Androgen "receptor" in rat liver: cytosol "receptor" deficiency in pseudohermaphrodite male rats

A distal activation domain is critical in the regulation of the rat androgen receptor gene promoter

The far upstream region of the rat androgen receptor (AR) gene has been cloned, and the nucleotide sequence up to -2656 bp established. Nested deletion mutants of rat AR 5' flanking sequences were ligated to the luciferase reporter gene, and their promoter activities were examined in transfected COS1 cells. Results show a critical cis-acting domain located between positions -960 and -940. Deletion of this cis element resulted in a greater than 90% decrease in the promoter activity. A nuclear protein that specifically binds to this 21-nucleotide sequence was identified by gel mobility shift analysis. The -960/-940 cis element has no identify to the binding sequence of any known transcription factor. Furthermore, the cognate binding protein is present in both rat and human (HeLa) cell nuclear extracts. We conclude that a novel trans-activator interacting at the -960/-940 region plays a critical role in the regulation of AR gene expression.

Can a single androgen receptor fill the bill?

If the above two hypotheses are correct, they would require at least one more specific nuclear receptor for T, and at least one membrane receptor to account for the very rapid effects induced by androgens on certain target tissues. If this is the case, clearly a single androgen receptor will not fill the bill.

Changes in hepatic androgen sensitivity and gene expression during aging

The hepatic tissue of the male rat exhibits a gradual decline and ultimate loss in androgen responsiveness during in vivo aging. Appearance of the age-associated androgen insensitivity can be delayed by dietary calorie restriction, an effective means for life-span extension. The androgen receptor mRNA is detectable in the liver only in its androgen-responsive state. Pubertal appearance of hepatic androgen sensitivity is remarkably correlated with the concomitant appearance of a cytoplasmic androgen binding (CAB) protein. Androgen resistance during senescence is associated with the loss of hepatic CAB activity as well. We are investigating the molecular basis for the temporal modulation of this hormone sensitivity through studies on the differential expression of two androgen-responsive marker genes. These are the androgen-repressible SMP-2, and the androgen-inducible alpha 2u-globulin. Androgen resistance of hepatocytes during aging results in repression of the alpha 2u-globulin gene, and derepression of the SMP-2 gene. The structural organizations for both of these genes have been characterized. The role of nuclear transcription factors (androgen receptor and any other transacting factor(s) which may be involved) in the coordinate regulation of alpha 2u-globulin and SMP-2 during aging and nutritional manipulation is being explored to establish the molecular mechanism of andropause in the liver.

Effects of chronic ethanol intake on aromatization of androgens and concentration of estrogen and androgen receptors in rat liver

The present study was carried out to investigate if ethanol alters aromatization of androgens and concentrations of hepatic estrogen and androgen receptors. Hepatic aromatization of androgen to estrogen was significantly increased by ethanol administration. There was a significant increase in serum estrogen level but a decreased circulating testosterone level in alcohol-fed rats. Furthermore, the concentration of estrogen receptors in liver cytosol was significantly higher in alcohol-fed rats (37 +/- 5.3 fmol/mg protein), as compared to the intact control value (21 +/- 4.8 fmol/mg protein). However, hepatic androgen receptor levels were much lower (4.4 +/- 0.5) in alcohol-fed rats than those (10.2 +/- 1.4 fmol/mg protein) in control animals. Similarly, castration increased hepatic aromatization of androgens and concentrations of serum estrogen and hepatic estrogen receptors, but it decreased contents of circulating androgen and hepatic androgen receptors. These findings indicate that alcohol administration is considered a chemical form of castration, altering the hepatic steroid metabolism and sex hormone receptor contents and contributing to the pathogenesis of feminization. A combination of alcohol-feeding and castration has no synergistic effect on the hepatic steroid receptors and aromatization, but this combination does have a more profound effect in lowering the concentration of circulating androgen.

Absence of a 23 kd protein in testes of testicular feminization rat

Cryptorchid testes of testicular feminization rats are very low in zinc in spite of normal zinc status of the animals. Analysis of the cytosol of the cryptorchid testes by gel permeation chromatography showed decreased zinc binding by proteins eluted at fractions corresponding to 30,000 dalton. Further analysis by sodium dodecylsulphate polyacrylamide gel electrophoresis indicated the absence of a protein with molecular weight of 23,000.

