ATP-dependent activation of glucocorticoid receptor from rat liver cytosol

Requirement of Hsp90 for centrosomal function reflects its regulation of Polo kinase stability

We have previously shown that the molecular chaperone heat shock protein 90 (Hsp90) is required to ensure proper centrosome function in Drosophila and vertebrate cells. This observation led to the hypothesis that this chaperone could be required for the stability of one or more centrosomal proteins. We have found that one of these is Polo, a protein kinase known to regulate several aspects of cell division including centrosome maturation and function. Inhibition of Hsp90 results in the inactivation of Polo kinase activity. It also leads to a loss in the ability of cytoplasmic extracts to complement the failure of salt-stripped preparations of centrosomes to nucleate microtubules. This effect can be rescued upon addition of active recombinant POLO: We also show that Polo and Hsp90 are part of a complex and conclude that stabilization of Polo is one of the mechanisms by which Hsp90 contributes to the maintenance of functional centrosomes.

Hsp90 is a core centrosomal component and is required at different stages of the centrosome cycle in Drosophila and vertebrates

To determine the molecular composition of the centrosome of a higher eukaryote, we carried out a systematic nano-electrospray tandem or MALDI mass spectrometry analysis of the polypeptides present in highly enriched preparations of immunoisolated Drosophila centrosomes. One of the proteins identified is Hsp83, a member of the highly conserved Hsp90 family including chaperones known to maintain the activity of many proteins but suspected to have other essential, unidentified functions. We have found that a fraction of the total Hsp90 pool is localized at the centrosome throughout the cell cycle at different stages of development in Drosophila and vertebrates. This association between Hsp90 and the centrosome can be observed in purified centrosomes and after treatment with microtubule depolymerizing drugs, two criteria normally used to define core centrosomal components. Disruption of Hsp90 function by mutations in the Drosophila gene or treatment of mammalian cells with the Hsp90 inhibitor geldanamycin, results in abnormal centrosome separation and maturation, aberrant spindles and impaired chromosome segregation. This suggests that another role of Hsp90 might be to ensure proper centrosome function.

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)

Interaction of cycloalkanoprogesterones with mammalian progesterone receptor: binding of pregna-D'-pentaranes in the calf uterine cytosol

Pregna-D'-pentaranes (pentaranes) are modified progesterones with demonstrable progestational activity and contraceptive effect. We have examined the steroid binding characteristics of the two newly synthesized progesterone analogs, Pentarane A (16 alpha, 17 alpha-cyclohexanoprogesterone) and Pentarane B (6 alpha-methyl, 16 alpha, 17 alpha-cyclohexanoprogesterone), and studied the nature of their interaction with progesterone receptor (PR) from the chicken oviduct and the calf uterine cytosols. Pregna-D'-pentaranes exhibited no affinity for the chick PR but interacted with the calf uterine PR as did R5020. The pentaranes, however, bound PR less tightly. R5020- or pentarane-bound PR sedimented as an 8S moiety in 8-30% linear glycerol gradients. Thermal transformation of receptor resulted in the reduction of the 8S form, and caused an increase in the binding of R5020- and progesterone-bound PR complexes to DNA-cellulose. The pentarane-bound PR bound poorly, if at all, to DNA-cellulose. Our data suggest that pentaranes exhibit both similarities and differences with natural and synthetic progestins with respect to their interaction with calf uterine PR. The lack of pentarane binding to chicken PR is reminiscent of the general phenomenon that antiprogestins (RU486, ZK98299, and Org 31710 and Org 31806) do not interact with chicken PR. Pentaranes, therefore, represent unique steroid analogs to investigate the molecular mechanism of steroid hormone action.

Nucleoside triphosphates promote the transformation of Ah receptor to its DNA-binding form

When it is bound to a specific ligand such as 2,3,7,8-tetrachlorodibenzo-p-dioxin, mild heating can convert the Ah (aryl hydrocarbon) receptor into a form capable of binding DNA. We found that physiological (1-3 mM) levels of ATP substantially increased the transformation of the receptor to its DNA-binding form. GTP, UTP and CTP had similar effects. ADP also promoted this transformation, but was less effective than ATP at low concentrations. Pyrophosphate too promoted transformation, but AMP had little effect. The process did not require nucleotide hydrolysis, since non-hydrolysable analogues of ATP such as adenosine 5'-[beta gamma-imido]triphosphate were nearly as effective as ATP itself. Inhibitors of ATP-stimulated proteases did not significantly affect the ability of ATP to promote receptor transformation, which suggests that the effect of ATP was not mediated by these proteases.

