Control of gene expression by glucocorticoid hormones

Induction of phenylethanolamine N-methyltransferase mRNA expression by glucocorticoids in cultured bovine adrenal chromaffin cells

The effects of glucocorticoids on the expression of phenylethanolamine N-methyltransferase (PNMT) mRNA and proenkephalin A (ProEnk A) mRNA in cultures of bovine adrenal chromaffin cells were examined. The expression of PNMT mRNA (approx. 1.1 kilobases) was induced in the presence of glucocorticoids. This induction was of high potency with an EC50 in the range of 1-10 nM for dexamethasone, and was blocked by high concentrations of the glucocorticoid antagonist RU-38486. Cortisol, prednisolone and Reichstein substance S (11-deoxy-17-hydroxycorticosterone) were all effective in stimulating PNMT mRNA expression while cortisone, progesterone and beta-estradiol were without effect. These results indicate that the effects are mediated by specific glucocorticoid receptor activation and exhibited a strict structural requirement for the ability of glucocorticoids to induce PNMT mRNA expression. By contrast, glucocorticoids had no significant effect on the expression of ProEnk A mRNA. In summary, this study provides evidence that glucocorticoids act to regulate PNMT (but not ProEnk A) at the transcriptional level. This differential effect of glucocorticoids suggests that different mechanisms govern the expression of mRNAs required for synthesis of the co-stored secretory components, the enkephalins and adrenaline within the chromaffin cells of the adrenal medulla.

Glucocorticoid-receptor complexes are associated with small RNA in vitro

Identification of RNA associated with soluble glucocorticoid-receptor complexes of HeLa cells was performed by immunoprecipitation of receptor complexes with a monoclonal antibody raised against rat liver glucocorticoid receptor. Polyacrylamide gel electrophoresis of RNA extracted from immunoprecipitates of cytosolic complexes revealed the presence of eight RNA bands, consisting of 28S, 18S, and small RNAs, including 5.8S, 5S and tRNA. A comparison of RNA species immunoprecipitated by monoclonal anti-glucocorticoid receptor antibody and IgG purified from normal mouse serum showed that four small RNAs were preferentially recovered after immunoprecipitation with anti-glucocorticoid receptor antibody. When these species were analyzed on sequencing gels, their nucleotide lengths coincided with those of 7-3, 7S, U2, and U1 RNA. Immunoprecipitation of nuclear extracts containing glucocorticoid-receptor-RNA complexes showed that the same set of small RNAs was preferentially immunoprecipitated by anti-glucocorticoid receptor antibody. The four small RNAs we detected represented minor species in whole extracts, and their preferential immunoprecipitation by anti-glucocorticoid receptor antibody was prevented by removal of glucocorticoid-receptor complexes from HeLa cell extracts. We conclude that 7-3, 7S, U2, and U1 RNA are associated with glucocorticoid-receptor complexes in vitro, and hypothesize that post-transcriptional effects of glucocorticoids may in part be mediated through interaction of receptor complexes with these small RNAs.

Effects of dexamethasone on expression and maintenance of cartilage in serum-containing cultures of calvaria cells

The effects of dexamethasone on the ability of cells enzymatically isolated from 21-day fetal rat calvaria to produce cartilage in vitro has been investigated. Primary cultures of single-cell suspensions of rat calvaria were grown for up to 28 days in vitro in alpha-minimal essential medium containing 15% fetal bovine serum, 50 micrograms/ml ascorbic acid, 10 mM Na beta-glycerophosphate and dexamethasone at concentrations of 1 microM to 1 nM. Two types of nodules were present in dexamethasone-containing cultures. One has been characterized previously as bone (Bellows et al. 1986). The second morphologically resembled hyaline cartilage, possessed a strong Alcian blue-positive matrix and contained type-II, but not type-I, collagen. Both bone and cartilaginous nodules were spatially distinct and developed in isolation from each other. Cartilaginous nodules were found in the highest number at a dexamethasone concentration of 100 nM. Time-course experiments revealed that while the number of bone nodules increased continuously at least to day 28, the number of cartilaginous nodules remained constant after cultures had reached confluency. When cells were isolated separately from frontal and parietal bones and sutural regions, the greatest number of cartilaginous nodules developed from parietal bones. Since 21-day fetal rat calvaria contains 2 distinct patches of cartilage at the periphery of the parietal bones, it seems likely that this cartilaginous tissue is the origin of the cartilage cells. The results demonstrate that cultures of rat calvaria cells contain chondrocytes and possibly chondroprogenitor cells that are distinct from osteoprogenitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Second generation model for prednisolone pharmacodynamics in the rat

An improved model describing receptor/gene-mediated pharmacodynamics of prednisolone is presented which consists of seven differential equations. Data for plasma prednisolone concentrations, free hepatic glucocorticoid receptors, and hepatic tyrosine aminotransferase activity (TAT) following low (5 mg/kg) and high (50 mg/kg) doses of prednisolone are used to quantitate the kinetics and dynamics of this synthetic steroid in the rat. In contrast to the earlier model, the newer model provides for a coupling and simultaneous fitting of receptor and TAT data and is able to describe the recycling of receptors between cytosol and nucleus and the return of cytosolic receptors to baseline following glucocorticoid elimination. A numerical technique to determine the efficiency of TAT induction based on area under the curve calculations is presented, which supports the hypothesis that nonlinear dose-response effects are due to dose and time-dependent receptor depletion in the cytosol. Simulations are presented to examine the major determinants of corticosteroid effects and to compare the effects of single- and multiple-dose regimens in maximizing drug effects.

Prolactin regulation of mouse mammary tumor virus (MMTV) expression in normal mouse mammary epithelium

The hormonal regulation of mouse mammary tumor virus (MMTV) RNA in normal mouse mammary epithelium was studied in an explant system. In tissue from parous mice, physiological concentrations of prolactin stimulated MMTV expression, while only pharmacological concentrations of cortisol were effective. Regulation in explants from virgin mice was similar to that in parous animals except that the former were less sensitive to prolactin; this relative unresponsiveness may explain why uninduced tissue from virgin mice does not express MMTV RNA, while that from parous mice does exhibit some basal production. These results suggest that prolactin plays a major role in MMTV expression in normal mammary epithelium and that glucocorticoids may only have a permissive effect or may act through an indirect mechanism requiring high concentrations. These data also suggest that the greater susceptibility of parous mice to MMTV-induced tumorigenesis may reflect the greater prolactin sensitivity in the glands from these animals.

