The glucocorticoid receptor protein binds to transfer RNA

Quantification of transcriptome changes to investigate the role of glucocorticoid receptor-RNA binding during dexamethasone treatment

OBJECTIVES

The glucocorticoid receptor (GR) is a well-studied, ligand-activated transcription factor and a common target of anti-inflammatory treatments. Recently, several studies have drawn attention the effects of binding of GR to RNA rather than DNA and the potential implications of this activity for GR function. The objective of our study was to further characterize the relationship between GR function and RNA binding by measuring changes in the glucocorticoid-driven transcriptome in the presence of a GR mutant that exhibited reduced RNA affinity.

DATA DESCRIPTION

GR was activated in three cell lines containing GR constructs (GR-HaloTag). One of the cell lines contained a wild-type GR-HaloTag. Another contained GR-HaloTag with a mutation that reduced RNA affinity and slightly reduced DNA affinity. The third cell line contained GR-HaloTag with a mutation that only slightly reduced DNA affinity. All three cell lines were treated with dexamethasone, a GR agonist. RNA-seq samples were collected every hour for 3 h. Moreover, transcriptome quantification was accomplished via labeling of RNAs transcribed in the final hour of dexamethasone treatment using 4-thiouridine. These labeled RNAs were then purified and sequenced. This data set is the first of its kind for GR and contains valuable insights into the function of RNA binding by GR.

The Biologist's Guide to the Glucocorticoid Receptor's Structure

The glucocorticoid receptor α (GRα) is a member of the nuclear receptor superfamily and functions as a glucocorticoid (GC)-responsive transcription factor. GR can halt inflammation and kill off cancer cells, thus explaining the widespread use of glucocorticoids in the clinic. However, side effects and therapy resistance limit GR's therapeutic potential, emphasizing the importance of resolving all of GR's context-specific action mechanisms. Fortunately, the understanding of GR structure, conformation, and stoichiometry in the different GR-controlled biological pathways is now gradually increasing. This information will be crucial to close knowledge gaps on GR function. In this review, we focus on the various domains and mechanisms of action of GR, all from a structural perspective.

The glucocorticoid receptor DNA-binding domain recognizes RNA hairpin structures with high affinity

The glucocorticoid receptor (GR) binds the noncoding RNA Gas5 via its DNA-binding domain (DBD) with functional implications in pro-apoptosis signaling. Here, we report a comprehensive in vitro binding study where we have determined that GR-DBD is a robust structure-specific RNA-binding domain. GR-DBD binds to a diverse range of RNA hairpin motifs, both synthetic and biologically derived, with apparent mid-nanomolar affinity while discriminating against uniform dsRNA. As opposed to dimeric recognition of dsDNA, GR-DBD binds to RNA as a monomer and confers high affinity primarily through electrostatic contacts. GR-DBD adopts a discrete RNA-bound state, as assessed by NMR, distinct from both free and DNA-bound. NMR and alanine mutagenesis suggest a heightened involvement of the C-terminal α-helix of the GR-DBD in RNA-binding. RNA competes for binding with dsDNA and occurs in a similar affinity range as dimer binding to the canonical DNA element. Given the prevalence of RNA hairpins within the transcriptome, our findings strongly suggest that many RNAs have potential to impact GR biology.

Conserved sequence-specific lincRNA-steroid receptor interactions drive transcriptional repression and direct cell fate

The majority of the eukaryotic genome is transcribed, generating a significant number of long intergenic noncoding RNAs (lincRNAs). Although lincRNAs represent the most poorly understood product of transcription, recent work has shown lincRNAs fulfill important cellular functions. In addition to low sequence conservation, poor understanding of structural mechanisms driving lincRNA biology hinders systematic prediction of their function. Here we report the molecular requirements for the recognition of steroid receptors (SRs) by the lincRNA growth arrest-specific 5 (Gas5), which regulates steroid-mediated transcriptional regulation, growth arrest and apoptosis. We identify the functional Gas5-SR interface and generate point mutations that ablate the SR-Gas5 lincRNA interaction, altering Gas5-driven apoptosis in cancer cell lines. Further, we find that the Gas5 SR-recognition sequence is conserved among haplorhines, with its evolutionary origin as a splice acceptor site. This study demonstrates that lincRNAs can recognize protein targets in a conserved, sequence-specific manner in order to affect critical cell functions.

