Action of glycerol and sodium molybdate in stabilization of the progesterone receptor from rat trophoblast

Goat endometrial heat shock protein-90 (Hsp-90): development of an expedient method for its purification and observations on its intracellular movement

An expedient method has been developed by which goat uterine Hsp-90 could be isolated and purified to homogeneity in less than 1day. The yield is roughly 1mg from 60g tissue. This method takes into advantage three of our earlier observation that (a) Hsp-90 gets linked to the non-activated estrogen receptor (naER) in the presence of 10mM sodium molybdate; (b) naER, but not Hsp-90 binds to phosphocellulose and (c) exposure to estradiol facilitates dissociation of Hsp-90 from naER through estradiol binding to naER and the possible change in naER conformation. Intracellular movement of Hsp-90 and naER was monitored in goat endometrial cells in culture following exposure of the cells to estradiol. Confocal microscopic analysis revealed a clear presence of both proteins within the nucleus within 3h after exposure to estradiol. Whether Hsp-90 has its own nuclear-transport machinery is debatable. Being an actin-binding protein, there is a distinct possibility that the nuclear entry of Hsp-90 is actin dependent. The functional significance of the nuclear entry of Hsp-90, along with naER, remains to be determined; it may, however, be speculated that the Hsp-90 might be directly involved in the naER to nER II transformation by functioning as a molecular chaperone and helping the protein in re-orienting its structural organization.

Flavin fluorescence dynamics and photoinduced electron transfer in Escherichia coli glutathione reductase

Time-resolved polarized flavin fluorescence was used to study the active site dynamics of Escherichia coli glutathione reductase (GR). Special consideration was given to the role of Tyr177, which blocks the access to the NADPH binding-site in the crystal structure of the enzyme. By comparing wild-type GR with the mutant enzymes Y177F and Y177G, a fluorescence lifetime of 7 ps that accounts for approximately 90% of the fluorescence decay could be attributed to quenching by Y177. Based on the temperature invariance for this lifetime, and the very high quenching rate, electron transfer from Y177 to the light-excited isoalloxazine part of flavin adenine dinucleotide (FAD) is proposed as the mechanism of flavin fluorescence quenching. Contrary to the mutant enzymes, wild-type GR shows a rapid fluorescence depolarization. This depolarization process is likely to originate from a transient charge transfer interaction between Y177 and the light-excited FAD, and not from internal mobility of the flavin, as has previously been proposed. Based on the fluorescence lifetime distributions, the mutants Y177F and Y177G have a more flexible protein structure than wild-type GR: in the range of 223 K to 277 K in 80% glycerol, both tyrosine mutants mimic the closely related enzyme dihydrolipoyl dehydrogenase. The fluorescence intensity decays of the GR enzymes can only be explained by the existence of multiple quenching sites in the protein. Although structural fluctuations are likely to contribute to the nonexponential decay and the probability of quenching by a specific site, the concept of conformational substates need not be invoked to explain the heterogeneous fluorescence dynamics.

Effects of dimethyl sulfoxide, glycerol, and ethylene glycol on secondary structures of cytochrome c and lysozyme as observed by infrared spectroscopy

Effects of 10-30% (v/v) of dimethyl sulfoxide, glycerol, and ethylene glycol on the H-O-H bending vibration of water and the amide I bands of horse heart cytochrome c and chicken egg white lysozyme in 25 mM sodium phosphate buffer (pH 7.4) were examined at 20 degrees C by Fourier transform infrared spectroscopy. The H-O-H bending mode of water was strongly affected by these cryoprotectant solvents. Increasing the concentration of cryosolvents from 0 to 30% shifts the water bending band maximum from 1645 to about 1650 cm-1. Second-derivative analysis reveals significant changes in conformation-sensitive amide I regions of lysozyme ascribed to alpha-helix (1657 cm-1), turn (1674 cm-1), and unordered (1646 cm-1) structures; each cryosolvent increases the intensity of the 1657 cm-1 band at the expense of bands at 1674 and 1646 cm-1. No changes in spectra deemed significant were observed for cytochrome c under the same conditions. There is no spectral evidence of structural randomization of proteins due to the presence of these cryosolvents. Cryosolvent-induced changes in secondary structure of proteins may result from changes in water structure which, in turn, perturb the structure of the protein and/or from direct interactions between cryosolvent and protein.