Proinsulin mRNA levels in fasting and fed ADX rats: evidence for an indirect effect of glucocorticoids

To determine whether glucocorticoids are required to maintain pancreatic proinsulin mRNA levels during dietary manipulation, rats were adrenalectomized (ADX) or sham operated (SO) and subsequently fasted or pair fed for 2 days. Proinsulin mRNA concentrations were 54 +/- 8% lower (P less than 0.05) in fed ADX rats and 47 +/- 10% lower (P less than 0.01) in fasted ADX rats relative to values in fed and fasted SO rats, respectively. When ADX rats were fasted for 24 h and either refed 20% sucrose for 30 h or injected with dexamethasone (DEX) 0.125 mg/kg ip every 12 h for three doses, circulating plasma glucose levels were restored and pancreatic proinsulin mRNA concentrations rose 3.3 and 2.7-fold, respectively (each P less than 0.05). Plasma glucose and proinsulin mRNA levels (n = 40) were correlated (r = 0.58, P less than 0.0001). We conclude that the regulation of proinsulin mRNA concentration does not absolutely require endogenous glucocorticoids, since either adequate sucrose intake in ADX rats or physiological glucocorticoid responses in fasted rats suffice to restore pancreatic mRNA concentrations. It appears that glucocorticoid stimulation of pancreatic proinsulin mRNA levels is mediated indirectly through its regulation of glucose metabolism.

Small cytoplasmic RNA associated with polyadenylated RNA is involved in the hormonal regulation of gene expression

The fraction of small RNA (sacc-RNA) associated with cytoplasmic rat liver poly(A)+ RNA by non-covalent, possibly complementary, interactions has been isolated and studied. Fingerprint analysis and Northern blot hybridization data reveal that the specific changes occur in the population of sacc-RNA in response to glucocorticoid treatment. The close similarity of the oligonucleotide composition of sacc-RNA and RNA-component of small nuclear RNP-acceptor of glucocorticoid hormones has been found. The hypothesis of the involvement of the small RNA in the hormonal regulation of posttranscriptional stages of gene expression in the cytoplasm has been put forward.

Modulation of urokinase-type plasminogen activator messenger RNA levels in human synovial fibroblasts by interleukin-1, retinoic acid, and a glucocorticoid

Previous studies have shown that mononuclear cell-conditioned medium (MCCM), interleukin-1 (IL-1), and all-trans-retinoic acid rapidly stimulate, while glucocorticoids lower, the urokinase-type plasminogen activator (u-PA) activity of human synovial fibroblast-like cells. It is now reported that MCCM, recombinant human IL-1 alpha (rHuIL-1 alpha), rHuIL-1 beta, and all-trans-retinoic acid elevate the u-PA messenger RNA (mRNA) levels to a steady-state value within 2 hours, while dexamethasone (10(-7)M) inhibits this increase. For both situations, when the u-PA activity is either stimulated or reduced, the changes in the u-PA mRNA levels parallel the changes in the u-PA activity, and it is suggested that modulation of gene transcription plays an important role.

Effect of glucocorticoids, monokines and growth factors on the spontaneously developing responses of the rabbit isolated aorta to des-Arg9-bradykinin

1. The mechanisms modulating the spontaneous induction of contractile responses to agonists of the B1-receptors for kinins have been studied by submitting the rabbit isolated aorta preparation to various in vitro treatments. Des-Arg9-bradykinin (Des-Arg9-BK), applied after 6 h of in vitro incubation was the standard stimulus to monitor this up-regulation process. 2. Specific inhibition of the development of the contractile response to des-Arg9-BK was obtained by exposing tissues continuously to dexamethasone, dexamethasone sodium phosphate (DSP) or cortisol, but not to oestradiol. The maximal extent of the inhibition obtained at high concentrations of glucocorticoids was 86%. 3. No gross inhibition of protein synthesis was observed in the presence of DSP as monitored by [35S]-methionine incorporation into incubated pieces of rabbit aorta. 4. In vivo pretreatment of rabbits with DSP did not reduce further the development of the responses in vitro. DSP applied 15 min before the 6 h recording did not antagonize the contractile effect of the BK fragment. 5. Interleukin 1 (IL-1) and interleukin 2 (IL-2) applied in vitro for the first 3 h of incubation increased the development of the contractile response to des-Arg9-BK. 6. Arachidonic acid (AA), nordihydroguaiaretic acid, tumour necrosis factor-alpha (TNF) and transforming growth factor-beta (TGF-beta) failed to influence the spontaneous development of the response to kinins. 7. Continuous exposure to DSP (100 microM) markedly inhibited the action of stimulants in this system: IL-1, IL-2, epidermal growth factor and muramyl dipeptide. Moreover, the presence of AA (30 microM) did not prevent the inhibitory effect of DSP (100 microM). 8. None of the treatments applied singly or in combination modified the contractile response of the rabbit aorta to noradrenaline. 9. The results are discussed in terms of the possible involvement of immunocompetent cells in the up-regulation of vascular responsiveness to B, receptor agonists.

Effects of SH-modifying reagents on the rat hepatic Ah receptor: inhibition of ligand binding and transformation, and disruption of the ligand-receptor complex

The importance of sulfhydryl (SH) groups in maintenance of physicochemical properties of the rat hepatic Ah receptor was demonstrated using a variety of sulfhydryl (SH)-modifying reagents. Inhibition of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) specific binding was approximately equivalent by 5,5'-dithiobis(2-nitrobenzoate), mersalyl, N-ethylmaleimide, and p-chloromercuriphenylsulfonate, whose inhibition curves were steep in the concentration range close to that of nonprotein SH groups in cytosol (ED50 values 50-200 microM or 13-48 nmol/mg cytosolic protein). Inhibition by p-hydroxymercuribenzoate (PHMB), although exhibiting a lower ED50, was more gradual over this range; iodoacetamide was an order of magnitude less potent. The ability of dithiothreitol to reverse binding inhibition induced by 150 microM (approximately 60 nmol/mg protein) mersalyl diminished with time; it decreased more rapidly in the simultaneous presence of TCDD and mersalyl than when mersalyl was present alone, consistent with increased accessibility of key SH group(s) due to conformational changes attending TCDD-receptor complex formation. Brief exposure of unoccupied receptor to mersalyl prior to TCDD binding caused slower sedimentation of the complex in 0-KCl sucrose gradients and alterations in its elution profiles on DEAE- and DNA-Sepharose suggestive of some impairment of the transformation process. When reagents were added to the transformed TCDD-receptor complex, loss of binding was observed only at concentrations which were an order of magnitude higher than those inhibiting TCDD binding. Loss of binding by each reagent was biphasic, and except for that caused by mersalyl, was not complete even after 6-8 h. Dithiothreitol was able to reverse the effects of mersalyl or PHMB only partially and only if added during the early phase (10-30 min) of binding loss. Mersalyl was much more potent in disrupting the untransformed than the transformed TCDD receptor complex. Physical alteration of the mersalyl-treated TCDD-receptor complex was evident from gel filtration, sucrose gradients, and DNA- and DEAE-Sepharose chromatography. Our results are in striking contrast to the effects of these reagents on steroid receptors, whose bound steroid hormone ligand is rapidly and reversibly displaced by lower concentrations of reagent.(ABSTRACT TRUNCATED AT 400 WORDS)