The structure, function and evolution of proteins that bind DNA and RNA

Proteins that bind both DNA and RNA typify the ability of a single gene product to perform multiple functions. Such DNA- and RNA-binding proteins (DRBPs) have unique functional characteristics that stem from their specific structural features; these developed early in evolution and are widely conserved. Proteins that bind RNA have typically been considered as functionally distinct from proteins that bind DNA and studied independently. This practice is becoming outdated, in partly owing to the discovery of long non-coding RNAs (lncRNAs) that target DNA-binding proteins. Consequently, DRBPs were found to regulate many cellular processes, including transcription, translation, gene silencing, microRNA biogenesis and telomere maintenance.

The human glucocorticoid receptor as an RNA-binding protein: global analysis of glucocorticoid receptor-associated transcripts and identification of a target RNA motif

Posttranscriptional regulation is emerging as a key factor in glucocorticoid (GC)-mediated gene regulation. We investigated the role of the human GC receptor (GR) as an RNA-binding protein and its effect on mRNA turnover in human airway epithelial cells. Cell treatment with the potent GC budesonide accelerated the decay of CCL2 mRNA (t(1/2) = 8 ± 1 min versus 62 ± 17 min in DMSO-treated cells) and CCL7 mRNA (t(1/2) = 15 ± 4 min versus 114 ± 37 min), but not that of CCL5 mRNA (t(1/2)=231 ± 8 min versus 266 ± 5 min) in the BEAS-2B cell line. This effect was inhibited by preincubation with an anti-GR Ab, indicating that GR itself plays a role in the turnover of these transcripts. Coimmunoprecipitation and biotin pulldown experiments showed that GR associates with CCL2 and CCL7 mRNAs, but not CCL5 mRNA. These methods confirmed CCL2 mRNA targeting by GR in human primary airway epithelial cells. Association of the GR was localized to the 5' untranslated region of CCL2 mRNA and further mapped to nt 44-60. The collection of transcripts associated with GR, identified by immunoprecipitation of GR-mRNA complexes followed by microarray analysis, revealed 479 transcripts that associated with GR. Computational analysis of the primary sequence and secondary structures of these transcripts yielded a GC-rich motif, which was shown to bind to GR in vitro. This motif was used to predict binding of GR to an additional 7889 transcripts. These results indicate that cytoplasmic GR interacts with a subset of mRNA through specific sequences and can regulate turnover rates, suggesting a novel posttranscriptional role for GR as an RNA-binding protein.

MacroRNA underdogs in a microRNA world: evolutionary, regulatory, and biomedical significance of mammalian long non-protein-coding RNA

The central dogma of molecular biology relegates RNAs to the role of "messengers" of genetic information, with proteins as the end products that perform key roles as regulators and effectors of biological processes. Notable exceptions include non-protein-coding RNAs, which function as adaptors (tRNAs) and ribosomal components (rRNAs) during translation, as well as in splicing (snRNAs) and RNA maturation including editing (snoRNAs). Genome and transcriptome projects have revealed, however, a significant number, rivaling the protein-coding transcripts, of non-protein-coding RNAs not related to these previously characterized transcript classes. Non-protein-coding RNA research has primarily focused on microRNAs, a small subclass of non-protein-coding RNAs, and their regulatory roles in gene expression, and these findings have been reviewed extensively. Here, we turn our attention to the larger, in number and size, long non-coding RNAs (lncRNAs), and review their evolutionary complexity and the growing evidence for their diverse mechanisms of action and functional roles in basic molecular and cellular biology and in human disease. In contrast to the focus on in-silico and expression studies in existing lncRNA literature, we emphasize direct evidence for lncRNA function, presenting experimental approaches and strategies for systematic characterization of lncRNA activities, with applications to known gene regulatory networks and diseases.

Science Signaling Podcast: 2 February 2010

A noncoding RNA competes with DNA for binding to the glucocorticoid receptor.

Noncoding RNA gas5 is a growth arrest- and starvation-associated repressor of the glucocorticoid receptor

The availability of nutrients influences cellular growth and survival by affecting gene transcription. Glucocorticoids also influence gene transcription and have diverse activities on cell growth, energy expenditure, and survival. We found that the growth arrest-specific 5 (Gas5) noncoding RNA, which is abundant in cells whose growth has been arrested because of lack of nutrients or growth factors, sensitized cells to apoptosis by suppressing glucocorticoid-mediated induction of several responsive genes, including the one encoding cellular inhibitor of apoptosis 2. Gas5 bound to the DNA-binding domain of the glucocorticoid receptor (GR) by acting as a decoy glucocorticoid response element (GRE), thus competing with DNA GREs for binding to the GR. We conclude that Gas5 is a "riborepressor" of the GR, influencing cell survival and metabolic activities during starvation by modulating the transcriptional activity of the GR.