Hormone specific phosphorylation and transformation of chicken oviduct progesterone receptor

Phosphorylation of chick progesterone receptor (PR) was attempted by incubating tissue minces from estrogen-primed oviducts with ortho [32P]phosphate in the absence and presence of different steroids. The phosphorylated PR was immunopurified from the cytosol using anti-PR monoclonal antibody alpha PR22 (Sullivan et al., 1986). Although all three known peptides of PR, peptides B (110K), A (79K) and the 90 kDa nonhormone binding peptide (heat shock protein, hsp-90), were phosphorylated, the presence of only progesterone increased the degree of phosphorylation of receptor peptides A and B and the dissociation of the hsp-90 from the PR heterooligomer. Other steroids, cortisol, estradiol and dihydrotestosterone (DHT) had no effect on the phosphorylation or on the dissociation of hsp-90 from the PR. Incubation of phosphorylated PR at 23 degrees C or at 4 degrees C with 0.3 M KCl or 10 mM ATP also caused dissociation of the hsp-90. Presence of progesterone in vitro increased dissociation of the hsp-90 and the subsequent PR binding to DNA-cellulose. Transformation in vivo or under cell free conditions did not alter the degree of phosphorylation of PR peptides A and B. Our results demonstrate that PR is phosphorylated in a hormone-specific manner and that its transformation by various agents leads to loss of the hsp-90 from the oligomeric structure without an apparent involvement of dephosphorylation.

Identification of a protein from rat liver cytosol that enhances activation of the glucocorticoid receptor

We have identified a factor from rat liver cytosol that enhances the DNA-cellulose-binding ability of the glucocorticoid receptor and lowers the sedimentation value from 9-10 S to 4-5 S. Cytosol is prepared in the presence of molybdate, and unactivated receptor is isolated by chromatography on DEAE-cellulose in the presence of molybdate. This receptor sediments at 9-10 S and has little affinity for DNA. If the molybdate is removed and the receptor is incubated at 25 degrees C with the low-salt wash of the DEAE-cellulose column, DNA binding is enhanced by 50-600% relative to controls incubated with buffer only. In addition, the factor present in the low-salt wash converts the 9-10 S receptor into a mixture of 5 S and 4 S forms. The factor must be present during the incubation in order to exert its maximal effect. Factor added after the incubation has only marginal effects on the DNA-binding ability of the receptor, indicating that the factor does not increase the DNA-binding ability of activated receptor. Moreover, the factor is significantly less effective on receptor that has been activated before incubation with the factor. These results suggest that the factor acts as an activation enhancer. Preliminary characterization indicates that the activation enhancer is a trypsin-sensitive protein of approx. 70,000 Da, whose activation-enhancing properties are inhibited by ATP. RNAase A, which has effects similar to those described above on the 7-8 S receptor, does not mimic the effects of the activation enhancer on the 9-10 S receptor.

Tight binding of glucocorticoid-receptor complexes to histone-agarose

"Activated" glucocorticoid-receptor complexes purified about 3,000-fold from rat liver were found to bind to histone-agarose. Because of their tight binding, they could not be eluted from the column by high salt solution (3 M KCl) or low salt plus polyol buffer (50% ethylene glycol), but their binding could be disrupted by pyridoxal 5'-phosphate; more than 70% recovery of the "activated" receptor complexes was achieved with buffer containing 20 mM pyridoxal 5'-phosphate. This interaction of "activated" glucocorticoid-receptor complexes of rat liver with histone-agarose suggests a role of histones in the mechanism of action of steroid hormone.