Synergistic antiproliferative effects of glucocorticoids and interferon-alpha on some lymphoid cell lines

The Daudi B lymphoblastoid cell line was previously demonstrated to be highly sensitive to the antiproliferative effect of recombinant interferon-alpha A (rIFN-alpha A). In the present study, glucocorticoid hormones were shown to act synergistically with rIFN-alpha A to further increase the sensitivity of Daudi cells to rIFN-alpha A. At 10(-6) M, dexamethasone, prednisolone, or hydrocortisone alone had little effect on Daudi cell growth, but they greatly potentiated the antiproliferative activity of rIFN-alpha A. The synergy between rIFN-alpha A and glucocorticoids on Daudi cells was not related to the inhibitory effects of glucocorticoids on prostaglandin or leukotriene synthesis, since no synergy was observed between rIFN-alpha A and indomethacin or nordihydroguaiaretic acid. Glucocorticoids and rIFN-alpha A also had appreciable synergistic antiproliferative effects on two out of five other IFN-sensitive lymphoid cell lines. When Raji B lymphoblastoid cells, which were quite resistant to the antiproliferative effect of rIFN-alpha A, were treated with the combination of glucocorticoids and rIFN-alpha A, no significant synergistic effects were observed. The synergistic antiproliferative effects of glucocorticoids and rIFN-alpha A observed with some IFN-sensitive lymphoid cell lines in this in vitro study may have clinical relevance in the treatment of certain lymphoid malignancies that are sensitive to rIFN-alpha A therapy.

Potentiation of glucocorticoid-induced lysis in refractory and resistant leukemia cells by inhibitors of ADP-ribosylation

Meta-iodo-benzylguanidine (MIBG; 3 x 10(-5) M), a novel inhibitor of mono(ADP-ribosylation)-and the general ribosylation inhibitor nicotinamide (NA; 5-20 mM) both stimulated the glucocorticoid-mediated lysis of sensitive L1210 leukemia cells and even induced susceptibility in various human and murine lines refractory or resistant to dexamethasone (DEX). Potentiation and induction of DEX-sensitivity by ADP-ribosylation inhibitors was accompanied by an increase in saturable 3H-DEX binding sites and by a 2-3 fold increase in the affinity of intracellular receptors for hormone binding. Moreover, the ribosylation inhibitors converted the glucocorticoid antagonist RU-486 into a potent agonist for cytolysis of L1210 cells. We conclude that the cytolytic action of glucocorticoid hormones in leukemic cells is negatively controlled by (mono)ADP-ribosylation of receptor proteins.

Development of glucose active transport in embryonic chick intestine. Influence of thyroxine and hydrocortisone

1. Glucose active transport is detectable in 12-day-old embryonic chick duodenum and increases at least 11-fold after 4 days of postnatal life. 2. Glucose active transport develops at the in vivo rate in 72-hr cultures of 14-day embryonic duodenum. 3. In the presence of either 1 nM thyroxine or 1 microM hydrocortisone in vitro, glucose active transport reaches levels approximately 200% of control values (equivalent to 18-19 day levels in vivo). 4. Thyroxine and hydrocortisone act by different mechanisms based on their antagonistic interaction and differences in time course of action, requirement for protein synthesis and modulation by extracellular calcium.

Glucocorticoid binding during the differentiation of 3T3-F442A fibroblasts into adipocytes. A possible regulatory effect of insulin

Until recently, few studies had been carried out on receptors for glucocorticoids in adipocytes, although the role of these steroids is considerable. In the present studies, we chose the pre-adipocyte line 3T3-F442A, which constitutes an excellent model for investigating the differentiation and function of adipocytes. Using a whole cell assay system, we showed the existence of a homogenous class of sites with the characteristics of glucocorticoid receptors, that is, high-affinity binding which is reversible, specific and saturable. Whatever the state of cellular differentiation, the affinity of the receptor for dexamethasone did not vary, although we observed an increase in the number of sites during differentiation. When cells were differentiated in the presence of insulin, there was a further increase in the binding capacity; moreover, insulin deprivation of such adipocytes caused a decrease in the number of sites. Our results therefore suggest that factors other than the glucocorticoids themselves influence dexamethasone binding. It is suggested that insulin plays a role in the regulation of the number of glucocorticoid receptors.

Plasminogen activator inhibitor type 1 biosynthesis and mRNA level are increased by dexamethasone in human fibrosarcoma cells

Dexamethasone increases type 1 plasminogen activator inhibitor (PAI-1) activity released from the human fibrosarcoma cell line HT-1080. We demonstrated that dexamethasone caused about 10-fold increases in the intracellular and extracellular levels of PAI-1 protein, as measured by an enzyme-linked immunosorbent assay, in the rate of PAI-1 biosynthesis, and in the PAI-1 mRNA level. The effects on PAI-1 biosynthesis and mRNA level were detectable within 4 h and were maximal 16 to 24 h after the addition of dexamethasone. Cycloheximide did not inhibit the dexamethasone-induced increases in the capacity of the cells to synthesize PAI-1 and in the PAI-1 mRNA level.

Cloning and 5' end nucleotide sequences of two juvenile hormone-inducible vitellogenin genes of the African migratory locust

Screening of lambda libraries prepared with locust (Locusta migratoria) genomic DNA yielded overlapping clones containing two complete vitellogenin genes, designated A and B, along with extensive 3'- and 5'-flanking sequences. Genes A and B are about 12 kb and 10.5 kb long, respectively, and both hybridize on Northern blots with 6300-nucleotide RNAs previously identified as vitellogenin mRNAs. Each gene contains a large intron near the 5' end and must also contain other introns. Repetitive "Lm1 elements," similar to the human Alu repetitive DNA elements, and other repeated sequences occur within the large intron and in the 3'- and 5'-flanking regions of each gene. Southern blots showed no cross-hybridization between the major portions of mRNA-coding sequences of genes A and B. DNA sequences have been determined for the 5' terminal exons and flanking regions of both genes. Both genes contain short (56-58 nucleotide) 5' leader exons, which, unlike the rest of the coding region, are highly conserved in sequence (87% identical) and code for amino acids that resemble the amino-terminal sequences of vertebrate vitellogenins. The upstream 5'-flanking sequences of the two genes contain several short stretches of similarity that may be involved in juvenile hormone regulated expression.