Neuropilin-1 Is Expressed on Bone Marrow Stromal Cells: A Novel Interaction With Hematopoietic Cells?

In adult bone marrow, hematopoietic stem cells are found in close association with distinctive stromal cell elements. This association is necessary for maintenance of hematopoiesis, but the precise mechanisms underlying the cross-talk between stromal cells and hematopoietic stem cells are poorly understood. In this study, we used a bone marrow stromal cell line (MS-5) that is able to support human long-term hematopoiesis. This hematopoietic-promoting activity cannot be related to expression of known cytokines and is abolished by addition of hydrocortisone. Using a gene trap strategy that selects genes encoding transmembrane or secreted proteins expressed by MS-5 cells, we obtained several insertions that produced fusion proteins. In one clone, fusion protein activity was downregulated in the presence of hydrocortisone, and we show that insertion of the trap vector has occurred into the neuropilin-1 gene. Neuropilin-1 is expressed in MS-5 cells, in other hematopoietic-supporting cell lines, and in primary stromal cells but not in primitive hematopoietic cells. We show that neuropilin-1 acts as a functional cell-surface receptor in MS-5 cells. Two neuropilin-1 ligands, semaphorin III and VEGF 165, can bind to these cells, and the addition of VEGF 165 to MS-5 cells increases expression of 2 cytokines known to regulate early hematopoiesis, Tpo and Flt3-L. Finally, we show that stromal cells and immature hematopoietic cells express different neuropilin-1 ligands. We propose that neuropilin-1 may act as a novel receptor on stromal cells by mediating interactions between stroma and primitive hematopoietic cells.

Potential mechanisms underlying autoregulation of glucocorticoid receptor mRNA levels in the DHD/K12/PROb rat colonic adenocarcinoma cell line

The DHD/K12/PROb rat colonic epithelial cell line, which was originally derived from a chemically induced adenocarcinoma, expresses functional glucocorticoid receptors (GR) and has been reported to be growth inhibited by glucocorticoid agonists. In the present study the potential mechanisms underlying corticosteroid-mediated autoregulation of GR mRNA levels in this colonic cell line were investigated. The GR mRNA levels in the various treatment groups were quantitated via the ribonuclease protection assay using a specific 32P-cRNA probe. Time-course experiments demonstrated that in contrast to several other cell lines that are also growth inhibited by glucocorticoids, treatment of confluent monolayers of PROb cells with the pure GR agonist RU 28362 (1 microM) elicits a rapid and significant (65%) down-regulation of GR mRNA levels that is sustained for at least 36 h. This down-regulation, which is also elicited to a lesser extent by weaker GR agonists including corticosterone and aldosterone, is blocked by the GR antagonist RU 38486. The protein synthesis inhibitor cycloheximide was utilized to demonstrate that the initial phase (6 h) of agonist-mediated down-regulation occurs independently of ongoing protein synthesis, although new protein synthesis, perhaps of the GR protein itself, is required to maintain this down-regulation. Although agonist-mediated down-regulation in these cells probably occurs primarily at the level of GR gene transcription, inhibition of ongoing RNA synthesis with actinomycin D or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) demonstrated that during the initial phase (1 h) of this down-regulation, but not following maximal (18 h) down-regulation, RU 28362 treatment also significantly reduces the stability of the GR mRNA.

Adrenalectomy-induced increase of brain protein synthesis is antagonized by corticosterone replacements in free-moving rats

The autoradiographic method with L-[35S]-methionine was used to determine whether changes in glucocorticoid circulating levels were associated with changes in local rates of protein synthesis in rat brain. Chronic bilateral adrenalectomy induced an increase of methionine incorporation rates into proteins in 60 of the 62 brain regions examined (mean effect, +50%). This effect was confirmed biochemically and quantified by correcting for the relative contribution of methionine derived from protein degradation to the precursor pool for protein synthesis in the whole brain. Acute or chronic administration of corticosterone, at doses that normalize basal levels of adrenocorticotrophic hormone, reversed or prevented the adrenalectomy-induced increase of protein synthesis in most regions. However, in nearly all the regions studied (59 of 62), acute corticosterone administration to sham-operated rats did not change the apparent rate of protein synthesis. These results demonstrate that glucocorticoids exert a generalized inhibitory action on brain protein synthesis, because the stimulatory and persistent effect of adrenalectomy on protein synthesis was antagonized by corticosterone replacements at physiological doses. Thus, the regulation of overall brain protein synthesis by glucocorticoids emphasizes the role of neuroendocrine events on long-term neurochemical processes.

