factors, and kinases, some of which are involved in cancer progression. Hsp70 and Hsp90 form a multichaperone complex, in which both are connected by a third protein called Hop. The connection of and the interplay between the two chaperone machineries is of crucial importance for cell viability. This review provides a detailed view of the Hsp70 and Hsp90 machineries, their cofactors and their mode of regulation. It summarizes the current knowledge in the field, including the ATP-dependent regulation of the Hsp70/Hsp90 multichaperone cycle and elucidates the complex interplay and their synergistic interaction.

Regulation of signaling protein function and trafficking by the hsp90/hsp70-based chaperone machinery

Nearly 100 proteins are known to be regulated by hsp90. Most of these substrates or "client proteins" are involved in signal transduction, and they are brought into complex with hsp90 by a multiprotein hsp90/hsp70-based chaperone machinery. In addition to binding substrate proteins at the chaperone site(s), hsp90 binds cofactors at other sites that are part of the heterocomplex assembly machinery as well as immunophilins that connect assembled substrate*hsp90 complexes to protein-trafficking systems. In the 5 years since we last reviewed this subject, much has been learned about hsp90 structure, nucleotide-binding, and cochaperone interactions; the most important concept is that ATP hydrolysis by an intrinsic ATPase activity results in a conformational change in hsp90 that is required to induce conformational change in a substrate protein. The conformational change induced in steroid receptors is an opening of the steroid-binding cleft so that it can be accessed by steroid. We have now developed a minimal system of five purified proteins-hsp90, hsp70, Hop, hsp40, and p23- that assembles stable receptor*hsp90 heterocomplexes. An hsp90*Hop*hsp70*hsp40 complex opens the cleft in an ATP-dependent process to produce a receptor*hsp90 heterocomplex with hsp90 in its ATP-bound conformation, and p23 then interacts with the hsp90 to stabilize the complex. Stepwise assembly experiments have shown that hsp70 and hsp40 first interact with the receptor in an ATP-dependent reaction to produce a receptor*hsp70*hsp40 complex that is "primed" to be activated to the steroid-binding state in a second ATP-dependent step with hsp90, Hop, and p23. Successful use of the five-protein system with other substrates indicates that it can assemble signal protein*hsp90 heterocomplexes whether the substrate is a receptor, a protein kinase, or a transcription factor. This purified system should facilitate understanding of how eukaryotic hsp70 and hsp90 work together as essential components of a process that alters the conformations of substrate proteins to states that respond in signal transduction.

Hsp90: chaperoning signal transduction

Hsp90 is an ATP dependent molecular chaperone involved in the folding and activation of an unknown number of substrate proteins. These substrate proteins include protein kinases and transcription factors. Consistent with this task, Hsp90 is an essential protein in all eucaryotes. The interaction of Hsp90 with its substrate proteins involves the transient formation of multiprotein complexes with a set of highly conserved partner proteins. The specific function of each component in the processing of substrates is still unknown. Large ATP-dependent conformational changes of Hsp90 occur during the hydrolysis reaction and these changes are thought to drive the chaperone cycle. Natural inhibitors of the ATPase activity, like geldanamycin and radicicol, block the processing of Hsp90 substrate proteins. As many of these substrates are critical elements in signal transduction, Hsp90 seems to introduce an additional level of regulation.

A model for the cytoplasmic trafficking of signalling proteins involving the hsp90-binding immunophilins and p50cdc37

A number of transcription factors and protein kinases involved in signal transduction exist in heterocomplexes with the ubiquitous and essential protein chaperone hsp90. These signalling protein x hsp90 heterocomplexes are assembled by a multiprotein chaperone system comprising hsp90, hsp70, Hop, hsp40, and p23. In the case of transcription factors, the heterocomplexes with hsp90 also contain a high molecular weight immunophilin with tetratricopeptide repeat (TPR) motifs, such as FKBP52 or CyP-40. In the case of the protein kinases, the heterocomplexes contain p50cdc37. The immunophilins bind to a single TPR acceptor site on hsp90, and p50cdc37 binds to an adjacent site so that binding is exclusive for p50cdc37 or an immunophilin. Direct interaction of immunophilins with the transcription factors or p50cdc37 with the protein kinases leads to selection of different heterocomplexes after their assembly by a common mechanism. Studies with the glucocorticoid receptor, for which translocation from the cytoplasm to the nucleus is under hormonal control, suggest that dynamic assembly of the heterocomplexes is required for rapid movement of the receptor through the cytoplasm along cytoskeletal tracts. As for the similar short-range trafficking of vesicles along microtubules, there must be a mechanism for linking the signalling protein solutes to the molecular motors involved in movement. We present here a model in which the immunophilins and p50cdc37 target, respectively, the retrograde or anterograde direction of signalling protein movement by functioning as connectors that link the signalling proteins to the movement machinery.