Plasminogen activator inhibitor type 1 biosynthesis and mRNA level are increased by dexamethasone in human fibrosarcoma cells

Dexamethasone increases type 1 plasminogen activator inhibitor (PAI-1) activity released from the human fibrosarcoma cell line HT-1080. We demonstrated that dexamethasone caused about 10-fold increases in the intracellular and extracellular levels of PAI-1 protein, as measured by an enzyme-linked immunosorbent assay, in the rate of PAI-1 biosynthesis, and in the PAI-1 mRNA level. The effects on PAI-1 biosynthesis and mRNA level were detectable within 4 h and were maximal 16 to 24 h after the addition of dexamethasone. Cycloheximide did not inhibit the dexamethasone-induced increases in the capacity of the cells to synthesize PAI-1 and in the PAI-1 mRNA level.

Glucocorticoid receptors bound to the antagonist RU486 are not downregulated despite their capacity to interact in vitro with defined gene regions

Modulation of gene expression by glucocorticoids involves interaction of these hormones with an intracellular receptor followed by 'transformation' of the hormone-receptor complex into a nuclear binding form. The molecular basis for the antiglucocorticoid action of high-affinity steroid analogues such as RU486 remains controversial. The effects of dexamethasone and RU486 on in vitro and in vivo properties of the receptor were compared using human lymphoblastoid IM-9 cells. In these cells, RU486 fully antagonized the glucocorticoid-specific induction of 5'-nucleotidase activity by dexamethasone. In vitro, however, RU486-bound receptor could be transformed and shown to interact specifically with cloned DNA fragments containing glucocorticoid response elements. These fragments included one from the mouse mammary tumour virus and two from the human growth hormone gene. In vivo, RU486-bound receptor did not behave like dexamethasone-bound receptor. While receptor downregulation, a property of the transformed receptor, was achieved by dexamethasone, this did not occur with RU486. Likewise, RU486 did not affect receptor half-life under conditions when this was shortened by dexamethasone. These seemingly contradictory results can be reconciled by proposing that receptor transformation by agonists involves dissociation of the receptor oligomer to reveal a DNA-binding site that pre-exists on this protein. Although cell-free receptor dissociation and therefore DNA binding can occur even when the receptor is bound to RU486, this steroid maintains receptors in the untransformed state in the intact cell and therefore behaves a glucocorticoid antagonist in vivo.

Glucocorticoid-induced growth inhibition of human neoplastic salivary gland duct cell line (HSG)

The purpose of this study was to examine the effect of glucocorticoid on human neoplastic salivary duct epithelial cell line (HSG). Dexamethasone was found to inhibit cell growth and to increase cell size and the ratio of protein content to DNA content in a cell. The inhibition of cell growth was dose-dependent; in comparison to the control (33.8 +/- 3.1 h), the population doubling time was 1.57-fold longer in 10(-5) M dexamethasone (P less than 0.01, N-K test). [3H] thymidine incorporation was inhibited in 45.5% of the control at 10(-5) M. Plating efficiency was 20.5 +/- 3.0% in 10(-5) M and 47.0 +/- 4.4% in the absence of dexamethasone. Cell diameters increased 1.29 fold in 10(-5) M dexamethasone in comparison to the control size (16.0 +/- 2.1 micron). The ratio of total protein content of DNA content increased 1.46 fold in 10(-5) M dexamethasone-treated cells on the seventh day of cultivation. Scatchard plot analysis using [6, 7-3H]-triamcinolone revealed that the HSG cells had apparent cytosolic glucocorticoid receptors with an equilibrium dissociation constant (Kd value) of 6.48 nM, whose number of binding sites (NBS) was 57.8 fmol/mg protein.

Identification of two forms of molybdate-stabilized, non-transformed glucocorticoid hormone-receptor complex by gel filtration chromatography

Glucocorticoid-receptor complexes in rat thymus cytosol were characterized by gel-filtration chromatography on Agarose A-1.5 m and Sephacryl S-300. Two forms of non-transformed complex were identified at low ionic strength in the presence of molybdate, with Stokes radii of approx 8 nm and 6 nm. The 8 nm molybdate-stabilized form could be converted to the 6 nm form by chromatography on Sephacryl S-300 or Lipidex 1000 or by incubation with dextran-charcoal or phospholipase C, but not by chromatography on Sephadex G-25; none of the treatments promoted receptor transformation. It is suggested that the change in Stokes radius from 8 to 6 nm results from the removal of a lipid factor responsible for maintaining the complex in the 8 nm form.

Regulation of hepatic glucokinase gene expression. Role of carbohydrates, and glucocorticoid and thyroid hormones

The present study investigates the effect of thyroid and glucocorticoid hormones on the induction of hepatic glucokinase mRNA activity, enzyme synthesis and activity in starved/refed adrenalectomized, thyroidectomized and intact rats. In intact rats glucose refeeding resulted within 2 h in a more than tenfold increase in the functional messenger, followed by a corresponding increase in glucokinase synthesis and, a little later, in enzyme activity. Glucokinase mRNA and synthesis remained elevated at this level for about further 6 h. Then the mRNA activity and enzyme synthesis declined considerably to a new steady state (a factor of about 4 above the starvation level) within a further 8 h, while enzyme activity remained constantly elevated. The half-life of glucokinase mRNA, as determined after administration of cordycepin, was identical during the different refeeding periods. Thus the overshoot phenomenon, provoked by carbohydrate refeeding, in glucokinase mRNA is not explained by alteration of the glucokinase mRNA decay rates. In thyroidectomized or adrenalectomized rats, glucose refeeding resulted in only a small increase in glucokinase mRNA, synthesis and activity. Application of thyroid hormones in thyroidectomized rats, refed a carbohydrate-rich diet, enhanced the specific mRNA considerably within 8-10 h, while it took 20-24 h to enhance glucokinase mRNA by glucocorticoids in adrenalectomized rats refed a carbohydrate-rich diet. The decay in translatable glucokinase mRNA, as determined after administration of cordycepin, was identical in the hypothyroid and euthyroid fed state, while adrenalectomy resulted in a significant decrease in the specific mRNA half-life. We conclude that refeeding a carbohydrate-rich diet rapidly stimulates glucokinase mRNA regeneration showing overshoot kinetics. 3,3',5-Triiodothyronine in its physiological concentration significantly enhances the response in glucokinase mRNA at the nuclear level, while glucocorticoids in their physiological concentration predominantly stabilize the translatable glucokinase mRNA.