The major RNA in prosomes of HeLa cells and duck erythroblasts is tRNA(Lys,3)

Two-dimensional gel electrophoresis of HeLa cell prosomal RNAs, 3'-end labeled by RNA ligase, revealed one prominent spot. Determination of a partial sequence at the 3'-end indicated full homology to the 18 nucleotides at the 3'-end of tRNA(Lys,3) from rabbit, the bovine and the human species. An oligonucleotide complementary to the 3'-end of tRNA(Lys,3) hybridized on Northern blots with prosomal RNA from both HeLa cells and duck erythroblasts. In two-dimensional PAGE, the major pRNA of HeLa cells co-migrated with bovine tRNA(Lys,3). Reconstitution of the CCA 3'-end of RNA from both human and duck prosomes, by tRNA-nucleotidyl-transferase, confirmed the tRNA character of this type of RNA. Furthermore, it revealed at least one additional tRNA band about 85 nt long among the prosomal RNA from both species. Finally, confirming an original property of prosomal RNA, we show that in vitro synthesized tRNA(Lys,3) hybridizes stably to duck globin mRNA, and to poly(A)(+)- and poly(A)(-)-RNA from HeLa cells.

A model for the determination of the 3D-spatial distribution of the functions of the hormone-binding domain of receptors that bind 3-keto-4-ene steroids

A method of comparing the hydrophobic clusters of proteins (hydrophobic cluster analysis, HCA) has revealed that the 3D-folding pattern of the hormone-binding domain (HBD) of steroid hormone receptors (SHRs) may have an unexpectedly high degree of analogy with the known 3D-crystal structures of proteins belonging to the serine proteinase inhibitor (SERPIN) superfamily, e.g. alpha 1-antitrypsin and ovalbumin. The present paper briefly reviews some of the biochemical evidence that supports the structural validity of the SERPIN model and shows how the model can be used to establish hypothetical 3D-locations for functions attributed to different amino-acids or peptide sequences of the HBD: i.e. heat-shock protein binding, transcription activation, phosphorylation, steroid binding, but also ATP-binding. Indeed, the model has enabled the identification of a Rossmann-fold in SHRs that might bind ATP. Visualization of all these functions should help to interpret the chain of concerted events induced by steroid binding.

Glucocorticoid receptors in human malignancies: a review

The present knowledge of the human glucocorticoid receptor (hGCR) in primary malignancies is reviewed. It is concluded that hGCR is present in a large number of these tissues; in all tissue specimens of lymphoid malignancies and in varying fractions of the different solid tumors. The hGCR functions as a hormone dependent, specific enhancer interacting protein in mediating the considerable effects of glucocorticoids on growth regulation, both through stimulation and inhibition of expression of the target genes, including other transcription regulation systems. The processes of receptor activation and regulation, as well as the effects of glucocorticoids, are tissue-specific. Subjects for future research are proposed: Establishment of more cell lines and animal models to extend investigation beyond the present concentration on only a few cell lines, especially CEM-C7, application of 'dynamic' assays to cells obtained from patients, in an attempt to predict development of glucocorticoid resistance, and further investigation of the relationships among GCR and growth factors and oncogenes.

Dexamethasone inhibits human interleukin 2 but not interleukin 2 receptor gene expression in vitro at the level of nuclear transcription

Glucocorticosteroids have an inhibitory effect on the expression of interleukin 2 (IL-2) and interleukin 2 receptor (IL-2R) genes. To determine the mechanisms of this inhibition, human T lymphocytes were stimulated with mitogens in the presence of dexamethasone. Nuclear transcription run-off assays showed that high doses of dexamethasone inhibited the transcription of the IL-2 gene but not that of the IL-2R gene. Post-transcriptionally, high doses of dexamethasone (10(-4) M) were required to inhibit IL-2R mRNA levels by 50%, whereas lower doses (10(-6) M) inhibited by greater than 70% the accumulation of IL-2 mRNA. IL-2 mRNA half-life decreased in the presence of dexamethasone (10(-6) M) by approximately 50%. At the protein product level, dexamethasone inhibited both IL-2 production, as well as cell surface and soluble forms of IL-2R. IL-2R gene expression was inhibited for at least 72 h after exposure of cells to dexamethasone. In the presence of exogenous IL-2, dexamethasone failed to exert a significant effect on the production of IL-2R protein. These data indicate that dexamethasone has a greater effect on the expression of the IL-2 gene than on the IL-2R gene. Dexamethasone both inhibits transcription of the IL-2 gene and decreases the stability of IL-2 mRNA. The effect of dexamethasone on the IL-2R gene is post-transcriptional and may result indirectly from decreased IL-2 production.