ATP-induced activation of purified rat hepatic glucocorticoid receptors

We have utilized unactivated rat hepatic glucocorticoid receptor complexes purified to near homogeneity by a three-step scheme which includes affinity chromatography, gel filtration and anion exchange chromatography, to demonstrate for the first time that ATP can interact directly with the receptor protein in stimulating activation. This stimulation is reflected by an increase in DNA-cellulose binding as well as by a shift in the elution profile of the purified receptor complexes from DEAE-cellulose. A concentration of 10 mM Na2MoO4 is able to block both of these effects. ATP stimulates activation in a dose-dependent manner (maximally at 10 mM), and elicits maximal activation within 30 min at 15 degrees C. There appears to be no nucleotide specificity since GTP, CTP and UTP, as well as ADP and GDP also stimulate activation. All of these observations closely parallel data obtained from similar activation experiments performed with crude rat hepatic receptors. ATP does not appear to stimulate activation of receptors (crude or purified) by initiating a phosphorylation reaction since hydrolysis-resistant analogues of ATP are also effective. Pyrophosphate (PPi) is as effective as ATP in promoting receptor activation, since it elicits similar increases in DNA-cellulose binding, shifts in elution patterns from DEAE-cellulose, and dose-response relationships. None of the compounds tested stimulate activation indirectly by pH or ionic strength effects. Despite the fact that high ATP concentrations (3-4-fold higher than those present in vivo) are necessary to stimulate maximal activation, a physiological role of ATP in directly regulating in vivo activation of glucocorticoid receptors cannot be ruled out.

Normal levels of serum corticosterone and hepatic glucocorticoid receptors in obese (fa/fa) rats

In an attempt to understand the hyper-responsiveness to glucocorticoids that is characteristic of genetically obese fa/fa rats, we have measured the levels of free corticosterone in serum from lean and obese rats as well as the number of "cytosolic" and "nuclear" binding sites in livers of these rats. Both the lean and obese rats had similar amounts of free corticosterone available for biological activity at 4 weeks and 10 weeks of age. Measurement of glucocorticoid binding to hepatic glucocorticoid receptors failed to show any differences between genotypes leading to the suggestion that the abnormal glucocorticoid response in obese rats may be due either to post-receptor defects or to a permissive action of the steroid in the expression of the fa/fa genotype.

Transformation of calf uterine progesterone receptor: analysis of the process when receptor is bound to progesterone and RU38486

Effects of different transforming agents were examined on the sedimentation characteristics of calf uterine progesterone receptor (PR) bound to the synthetic progestin [3H]R5020 or the known progesterone antagonist [3H]RU38486 (RU486). [3H]R5020-receptor complexes [progesterone-receptor complexes (PRc)] sedimented as fast migrating 8S moieties in 8-30% linear glycerol gradients containing 0.15 M KCl and 20 mM Na2MoO4. Incubation of cytosol containing [3H]PRc at 23 degrees C for 10-60 min, or at 0 degrees C with 0.15-0.3 M KCl or 1-10 mM ATP, caused a gradual transformation of PRc to a slow sedimenting 4S form. This 8S to 4S transformation was molybdate sensitive. In contrast, the [3H]RU486-receptor complex exhibited only the 8S form. Treatment with all three activation agents caused a decrease in the 8S form but no concomitant transformation of the [3H]RU486-receptor complex into the 4S form. PR in the calf uterine cytosol incubated at 23 or at 0 degrees C with 0.3 M KCl or 10 mM ATP could be subsequently complexed with [3H]R5020 to yield the 4S form of PR. However, the cytosol PR transformed in the absence of any added ligand failed to bind [3H]RU486. Heat treatment of both [3H]R5020- and [3H]RU486-receptor complexes caused an increase in DNA-cellulose binding, although the extent of this binding was lower when RU486 was bound to receptors. An aqueous two-phase partitioning analysis revealed a significant change in the surface properties of PR following both binding to ligand and subsequent transformation. The partition coefficient (Kobsd) of the heat-transformed [3H]R5020-receptor complex increased about 5-fold over that observed with PR at 0 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Transformation and phosphorylation of purified molybdate-stabilized chicken oviduct progesterone receptor

The non-transformed, molybdate-stabilized chick oviduct cytosol progesterone receptor was purified approx. 7000-fold using biospecific affinity resin (NADAC-Sepharose), DEAE-Sephacel chromatography and gel filtration on Bio-Gel A-0.5m agarose. The purified preparation contained progesterone receptor which sedimented as a 7.9S molecule, had a Stokes' radius of 7.5 nm, was composed of three major peptides corresponding to Mr 108,000, 90,000 and 79,000. Upon removal of molybdate, the purified [3H]progesterone-receptor complex could be transformed from the 8S form to a 4S form by exposure to 23 degrees C or by an incubation with 10 mM ATP at 0 degrees C. The purified thermally transformed receptor could be adsorbed to columns of ATP-Sepharose. No cytosol factor(s) appeared to be required for the 8S to 4S transformation of purified receptor or for its subsequent binding to ATP-Sepharose. Incubation of purified non-transformed receptor preparation with [gamma-32P]ATP and cAMP-dependent protein kinase led to incorporation of radioactivity in all the three major peptides at serine residues. The results of this study show for the first time that purified 8S progesterone receptor can be phosphorylated in vitro by a cAMP-dependent protein kinase, and that it can be transformed to a 4S form by 0 degrees C incubation with 10 mM ATP.