Analysis of the glucocorticoid antagonist action of dexamethasone 21-mesylate in HeLa S3 cells

Several properties of human glucocorticoid receptors complexed to the synthetic glucocorticoid agonists dexamethasone (DEX) and triamcinolone acetonide (TA) and the antagonist dexamethasone 21-mesylate (DM) are compared in an attempt to define the mode of action of DM. Both DEX and TA induce an increase in alkaline phosphatase activity in HeLa S3 cells. Not only is DM without effect on alkaline phosphatase activity at concentrations as great as 10(-7) M, it blocks the action of DEX and TA on enzyme induction, thus acting as a pure antagonist in this system. DM-receptor complexes, like agonist-receptor complexes, are recovered in the cytosol when cells are incubated with ligand at 0 degrees C but are recovered from the nucleus when incubation is shifted to 37 degrees C, suggesting that activation of the antagonist-receptor complex occurs in vivo. The molecular species that undergoes this temperature-dependent shift from the cytosolic compartment to the nuclear compartment exhibits saturable binding to the antagonist. Both the cytosolic and nuclear species exhibit a relative molecular mass of approximately equal to 94,000 Daltons when analysed by SDS-polyacrylamide gel electrophoresis. Receptors labeled in intact cells with [3H]DM at 0 degrees C sediment at approximately 8S in sucrose gradients, shifting to 4S when the gradients contain 0.4 M KCl. DEX- and TA-labeled receptors show the same sedimentation behavior, which has been accepted as one criterion of receptor subunit dissociation, or activation.

Glucocorticoid regulation of glycerol phosphate dehydrogenase and ornithine decarboxylase activities in the spinal cord of the rat

We examined the effects of glucocorticoids on induction of glycerol phosphate dehydrogenase (GPDH) and ornithine decarboxylase (ODC) in the spinal cord of rats. After a single subcutaneous dose of 5 mg/kg of dexamethasone (DEX) phosphate, GPDH activity was maximally increased at 20 h with the effect still persisting for 46 h, in contrast to ODC activity, which was already stimulated at 4 h. The enzyme induction was accompanied by a reduction in number of cytosolic glucocorticoid receptors already at 1 h after DEX treatment, with replenishment at 22 h. A dose-response curve for DEX demonstrated that the minimal effective dose (0.2 mg/kg) for enzyme induction also reduced the number of cytosolic receptors because of occupation/depletion. The effects were specific for natural and synthetic glucocorticoids, as GPDH and ODC activities were not stimulated by aldosterone, testosterone, estradiol, or progesterone. ODC was induced in the cervical region of the spinal cord as well as in the horse tail plus filum terminale, whereas GPDH responded in the former but not the latter region. Previous work has demonstrated that glucocorticoid receptors are slightly more concentrated in the cervical spinal cord. It is suggested that glucocorticoid induction of these two predominantly glial enzymes occurs by a steroid receptor-mediated event, as postulated in other regions of the nervous system. In view of the short latency required for induction of ODC, we also examined the effect of inhibitors of transcription and translation. Whereas cycloheximide reduced the stimulatory effect of DEX, a paradoxical stimulation was obtained when DEX and dactinomycin (actinomycin D) were given concomitantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleotide sequences required for the regulation of a rat alpha 2u-globulin gene by glucocorticoids

alpha 2u-Globulin is a rat protein of as yet unknown function whose synthesis can be induced by glucocorticoids and several other hormones. Induction by glucocorticoids is a secondary response to the hormone: protein synthesis is required before the hormone can exert its stimulatory effect on alpha 2u-globulin transcription. We have used the linker-scanning mutagenesis procedure, followed by transfer of the mutant genes into mouse L-cells for analysis of their phenotype, to determine sequences within a cloned alpha 2u-globulin promoter that are required for its regulation by glucocorticoids. Mutations between positions -115 and -160 abolish or greatly reduce the inducibility of alpha 2u-globulin by the hormone. Mutations just upstream from this region, between positions -177 and -220, have an opposite effect; they increase induction two- to fourfold.

Effects of phenobarbital and 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene on differentiated functions in mouse liver

The promoters of murine hepatocarcinogenesis phenobarbital (PB) and 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) given to adult C3Hf female mice increased the content of total liver DNA by 1.6-1.8-fold each week after the beginning of treatment. Both compounds increased the aminopyrine-N-demethylase activity, decreased the glucose 6-phosphatase (G6Pase), alkaline phosphodiesterase I and alkaline phosphatase specific activities, but did not modify the gamma-glutamyltransferase levels. Both compounds decreased the abundance of tyrosine aminotransferase- and metallothionein I-related RNA transcripts. These findings confirmed the PB-like activity of TCPOBOP and showed that both chemicals had a pleiotropic effect on mouse liver, that was not limited to stimulation of drug metabolism, but also affected other hepatocyte functions.

Effects of nutritional and hormonal factors on the metabolism of retinol-binding protein by primary cultures of rat hepatocytes

Studies were conducted to explore hormonal and nutritional factors that might be involved in the regulation of retinol-binding protein (RBP) synthesis and secretion by the liver. The studies employed primary cultures of hepatocytes from normal rats. When cells were cultured in Dulbecco's modified Eagle's medium alone, a high rate of RBP secretion was observed initially, which declined and became quite low by 24 hr. Supplementing the medium with amino acids maintained RBP and albumin secretion at moderate (but less than initial) rates for at least 3 days. Further addition of dexamethasone maintained the production and secretion rates of RBP, transthyretin, and albumin close to the initial rates for up to 3-5 days in culture. The effects of dexamethasone were not rapid and were not specific for RBP; half-maximal effects were seen at 10(-9) to 10(-8) M levels. Hormonally treated hepatocytes produced and secreted RBP, transthyretin, and albumin at both absolute and relative rates similar to physiological values, as estimated from rates reported by others from studies in vivo (with both rats and humans) and with perfused livers. Glucagon addition partially maintained the secretion rates of these 3 proteins, but less effectively than did dexamethasone. A number of other hormones, added singly or in combination, did not affect RBP production or secretion. Addition of retinol to the cultured normal hepatocytes was without effect upon RBP secretion. These studies show that supplementing the culture medium of hepatocytes with amino acids and dexamethasone maintains RBP production and secretion for several days. In normal hepatocytes, with ample supply of retinol available within the cell, addition of exogenous retinol does not appear to influence RBP metabolism or secretion by the cells.

