Mechanism of action of steroid hormones

Direct regulation of genes involved in sperm release by estrogen and androgen through their receptors and coregulators

Steroid hormones, estrogen and androgen, control transcription in various reproductive and non-reproductive tissues. Both hormones are known to be important for control of sperm release from the seminiferous epithelium (spermiation), a process characterized by extensive remodeling of actin filaments and endocytosis. Earlier studies with an estrogen (E2)-induced rat model of spermiation failure revealed genes involved in actin remodeling (Arpc1b and Evl) and endocytosis (Picalm, Eea1, and Stx5a) to be differentially regulated. Further, among these genes, Arpc1b and Evl were found to be estrogen-responsive whereas Eea1 and Stx5a were androgen-responsive and Picalm was responsive to both hormones in seminiferous tubule cultures. Yet, the mechanism by which these genes are regulated by estrogen and androgen in the testis was unclear. Here, we report the presence of a functional estrogen response element (ERE) upstream of Arpc1b and Evl genes and androgen response element (ARE) upstream of Picalm, Eea1, and Stx5a genes. Chromatin immunoprecipitation in control versus E2-treated testes revealed significant changes in estrogen receptor beta (ERβ) recruitment along with coregulators to the EREs upstream of Arpc1b and Evl genes and androgen receptor (AR) at AREs upstream of Picalm, Eea1, and Stx5a genes. Enrichment patterns of these EREs/AREs with coregulators, activating and repressing histone modifications along with RNA polymerase II recruitment, correlated with the observed expression patterns of these genes upon E2 treatment. Taken together, our results reveal direct targets of estrogen and androgen in the testes and provide insights into transcriptional control of sperm release by the two steroid hormones.

Steroid-induced inhibition of adenosine transport in cultured chromaffin cells

1. Adenosine transport is subjected to regulation by hormones. Glucocorticoids, sexual steroids, and retinoic acid inhibit adenosine transport in chromaffin cells after a long-term incubation period (24 hr). No effects were observed after a short-term incubation period (10 min). 2. The kinetic parameters of transporters were studied. No significant changes were observed for the affinity constant (Km), whose value remains at 1 +/- 0.2 microM after 24-hr incubation in the presence of these compounds. The maximal velocity (Vmax) was significantly modified, with a decrease of about 20% in all cases. 3. NBTI binding was not modified in its affinity constant or maximal bound capacity (Bmax) by the presence of these compounds for a 24-hr incubation period. Thus the efficiency of transporters (quotient Vmax/Bmax) changed from 10.9 +/- 0.08 adenosine molecules transported per transporter per sec in the control cells to 9.1 +/- 0.07 in hormone-treated cultured cells. 4. The thyroid hormone (T3) significantly increased adenosine transport in a long-term incubation period in chromaffin cells (24 hr). This activatory effect is antagonized by steroid hormones and retinoic acid.

Time course of sodium-induced Na(+)-K(+)-ATPase recruitment in rabbit cortical collecting tubule

In cortical collecting tubules (CCD) of aldosterone-repleted rabbit kidney, an increase in intracellular sodium concentration (Nai) induces the recruitment and/or activation of latent Na(+)-K(+)-ATPase pumps (Blot-Chabaud et al., J. Biol. Chem. 265: 11676-11681, 1990). The present study was addressed to determine the time course of this Nai-dependent pump recruitment and to examine some of the factors possibly involved in this phenomenon. CCD from adrenalectomized rabbits complemented with aldosterone and dexamethasone were incubated at 4 degrees C either in a K(+)-free saline solution (Na(+)-loaded CCD) or in a sucrose solution (control CCD) and then rewarmed for various time periods to allow pump recruitment to occur. The number of pumps in the membrane was determined by specific [3H]ouabain binding; Nai was measured using 22Na. A rise in Nai induced a threefold increase in the number of basolateral pumps, which was fully achieved within 1-2 min. This pump recruitment was reversible within 15 min after restoration of low Nai. It was unaffected by inhibitors of cytoskeleton and Ca2+ ionophore A 23187. The blocker of the Na(+)-H+ antiporter, amiloride, did not prevent it. The protein kinase C activator, phorbol 12-myristate 13-acetate, did not induce it in the absence of Na+. We conclude that Nai is a major determinant of pump recruitment and/or activation, which occurs over a very short period of time. It may constitute a rapid adaptative response to an increase in the cell Na+ load.