In vitro transformation of androgen receptor from murine skeletal muscle by cAMP

Sedimentation constants and DNA-cellulose-binding of cytosolic androgen receptor from murine skeletal muscle were determined in presence of cyclic nucleotides. Without cAMP, two testosterone-binding fractions of similar amount at 4-5S and 8-9S were obtained. With 3 microM cAMP the receptor sedimented predominantly at 4-5S. Binding of testosterone-receptor-complexes to DNA-cellulose was enhanced by increasing cAMP-concentrations and reached a maximum at 20-90 nM cAMP depending on the DNA-concentrations in the test. A similar DNA-binding characteristic was obtained after partial purification of the receptor by affinity chromatography. cGMP had no effect. We conclude that the androgen receptor is transformed in vitro by cAMP.

Activation of rat liver glucocorticoid receptor bound to the antiglucocorticoid RU38486

The kinetics of steroid binding to rat liver glucocorticoid receptor (GR) and receptor denaturation were dependent upon the nature of the molecule occupying GR. Both the agonist [triamcinolone acetonide (TA)] and the antagonist (Ru38486) however competed for the same saturable binding site. Despite opposing physiological action, both steroid analogues permitted receptor activation as evident by binding to DNA-cellulose and 9S to 4S shift on sucrose gradient sedimentation. It therefore seems necessary to reevaluate a current notion that antagonist action of RU38486 in rat liver is a result of impaired receptor activation.

Modulation of DNA binding of glucocorticoid receptor by aurintricarboxylic acid

Effects of aurintricarboxylic acid (ATA) were examined on the DNA binding properties of rat liver glucocorticoid-receptor complex. The DNA-cellulose binding capacity of the glucocorticoid-receptor complex was completely abolished by a pretreatment of receptor preparation with 0.1-0.5 mM ATA at 4 degrees C. The half-maximal inhibition (i.d.50) in the DNA binding of [3H]triamcinolone acetonide-receptor complex [( 3H]TARc) was observed at 130- and 40 microM ATA depending upon whether the inhibitor was added prior to or following the receptor activation. The entire DNA-cellulose bound [3H]TARc could be extracted in a concentration-dependent manner by incubation with 2-100 microns ATA. The [3H]TARc remained intact under the above conditions, the receptor in both control and ATA-treated preparations sedimented in the same region in salt-containing 5-20% sucrose gradients. The action of ATA appeared to be on the receptor and not on DNA-cellulose. The DNA-binding capacity of ATA-treated receptor preparations could be recovered upon exhaustive dialysis. The treatment with ATA did not appear to change the ionic behavior of heat activated GRc; the receptor in both control and the ATA-treated preparations showed similar elution profiles. Therefore, ATA appears to alter the binding to and dissociation of glucocorticoid-receptor complex from DNA. The use of ATA should offer a good chemical probe for analysis of the DNA binding domain(s) of the glucocorticoid receptor.

Characterization of nontransformed and transformed androgen receptor from rat submandibular gland

Rat submandibular gland cytosol contained androgen receptor which had a single class of specific binding and an apparent dissociation constant of (1.1-1.2) X 10(-9) M. The process of transformation was investigated by a slightly modified minicolumn method in which the transformed receptor complexes were separated from the nontransformed receptor and meroreceptor. 10 mM ATP or pyrophosphate at 0 degrees C induced transformation of androgen receptor as did heat or salt treatment. 20 mM of sodium molybdate completely inhibited transformation that resulted from ATP, heat or salt treatment. The nontransformed androgen receptor complexes sedimented at 8 S and eluted at 250-260 mM KCl from DEAE-Sephacel, and its molecular weight was found to be 220 000 on Sephacryl S300 gel chromatography. On the other hand, the transformed androgen receptor complexes sedimented at 4.1-4.3 S (ATP or KCl treatment) or 3.5-3.8 S (heat treatment) and eluted at 60-80 mM KCl from DEAE-Sephacel. The molecular weight of the transformed androgen receptor complexes was 80 000-85 000 (ATP or KCl treatment) or 70 000-80 000 (heat treatment). These results suggest that the transformation of androgen-receptor complexes from rat submandibular gland was induced by the subunit dissociation and that salt bridges may be involved in the subunit interaction.