Localization and measurement of occupied androgen receptors in thaw-mounted rat and human prostate tissue sections by in vitro autoradiography

In this paper we present an in vitro exchange binding assay procedure for measurement of androgen receptors in slide-mounted tissue sections. This method allows quantitative autoradiographic determinations with an anatomical resolution approaching the cellular level. Tissue sections are incubated with the synthetic androgen [3H]R1881 in the presence of triamcinolone acetonide to suppress possible binding of the radioligand to the progestin receptor. Adjacent tissue sections are incubated with [3H]R1881 in the presence of excess unlabeled 5 alpha- dihydrotestosterone or R1881 to assess nonspecific binding. Following incubation, the tissue sections are washed to remove unbound radioligand and either scraped for immediate determination of androgen receptor binding or placed against emulsion-coated film for the production of an autoradiographic image. In validation experiments with rat prostate sections from castrated, gonad-intact, and androgen-supplemented animals, maximum levels of androgen binding were observed with incubation at 4 degrees C or 72 h. Markedly less binding was detected with shorter incubations or with incubations at even slightly elevated temperatures. Very little androgen receptor binding was detected in castrated animals whereas receptor levels in intact and androgen-supplemented animals were 79.3 fmol/mg and 143.6 fmol/mg protein, respectively, suggesting that the method is selective for occupied receptors. Saturation binding analysis revealed binding to a single class binding site with high affinity (kd = 1.475 +/- 0.12 nM). Autoradiographic images of androgen binding in the prostate reflected the findings with the scraped sections: essentially no specific binding was present in sections from castrated animals whereas much heavier labeling was present in sections from intact animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Antiprogestin ZK-98.299 and progesterone display differential binding characteristics in the human myometrial cytosol

To investigate whether the synthetic progesterone antagonist ZK-98.299 binds to progesterone receptor or also has distinct binding sites, the binding characteristics of ZK-98.299 were compared with those of progesterone in the human myometrial cytosol. [3H]ZK-98.299 and [3H]progesterone showed specific binding in the myometrial cytosol and the binding of each radiolabelled ligand could be displaced with the respective ligand in a dose-response manner. However, while the binding of [3H]progesterone could be completely blocked with progesterone or ZK 98.299, the binding of [3H]ZK-98.299 could not be displaced more than 50%. The non-specific binding of [3H]ZK-98.299 was very high as compared to that of [3H]progesterone. Using [3H]progesterone, the relative binding affinity (RBA) of progesterone was more than that of ZK 98.299, whereas using [3H]ZK-98.299 the RBA of ZK 98.299 exceeded that of progesterone. Treatment of myometrial cytosol with increasing concentrations of -SH-modifying agents (iodoacetamide (IA) 0-10 mM or N-ethylmaleimide (NEM) 0-1000 nM) decreased the binding of progesterone by over 80%, whereas similar treatment did not have appreciable effect on the binding of [3H]ZK-98.299. Although both preformed ligand-receptor complexes were relatively stable in the presence of IA and NEM, the [3H]progesterone-receptor complex was more sensitive as compared to the [3H]ZK-98.299-receptor complex. The addition of 20 mM molybdate in the cytosol had a protective effect against the -SH-modifying agents. [3H]ZK-98.299 and [3H]progesterone-receptor complexes also showed differential stability when incubated at elevated temperatures (25 degrees C and 37 degrees C), [3H]ZK-98.299-binding sites being more thermolabile as compared to [3H]progesterone binding sites. Prior occupation of the receptor by the two ligands gave the complexes the ability to resist an elevated temperature of 25 degrees C. Moreover, molybdate stabilized both the liganded and unoccupied receptors at 25 degrees C. When the ligand-receptor complexes were applied onto a prefocused polyacrylamide gel, the progesterone and ZK-98.299-receptor complexes were resolved and focused at pH 7.2 and 8.4, respectively. The results of this study suggest that although progesterone and ZK-98.299 are mutually competitive for binding to progesterone receptor, ZK-98.299 also has distinct binding sites.