Expression of estradiol and progesterone receptors by histologically normal endometria of women with postmenopausal bleeding

Estradiol and progesterone receptor levels (RE2, RP) were measured in histologically normal endometria of women with postmenopausal bleeding (PMB) and the results were compared to those in histologically normal endometria of premenopausal and postmenopausal (PM) women and to those in pathological PM endometria. In histologically normal PMB endometria, RP levels were comparable to those in secretory premenopausal endometria and significantly higher than those in PM atrophic endometria. The RP levels in the former group correlated with the respective RE2 levels and the values of the ratio RP/RE2 occupied a mid-zone between those ratio values of normal premenopausal or pathological PM endometria on the one hand and normal PM endometria, on the other hand. The cytosolic/nuclear distribution of both receptor levels revealed that in both PMB and in pathological PM endometria, only a small fraction of the receptor was recovered in the nuclear extract. Expression of the RE2 and RP in the PMB and in the pathological PM endometria were associated with undetectable plasma E2 levels. These results indicate that histologically normal PMB endometria are biochemically active and suggest that endometrial growth and RE2, RP expression in PMB and pathological PM endometria are stimulated by a factor which acts distal to the RE2 acceptor.

Specific binding sites for corticosterone in isolated cells and plasma membrane from rat liver

The specific binding of [3H]corticosterone to hepatocytes is a nonsaturable, reversible and temperature-dependent process. The binding to liver purified plasma membrane fraction is also specific, reversible and temperature dependent but it is saturable. Two types of independent and equivalent binding sites have been determined from hepatocytes. One of them has high affinity and low binding capacity (KD = 8.8 nM and Bmax = 1477 fmol/mg protein) and the other one has low affinity and high binding capacity (KD = 91 nM and Bmax = 9015 fmol/mg). In plasma membrane only one type of binding site has been characterized (KD = 11.2 nM and Bmax = 1982 fmol/mg). As it can be deduced from displacement data obtained in hepatocytes and plasma membrane the high affinity binding sites are different from the glucocorticoid, progesterone nuclear receptors and the Na+,K(+)-ATPase digitalis receptor. Probably it is of the same nature that the one determinate of [3H]cortisol and [3H]corticosterone in mouse liver plasma membrane. Beta- and alpha-adrenergic antagonists as propranolol and phentolamine did not affect [3H]corticosterone binding to hepatocytes and plasma membranes; therefore, these binding sites are independent of adrenergic receptors. The binding sites in hepatocytes and plasma membranes are not exclusive for corticosterone but other steroids are also bound with very different affinities.

Steroid hormone receptors

In the three decades since the original discovery of receptors for steroid hormones, much has been learned about the biochemical processes by which these regulatory agents exert their effects in target tissues. The intracellular receptor proteins are potential transcription factors, needed for optimal gene expression in hormone-dependent cells. They are present in an inactive form until association with the hormone converts them to a functional state that can react with target genes. Transformation of the receptor protein to the nuclear binding form appears to involve the removal of both macromolecular and micromolecular factors that act to keep the receptor form reacting with DNA. Much of the native receptor is present in the nucleus, loosely bound and readily extractable, but for some and possibly all steroid hormones, some receptor is in the cytoplasm, perhaps in equilibrium with a nuclear pool. Methods have been developed for the stabilization, purification, and characterization of receptor proteins, and through cloning and sequencing of their cDNAs, primary structures for these receptors are now known. This has led to the recognition of structural similarities among the family of receptors for the different steroid hormones and to the identification of regions in the protein molecule responsible for the various aspects of their function. Monoclonal antibodies recognizing specific molecular domains are available for most receptors. Despite the knowledge that has been acquired, many important questions remain unsolved. How does association with the steroid remove factors keeping the receptor protein in its native state, and how does binding of the transformed receptor to the response element in the promoter region enhance gene transcription? Once it has converted the receptor to the nuclear binding state, is there a further role for the steroid in modulating transcription? Still not entirely clear is the involvement of phosphorylation and/or dephosphorylation in hormone binding, receptor transformation, and transcriptional activation. Less vital to basic understanding but important in the overall picture is whether the native receptors for gonadal hormones are entirely confined to the nucleus or whether there is an intracellular distribution equilibrium. With the effort now being devoted to this field, and with the application of new experimental techniques, especially those of molecular biology, our understanding of receptor function is progressing rapidly. The precise mechanism of steroid hormone action should soon be completely established.

Distribution of total progesterone receptor levels in various segments and tissues of the normal human uterus: the effect of short-term estrogen administration

Total progesterone receptor levels (TRP) were measured in various tissues and segments of normal human uteri in basal conditions (late proliferative phase, control group, n = 6) and after short term estrogen administration (test group, n = 8). Similar trends of distribution were observed in both groups in basal endometrial TRP levels along the longitudinal axis, i.e. the highest levels were found at the height of the body and the lowest at the height of the internal os. Differences were found in the trends of distribution of the TRP levels between the two groups along the transverse axis of the uterus at the height of the fundus. In the control group TRP levels in the functional endometrium were higher than those in the basal endometrium and myometrium. In the test group, however, the trend was reversed. Since the RP is estradiol induced and dependent, these results indicate the possibility of a selective estrogen effect on various segments or tissues in the human uterus.