Hsp90 as an anti-cancer target

Heat shock protein 90 is one of the most abundant cellular proteins. Although its functions are still being characterized, it appears to serve as a chaperone for a growing list of cell signaling proteins, including many tyrosine and serine/threonine kinases, involved in cell proliferation and/or survival. The recent discovery of natural products which are able to inhibit Hsp90 function have allowed for both identification of its client proteins and for a better understanding of its role in their activity. Accumulating data have suggested that targeting Hsp90 in cancer cells may be of clinical benefit. Copyright 1999 Harcourt Publishers Ltd.

The 90-kDa molecular chaperone family: structure, function, and clinical applications. A comprehensive review

The 90-kDa molecular chaperone family (which comprises, among other proteins, the 90-kDa heat-shock protein, hsp90 and the 94-kDa glucose-regulated protein, grp94, major molecular chaperones of the cytosol and of the endoplasmic reticulum, respectively) has become an increasingly active subject of research in the past couple of years. These ubiquitous, well-conserved proteins account for 1-2% of all cellular proteins in most cells. However, their precise function is still far from being elucidated. Their involvement in the aetiology of several autoimmune diseases, in various infections, in recognition of malignant cells, and in antigen-presentation already demonstrates the essential role they likely will play in clinical practice of the next decade. The present review summarizes our current knowledge about the cellular functions, expression, and clinical implications of the 90-kDa molecular chaperone family and some approaches for future research.

Steroid receptor interactions with heat shock protein and immunophilin chaperones

We have provided a historical perspective on a body of steroid receptor research dealing with the structure and physiological significance of the untransformed 9S receptor that has often confused both novice and expert investigators. The frequent controversies and equivocations of earlier studies were due to the fact that the native, hormone-free state of these receptors is a large multiprotein complex that resisted description for many years because of its unstable and dynamic nature. The untransformed 9S state of the steroid and dioxin receptors has provided a unique system for studying the function of the ubiquitous, abundant, and conserved heat shock protein, hsp90. The hormonal control of receptor association with hsp90 provided a method of manipulating the receptor heterocomplex in a manner that was physiologically meaningful. For several steroid receptors, binding to hsp90 was required for the receptor to be in a native hormone-binding state, and for all of the receptors, hormone binding promoted dissociation of the receptor from hsp90 and conversion of the receptor to the DNA-binding state. Although the complexes between tyrosine kinases and hsp90 were discovered earlier, the hormonal regulation or steroid receptor association with hsp90 permitted much more rapid and facile study of hsp90 function. The observations that hsp90 binds to the receptors through their HBDs and that these domains can be fused to structurally different proteins bringing their function under hormonal control provided a powerful linkage between the hormonal regulation of receptor binding to hsp90 and the initial step in steroid hormone action. Because the 9S receptor hsp90 heterocomplexes could be physically stabilized by molybdate, their protein composition could be readily studied, and it became clear that these complexes are multiprotein structures containing a number of unique proteins, such as FKBP51, FKBP52, CyP-40, and p23, that were discovered because of their presence in these structures. Further analysis showed that hsp90 itself exists in a variety of native multiprotein heterocomplexes independent of steroid receptors and other 'substrate' proteins. Cell-free systems can now be used to study the formation of receptor heterocomplexes. As we outlined in the scheme of Fig. 1, the multicomponent receptor-hsp90 heterocomplex assembly system is being reconstituted, and the importance of individual proteins, such as hsp70, p60, and p23, in the assembly process is becoming recognized. It should be noted that our understanding of the mechanism and purpose of steroid receptor heterocomplex assembly is still at an early stage. We can now speculate on the roles of receptor-associated proteins in receptor action, both as individuals and as a group, but their actual functions are still vague or unknown. We can make realistic models about the chaperoning and trafficking of steroid receptors, but we don't yet know how these processes occur, we don't know where chaperoning occurs in the cell (e.g. Is it limited to the cytoplasm? Is it a diffuse process or does chaperoning occur in association with structural elements?), and, with the exception of the requirement for hormone binding, we don't know the extent to which the hsp90-based chaperone system impacts on steroid hormone action. It is not yet clear how far the discovery of this hsp90 heterocomplex assembly system will be extended to the development of a general understanding of protein processing in the cell. Because this assembly system is apparently present in all eukaryotic cells, it probably performs an essential function for many proteins. The bacterial homolog of hsp90 is not an essential protein, but hsp90 is essential in eukaryotes, and recent studies indicate that the development of the cell nucleus from prokaryotic progenitors was accompanied by the duplication of genes for hsp90 and hsp70 (698). (ABSTRACT TRUNCATED)