Modulation of steroid affinity for the androgen receptor by sucrose

The effects of sucrose on androgen binding to its receptor were investigated. Sucrose decreased the rate of thermal inactivation of unoccupied and occupied androgen receptor (AR) and the rates of [3H]5 alpha-dihydrotestosterone [( 3H]DHT) dissociation from both activated and nonactivated AR complexes. Binding of [3H]DHT to AR in vivo, or in intact cells at 37 degrees C, caused reduction of [3H]DHT dissociation from cytosolic and nuclear complexes, as compared to in vitro labeled receptor complexes. Further, exposure of these complexes to sucrose at 0 degrees C caused an additional reduction of dissociation rates. Thus, the decrease of [3H]DHT dissociation induced by sucrose is independent of the reaction that reduces DHT dissociation from activated and transformed AR. Sucrose also reduced the ability of mersalyl acid to inactivate AR complexes. This effect of sucrose was markedly diminished in the presence of 2M urea. Sucrose did not significantly affect the association rate, sedimentation properties, or nuclear binding ability of AR complexes, but it did decrease the equilibrium dissociation constant. Other monosaccharides and disaccharides also stabilized AR. These data suggest that sucrose induces conformational changes in the steroid binding domain of androgen receptor, thereby reducing the rates of inactivation, steroid dissociation, and the accessibility of sulfhydryl groups to mersalyl.

Effects of polyhydric and monohydric compounds on the stability of type I receptors for adrenal steroids in brain cytosol

We have shown previously that unoccupied type I receptors for adrenal steroids in brain cytosol lose their capacity to bind [3H]aldosterone ([3H]ALDO) in a time- and temperature-dependent manner. Based on reports that sugars and polyvalent alcohols are capable of stabilizing a variety of globular proteins, we attempted in the present study to stabilize type I receptors by including polyhydric compounds in our brain cytosol preparations. However, contrary to expectations, adjusting cytosol to a 10% (g/dl) concentration of ethylene glycol, glycerol, erythritol, xylitol, ribitol, or sorbitol failed to stabilize these receptors at 0 degree C and in fact produced a slight reduction in [3H]ALDO binding capacity. The magnitude of this reduction was greater when cytosol was incubated for 2 h at 22 degrees C prior to incubation with [3H]ALDO. In contrast to these results, when brain cytosol was adjusted to a 10% (g/dl) concentration of the monohydric compound, ethanol, a significant increase in [3H]ALDO binding to type I receptors was found. Under identical conditions, methanol and propanol failed to have a significant effect on the binding capacity of these receptors. When cytosol was aged for 2 h at 22 degrees C, all three of these monohydric compounds produced a marked loss in the [3H]ALDO binding capacity of type I receptors. An investigation of various doses of ethanol at 0 degree C on the subsequent binding of [3H]ALDO yielded an inverse U-shaped curve with 10% ethanol producing the highest level of specific binding, as reflected by an increase in maximal binding in Scatchard plots, and 40% ethanol producing a complete loss in type I receptor binding capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Molybdate stabilized rat uterine progesterone receptors: evidence for two mechanisms