Specific binding of dexamethasone to plasma membranes from skeletal muscle

A procedure was developed to isolate plasma membranes from rabbit skeletal muscle. K+-dependent phosphatase activity was used as marker enzyme for plasma membranes and was determined in the presence of CHAPS (3-( (3-cholamidopropyl)dimethylammonio)-1-propanesulfonate), a zwitterionic detergent. Ca2+-ATPase and succinate dehydrogenase activities were used as marker enzymes for sarcoplasmic reticulum and mitochondria, respectively. Electron-microscopy revealed that plasma membranes were in the form of vesicles. Significant proteolysis of membrane proteins was observed during extraction, which was inhibited by EGTA and 20 mM molybdate. SDS-polyacrylamide gel electrophoresis revealed the disappearance of an intense 96 kDa protein band when membranes were purified in the absence of EGTA and molybdate. Specific binding sites for [3H]dexamethasone were identified in plasma membranes after freezing and incubation with CHAPS. Dithiothreitol was essential for steroid binding and ATP increased it. Under standardized assay conditions, binding was complete with 50 min a 37 degrees C. No binding occurred at 0 degrees C, nor if EGTA and molybdate were absent from the extraction medium.

Protein kinase activity of purified rat liver glucocorticoid receptor

Molybdate-stabilized nonactivated rat liver glucocorticoid receptor (GR) was purified to near homogeneity using a biospecific affinity adsorbent, Bio Gel A 0.5 m and DEAE-Sephacel. The purified GR sedimented in the 9-10S region in 5-20% sucrose gradients containing 0.10M KCl and 20mM Na2MoO4. SDS-polyacrylamide gel electrophoresis revealed a major single band with an apparent molecular weight of 90,000 +/- 2,000. Affinity labeling of GR with [3H]-dexamethasone mesylate showed association of the radioactivity with a peptide of 90,000 molecular weight. Purified receptor preparation was dialyzed to remove molybdate and was incubated with different protein substrates in the presence of 50 microM [gamma-32P]-ATP and divalent cations. Radioactive phosphate from [gamma-32P]-ATP was seen to be incorporated into calf thymus histones, turkey gizzard myosin light chain kinase and rabbit skeletal muscle kinase in the presence of Mg2+ and Ca2+ ions. Addition of steroid ligand exogenously to the reaction mixture appeared to increase the extent of protein phosphorylation. No autophosphorylation of GR was evident under the above conditions. The data suggest that purified rat liver GR displays protein kinase activity.

ATP-dependent activation of glucocorticoid-receptor complexes from the rat's heart

The effect of ATP on the cytosolic rat heart glucocorticoid receptor was studied by employing different methods for evaluation of the changes in molecular properties of the receptor, induced by activation. Incubation of triamcinolone acetonide labelled cytosol at 25 degrees C or with 10 mM ATP at 4 degrees C leads to the increase in the partition coefficient of the receptor in the aqueous dextran-polyethylene glycol two-phase system and also nuclear uptake of the complexes. The effect of ATP on the partition coefficient was more pronounced, compared with that of thermal treatment or dilution of the cytosol and totally inhibited by 10 mM sodium molybdate. The activating effect of ATP on the glucocorticoid-receptor complexes and sensitivity of this activation to sodium molybdate was also confirmed by DEAE-cellulose chromatography of cytosolic receptor preparations. The results suggest that ATP may be involved in the glucocorticoid receptor activation and through this regulates the translocation of complexes into the nucleus under in vivo conditions.

Enhancement of adenosine 3',5'-monophosphate in human mononuclear and polymorphonuclear leukocytes by snake venoms

Snake venoms contain compound(s) that enhanced cyclic AMP content in human mononuclear leukocytes maximally after 5 min of incubation at 37 degrees C. The effect was time- and dose-dependent. The half-maximal stimulation of cyclic AMP production by black cobra venom was found at 0.45 micrograms of venom/ml and the value of the Hill coefficient was 0.7. The black cobra venom enhanced the cyclic AMP content in the cells at 4, 22, and 37 degrees C. Similar increase in the cyclic AMP content by six snake venoms was found in human polymorphonuclear leukocytes. The most active venom was from puff adder (Bitis arietans). The data suggest that one of the effects of the snake venoms may be rapid enhancement of cyclic AMP level in the affected cells.