Cdc37: a protein kinase chaperone?

The activity of most protein kinases is highly regulated, typically via phosphorylation and/or subunit association. However, the folding of protein kinases into an active state or a form capable of activation is now emerging as another important step through which they can be regulated. The 50-kDa protein Cdc37 and the associated heat-shock protein Hsp90 have been found to bind to, and be required for the activity of, diverse protein kinases, including Cdk4, v-Src, Raf and SEVENLESS. Together, Cdc37 and Hsp90 may act as a general chaperone for protein kinases, in particular those involved in signal-transduction pathways and cell-cycle control.

The role of the hsp90-based chaperone system in signal transduction by nuclear receptors and receptors signaling via MAP kinase

The multicomponent heat-shock protein (hsp) 90-based chaperone system is an ubiquitous protein-folding system in the cytoplasm of eukaryotes. Several signal transduction systems utilize an interaction with hsp90 as an essential component of the signaling pathway. The steroid and dioxin receptors are bound to hsp90 through their hormone-binding domains, and several of them must be bound to hsp90 in order to have a ligand-binding site. The binding of ligands to these receptors promotes their dissociation from hsp90, an event that is the first step in their signaling pathways. Several protein kinases, including the Src and Raf components of the MAP kinase system, are also bound to hsp90. Genetic studies in yeast have demonstrated that hsp90 is required for normal signaling via steroid and dioxin receptors and for the activity of Src in vivo. The hsp90-based chaperone system has been reconstituted from purified components, permitting detailed analysis of the molecular basis of the chaperone's role in signal transduction.

Molecular chaperoning of steroid hormone receptors

The study of the large, unactivated form of steroid receptors has led to the discovery of an hsp90/hsp70-based multicomponent protein folding system(s). For steroid receptors, the hsp90 chaperone system determines both repression of transcriptional activity in the absence of hormone and the proper folding of the hormone binding domain to produce the steroid binding conformation. Like steroid receptors, a number of other regulators of transcription and some protein kinases are now known to be associated with hsp90. Given the abundance of the proteins comprising the hsp90 chaperone system and the apparent ubiquity of the system in the animal and plant kingdoms, this system is thought to serve a fundamental role for protein folding, function and possibly trafficking within the cytoplasm and nucleus. In this chapter, we discuss the work on steroid receptor heterocomplex composition that has led to the discovery of new chaperone proteins and we summarize the mechanistic information developed in cell-free studies of receptor heterocomplex assembly.

Evidence for aestivation specific proteins in Otala lactea

Changes in [35S]methionine protein labeling patterns were examined by following incorporation into the acid precipitate protein fraction of land snails, Otala lactea (Müller) (Pulmonata, Helicidae). Labeled proteins were analyzed by SDS polyacrylamide gel electrophoresis and isoelectric focusing columns. Snails in four different physiological states were compared: active controls, short term aestivating snails (injected and allowed to enter aestivation), long term aestivating snails (aestivated for 14 days, injected, and maintained in the aestivating state), and snails aroused after aestivation (aestivated, injected, and aroused). Protein associated radioactivity was measured over a 7 day time course post injection. Autoradiographic analysis of SDS-polyacrylamide gels showed increases in the radioactivity of four proteins: 91 kDa (hepatopancreas, day 1 in long term aestivating animals), 50 kDa (hepatopancreas, day 2 in short term aestivating snails), 70 kDa and 30 kDa (foot, day 2 in short term aestivating animals). Hepatopancreas and foot from day 1 long term aestivating and day 2 short term aestivating animals were also analyzed by isoelectric focusing columns. Several pH-specific differences were apparent when controls and aestivating animals were analyzed. In particular a peak of radioactivity was observed at pH 5.05 in 1 d long term aestivating hepatopancreas and at pH 4.30 in 2d short term aestivating animals. Several differences were noted in foot with no specific pattern emerging. SDS-polyacrylamide gel electrophoresis analysis of the hepatopancreas peaks showed the appearance of several bands with increased radioactivity, including the 91 kDa and 50 kDa proteins described above. These results suggest that O. lactea aestivation specific proteins may be involved in the transition to a depressed metabolic state.