Mechanisms of physiological and pharmacological sex hormone action on the mammalian liver

Androgen and oestrogen receptors have been demonstrated in mammalian liver, but since it is generally accepted that they are probably non-functional at endogenous steroid concentrations, it is not apparent how they mediate physiological influences on this organ. Nor is it certain to what extent pharmacological actions of sex hormones reflect overstimulation of physiological routes or whether alternative mechanisms become available once threshold values have been reached. In this presentation an attempt has been made to answer some of these questions using data obtained from a study of the regulation of the activities of microsomal 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSDH) and 5 alpha-reductase in rat liver. Androgens exert their primary physiological and pharmacological influences at the level of the hypothalamus. Oestrogens can elicit three different types of effect-physiological, antiandrogenic and pharmacological--of which the first two involve primary effects on the pituitary. Hepatic oestrogen receptors only become activated when oestrogen concentrations reach pharmacological levels. Progestins probably have no physiological influence on the livers of non-pregnant rats. Their pharmacological actions may either be traced back to secondary androgenic (e.g. medroxyprogesterone acetate, levonorgestrel) or oestrogenic (e.g. norethynodrel, lynestrenol) properties, involving the routes described above, or to independent effects on the central nervous system (e.g. cyproterone acetate modulation of 5 alpha-reductase activity).

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.

Androgen receptors in the brain of neonatal normal male and androgen insensitive rats

Androgen binding was investigated in the cytosol of brains from neonatal normal and tfm rats using sucrose gradient and charcoal assay. The neonatal normal rat brain contains androgen receptors which sediment at 8S in a sucrose gradient at low ionic strength and at 4S in the presence of 0.5M KC1. These receptors have a high affinity (Kd = 1.2 X 10(-9)M) for dihydrotestosterone (DHT), with a binding capacity of 7.3 X 10(-15) moles/mg cytosol protein. By contrast, there is very little, if any, high affinity androgen receptors in the neonatal tfm rat brain. Apparently, metabolism of testosterone does not affect androgen binding in the neonatal rat brain. The presence of these receptors and the occurrence of aromatization in the brain of neonatal rats are discussed in relation to their possible roles in sexual differentiation of the brain.

Multihormonal induction of alpha 2u-globulin in an established rat hepatoma cell line

A subclone of the FU5-5 rat hepatoma cell line has been isolated which is inducible more than several hundred fold for the 20,000 dalton form of the major rat urinary protein alpha 2u-globulin. The basal relative synthetic rate (RSR) in growth medium containing 10% fetal calf serum was less than 2 X 10(-6) of total protein synthesis. Both dexamethasone and insulin were necessary for induction, and yielded a maximum induced RSR of 4-8 X 10(-3). Triiodothyronine (T3), dihydrotestosterone (DHT), rat growth hormone (GH), and estrogen, all of which have been shown to influence the induction of alpha 2u-globulin in the intact rat, were without effect on the cell line. A factor present in fetal calf serum was also necessary for maximum induction, since dexamethasone plus insulin in serum-free medium raised the RSR to only 3 X 10(-5); exogenous T3, GH, and DHT could not substitute for this serum factor. The kinetics of induction by dexamethasone were slow, with a lag of approximately 48 hr followed by a period of increasing RSR for 6-20 days. Removal of dexamethasone from induced cells led to an exponential decline in the RSR (t 1/2 15 hr). The concentrations of dexamethasone and insulin that could yield half maximum induction were 5 X 10(-8)M and 3 X 10(-11)M, respectively. Higher concentrations of insulin, although still in physiological range (10(-9)M), inhibited induction. At yet higher insulin levels, beyond the physiological range, alpha 2u-globulin synthesis returned to maximum values. The lack of DHT, T3, and GH requirement for alpha 2u-globulin induction in this cell line may mean that a regulatory aberrancy has occurred in this transformed cell line, or, alternatively, that these hormones act indirectly in the intact animal. This cell line should prove useful for the study of the molecular events associated with alpha 2u-globulin induction and for genetic approaches to the problem of multihormonal regulation of gene expression.

Some theoretical questions of the peptide and steroid hormone regulation. Part I.: The receptor-steroid variable complex (RSVC) hypothesis of genetic regulation

Steroids exert their known biological and biochemical effects in connection with specific receptors. These effects are so various and complex that it is impossible to explain them on the basis of a concept supposing the presence of only one unique receptor molecule in the target organs. The heterogeneity in the function of steroids requires a heterogeneity in the molecular composition of the receptor-steroid complexes. Direct and indirect evidence is presented to support a multiplex, heterogene receptor theory. The possible origin of this complexity is analyzed and a new concept of specific gene regulation by heterogene receptor-steroid complexes is suggested. in this theory the distribution and sequence of one or more steroids on the receptor can carry and serve highly specific and unique information capable or recognizing and binding to the acceptor site of the chromatin and regulating gene expressions specific for steroids. The formation of such Receptor-Steroid Variable Complexes (RSVC) has been mathematically analyzed and the properties of a chromatin protein capable of detecting both the DNA and the steroid sequences on the receptor are discussed.