Activation and changes in the sedimentation properties of rat liver glucocorticoid receptor

The glucocorticoid receptor in rat liver cytosol was studied by sucrose gradient sedimentation, DEAE-Sephadex A-50 column chromatography and DNA-cellulose binding in order to assign specific hydrodynamic properties to both the unactivated and the activated glucocorticoid--receptor complex with [3H]-dexamethasone. Activation was effected by heat, NaCl (0.4 M) or KSCN (0.1 M) treatment. The state of activation was judged by both DNA-cellulose binding and DEAE-Sephadex A-50 anion exchange chromatography. In isotonic phosphate buffer, unactivated and activated glucocorticoid--receptor complex sedimented as a 5 S and a 4 S peak, respectively. This 5 S-4 S transformation was blocked by sodium molybdate. In hypotonic phosphate buffer, both the unactivated and the activated glucocorticoid--receptor complex assumed higher s values due to aggregation. The activated complex (4 S) yielded aggregates of 5-6 S in a reversible manner, neither complex being affected by sodium molybdate. The unactivated complex was shown to assume two distinct aggregation states of 6 S and 8-9 S, which yielded a 10-11 S heavy aggregate upon addition of molybdate. This effect on the unactivated glucocorticoid--receptor complex was readily reversed by removing the molybdate. Aggregation at low ionic strength was promoted by a low mol. wt. component(s), separated from cytosol by gel filtration through Sephadex G-10. The state of aggregation had no pronounced effect on the DNA binding properties of the activated forms or on the sensitivity of the unactivated forms to molybdate.

Aqueous two-phase partition studies of glucocorticoid receptors exposed to limited trypsination

In a previous investigation the properties of glucocorticoid receptors exposed to partial proteolysis by chymotrypsin were studied by aqueous two-phase partitioning (Andreasen, P.A. and Gehring, U. (1981) Eur. J. Biochem. 120, 443-449). This paper describes studies of the properties of cytosolic glucocorticoid receptors submitted to limited trypsination, employing phase partitioning of rat thymocyte cytosol labelled with tritiated triamcinolone acetonide. Trypsin treatment of labelled cytosol at 0 degrees C does not result in any dissociation of steroid from the receptor. The partition properties of the trypsin-treated receptors exposed to receptor-activating conditions are indistinguishable from those of the activated native and chymotrypsin-treated receptors, although the trypsin-treated receptors have lost the affinity for DNA and dextran sulphate. Trypsin treatment of cytosol not exposed to receptor-activating conditions results in a rapid change in the receptor partition coefficients identical to that following chymotrypsin treatment. However, during incubations under conditions at which activation of native and chymotrypsin-treated receptors is very slow, the trypsin-treated receptor is converted to a form with partition properties indistinguishable from those of the activated receptors. During exposure of the cytosol to activating conditions, the time-course of the partition coefficient of the trypsin-treated receptors is only slightly different from that of the native and chymotrypsin-treated receptors, but the trypsin-treated receptors are far less susceptible to the activation inhibitors ATP, Li+ and MoO42-. We conclude that the proteolytic cleavages induced by trypsin in the non-activated receptor do not lead to any immediate changes in the charge and surface properties of the receptor different from those following chymotrypsin treatment, but that the trypsin-treated receptor is not able to maintain a non-activated state and a normal susceptibility to activation inhibitors.

Inactivation by Na+,K+-ATPase of cytosol glucocorticoid receptors from rat brain and liver

We have examined the effect of Na+,K+-ATPase on 3H-triamcinolone acetonide binding capacity of cytosol glucocorticoid receptors from rat brain and liver. Preincubation of the brain or liver cytosol with Na+,K+-ATPase (10 units/ml) at 30 degrees C resulted in a rapid loss of specific 3H-triamcinolone acetonide binding, with a half-life of approximately 7 min. The ATPase effect could be prevented by the addition of 10(-5) M ouabain, or substantially reduced by the omission of Na+,K+ or Mg+2. The cytosol receptor bound with 3H-triamcinolone acetonide was totally resistant to the inactivation by the ATPase. Since there is some evidence that ATP may bind to glucocorticoid receptor, our findings indicate that an ATP-receptor complex may be essential for steroid binding. The effects of the ATPase in the inactivation of the receptor are very similar to those of alkaline phosphatase reported by others. This raises doubts about the proposal based on the phosphatase inactivation that the cytosol glucocorticoid receptor may be phosphorylated.