Phorbol esters potentiate glucocorticoid-induced cytotoxicity in CEM-C7 human T-leukemia cell line

Phorbol ester tumor promoter, such as 12-O-tetradecanoylphorbol-13-acetate (TPA), is synergistic with dexamethasone to cause growth inhibition of CEM-C7 human T-leukemia cell line. A specific saturable binding component which may mediate the phorbol ester effects has been identified by using [20-(3)H]phorbol 12,13-dibutyrate in a whole cell binding assay. Saturation of the specific binding occurs at a concentration (approx. 100 nM) consistent with causing maximal cytotoxicity. Scatchard analysis of the binding after 15 min at 37 degrees C demonstrates a single class of binding sites. The number is 194,000 sites per cell. Other phorbol esters are also cytotoxic to CEM-C7 cell in the presence of 30 nM dexamethasone in an approximate proportion to their activity in competing for [20-(3)H]phorbol 12,13-dibutyrate binding. Phorbol 12, 13-didecanoate, 4-O-methyl PMA, 4-beta-phorbol do not compete for specific binding. The synergism of phorbol esters and dexamethasone on CEM-C7 cells is reversible by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine(H-7). However, by treating CEM-C7 cells with TPA for 48 h there is not any increase in the affinity or levels of glucocorticoid receptor. It is tentatively concluded that phorbol esters may play an important role linked to the glucocorticoid-induced growth inhibition in CEM-C7 human T-leukemic cell.

Progesterone challenge test in postmenopausal women with pathological endometrium

Cytosolic and nuclear progesterone receptor levels (RPC, RPN) were measured in normal and in pathological human endometria after single-dose progesterone injection 1-3 h before tissue collection (test subjects) and the results compared to those obtained in controls (no progesterone treatment). In test cases of late proliferative or midcycle normal endometria and in estrogen-primed normal postmenopausal endometria, RPN levels were higher and RPC levels were lower compared with those obtained in control samples. In test cases of postmenopausal pathological endometria, histologically normal endometria of women with postmenopausal bleeding and in one case of endometrial polyp, RPN levels were also higher and RPC levels lower than those in the respective controls, but the change of distribution of the RP (cytosol/nuclear extract) was significantly lower than in normal endometrium.

Atrial natriuretic peptide is only a minor diuretic factor in dehydrated subjects immersed to the neck in water

To determine if the atrial natriuretic peptide (ANP) is an important factor for inducing diuresis during head-out water immersion even in dehydrated subjects, six healthy volunteers were immersed up to the neck in water at 34.5 degrees C for three hrs. Significant diuresis and natriuresis occurred, but urine osmolality decreased and negative CH2O was restored in a positive direction toward zero, even though subjects were still in a state of considerable dehydration. Plasma renin activity and plasma angiotensin I and II concentrations decreased but that of plasma aldosterone remained unchanged during water immersion, and plasma ANP did not increase throughout the examination. On the basis of the data of the present study, the factor inducing diuresis during head-out water immersion in hydrated subjects appears to differ from that in dehydrated subjects, and the main factor inducing diuresis during water immersion in dehydrated subjects may be the suppression of vasopressin release and not ANP.

On the possible mechanism of recognition of DNA base sequence by steroid hormones

Geometry of the complex of a steroid hormone, dexamethasone, with a hexanucleotide sequence from the glucocorticoid responsive element d(TGTTCT)2, is optimised here using computer aided geometry simulation with an energy minimization technique. We have also optimised its geometries with genetically modified and arbitrarily chosen DNA sequences. The drug molecule is considered to have both intercalative as well as non-intercalative binding. Comparison of energetics and stereochemical aspects, as well as the H-bonding scheme, is used here to bring out salient features about the mechanism of DNA sequence recognition by steroid hormones.

Regulation of cation transport by low doses of glucocorticoids in in vivo adrenalectomized rat colon

A dose response curve for glucocorticoid-induced proximal and distal colonic cation transport in vivo was established in adrenalectomized rats. All doses (0.5-50 nmol/100 g body wt) stimulated sodium absorption. Distal sodium absorption did not saturate at dexamethasone levels that saturate the glucocorticoid receptor but also bind to greater than 35% of aldosterone receptors. Saturation of the pure glucocorticoid response occurred in both segments with RU26988, a synthetic glucocorticoid that does not occupy aldosterone receptors. Maximum velocities for pure glucocorticoid-induced sodium absorption were 15 and 16 mu eq/min per g dry tissue, and Michaelis constants (Km) were 4.2 and 4.6 X 10(-9) mol/liter for proximal and distal colon. Kms are similar to the dissociation constant for the colonic glucocorticoid receptor and too low for significant aldosterone receptor occupancy. Dexamethasone increased sodium absorption significantly within 30 min of injection, suggesting the response is not dependent on new protein synthesis. Similar time and dose responses in proximal and distal colon suggest glucocorticoids stimulate the same pathway in both segments.