Purification and phosphorylation of elongation factor-2 kinase from rabbit reticulocytes

Eukaryotic elongation-factor-2 kinase has been purified to homogeneity from rabbit reticulocytes through a seven-step procedure and has been identified as a protein with a molecular mass of approximately 103 kDa as judged by SDS/PAGE. A degradation product of about 95 kDa was also evident in some preparations. The activity of the purified kinase was completely dependent on calcium and calmodulin. The kinase rapidly underwent extensive autophosphorylation, incorporating 1 mol phosphate/mol within 1 min; 5 mol phosphate/mol were incorporated within 1 h. The autophosphorylation was Ca2+/calmodulin-dependent; phosphopeptide mapping revealed multiple phosphopeptides even after just 0.5 min of autophosphorylation, suggesting that a number of sites became rapidly phosphorylated. Autophosphorylation occurred on serine and threonine residues. Preincubation in the presence of Ca2+, Mg2+ and ATP produced a rapid 2-3-fold activation of the kinase and also induced partial Ca(2+)-independent activity. Preincubation in the absence of the ligands showed that all three were required for full activation and induction of Ca(2+)-independent activity.

A novel monoclonal anti-rabbit hsp90 antibody: usefulness for studies on hsp90-steroid receptor interaction

The M(r) 90,000 protein associated with steroid receptors in their non-transformed state has been identified as a heat shock protein (hsp90) but the relationship between hsp90 binding and receptor function is still poorly understood. In this work, we have obtained and characterized one monoclonal anti-rabbit hsp90 antibody (7C10), among more than 2000 wells plated. This antibody was able to complex both free and rabbit uterine progesterone receptor-associated hsp90 as demonstrated by sedimentation analysis on sucrose gradients. As assessed by ELISA, 7C10 displayed a high binding affinity for hsp90 (approximately 4 nM). A standardized and specific competitive binding assay was developed for accurate quantification of hsp90 in rabbit tissues including reticulocyte lysate. 7C10 also permitted immunolocalization of hsp90 in various rabbit tissues. In Western blot, the monoclonal antibody recognized a single polypeptide band of M(r) approximately 90,000 in crude or purified rabbit preparations but failed to cross-react with any other mammalian or avian hsp90. These findings suggest that hsp90, a highly conserved protein, is a weak immunogen and elicits a strict species specific immunological response. Owing to its high affinity and specificity for rabbit hsp90, the monoclonal antibody 7C10 was used for purification and total depletion of hsp90 from the reticulocyte lysate, an efficient system for in vitro receptor translation and reconstitution studies. Thus, 7C10 represents a new powerful tool to further investigate the importance of hsp90 in steroid hormone receptor function.

Mapping of the gene family for human heat-shock protein 90 alpha to chromosomes 1, 4, 11, and 14

The HSP90 family of heat-shock proteins (encoded by genes for HSP90 alpha and beta) constitutes one of the major groups of proteins that are synthesized at increased rates in response to heat and other forms of stress. We previously isolated two distinct cDNA clones for HSP90 alpha from human peripheral blood lymphocytes and from HeLa cells transfected with the adenovirus E1A gene, respectively. To determine the organization of this complex multigene family in the human genome, we used three complementary approaches: Southern analysis of a panel of human/hamster somatic cell hybrids, molecular cloning of the cosmid HSP90 alpha clones from libraries prepared with DNAs from human lymphoblastoid cells, and in situ hybridization to human chromosomes. We demonstrate here that nucleotide sequences that encode HSP90 alpha map to human chromosomes 1q21.2-q22, 4q35, 11p14.1-p14.2, and 14q32.3. The chromosomal mapping of the loci, HSPCAL1, HSPCAL2, HSPCAL3, HSPCAL4, and the characterization of the respective genes should facilitate clarification of the organization of this gene family and lead to a better understanding of the biological functions of the gene product.