Inhibition of nuclear uptake of glucocorticoid-receptor complex by aurintricarboxylic acid

The presence of 50-200 microM aurintricarboxylic acid (ATA) blocked the uptake of [3H]-triamcinolone acetonide (3H-TA)-receptor complex from rat liver cytosol by isolated nuclei. The half-maximal inhibition (I.D.50) in the nuclear uptake of [3H]-TA-receptor complex was observed at 70- and 80 microM ATA depending upon whether the inhibitor was added prior to or following receptor activation. In addition, the nuclear-bound [3H]-TA-receptor complex from control samples could be completely extracted by an incubation with 20-100 microM ATA. The amount of [3H]-TA-receptor complex remained unchanged under these conditions. The effects of ATA may result due to its interaction with the glucocorticoid receptor at/near the sites that are involved in its nuclear uptake. ATA, therefore is a potentially useful chemical probe for analysis of glucocorticoid receptor.

Interaction of rat liver glucocorticoid receptor with sodium tungstate

Effects of sodium tungstate on various properties of rat liver glucocorticoid receptor were examined at pH7 and pH 8. At pH 7, [3H]triamcinolone acetonide binding in rat liver cytosol preparations was completely blocked in the presence of 10--20 mM-sodium tungstate at 4 degrees C, whereas at 37 degrees C a 30 min incubation of cytosol receptor preparation with 1 mM-sodium tungstate reduced the loss of unoccupied receptor by 50%. At pH 8.0, tungstate presence during the 37 degrees C incubation maintained the steroid-binding capacity of unoccupied glucocorticoid receptor at control (4 degrees C) levels. In addition, heat-activation of cytosolic glucocorticoid-receptor complex was blocked by 1 mM- and 10 mM-sodium tungstate at pH 7 and pH 8 respectively. The DNA-cellulose binding by activated receptor was also inhibited completely and irreversibly by 5 mM-tungstate at pH 7, whereas at pH 8 no significant effect was observed with up to 20 mM-tungstate. The entire DNA-cellulose-bound glucocorticoid-receptor complex from control samples could be extracted by incubation with 1 mM- and 20 mM-tungstate at pH 7 and pH 8 respectively, and appeared to sediment as a 4.3--4.6 S molecule, both in 0.01 M- and 0.3 M-KCl-containing sucrose gradients. Tungstate effects are, therefore, pH-dependent and appear to involve an interaction with both the non-activated and the activated forms of the glucocorticoid receptor.

Inactivation of rat liver glucocorticoid receptor by molybdate. Effects on both non-activated and activated receptor complexes

When freshly prepared glucocorticoid-receptor complex from rat liver cytosol was incubated at 23 degrees C in the presence of sodium molybdate, its subsequent binding to isolated nuclei, DNA-cellulose and ATP-Sepharose was blocked. In addition, binding to these acceptors by cytosol receptor complex fractionated with (NH4)2SO4 was also blocked by incubation of the complexes with 50 mM-sodium molybdate. However, molybdate had no effect on the binding of activated receptor complexes to ATP-Sepharose. Molybdate was also effective in extracting the nuclear- and DNA-cellulose-bound glucocorticoid-receptor complexes in a dose-dependent manner. Molybdate appears to exert its effects directly on the receptor by interacting with both non-activated and activated receptor forms.

Activation of progesterone receptor by ATP

Progesterone-receptor complex from freshly prepared hen oviduct cytosol acquired the ability to bind to isolated nuclei, DNA-cellulose and ATP-Sepharose when incubated with 5-10 mM ATP at 4 degrees C. The extent of this ATP-dependent activation was higher when compared with heat-activation achieved by warming the progesterone-receptor complex at 23 degrees C. The transformation of progesterone-receptor complex which occurred in a time-dependent manner was only partially dependent on hormone presence. The ATP effect was selective in causing this transformation whereas ADP, AMP and cAMP failed to show any such effect. The non-hydrolyzable analogs of ATP, adenosine 5'-[alpha, beta-methylene]triphosphate and adenosine 5-[beta, gamma-imido]triphosphate were also found to be ineffective. Presence of 10 mM sodium molybdate blocked both the ATP and the heat-activation of progesterone-receptor complex. Mn2+ and Mg2+ had no detectable effect on the receptor activation but the presence of Ca2+ increased the extent of ATP-activation slightly. EDTA presence (greater than 5 mM) decreased the extent of receptor activation by about 40% and was, therefore, not included in the buffers used for activation studies. Divalent cations were also ineffective when tested in the presence of 1-5 mM EDTA. The steroid-binding properties of progesterone-receptor complex remained intact under the above conditions when analyzed for steroid-binding specificity and Scatchard analysis. However, the ATP-activated progesterone-receptor complex lost the ability to aggregate when tested on low-salt sucrose gradients. ATP was equally effective in activating the rat-uterine-estradiol-receptor complex at 4 degrees C and influenced the transformation of 4-S receptor form into a 5-S form when analyzed on sucrose gradients containing 0.3 M KCl. The presence of ATP also increased the rate of activation of progesterone-receptor complex at 23 degrees C. These findings suggest a role for ATP in receptor function and offer a convenient method of studying the process of receptor activation at low temperature and mild assay conditions.