Molybdate (Mo), EGTA, or protease inhibitors substantially increase detectable rat uterine progesterone (Pg) receptors. Rehomogenization experiments demonstrated that receptor levels decreased in the absence of Mo or protease inhibitors and were not regenerated. Thus Mo prevents an EGTA and protease-inhibitor-sensitive loss of uterine Pg receptors during homogenization. This effect was compared with receptor stabilization at elevated temperature. In contrast to the stability of receptors in the presence of Mo, receptors decreased rapidly to minimal levels by 30 min at 30 degrees C in TESHG (10 mM Tris, 1.5 mM EGTA, 12 mM thioglycerol, 10% glycerol) or TG buffers. The ability of EGTA to mimic receptor stabilization by Mo during homogenization, compared with its ineffectiveness at 30 degrees C, suggested fundamentally different mechanisms for these two phenomena. Similarly, 0.3 M KCl prevented Mo stabilization of the receptors at 30 degrees C, but did not change their recovery after homogenization. Results with protease inhibitors were also consistent: addition of 2-5 mM leupeptin and 500 microM PMSF to TG during homogenization resulted in substantially increased (P less than 0.01) receptor recovery, but leupeptin (+/- the temperature-labile PMSF) did not prevent the Pg receptor losses at 30 degrees C. The transformation state of the receptors may be important, since receptors were untransformed in the presence of either EGTA or Mo. Moreover, KCl transformed the receptors in parallel to their instability at 30 degrees C. In conclusion, Mo stabilizes Pg receptors during temperature elevation by a different mechanism from that involved during homogenization. Although the parallel effects by EGTA, molybdate, and the protease-inhibitors during homogenization is consistent with inhibition of Ca2+-dependent proteolysis, other possible mechanisms must be considered in future studies.

Glucocorticoid and progesterone receptors in yolk sac placenta

The parietal yolk sac (PYS) of the rat fetus at the 14th day of gestation contains glucocorticoid as well as progesterone receptors; both are present in the trophoblast cell layer. Following heat activation the receptors are capable of binding to deoxyribonucleic acid- (DNA-)cellulose. Glucocorticoid receptors, but not progesterone receptors, are also present in the visceral yolk sac (VYS) at the 14th day of gestation. Greater amounts (some 250 femtomoles/mg cytosol protein) of a glucocorticoid receptor are present in the VYS on the 17th day of gestation. The Kd is approximately 4 X 10(-9) M; following activation it also binds to DNA-cellulose. The elution pattern of the activated VYS receptor from diethylaminoethyl-(DEAE-)Sephadex, however, is similar to that found with kidney and colon rather than that of liver (i.e., it resembles corticosteroid binder IB rather than binder II) indicating a possible role in transport. Although the receptors are separate entities, progesterone competes as effectively as corticosterone for binding to the glucocorticoid receptors in both the PYS and and VYS, thus raising the question of the possible effect of changes in progesterone concentrations on the functioning of glucocorticoids during development.

Evidence for nuclear processing of progesterone receptors in rat placenta

The distribution of the progesterone receptor (Rp) in cytosolic and nuclear compartments of placenta has been studied in intact and ovariectomized (Ovx) rats on the 14th day of pregnancy. Removal of estradiol (E) and progesterone (P) by Ovx caused a 50% decrease in progesterone receptors from cytosolic and nuclear compartments. Estradiol replacement restored binding to intact levels. Progesterone, given 19 h after E, induced an additional 3-fold increment in the number of cytosolic and nuclear binding sites 1 h later. Four hours after progesterone the number of receptor sites in the placenta fell 60%, signifying processing. This was followed 4 h later by reversal of processing mechanisms leading to full recovery of nuclear and cytoplasmic binding sites. Actinomycin D (0.6 mg/ani) was found to have no influence on these events. On the other hand cycloheximide (0.5 mg/ani) completely prevented processing of binding sites when administered at the same time as progesterone or 2 h before, but did not influence the unmasking of nuclear sites which occurred 1 h after a progesterone challenge. The cycloheximide block to processing was partial when given 2 or 3 h after progesterone (61 and 43% complete, respectively). The full complement of receptors was processed when cycloheximide treatment was delayed 3.75 h after progesterone administration. These findings have led to the view that processing represents rapid and reversible changes in binding properties of the receptor rather than a gain or loss of receptor protein per se. The findings of this study suggest that a hypothetical substance, "processin", whose production is blocked by cycloheximide binds to the receptor and in some undefined manner inhibits ligand-receptor interaction within 4 h after an in vivo progesterone challenge. Nuclear accumulation of receptor induced by progesterone was not accompanied by cytoplasmic depletion of receptor nor was the apparent loss of processed nuclear receptor due to recycling of receptor to cytoplasm. We propose that nuclear receptors continually recycle within the nucleus in masked and unmasked states regulated by delicate interplay between progesterone and processin.