Cellular HSP90 (HSP86) mRNA level and in vitro differentiation of mouse embryonal carcinoma (F9) cells

Treatment of mouse embryonal carcinoma (F9) cells with retinoic acid, an inducer of F9 cell differentiation, greatly increased the level of mRNA specific to one of the heat-shock proteins (HSP86). Experiments including the one employing differentiation-resistant mutant F9 cells suggested that the increase represents early molecular events associated with the embryonal differentiation. The increased HSP86 mRNA declined to the original level during further incubation. The presence of cyclic AMP, which stimulates conversion of the retinoic acid-induced primitive endoderm cells to parietal endoderm cells, prevented the decline. These results suggest that not only the elevation of HSP86 mRNA level represents early molecular events in F9 cell differentiation but also that sustaining the elevated level (by cyclic AMP) is associated with further differentiation of the embryonal cells.

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

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

Soluble and membrane-associated human low-affinity adenosine binding protein (adenotin): properties and homology with mammalian and avian stress proteins

A low-affinity adenosine binding protein has recently been distinguished from the adenosine A2 receptor and purified from human placental membranes. Soluble human placental extracts contain an adenosine binding activity that has properties similar to those of the membrane low-affinity adenosine binding protein. The binding protein was purified from soluble human placental extracts 134-fold to 89% purity with a Bmax of 2.5 nmol/mg. It comprises 0.7-0.9% of the soluble protein. The major purified soluble protein has a subunit molecular mass of 98 kDa and a Stokes radius identical with that of the membrane-bound adenosine binding protein. Competition analysis of the soluble protein revealed similar affinities and an identical potency order for displacement of 5'-(N-ethylcarbamoyl)[2,8-3H]adenosine ([3H]NECA) as follows: NECA greater than 2-chloroadenosine greater than adenosine greater than (R)-N6-(2-phenylisopropyl)adenosine. The soluble binding protein was more acidic than the membrane binding protein as revealed by a comparison of the elution properties during ion exchange chromatography. A second form of soluble adenosine binding activity comprised 17% of the major form and had a charge similar to that of the membrane binding protein, a smaller Stokes radius, and a subunit molecular mass of 74 kDa. Carbohydrate composition analysis revealed that the major soluble form has 4.3% carbohydrate by weight as compared to the membrane-associated form, which has 5.5% carbohydrate by weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and some properties of bovine brain 100 kDa heat shock protein

1. The 100 kDa protein was purified from bovine brains. 2. The antibody against the 100 kDa brain protein was prepared and was monospecific to the antigen. 3. The antibody cross-reacted with HeLa cell HSP100 (100 kDa heat shock protein). 4. The physicochemical, immunochemical properties and a partially amino acid sequence indicated that the 100 kDa protein was HSP100. 5. Peptide mapping using Staphylococcus aureus V8 protease showed a core peptide with 10 kDa molecular mass common to both HSP100 and HSP90. 6. The amino acid sequence of the 10 kDa fragment of the 100 kDa protein showed a high homology with that of human HSP90 (38-60); the difference was only two of 23 amino acid residues determined.

Heat shock induction of HSP 89 is regulated in cellular aging

Induction of heat shock proteins (HSPs) was evaluated as a function of age of the IMR-90 human diploid fibroblasts. Heat shock (42 degrees C) markedly increased the synthesis of proteins with apparent molecular weights of 98, 89, 72, 50, 42 and 25 KDa, with HSP 89 and 72 being most prominent. This heat shock induction of HSPs was inversely correlated to the population doubling level (PDL) of the cell cultures used. For example, the synthesis rate of HSP 89 increased from a basal heat shock of young cells (PDL 18); in the old cells (PDL 51), the increase was from 1% to a maximum of 4% at 10-12 hrs after initiation of the heat shock. Western blot analysis showed that HSP 89 constituted approximately 2 and 10% of total cellular proteins in control and heat shocked (42 degrees C, 12-24 hrs) young cells; corresponding values for the old cells were 2 and 4.5%, respectively. Northern blot quantitation of the amount of mRNA hybridizable to cDNA probes of HSP 89 provided evidence that this age-dependent decrease in induction of HSP 89 in IMR-90 cells was attributable to a transcriptional/pre-translational mechanism.