Glucocorticoid binding in the hen oviduct

[(3)H]Triamcinolone acetonide (15nm) was incubated with cytosol (150000g fraction) prepared from oviducts of egg-laying hens. The extent of steroid binding, as determined by charcoal assays, was greatest between 2-4h at 4 degrees C. A similar time curve was obtained when cytosol preparations were first fractionated with (NH(4))(2)SO(4) before labelling. The addition of 10mm-Na(2)MoO(4) or 10mm-ATP during the incubation of hen oviduct cytosol with [(3)H]triamcinolone acetonide lowered the extent of steroid binding. The presence of glycerol (20%), however, increased the extent of [(3)H]triamcinolone acetonide binding in cytosol fractions from chick (330%) and hen (160%) oviducts. The [(3)H]triamcinolone acetonide-receptor complex was stable for over 4h at 4 degrees C, but dissociated rapidly at 37 degrees C, exhibiting a half-life of about 10min. The presence of 10mm-Na(2)MoO(4) and 10mm-ATP or both had a small protective effect on the dissociation of [(3)H]triamcinolone acetonide-receptor complex. The receptor from hen oviduct showed significant affinity for unlabelled triamcinolone acetonide, cortisol, compound R5020 and dihydrotestosterone and, to a lesser extent, for oestradiol, oestrone and progesterone. Diethylstilboestrol treatment of immature chicks appeared to induce a more specific binder, which showed affinity for unlabelled triamcinolone acetonide, cortisol and compound R5020 only. Scatchard analysis of [(3)H]triamcinolone acetonide binding in hen oviduct cytosol revealed a K(d) value of 6.4nm. The steroid-receptor complex sedimented as a 7-8S and a 4S entity on low-salt (0.01m-KCl)- and high-salt (0.3m-KCl)-containing sucrose gradients respectively. The cytosol [(3)H]triamcinolone acetonide-receptor complex showed no affinity for ATP-Sepharose or DNA-cellulose, but acquired this ability on heat activation (23 degrees C, 40min). The data indicate the avian oviduct possesses a high-affinity binding molecule that fulfils the criteria of a glucocorticoid receptor.

Interaction of rat liver glucocorticoid receptor with adenosine 5'-triphosphate. Characterization of interaction by use of ATP-sepharose affinity chromatography

An interaction between rat liver glucocorticoid--receptor complex and immobilized ATP was identified. Rat liver cytosol preparations were incubated with [3H]triamcinolone acetonide for 4 h at 4 degrees C and partially purified by precipitation with (NH4)2SO4 before use. The resulting glucocorticoid--receptor complex could be selectively adsorbed on to columns of ATP--Sepharose. The freshly prepared cytosol [3H]triamcinolone acetonide--receptor complex had very little affinity for binding to the ATP--Sepharose column, but acquired this ability on temperature- or salt-activation. The presence of 10 mM-sodium molybdate during this salt- or temperature-dependent activation blocked the binding of the receptor complex to ATP--Sepharose. The interaction is reversible, since it can be disrupted by high-salt conditions. A competitive binding assay, using free nucleotides in samples to be chromatographed, revealed a preferential interaction between ATP and the glucocorticoid--receptor complex. Buffer containing ATP was also used to elute the glucocorticoid--receptor complex from ATP--Sepharose columns successfully. When ATP was added to the preparations containing [3H]triamcinolone acetonide--receptor complexes, the steroid specificity or sedimentation properties of the complex remained unaltered. Our results demonstrate an interaction between rat liver glucocorticoid--receptor complex and immobilized ATP and suggest a role of this nucleotide in receptor function.