Approach to the molecular mechanisms of the modulation of growth hormone gene expression by glucocorticoid and thyroid hormones

Glucocorticoid and thyroid hormones modulate the expression of the growth hormone gene. To investigate this control mechanism, we have determined whether this gene contains sites that bind the human glucocorticoid and thyroid hormone receptors in vitro. To do so, we have designed a novel assay for studying binding of the purified glucocorticoid receptor to cloned fragments of the human growth hormone (hGH) gene, and have adapted a DNA-competition assay for the thyroid receptor in nuclear cell extracts. Two glucocorticoid receptor binding regions were found in the hGH gene, one of high affinity in a fragment of the gene containing the first intron, and one of low affinity located within a 290 bp-fragment of 5'-flanking DNA. In contrast, the thyroid receptor bound with high affinity to the 5'-flanking fragment. Homologous binding regions for the two types of receptor were found in the human placental lactogen (chronic somatomammotropin) gene. DNA binding of the two receptor types appeared to depend on the presence of the hormone, yet antagonist-bound glucocorticoid receptor was still capable of interacting specifically with DNA. There was no evidence for synergism or antagonism of the two receptor types in binding to their respective sites on the hGH gene. The data also make it unlikely that the thyroid receptor negatively controls gene transcription and that the stimulatory effect of thyroid hormone results from a derepression mechanism.

Genetics of glucocorticoid receptors

The lymphocytolytic effect of glucocorticoids has been used for isolating receptor mutants. They fall into several groups with defects either in the hormone binding domain or the DNA binding domain or with part of the receptor polypeptide missing. These truncated receptors have increased binding affinity for general DNA and are synthesized from 5'-truncated messages. In addition, a phenotype has been identified in which a receptor allele, although apparently normal, is shut-off with no gene product detectable. The wild-type receptor polypeptide of about 95,000 molecular weight is synthesized from two mRNAs of 7 kb and 5 kb which differ in the lengths of their 3'-untranslated regions. A receptor model with three linearly arranged and functionally distinct domains is discussed. The DNA binding domain is rich in basic amino acids and cysteines and is located in the middle of the polypeptide. This region has the highest degree of homology with the estrogen receptor and with the v-erb-A oncogene product.

Regulation of ketogenesis, gluconeogenesis and the mitochondrial redox state by dexamethasone in hepatocyte monolayer cultures

The effects of the glucocorticoid dexamethasone on fatty acid and pyruvate metabolism were studied in rat hepatocyte cultures. Parenchymal hepatocytes were cultured for 24 h with nanomolar concentrations of dexamethasone in either the absence or the presence of insulin (10 nM) or dibutyryl cyclic AMP (1 microM BcAMP). Dexamethasone (1-100 nM) increased the rate of formation of ketone bodies from 0.5 mM-palmitate in both the absence and the presence of BcAMP, but inhibited ketogenesis in the presence of insulin. Dexamethasone increased the proportion of the palmitate metabolized that was partitioned towards oxidation to ketone bodies, and decreased the cellular [glycerol 3-phosphate]. The latter suggests that the increased partitioning of palmitate to ketone bodies may be associated with decreased esterification to glycerolipid. The Vmax. of carnitine palmitoyltransferase (CPT) and the affinity of CPT for palmitoyl-CoA were not affected by dexamethasone, indicating that the increased ketogenesis was not due to an increase in enzymic capacity for long-chain acylcarnitine formation. Dexamethasone and BcAMP, separately and in combination, increased gluconeogenesis. In the presence of insulin, however, dexamethasone inhibited gluconeogenesis. Changes in gluconeogenesis thus paralleled changes in ketogenesis. Dexamethasone decreased the [3-hydroxybutyrate]/[acetoacetate] ratio, despite increasing the rate of ketogenesis and presumably the mitochondrial production of reducing equivalents. The more oxidized mitochondrial NADH/NAD+ redox couple with dexamethasone is probably due either to an increased rate of electron transport or to increased transfer of mitochondrial reducing equivalents to the cytoplasm.

Spermine antagonises the effects of dexamethasone, glucagon and cyclic AMP in increasing the activity of phosphatidate phosphohydrolase in isolated rat hepatocytes

Rat hepatocytes were incubated in monolayer culture, under serum free conditions, for 8 h. Glucagon (10 nM), 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (100 microM) and dexamethasone (100 nM) increased the activity of phosphatidate phosphohydrolase by approx. 2-, 3.6- and 3.3-fold, respectively. Spermine alone had no significant effect. Spermine (2.5 mM) almost completely inhibited the glucagon induced increase in phosphohydrolase activity. It only partially inhibited the dexamethasone and cyclic AMP mediated inductions. Spermidine had no significant effect in this respect. The results are discussed in relation to the known effects of polyamines on glycerolipid synthesis, in particular, and on intermediary metabolism.

Studies with chymotrypsin and RNAase showing a heterooligomeric structure of the glucocorticoid receptor complex from rat liver which is stabilized by a low molecular weight factor

The glucocorticoid receptor from rat liver displays a differential sensitivity toward digestion by chymotrypsin and RNAase A that is dependent on its activation state. Unactivated (9-10 S) receptor is not digested by these enzymes, while activated 7-8 S receptor is. Chymotrypsin treatment yields an approx. 3 S form, while RNAase treatment yields a 4.9 S form that is distinct from the high-salt 4 S form. To firmly establish that the results are due to specific hydrolytic activities of the particular enzymes, we show that the chymotrypsin effect is inhibited by diisopropylfluorophosphate and not RNAasin, while the reverse is true for RNAase A. We further show that the differential sensitivity toward chymotrypsin is due to the association of a proteinase-resistant, heat-stable low molecular weight factor with the unactivated glucocorticoid receptor. When this factor is removed by warming, dialysis or molecular sieving of the receptor complex, the complex becomes sensitive to chymotrypsin. We also show that moderate chymotrypsin treatment yields a 6-7 S form of the receptor which is composed of, at least, RNA and the 4 S receptor. On the basis of these results, we propose that the 9-10 S receptor is composed of a low molecular weight stabilizing factor whose presence apparently alters the conformation of the complex such that the RNA and the RNA-binding site of the receptor are protected, a chymotrypsin-sensitive factor, RNA and the 4 S receptor itself.