Characterization of progesterone binding to nuclear receptors in rat placenta

Exchange assays have been validated to study several forms of the progesterone receptor found to occur in nuclei of rat placenta after extraction with high salt. One form was solubilized by the extraction procedure (KCl extractable Rpn) and another form remained attached to nuclear structures (KCl resistant Rpn). Specific binding of progesterone was optimized in both forms using buffered media containing 0.01 M Tris, 30%-glycerol (v/v), 0.2 mM leupeptin, and 1 mM dithiothreitol (TDGL), pH 7.8, at 0-4 degrees C for 18-24 h. At 0-4 degrees C the nuclear receptors were stable and degradation was negligible even after 44 h of in vitro incubation. The binding reaction between progesterone and receptor demonstrated mass action principles of ligand exchange throughout this interval. Saturation analysis indicated the presence of a single binding moiety of high affinity (app Kd = 2.9-3.2 nM) for both forms of the receptor. However, the nuclear progesterone receptor was thermolabile and after a 10 min exposure to 30 degrees C no longer complexed ligand. At an intermediate incubation temperature of 22 degrees C the binding reaction was stable for about 30 min. The KCl resistant binding sites were markedly more thermolabile. Addition of 10 mM Na molybdate protected all forms of the nuclear progesterone receptor from thermal denaturation and extended the life of the complex 3-4-fold. The dissociation rate constant of progesterone-nuclear receptor complex in each preparation was 6-8 X 10(5) s-1 resulting in a half-life of about 3 h. The KCl resistant and extractable binding sites were sensitive to blockade by 1 mM N-ethylmaleimide which was reversed by co-incubation with a 2-fold molar excess of dithiothreitol. This suggested that reduced sulfhydryl groups located on or near the surface of the ligand binding domain of the receptor were necessary to bind hormone. These studies showed that the interactions between ligand and the KCl resistant and extractable receptor sites found in rat placenta were of high affinity, saturable, and heat sensitive. Thus, these binding moieties exhibited physicochemical behavior very similar to each other and to the placental receptor which has previously been partially purified from the cytosol. The conclusion is made that all of the nuclear receptor binding sites for progesterone are structurally identical. Thus, the distinctive physicochemical properties responsible for KCl resistant and extractable forms of the nuclear progesterone receptor must reside in other domains of the receptor molecule.

Chemical differentiation of type I and type II receptors for adrenal steroids in brain cytosol