Characterization and assay of the nuclear and cytosolic progesterone (P) receptors in Premarin-primed human endometrium and myometrium after single-dose P administration

Progesterone receptors (RP) were characterized and measured in the 0.4 M KCl nuclear extract and in the cytosol of 7 to 11 days Premarin (Premarin, Ayerst Laboratories, New York, NY) primed human endometrium and myometrium with [3H]R5020 as the ligand. The test group comprised 12 women who received progesterone injection 1 to 3 hours before tissue collection; the control group numbered 10 women. Receptor characteristics in both the endometrium and the myometrium, in the nuclear extract and cytosol in the test group and in the cytosol in the control group, were similar and were demonstrated by (1) high specificity, (2) sedimentation constant of 4.7 to 6.5S in the cytosols and 2.8 to 3.9S in the nuclear extract, (3) saturable affinity with Kd of 2.2 to 3.5 nM and 1.9 to 3.3 nM, respectively. Total RP levels (nuclear extract and cytosol) ranged from 1030 to 13,270 and 1280 to 17,300 fmol/mg DNA, respectively, in the endometria of women in the test and control groups. In 13 of 14 women myometrial total RP levels were higher than in the endometrium. There was a significant difference in the distribution of the RP between the test and the control groups: 50% and 48% of the receptor were measured in the nuclear extract in the endometrium and myometrium, respectively, in the test group, compared with 25% and 21% in the control group (P less than 0.001).

Dexamethasone blocks arachidonate biosynthesis in isolated hepatocytes and cultured hepatoma cells

The effect of dexamethasone on the incorporation and conversion of [1-14C]eicosa-8,11,14-trienoic acid to arachidonic acid in isolated hepatocytes and in hepatoma tissue culture (HTC) cells was studied. In both kinds of cells, no changes in the exogenous acid incorporation were found when the hormone was added to the incubation media at 0.1 or 0.2 mM concentration, while the biosynthesis of arachidonic acid was significantly depressed. The effect on the biosynthesis was faster in isolated normal liver cells (60 min) than in tumoral cells (120 min) and reached an inhibition of ca. 50% after 3 hr of treatment. The addition of cycloheximide (10(-6) M) also caused a marked decrease in the biosynthesis of this polyunsaturated fatty acid, but when dexamethasone was added to the media simultaneously with cycloheximide, a synergistic action was not observed. The results obtained show that protein synthesis would be involved in the modulation of the biosynthesis of arachidonic acid by glucocorticoids. The changes in the delta 5 desaturation of labeled 20:3 omega 6 to arachidonic acid correlated with changes in the fatty acid composition in isolated cells.

Characteristics and specificity of the glucocorticoid "carrier" of rat liver plasma membrane

The uptake of corticosterone by highly purified plasma membrane vesicles of rat liver was studied by a rapid-centrifugation technique which allows uptake measurements within 5 s. The vesicles are free of soluble cytoplasmic constituents. Therefore, association of hormone with the vesicle is attributed entirely to components of the vesicle-membrane. Half maximal uptake is reached at 8 s at 21 degrees C. At 15 degrees C transition of the lipid state in the membrane leads to a decrease of uptake, a characteristic property common to membrane mediated processes. The uptake of corticosterone is saturable and reversible but does not follow normal saturation kinetics. The apparent dissociation constants of three uptake systems bear direct relation to the concentration of free corticosterone in rat plasma (4-16 nM) supporting a physiological role for the system. Uptake of corticosterone decreases with decreases in vesicular volume; about 50% of the hormone is bound specifically and 50% is transported to the lumen of the vesicle. Since outflow of intravesicular hormone also occurs readily, the uptake and transport is proposed to be mediated by putative "carriers". The "carrier" preferentially transports glucocorticoids; dexamethasone is not taken up by this putative molecule. Steroids with 5 alpha conformation are more potent inhibitors of the "carrier" for corticosterone than 5 beta-steroids. Androgens and estrogens are weak competitors of corticosterone. The affinity of the "carrier" for several hormones differs considerably from that of the cytoplasmic receptor. Morris hepatoma cells (MH 3924) do not take up corticosterone. Our results prompt us to propose the hypothesis that the transport function of the "carrier" and the binding of the hormone by the cytoplasmic receptor are two different entities; perturbation of the "carrier" may lead to steroid unresponsiveness. Normal expression of steroid hormone activity is manifested in the concerted action of the functionally sound cell membrane "carrier" and the intracellular receptor.