The non-activated glucocorticoid receptor: structure and activation

Glucocorticoid hormone receptors are present in the soluble fraction of target cell homogenates as large entities (Mr approximately 300,000) that are unable to interact with DNA. These large complexes contain an Mr approximately 94,000 steroid- and DNA-binding polypeptide, in association with an Mr approximately 90,000 non-ligand-binding entity, which has been identified as a heat shock protein, hsp90. This protein has been purified to near homogeneity as a component of the non-activated receptor complex. Characterization of the purified protein revealed its presence as a dimer in the large receptor form. Dissociation of the receptor-hsp90 complex can be induced by heat treatment only when ligand is bound to the receptor, as demonstrated by specific DNA-binding assay and sucrose gradient ultracentrifugation, hsp90 represents ca 1% of total proteins in rat liver cytosol, and milligram amounts were purified using a combination of high performance ion exchange and gel permeation chromatography. Monospecific antibodies were raised in rabbits. They were found to precipitate the intact non-activated glucocorticoid receptor, as well as the Mr approximately 27,000 steroid-binding fragment of the receptor generated by trypsin treatment, indicating that hsp90 interacts with the steroid-binding domain of the glucocorticoid receptor. Finally, translation of glucocorticoid receptor mRNA in reticulocyte lysate yields a protein which also interacts with hsp90 and binds to DNA only after ligand-binding and heat treatment. Thus, the glucocorticoid receptor is synthesized in a non-activated form also in vitro.

Purification and characterization of the 90-kDa heat-shock protein from mammalian tissues

The 90-kDa heat-shock protein (HSP90) has been purified from mammalian tissues, mouse liver and porcine brain, with a good yield by a new method involving hydrophobic chromatography. Mouse liver HSP90 and porcine brain HSP90 were compared with mouse lymphoma HSP90 which was purified from T lymphoma cell line, L5178Y, by a modification of the previously reported method. These three HSP90s were indistinguishable from one another in amino acid composition, one-dimensional peptide mapping, elution pattern of proteolytic fragments (trypsin- or V8-protease-cleaved) in reverse-phase high-performance liquid chromatography, reactivity with the antibody against mouse T lymphoma HSP90 and the ability to bind to F-actin. The amino acid sequences of three portions (total 47 amino acid residues) of lymphoma HSP90 were determined and they were homologous to those of the corresponding portions of Drosophila HSP83A and yeast HSP90. These results suggest that HSP90 is a highly conserved protein during evolution.

Characterization of purified avian 90,000-Da heat shock protein

The so-called 90,000-Da heat shock protein (hsp90) from chicken liver has been purified and physically characterized in the presence of high levels of the serine phosphatase inhibitor fluoride. The protein is an elongated dimer with a molecular weight of 160,000 and a frictional ratio of 1.6. On two-dimensional electrophoresis it exhibits several isoelectric forms lying between pH 5.1 and 5.8. It contains an average of 5.8 mol of covalently bound phosphate per dimer and is thus extensively phosphorylated. Analysis of the ultraviolet spectrum showed the purified protein to be free of nucleotide-containing components. Molybdate has been shown to stabilize complexes between the 90,000-Da heat shock protein and steroid receptors. However, molybdate has no effect on the sedimentation of the purified heat shock protein. Proteins structurally related to hsp90 have been reported to penetrate the endoplasmic reticulum. However, when purified hsp90 was tested using the partition method of Bordier, which distinguishes hydrophilic and lipophilic proteins, it partitioned totally into the aqueous phase.

Effect of the 90 kDa heat shock protein, HSP90, on glucocorticoid receptor binding to DNA-cellulose

Glucocorticoid receptors in the IM-9 human lymphoblastoid cell line were affinity labeled with [3H]dexamethasone 21-mesylate and activated to a DNA-binding form by filtration through a Bio-Gel A-1.5m column. The 90 kDa heat shock protein, HSP90, was identified by labeling IM-9 cells with 35S-methionine at both 37 degrees C and 42 degrees C and purified to near homogeneity by sequential chromatography through DE52 and hydroxyapatite. Addition of purified HSP90 to activated, affinity labeled glucocorticoid receptors in a molecular ratio of 16 to 1 inhibited the binding of the receptors to DNA-cellulose. HSP90 did not affect the binding of other proteins to DNA-cellulose, indicating that the inhibitory effect of HSP90 was specific for the glucocorticoid receptor. These results suggest that HSP90 may associate with the glucocorticoid receptor, masking its DNA-binding site and thereby inhibiting receptor interaction with DNA.