Binding of dihydrotestosterone to a nuclear-envelope fraction from the male rat liver

Intact nuclear 'ghosts' containing small amounts of DNA were obtained from rat liver. Incubation of radiolabelled dihydrotestosterone with isolated nuclear-envelope fraction from male rat liver resulted in specific binding of the dihydrotestosterone to the membranes. Optimal binding occurred at 20 degrees C after 20h incubation. Storage for 2 weeks at -80 degrees C resulted in little loss of specific binding. Scatchard analysis revealed a class of binding sites with a KD of 23.2 nM. Pronase and heat treatment destroyed the binding site. Androgens and glucocorticoids competed for labelled dihydrotestosterone binding to the ghosts, whereas oestrogens did not compete. Castration 24h before preparation of ghosts did not alter the binding site, and a similar class of binding sites was identified on female rat liver nuclear envelopes.

Testosterone: a major determinant of extragenital sexual dimorphism

Sexual dimorphism in selected extragenital tissues is described with emphasis on the molecular basis of the differences. Testosterone rather than 5 alpha-dihydrotestosterone appears to be the major intracellular androgen in organs other than skin and reproductive tract, but other steroid metabolites and their receptors are required to produce the diverse tissue differences observed in males and females. There is also evidence that multiple hormones from several endocrine glands are required to act in concert with androgens to produce and maintain their effects. Although many of the consequences of sexual dimorphism, such as body size and strength, have been evident for centuries, other differences between males and females such as disease incidence, response to drugs and toxins, and the metabolism and assimilation of dietary constituents have only recently been discovered.

Early events in the steroidal regulation of alpha2mu globulin in rat liver. Evidence for both androgenic and estrogenic induction

1. A double-antibody radioimmunoassay for alpha2mu globulin has been developed. With the help of this highly sensitive radoimmunoassay the early effects of both androgen and estrogen treatments on the hepatic synthesis of alpha2mu globulin in the rat have been investigated. 2. Results show that the earlier observation of the long lag period in the androgenic induction of alpha2mu globulin is more apparent than real. 3. Single injections of either 5alpha-dihydrotestosterone(5alpha-dihydro-17beta-hydroxy-4-androsten-3-one) or its physiological antagonist estradiol-17beta (1,3,5(10)-estratriene-3,17beta-idol) to castrated female rats resulted in the induction of alphamu globulin reaching maximum hepatic level of the protein between 6--9 h after the hormone administration. Administration of cycloheximide 15 prior to hormone treatment blocked both androgenic andestrogenic induction of alpha2mu globulin. 4. Daily pretreatments with 5alphamu-dihydrotestosterone increased the sensitivity of subsequent androgenic response to alpha2muglobulin synthesis. On the other hand, daily pretreatments with estradiol 17beta decreased and ultimately abolished the estrogenic induction of alpha2mu globulin. 5. The possible mechanism of both androgenic and estrogenic induction of alpha2mu globulin in rat liver mediated through a sex-hormone-binding protein with dual affinity for both dihydrotestosterone and estradiol has been suggested.

Bone marrow ribonucleic acid polymerase. Effect of testosterone on nucleotide incorporation into nuclear RNA

The incorporation of 3H-UTP into RNA by isolated rat bone marrow nuclei is stimulated by testosterone. This effect is hormone and tissue specific. Using alpha-amanitine and different ionic strength conditions it was found that testosterone enhances preferentially RNA polymerase I activity. The sedimentation pattern of RNA isolated from bone marrow nuclei shows that the synthesis of RNA species within the 14-30 S range is mainly stimulated by the hormone.

Hormonal regulation of the hepatic messenger RNA levels for alpha2u globulin

The messenger RNA rat alpha2u globulin has been identified and quantitated in a cell-free translational system derived from Krebs II ascites cells. Hepatic tissue of the mature male rats which normally produce alpha2u globulin was also found to contain a high level of alpha2u mRNA. Approximately 1.6 per cent of all poly(A) containing RNA of the adult male rat liver could be accounted for alpha2u messenger activity. Female rats do not produce alpha2u globulin and no alpha2u mRNA activity could be detected in the poly(A) containing RNA fraction obtained from the livers of these animals. However, androgen treatment to spayed female rats was found to induce the parallel appearance to both alpha2u globulin and its corresponding mRNA. Both hypophysectomy and adrenalectomy which are known to reduce the level of alpha2u globulin in the urine of male rats were found also to reduce the hepatic level of alpha2u mRNA. The results indicate that hormonal control of alpha2u globulin synthesis in rat liver is achieved primarily through regulation of its translatable mRNA level and that more than one hormone may participate in this regulation.