A study of [3H]aldosterone binding by nuclear and cytoplasmic receptors of the rat kidney with different content of aldosterone in the organism

The distribution of specific mineralocorticoid receptors in rat kidney cells was found to depend on aldosterone concentration. With increasing aldosterone concentrations the number of specific receptors for aldosterone in the cytoplasm decreased and their quantity in the nuclei increased. This was evidently due to their enhanced transport from the cytoplasm to the nuclei. It was found that aldosterone (its complex with the receptor) attached to non-histone proteins of chromatin and that the structural integrity of DNA is needed to provide the binding of this complex to the cell nuclei. The quantity of aldosterone acceptor sites in the kidney cell nuclei remained constant when aldosterone concentrations in the organism changed, and, hence, the functional states of the target organ changed too.

[Neurocryptococosis and immunosuppression: experimental model in mice]

In order to accomplish a model for immunosuppression in experimental conditions two lots of 50 young mice were divided into groups of 10, and submitted to dexamethasone ingestion. Two experiments were considered in the study. In the first experiment conditions for immunosuppression were established in 50 mice, by per os supply of several concentrations of dexamethasone in the water given for normal daily intake ad libitum. Criteria of immunosuppression considered include: hair standing on end; leukopenia by decrease of lymphocyte population; spleen atrophy in relation to controls, with severe hypoplasy of all lymphoid structures. In the second experiment another lot of 50 mice in similar conditions established for the first experiment and concerning the immunosuppression were submitted to intraperitoneal inoculation of near 10(6) Cryptococcus neoformans. Culture suspensions of cryptococci isolated from cerebrospinal fluid samples of human neurocryptococcosis cases were used for this purpose. Although fungi could be recognized in lungs, liver and spleen from every mice inoculated, only those with central nervous system involvement (near by an half of all) died. The discussion included considerations about the role of the blood-brain barrier function in the findings registered.

Aldosterone does not stimulate the Na:K pump in isolated turtle colon

The study of the mechanisms by which mineralocorticoids stimulate sodium absorption across distal epithelia has focused on three possible sites of action: apical sodium permeability, the basolateral Na:K pump, and the production of high-energy substrates. Recently we developed a method for direct measurement of the current generated by the basolateral Na:K pump of the turtle colon [15]. In the presence of mucosal amphotericin-B and serosal barium the short-circuit current across the colon can be equated with the current produced by active electrogenic exchange of sodium for potassium across the basolateral membrane. This pump current is a measure of the transport capacity of the epithelial Na:K pump that is uncomplicated by changes in apical membrane sodium permeability. Pump currents, thus defined, were compared in control tissues and tissues treated with aldosterone in vitro. After 9 h Na absorption was increased 4-fold in the aldosterone-treated tissues but the values of the pump current were identical in the two groups. This result indicates that acute stimulation of sodium absorption by aldosterone does not occur by stimulating the Na:K pump directly.

Glucocorticoid receptors of normal and leukemic cells: role of proliferation conditions

A published whole-cell binding assay of 3H-dexamethasone (3H-DEX) was combined with cell sedimentation analysis to investigate various factors influencing specific binding of glucocorticoids by leukemic lymphoblasts. Studies with mouse L1210 and human HL-60 cell lines revealed that glucocorticoid (GC) receptors accumulate during G1 phase of the cell cycle. In human lymphoblastic leukemia, the per cell receptor number was highest in cells in S and G2 phase and lowest in small, noncycling cells. In normal human white blood cells, GC receptor content was maximal in large lymphocytes and monocytes while no receptors were present in small lymphocytes. However, the receptor density of large lymphocytes was still 3-4 fold lower than of leukemic lymphoblasts of similar size. In L1210 cells the number of GC receptors decreased considerably in stationary cultures or following inhibition of cell cycle progression by dibutyryl cyclic AMP (dbc-AMP). Receptor content was also reduced in cells growing as ascites tumors in hosts with terminal disease. Accordingly, the receptor content in leukemic blasts appeared highly dependent on cell cycle distribution and on the proliferative status of the tumor cells. These findings may in part explain the large interpatient variation and the conflicting views regarding GC receptor content and prognosis in acute lymphoblastic leukemia.