Glucocorticoid stimulation of choline-phosphate cytidylyltransferase activity in fetal rat lung: receptor-response relationships

A number of previous studies using in vivo and cultured fetal lung models have shown that the activity of choline-phosphate cytidylyltransferase, the enzyme which catalyzes a rate-limiting reaction in de novo phosphatidylcholine synthesis, is increased by glucocorticoids and other hormones which accelerate fetal lung maturation. To examine the mechanism of this glucocorticoid action further, we examined the effect of dexamethasone on cytidylyltransferase activity in cultured fetal rat lung explants and related it to specific dexamethasone binding. Dexamethasone stimulated cytidylyltransferase activity in the homogenate, microsomal and 105,000 X g supernatant fractions. The hormone did not alter the subcellular distribution of the enzyme, however; the bulk of the activity was in the supernatant fraction in both the control and dexamethasone-treated cultures. The dose-response curves for stimulation of cytidylyltransferase activity in the supernatant fraction and specific nuclear binding of dexamethasone were similar and both plateaued at approx. 20 nM. The EC50 for cytidylyltransferase stimulation was 6.6 nM and the Kd for dexamethasone binding was 6.8 nM. The relative potencies of various steroids for stimulating choline-phosphate cytidylyltransferase and for specific nuclear glucocorticoid binding were the same: dexamethasone greater than cortisol = corticosterone = dihydrocorticosterone greater than progesterone. The stimulation by dexamethasone of cytidylyltransferase activity and of choline incorporation into phosphatidylcholine were both abolished by actinomycin D. These data show that the stimulatory effect of dexamethasone on fetal rat lung choline-phosphate cytidylyltransferase activity is largely on the enzyme in the supernatant fraction and does not involve enzyme translocation to the microsomes as has been reported for cytidylyltransferase activation in some other systems. This effect of dexamethasone is a receptor-mediated process dependent on RNA and protein synthesis.

Cooperative effect of thyroid and glucocorticoid hormones on the induction of hepatic phosphoenolpyruvate carboxykinase in vivo and in cultured hepatocytes

The present study investigates the effect and interaction of glucocorticoid and thyroid hormones on the induction of phosphoenolpyruvate carboxykinase (PEPck) mRNA and enzyme protein under in vivo conditions and in serum-free cultured hepatocytes from hypothyroid rats. In hypothyroid/adrenalectomized rats T3 significantly enhanced the cAMP induced PEPck mRNA activity within 3-6 h. This effect was further enhanced by the presence of glucocorticoids. The half-life of PEPck mRNA, as determined after administration of cordycepin, was not affected by hypothyroidism or hyperthyroidism (t 1/2 approximately equal to 45 min), but considerably prolonged by the absence of glucocorticoid hormones (t 1/2 less than 80 min). In hepatocytes in culture Bt2cAMP (0.2 mM) provoked an increase in translatable PEPck mRNA within 2 h incubation time. Preincubation with either T3 (0.1 microM) or dexamethasone (0.1 microM) for 4 h significantly enhanced the cAMP response on PEPck mRNA. Addition of both, T3 plus dexamethasone further enhanced this Bt2cAMP-mediated effect. By measurement of PEPck synthesis corresponding findings were observed. It is concluded that glucocorticoid and thyroid hormones predominantly enhance the cAMP-provoked induction of hepatic PEPck mRNA and, consequently, of PEPck synthesis. Their effect is rapid, significant and additive, indicating an independent action. While glucocorticoids, in addition, accelerate PEPck mRNA degradation, the PEPck mRNA decay rate is similar in the presence and absence of thyroid hormones.

Down-regulation of glucocorticoid receptor mRNA by glucocorticoid hormones and recognition by the receptor of a specific binding sequence within a receptor cDNA clone

A cDNA clone for the rat glucocorticoid receptor (GR) was used to study mechanisms of GR mRNA regulation. Treatment of rat hepatoma culture cells with 0.5 microM dexamethasone caused a small, initial increase in the GR mRNA level after 6 hr as well as a 50% to 95% reduction of the GR mRNA level after 24 hr of incubation when studied by RNA blot hybridization. After 72 hr, the initial GR mRNA level was restored. The down-regulation of GR mRNA levels appears to be independent of protein synthesis, since it also was observed in the presence of cycloheximide. However, cycloheximide caused a 4-fold increase in intracellular levels of GR mRNA. Using an immunoprecipitation assay, we could demonstrate that the GR specifically interacts with a GR cDNA clone, which represents a 2.6-kilobase fragment of the 3' nontranslated region of the GR mRNA. Nuclease protection experiments indicate the presence of several internal GR-binding regions in the above fragment.

Nucleotide sequences required for the regulation of a rat alpha 2u-globulin gene by glucocorticoids

alpha 2u-Globulin is a rat protein of as yet unknown function whose synthesis can be induced by glucocorticoids and several other hormones. Induction by glucocorticoids is a secondary response to the hormone: protein synthesis is required before the hormone can exert its stimulatory effect on alpha 2u-globulin transcription. We have used the linker-scanning mutagenesis procedure, followed by transfer of the mutant genes into mouse L-cells for analysis of their phenotype, to determine sequences within a cloned alpha 2u-globulin promoter that are required for its regulation by glucocorticoids. Mutations between positions -115 and -160 abolish or greatly reduce the inducibility of alpha 2u-globulin by the hormone. Mutations just upstream from this region, between positions -177 and -220, have an opposite effect; they increase induction two- to fourfold.

Regulation of the synthesis of lipoprotein lipase in adipose tissue by dexamethasone

The incorporation of [3H]leucine into lipoprotein lipase during incubations of rat epididymal fat-bodies in vitro was significantly stimulated by dexamethasone, whereas total protein synthesis was unaffected. The stimulation by dexamethasone required the presence of insulin. The results suggest that dexamethasone, in the presence of insulin, may specifically induce lipoprotein lipase synthesis in adipose tissue.

Glucocorticoids and the isolated rat hepatocyte

Following incubation at 37 degrees C with tritiated glucocorticoids isolated hepatocytes prepared from non-adrenalectomized rats show rapid uptake of label. Uptake is non-saturable, and non-linear over the first 60 sec of exposure to steroids. HPLC separation of aqueous extracts of cells and incubation medium shows that polar metabolites of the natural steroid, corticosterone, appear within 10 sec, whereas the synthetic glucocorticoid, dexamethasone, is not altered. Our results suggest that diffusion is the most important process by which glucocorticoids enter liver cells, and that the predominant fate of corticosterone is rapid metabolism.