Induction of the stress response: alterations in membrane-associated transport systems and protein modification in heat shocked or Sindbis virus-infected cells

Heat shock or Sindbis virus infection of chick embryo (CE) or baby hamster kidney (BHK) cells resulted in a decrease in the uptake of 86Rubidium+, a K+ tracer. Both stressful treatments decreased 86Rb+ uptake by inhibition of the ouabain-sensitive Na+/K+ ATPase. Alterations in the intracellular levels of monovalent ions may be involved in translational or transcriptional control of the stress response. Heat shock or Sindbis virus infection also resulted in an increase in rate of uptake of [3H]deoxy-D-glucose and a decrease in the incorporation of [3H]glucosamine or [3H]mannose into most cellular proteins. These results suggested that heat shock or Sindbis virus infection alter hexose metabolism and that abnormally glycosylated proteins may accumulate in stressed cells. Exposure of uninfected chick embryo cells to elevated temperature had little effect on the overall rate of incorporation of [32P]orthophosphate into cellular proteins. However, one protein (Mr 31,000; pp31) displayed increased incorporation of [32P]orthophosphate and two other proteins (Mr 33,000 and 20,000; pp33 and pp20) displayed decreased incorporation. Sindbis virus infection failed to mimic or to modify these heat shock induced alterations in protein phosphorylation.

Transformation of glucocorticoid and progesterone receptors to the DNA-binding state

This brief review explores some recent observations relating to the structure of untransformed glucocorticoid and progesterone receptors and the mechanism by which the receptors are transformed to the DNA-binding state. In their molybdatestabilized, untransformed state, progesterone and glucocorticoid receptors exist as a heteromeric 8-9S complex containing one unit of steroid binding phosphoprotein and one or two units of the 90 kD heat shock protein hsp90. When the receptors are transformed, the steroid-binding protein dissociates from hsp90. In cytosol preparations, temperature-mediated dissociation proceeds much more rapidly in the presence of hormone. The dissociated receptor binds to DNA with high affinity, regardless of whether it is in the hormone-bound or the hormone-free state. These observations raise the possibility that the primary, and perhaps the only, role for the hormone is to promote dissociation of the receptor-hsp90 complex. Molybdate, vanadate, and tungstate inhibit receptor transformation to the DNA-binding form, an effect that appears to reflect the ability of these transition metal oxyanions to stabilize the complex between the steroid receptor and hsp90. By promoting the formation of disulfide bonds, hydrogen peroxide also stabilizes the glucocorticoid receptor-hsp90 complex and prevents receptor transformation. A small, heat-stable factor present in all cytosol preparations inhibits receptor transformation, and, when the factor is removed, glucocorticoid receptors are rapidly transformed. This ubiquitous factor has the physical properties of a metal anion, and it is proposed that molybdate and vanadate affect steroid receptor complexes by interacting with a metal anion-binding site that is normally occupied by this endogenous receptor-stabilizing factor.

Mouse 89 kD heat shock protein. Two polypeptides with distinct developmental regulation

Unstressed early mouse embryos have been previously shown [1] to synthesize at very high rates 70 and 89 kD proteins belonging to the heat shock protein (HSP) family. But it was not clear whether expression of heat shock-inducible or non-inducible (cognate) genes accounted for this spontaneous synthesis. In this report we show that the 89 kD mouse HSP can be separated into two proteins by high resolution PAGE. These two components show distinct but related peptide pattern after limited proteolysis. They are synthesized from distinct mRNAs. One of these proteins--HSP89f--is synthesized at a high rate by unstressed cells and its synthesis is rather insensitive to stress, whereas synthesis of the other protein--HSP89s--is strongly stimulated by heat shock in fibroblasts. Both HSP89f and HSP89s are major proteins synthesized in unstressed mouse preimplantation embryos and embryonal carcinoma (EC) cells. After in vitro differentiation of the EC cells the spontaneous synthesis of HSP89s decreases. Thus spontaneous expression of a mammalian inducible HSP is developmentally regulated.

The amino-terminal sequence of the 85-90K nonhormone binding component of the molybdate-stabilized estradiol receptor from calf uterus

The first six N-terminal amino acid residues of the 85-90K non-estrogen binding component of the calf uterine, molybdate-stabilized estradiol receptor have been determined by Edman degradation. After affinity chromatography of the stabilized receptor oligomer, the 85-90K unit was purified to homogeneity by preparative gel electrophoresis using electroelution for protein recovery. Inverse-gradient high performance liquid chromatography provided the 85-90K protein suitable for amino-terminal sequence analysis.