Studies outlined here compare the properties of mineralocorticoid (Type I) and glucocorticoid (Type II) receptors in cytosol from adrenalectomized mouse brain. Pretreating cytosol with dextran-coated charcoal (DCC) produced a 4.7-fold increase in the subsequent macromolecular binding of the mineralocorticoid, [3H]aldosterone (20 nM ALDO, in the presence of a 50-fold molar excess of the highly specific synthetic glucocorticoid, RU 26988), whereas it produced a 55% decrease in the binding of the glucocorticoid, [3H]triamcinolone acetonide (20 nM TA). Scatchard analyses revealed that DCC pretreatment had no effect on the affinity or maximal binding of Type I receptors for [3H]ALDO (in the presence of a 0-, 50- or 500-fold excess of RU 26988), whereas it produced a 3- to 6-fold increase in the Kd, and an 8-43% decrease in the maximal binding, of Type II receptors for [3H]TA and [3H]dexamethasone. Optimal stability of unoccupied Type I receptors at 0 degree C was found to be achieved in buffers containing glycerol, but lacking molybdate. Although the addition of molybdate was found to reduce the loss in Type I receptor binding observed after incubating unlabelled cytosol at 12 or 22 degrees C, this stabilization was accompanied by a concentration-dependent reduction in the binding of [3H]ALDO at 0 degree C. Scatchard analyses showed that this reduction was due to a shift in the maximal binding, and not the affinity, of the Type I receptors for [3H]ALDO. The presence or absence of dithiothreitol in cytosol appeared to have little effect on the stability of Type I receptors. In contrast to our finding for Type I receptors, it was possible to stabilize the binding capacity of unoccupied Type II receptors, even after 2-4 h at 12 or 22 degrees C, if the glycerol containing buffers were supplemented with both molybdate and dithiothreitol. In summary, these results indicate distinct chemical differences between Type I and Type II receptors for adrenal steroids.

Effects of metal ions and chelating agents on in vitro stability of glucocorticoid receptors in brain cytosol

In vitro studies in a variety of tissues and cell types suggest that glucocorticoid receptor binding capacity is not static and that binding sites are subject to up- and down-regulatory mechanisms. The interpretation of such studies, however, is often complicated by factors affecting the stability of the receptor. This situation is particularly acute in the absence of ligand because of the increased lability of the unoccupied receptor. Studies reported here investigate effects of various metal ions and chelating agents on the stability of unoccupied [3H]dexamethasone binding sites in whole mouse brain cytosol. Variation in the ionic strength of cytosol, as created by the additions of various monovalent cations (Li+, Na+, K+, Rb+ and Cs+), was found to be an important factor affecting the increased stability of the receptor in vitro. Additions of divalent (Mg++, Ca++, Ba++, and Mn++) and trivalent (La , Cr and Al ) cations to cytosol, however, were generally found to produce a dose-dependent decrease in the stability of the unoccupied receptor. Additions of the chelating agents EDTA, EGTA and 1,10-phenanthroline to cytosol, resulted in differential, and sometimes complex, dose-dependent effects on receptor stability. The complex effects of various combinations of cations and the chelator EDTA were also investigated.

Binding of [3H]methyltrienolone to androgen receptor in rat liver

The synthetic androgen methyltrienolone is superior to testosterone and androstenedione for the measurement of androgen receptor in tissues where the native ligands are metabolized into inactive derivatives. [3H]Methyltrienolone binds with a high affinity to androgen receptor in cytosol prepared from male rat livers, as the Scatchard analysis revealed that the Kd value was 3.3 X 10(-8) M and the number of binding sites was 35.5 fmol/mg protein. Since methyltrienolone also binds glucocorticoid receptor which exists in rat liver, the apparent binding of androgen receptor is faulty when measured in the presence of glucocorticoid receptor. The binding of methyltrienolone to glucocorticoid receptor can be blocked by the presence of a 100-fold molar excess of unlabeled synthetic glucocorticoid, triamcinolone acetonide, without interfering in its binding to androgen receptor, because triamcinolone does not bind to androgen receptor. Triamcinolone-blocked cytosol exhibited that the Kd value was 2.5 X 10(-8) M and the number of binding sites was 26.3 fmol/mg protein, indicating a reduction to 3/4 of that in the untreated cytosol. The profile of glycerol gradient centrifugation indicated that [3H]methyltrienolone-bound receptor migrated in the 8-9 S region in both untreated and triamcinolone-blocked cytosols, but the 8-9 S peak in triamcinolone-blocked cytosol was reduced to about 3/4 of that of untreated cytosol.