Functional analysis of the purified glucocorticoid receptor

Glucocorticoid-receptor complex (GR) has been purified from rat liver by differential affinity for DNA before and after activation, followed by ion-exchange chromatography. The purified GR has mol. wt 94,000 dalton. The protein contains three functional domains: (A) a steroid-binding domain; (B) a DNA-binding domain; and (C) a domain necessary for normal biological function. A second protein, with mol. wt 72,000 dalton, copurifies with the GR. This protein does not bind steroid, does not interact with antibodies raised against the GR and does not show the same susceptibility to limited proteolytic cleavage as the 94,000 dalton protein. Analysis of the specific interaction of the purified GR with the mouse mammary tumour virus gene, assayed by glycerol-gradient centrifugation, shows that one molecule of 94,000 dalton protein binds to each of the specific binding sites in the long terminal repeat region. Analysis of the fractions from the glycerol gradients show that the 72,000 dalton protein is associated to the binding species (94,000 dalton receptor protein) in about equimolar amounts. Analysis of the molybdate-stabilized non-activated receptor complex using monoclonal antibodies raised against the 94,000 dalton receptor protein indicates that the molybdate-stabilized complex is a hetero-oligomer. The hetero-oligomer consists of only one molecule of the 94,000 dalton receptor protein, in association with other non-steroid-binding proteins.

Affinity-labeling steroids as biologically active probes of antiglucocorticoid hormone action

The role of the glucocorticoid receptor in the expression of antiglucocorticoid action has been investigated with a chemically-reactive derivative of three glucocorticoid steroids with differing biological potencies, i.e. the C-21 mesylates of cortisol, dexamethasone and deacylcortivazol. Dexamethasone 21-mesylate (Dex-Mes) was the most useful derivative due to its favorable balance of high receptor affinity and predominantly irreversible antiglucocorticoid activity. A number of criteria have been used to conclude that [3H]Dex-Mes covalently labels glucocorticoid receptors in the steroid-binding cavity. The available data indicate that covalent Dex-Mes-labeled receptors (mol. wt approximately equal to 98,000) are responsible for the irreversible antiglucocorticoid activity while the partial agonist activity of Dex-Mes is due to non-covalent Dex-Mes-bound receptors. Further support for this hypothesis comes from the observations that deacylcortivazol 21-mesylate was a full glucocorticoid and did not affinity label receptors (and marginally labeled cytosol proteins) although it was capable of covalently-labeling bovine serum albumin. Several mechanisms for the expression of irreversible antiglucocorticoid activity by covalent Dex-Mes-labeled receptors were examined and can be eliminated. Covalent receptor-Dex-Mes complexes formed in whole HTC cells were found to have a decreased capacity for nuclear binding. This decreased nuclear-binding capacity could be responsible for the whole-cell irreversible antiglucocorticoid activity of Dex-Mes.

Binding of the human glucocorticoid receptor to defined regions in the human growth hormone and placental lactogen genes

An in vitro competition assay was used to investigate whether binding sites for the human glucocorticoid receptor occur in the human genes for growth hormone (hGH) and placental lactogen (chorionic somatomammotropin, hCS). These genes display 95% sequence homology. Two receptor-binding regions were found in the hGH gene, one of which is located within 290 bp upstream, and one within 251 bp downstream from the transcription initiation site. Two binding regions homologous to those in the hGH gene were found in the hCS gene. The receptor-binding DNA fragment from the structural part of the genes, but not that from their promoter area, contained a sequence homologous to a 15-bp consensus sequence proposed earlier for the glucocorticoid receptor binding site. It is unlikely that the putative difference in glucocorticoid sensitivity between the hGH and hCS genes is accounted for by major differences in glucocorticoid receptor binding pattern.

Rapid induction of selective transcription by auxins

Nuclei isolated from excised soybean plumules that were treated with 2,4-dichlorophenoxyacetic acid (2,4-D) were active in transcription of four auxin-regulated genes or DNA sequences, which have been described previously (G. Hagen, A. Kleinschmidt, and T. Guilfoyle, Planta 162:147-153, 1984). The rates of transcription of the auxin-responsive sequences were 10- to 100-fold greater with nuclei isolated from auxin-treated plumules than with those from untreated plumules. The transcriptional response was also observed with hypocotyls of intact soybean seedlings and hypocotyl sections, as well as with green bean and mung bean plumules that were treated with 2,4-D. Other auxins, including 2,4,5-trichlorophenoxyacetic acid, alpha-naphthaleneacetic acid, and indole-3-acetic acid, also induced the transcriptional response. Increased transcription rates were observed within 5 min after application of auxins to excised plumules, and half-maximal to maximal transcription rates were achieved by 15 min after application of auxins. As little as 10(-7) to 10(-8) M 2,4-D induced a transcriptional response, but maximal transcription rates were achieved at 10(-3) M 2,4-D. Brief treatment with the protein synthesis inhibitor cycloheximide did not inhibit the induction of transcription by auxins. These results clearly demonstrated that auxin-regulated gene expression is under rapid transcriptional control.

Post-transcriptional regulation of rat liver gene expression by glucocorticoids

We have investigated the mechanisms whereby glucocorticoids control the expression of specific genes in the livers of adult male rats. Construction and differential screening of a cDNA library representing normal rat liver polysomal poly(A)+ RNAs allowed selection of probes for hormonally regulated genes. The mechanism of this regulation was analysed by studying the changes in relative abundance of the RNA sequences homologous to four selected recombinants in RNA from subcellular fractions of liver, and comparing them with that of albumin mRNA. The relative abundance of these four RNA sequences increased to varying degrees in the nucleus, whilst that of three of them was concomitantly depleted in polysomal RNA when circulating levels of glucocorticoids were negligible, i.e. 14 days after adrenalectomy. One of the sequences was identified as alpha 2U-globulin mRNA. Within 2 hours of injecting Dexamethasone (a synthetic glucocorticoid) into rats that had been adrenalectomised 14 days previously, the relative abundances of alpha 2U-globulin RNA in nuclear and polysomal RNA returned to those found in normal rat liver. The data indicate that reduced glucocorticoid levels lead to sequence specific retention of RNA in the nucleus and that the RNA retained is released to the cytoplasm following glucocorticoid injection. Our results provide an example, for the first time, of glucocorticoid regulation of gene expression at the post-transcriptional level of nucleo-cytoplasmic transport.

Regulation of type IV collagen degrading enzyme by cortisol during human skin fibroblast growth

The effects of cortisol on type IV collagenolytic enzyme activity were studied in human skin fibroblast cultures. Cortisol reduced the production of the enzyme, both in normally dividing fibroblasts, and also when the secretion was induced by the administration of the tumor promoter 12-O-tetradecanoyl phorbol 13-acetate (TPA) to the subconfluent culture. TPA decreased the glucocorticoid receptor activity and augmented the cGMP content of subconfluent fibroblasts. Type IV collagenolytic activity appeared to be correlated positively with the cGMP/cAMP ratio, and negatively with the glucocorticoid receptor activity, and the activity was increased by the addition of dibutyryl cGMP. This suggests that this enzyme may at least partly be under glucocorticoid control during fibroblast growth, and that TPA may to some degree act via the inactivation of glucocorticoid receptors.