Effect of aldosterone on urinary kallikrein and prostaglandin excretion in the rat

In an attempt to study the interrelationship between aldosterone, Na balance, prostaglandin (PG) and kallikrein excretion, we investigated the influence of adrenalectomy and aldosterone administration on kallikrein and PG excretion during dietary manipulation of extracellular volume in Sprague-Dawley rats. Adrenalectomy decreased while aldosterone administration increased urinary kallikrein and PG excretion during both low and high Na intake. Aldosterone induced a prompt change in Na/K ratio; however, kallikrein and PG excretion increased gradually during the 7 days of treatment. When the animals were forced into a negative Na balance during the administration of aldosterone by reducing their Na intake, kallikrein and PG excretion still increased but to a lesser extent than on a constant diet. In adrenalectomized rats given only vehicle, shifting the diet to a low Na intake caused a decrease in kallikrein and PG excretion. Corticosterone failed to correct the changes evoked by adrenalectomy, and it did not reproduce the effects of aldosterone. It is concluded that the effect of aldosterone on kallikrein and PG excretion is not mediated by changes in extracellular volume; however, in the absence of aldosterone a change in Na balance itself may influence kallikrein and PG excretion.

Impact of treatment efficacy on the prognostic value of glucocorticoid receptor levels in childhood acute lymphoblastic leukemia

Glucocorticoid receptor (GR) levels were quantitated in leukemic blasts from bone marrow aspirates of 249 children with acute lymphoblastic leukemia (ALL) who were entered on two St. Jude Total Therapy Studies. Of these, 235 were evaluable for analysis of the relation of GR levels to clinical outcome. For the 42 patients in the earlier Total Therapy Study IX, lower GR levels (less than 16,000 sites/cell) were associated with both induction failure and more frequent relapse (p less than 0.01) [Cancer Research, Vol. 42, p. 4801 (1982)]. When patients with 'high-risk' features (leukocyte count greater than 100 X 10(3)/mm3, positive erythrocyte rosette test, central nervous system involvement, and mediastinal mass) were excluded, lower receptor levels were still associated with early and more frequent relapse (p less than 0.02). The other 193 evaluable patients were consecutively admitted to Total Therapy Study X, in which patients with 'standard-risk' or 'high-risk' features were assigned to separate protocols--XS and XH, respectively. Induction chemotherapy in both protocols consisted of prednisone, vincristine and L-asparaginase; patients in the XH protocol received additional epipodophyllotoxin (VM-26) and cytosine arabinoside twice a week for 2 weeks preceding the conventional induction therapy. To compare the prognostic value of GR level in Study X with that of Study IX (which included both 'high-risk' and 'standard-risk' patients but did not separate them into different protocol groups), children in the XH and XS protocols were analysed together. The proportion of patients with 'standard-risk' features was the same in the two studies: 69% in Study IX and 73% in Study X. In Study X, which had a significantly better treatment result (p less than 0.001), lower receptor levels were not associated with induction failure, but were correlated with more frequent relapse (p less than 0.05). When patients in XH and XS protocols were analysed separately, however, receptor levels were no longer related to treatment outcome. Thus, GR level in childhood ALL has prognostic value, but it is not an independent factor and its importance is related to the efficacy of treatment.

The relationship of blast cell glucocorticoid receptor levels to response to single-agent steroid trial and remission response in children with acute lymphoblastic leukemia

Of 263 children with glucocorticoid receptor (GR) levels measured at diagnosis of acute lymphoblastic leukemia (ALL), 27 received single-agent glucocorticoid before combination induction chemotherapy and were evaluable for in vivo clinical response to steroid. Twenty-one were glucocorticoid-responsive and 6 were resistant. There was no difference between the two groups in the distribution of age, sex, white blood cell count, immunophenotype of blasts, initial central nervous system disease or mediastinal mass. The median GR level, however, was appreciably lower in the group of patients with resistant disease (6250 vs 17,800 sites/cell, p = 0.06). Five of 12 patients with GR levels of less than 10,000 sites/cell compared to 1 of 15 with higher levels had glucocorticoid-resistant ALL (p = 0.03). All 21 patients with glucocorticoid-sensitive disease achieved a complete remission after combination induction chemotherapy, but only 3 of 5 evaluable patients in the other group did (p less than 0.04). Two patients were studied both at diagnosis and at relapse; both had decreased GR levels at relapse (below detection in one) and failed to respond to glucocorticoid. We conclude that a lower GR level is associated with glucocorticoid resistance and furthermore that a decrease in the level of GR is a mechanism of acquiring steroid resistance.

Studies on the mechanism of glucocorticoid hormone induced alterations in rat thymic transcription--I. Evidence from reconstituted cross-over transcription assays that sequential increases and decreases in transcription are due to changes in the activity of RNA polymerase II rather than in the activity of chromatin template

In experiments to determine the mechanism of glucocorticoid induced decreases in thymic transcription, adrenalectomized rats were injected with hydrocortisone (50 mg/kg) or vehicle. Thymic nuclei were used to prepare chromatins and soluble nuclear extracts containing RNA polymerase II for cross-over experiments. With calf thymus DNA or rat thymic chromatins as templates limiting RNA polymerase II from rats treated with hydrocortisone 3 h previously had 130% of the [3H]UMP incorporating activity of RNA polymerase II from control vehicle treated rats. In contrast, limiting RNA polymerase II from rats treated with hydrocortisone 12 h previously had 40-50% of the [3H]UMP incorporating activity of RNA polymerase II from controls. When limiting calf thymus DNA or rat thymic chromatins were used in 12 h cross-over experiments. Individual RNA polymerases II produced equal [3H]UMP incorporations, but RNA polymerase II activity from hydrocortisone treated rats was again only 50% of control values. Thus with template saturation, RNA polymerase II from hydrocortisone treated rats could not transcribe rat thymic chromatin templates to the level achieved by RNA polymerase II from control rats. This suggests that the activity, rather than the amount, of RNA polymerase II from hydrocortisone treated rats is reduced. Double reciprocal plots of [3H]UMP incorporation on rat chromatins with increasing concentrations of RNA polymerases II were made at 12 h. The apparent Km for RNA polymerase II from animals treated with hydrocortisone was identical to that of RNA polymerase II from controls, but the Vmax of RNA polymerase II from hydrocortisone treated animals was reduced. These data suggest the presence of an inhibitor of transcription or an RNA polymerase II defective in its capacity to initiate and/or elongate RNA transcripts. Further experiments demonstrated that these effects were not due to steroid induced changes in ribonuclease or protease activities.

Characterization and assay of progesterone-binding components in DMBA-induced rat mammary carcinoma tissue after progesterone administration

Nuclear and cytoplasmic progesterone-binding components were characterized and measured in DMBA-induced rat mammary carcinoma tissue, before and after progesterone administration. Rats, bearing growing tumors, were ovariectomized and then primed for two days with estradiol. Biopsy specimens were taken prior to or following administration of progesterone. Nuclear binding was assayed in the 0.4 M KCl extract of the nuclear fraction using [3H]R5020 as ligand. The receptor character of the binding was demonstrated by: (1) high affinity (Kd approximately 2 nM); (2) specificity: competition by R5020 and progesterone, minimal competition by 17 alpha-hydroxyprogesterone, corticosterone, testosterone and estradiol; (3) sedimentation constant at about 3S in a sucrose density gradient. Similar characteristics displayed the cytoplasmic receptor before and after progesterone administration. Progesterone receptor distribution in the nuclear extract and cytosol were determined in 36 tumors. The levels of total receptors (cytoplasmic plus nuclear) before and after progesterone administration varied widely, however the average values found after progesterone administration were significantly lower, 1.59 +/- 0.20 pmol/mg DNA compared to 2.58 +/- 0.32 pmol/mg DNA. Before progesterone administration only cytoplasmic receptors were found. One hour after progesterone administration a variable amount of the receptor (0-40%) was found in the nucleus of the tumorous tissue. In uteri of the same rats a uniform distribution of receptors (about 40% in the nucleus) was found after progesterone administration. A defect in the translocation process might be considered in the tumors with low receptors level, which suggests that DMBA-tumors may not respond uniformly to progesterone administration.

Blockade of the renal tubular effects of vitamin D by cycloheximide in the rat

To further characterize the mechanisms by which 25(OH) vitamin D3 (25(OH)D3) and 1.25(OH)2 vitamin D3 (1,25(OH)2D3) suppress the phosphaturic action of parathyroid hormone (PTH) we have studied the effects of cycloheximide (cyclohex), a protein synthesis inhibitor, on the interaction between PTH and vitamin D metabolites in parathyroidectomized (PTX) rats, both in vivo and in vitro experiments. In clearance studies PTX PTH-infused rats were pretreated with cyclohex 2 h before the administration of vitamin D. In control, PTX PTH-infused rats not pretreated with cyclohex, the administration of 25(OH)D3 and 1,25(OH)2D3 was associated with a fall in fractional excretion of phosphate (CP/CIN) from 0.30 +/- 0.05 to 0.16 +/- 0.02 and from 0.31 +/- 0.05 to 0.13 +/- 0.01 (P less than 0.005) respectively. Cyclohex-pretreated PTX PTH-infused rats failed to respond to both 25(OH)D3 and 1,25(OH)2D3, and CP/CIN, which rose after PTH, remained 0.32 +/- 0.05 and 0.29 +/- 0.03 respectively. In vitro, both 25(OH)D3 and 1,25(OH)2D3 inhibited the PTH-induced activation of adenylate cyclase in the renal isolated membrane fractions. Pretreatment with cyclohex abolished this effect of vitamin D metabolites. These results show that cyclohex blocks the antiphosphaturic effects of both 25(OH)D3 and 1,25(OH)2D3 but does not alter the response to PTH. These findings are consistent with the possibility that the acute renal action of vitamin D depends on de novo synthesis of protein.

The strong hydrophobic domain of the activated estrogen receptor of porcine uterus

Basic estrogen receptor (ER) molecule (vero-ER) of porcine uterus, which was previously shown to be the activated ER necessary to translocate from the cytoplasm into the nucleus, possesses a strongly hydrophobic nature. The strong hydrophobicity of vero-ER was concealed through binding with ER-binding factors (ERBFs). Vero-ER lost its strong hydrophobicity and its capability to bind with ERBFs after limited proteolysis by endogenous protease. The strong hydrophobic domain of vero-ER, indispensable for the nuclear translocation, was assumed to be located near the binding site with ERBFs.

Current concepts: II. Hormonal regulation of molecular events during aging

This review is an attempt to establish a role for both glucocorticoid and thyroid hormones in the aging process as factors which mediate the regulation of transcription and translation of specific genetic domains. Furthermore, through a review of the current knowledge of the effect of long-term hypophysectomy on physiological and biochemical functions which change with age in the rat an attempt has been made to establish a role for a pituitary factor in the regulation of the aging process through an affect on transcription and translation of hormonally induced genetic domains. Although we can propose a possible mechanism of action of this factor, the proposal is premature and requires extensive systematic testing. It will be interesting to carefully consider the possible relationship, if any, of this pituitary factor to the effects of dietary restriction on animal longevity. How this pituitary-aging interaction might be exploited is open to speculation but it is certainly worth further consideration based on evidence currently at hand.

Metabolism of poly(A)(+)RNA in toad bladder epithelial cells

Previous studies have characterized the induction of poly(A)(+)RNA synthesis by aldosterone during the latent period, preceding the increased active transepithelial sodium transport (measured as short-circuit current, SCC). To assess the role of aldosterone in the maintenance of the response in general and the metabolism of this RNA in particular, the decay of the increased SCC and of the newly synthesized poly(A)(+)RNA was monitored. On removal of the hormone, the SCC decayed with a half-life of 6.5 hr after a lag period of 2-3 hr. Studies on the disappearance from the cytoplasm of poly(A)(+)RNA synthesized in the first two hours after addition of aldosterone revealed a number of RNA species with diverse size decaying at a relatively slow rate after removal of aldosterone, and RNA sedimenting in the 10-14 S region decaying at a faster rate closely related to the decay in SCC. Maintenance of aldosterone in the media resulted in a much slower rate of decay of this 10-14 S. It is concluded that the decay of the 10-14 S poly(A)(+)RNA is closely related to the decay in SCC and the stability of this RNA is influenced by the retention of aldosterone in the medium.

Influence of steroid-hormone-receptor-protein complexes on initiation of ribonucleic acid synthesis in liver nuclei isolated from rats of various ages

The effect of age on the induction of the initiation of RNA synthesis was investigated in liver nuclei isolated from adrenalectomized rats of various ages after binding of a dexamethasone-receptor-protein complex. Binding of this complex to nuclear chromatin resulted in increased initiation of nuclear RNA synthesis at all ages; however, an age-associated decline in the extent of this induction was observed. This suggests an age-related decrease of total rat liver nuclear RNA synthesis with a decreased response to glucocorticoid hormones.

Binding of aldosterone to cytoplasmic and nuclear receptors of the rabbit kidney

The binding characteristics of [3H]aldosterone ([3H]A) in the rabbit kidney were compared with those described in other species, and experimental conditions suitable for both the isolation of renal tubules and the retention of aldosterone receptors were examined. Specific binding of [3H]A to cytoplasmic (C) and nuclear (N) receptors was determined on kidney slices incubated at +30 degrees C in rabbits fed a low K+-high Na+ diet. Results indicate the presence of at least two binding sites in N fractions, one of high affinity (Kd (I)) 1.8 X 10(-8) M) and low capacity (Nmax (I) 4.6 X 10(-14) mol/mg DNA), called type I sites, and the other of lower affinity (Kd (II) 8.9 X 10(-8) M) and more numerous sites (Nmax (II) 13.1 X 10(-14) mol/mg DNA). Competition studies showed that type I sites have higher affinity for [3H]A than for other steroids. Incubation at +37 degrees C resulted in a loss of type I sites. In adrenalectomized rabbits the C binding was improved but not the N binding (Kd (I) 1.2 X 10(-8) M; Kd (II) 5.6 X 10(-8) M). In rabbits treated with aminoglutethimide, an inhibitor of steroid synthesis, the N binding was lower than in other series. It was concluded that 1) [3H]A binding in the rabbit kidney does not differ from that described in other species; 2) a low K+-high Na+ diet is a satisfactory condition for study of [3H]A binding; and 3) incubation at +30 degrees C, a temperature necessary for microdissection procedures, is suitable for aldosterone binding studies.