Depletion of rat liver glucocorticoid receptor hormone-binding and its mRNA in sepsis

Glucocorticoid receptor (GR) hormone-binding activity, its physical characteristics, and GR mRNA levels were studied in the liver, brain and muscle of normal (saline-injected) and hypermetabolic septic rats 24 h after the subcutaneous injections of E. coli. The GR levels (hormone-binding activity) declined by about 40%, 56%, and 40% in septic liver, brain, and muscle cytosol, respectively. The mechanism of the decrease in the GR levels in sepsis was studied in liver. The GR levels remained low (45% of control hormone-binding) even after 48 h of E. coli administration. The decrease in the liver GR occurred in the 9S untransformed GR. The 9S GR from septic liver transformed to the 4S form in proportions comparable to the control liver GR. In addition, the 4S GR from control and septic liver was capable of binding to DNA-cellulose to a similar extent. The GR mRNA level in septic liver declined by about 30%. Thus, a decrease in GR hormone-binding activity in sepsis appears to be due to a decline in the steady-state GR mRNA level and not from a change in the qualitative properties of the GR protein.

Purification and characterization of the activated mineralocorticoid receptor from rat myocardium

Cardiac cytosol from adrenalectomized rats was radiolabelled with 10 nM tritiated RU 26752, R 5020 or aldosterone, to saturate the mineralocorticoid receptor (MCR) in the presence of 1 microM RU 38486 to block the glucocorticoid and progestin receptors. Free steroids were removed by charcoal treatment and the radiolabelled cytosol was passed through a phosphocellulose column. The MCR peak in the phosphocellulose eluate was activated at 25 degrees C for 45 min, adsorbed onto the DNA-cellulose and finally extracted once each with buffers containing 1 M potassium chloride or 25 mM magnesium chloride. The pooled DNA-cellulose extracts, reequilibrated with 10 nM [3H]RU 26752, were resolved as a single, homogeneous band of 78 kDa upon polyacrylamide gel electrophoresis. Ion-exchange analysis of the purified MCR on DEAE-cellulose-52 revealed a single peak in the 0.017 M sodium phosphate region with both RU 26752 and R 5020, but aldosterone dissociated during this procedure. Molecular filtration on Ultrogel AcA-44 columns revealed a major 145 kDa peak, with some smaller components of 40 and 80 kDa. These hydrodynamic properties of the purified MCR are at variance with those of the native receptor in crude myocardial cytosol, and suggest that some post-translational modifications in vivo may be required for the expression of MCR-mediated responses.

Purification and characterization of the activated mineralocorticoid receptor from rat kidney

1. The mineralcorticoid receptor (MR) from rat kidney was purified within 8 hr by the following, successive steps: stabilization with synthetic, tritiated steroids (RU 26752 or R 5020), phosphocellulose passage, heat activation (25 degrees C), and DNA-cellulose batch elution. 2. The purified preparation was resolved as a single, 75 KDa band on SDS-PAGE electrophoresis although the exact degree of purity was difficult to assess by the charcoal assay due to denaturation. 3. The natural hormone, aldosterone, was unsuitable for receptor purification and characterization. 4. The MR purified with different ligands behaved identically during ion exchange and gel permeation analyses, suggesting post-translational modifications of the native receptor in whole cytosol that exhibits molecular heterogeneity.

Mapping contacts between unpurified human progesterone receptor and the hormone response element of mouse mammary tumor virus

Binding of steroid hormone receptors to specific recognition sites of hormone-inducible genes is one of the events required for hormonal regulation of gene transcription. We have employed an immunoprecipitation assay to map the interaction between unpurified human progesterone receptors from crude nuclear extracts of T47D cells and the hormone response element of the mouse mammary tumor virus (MMTV). DNase I footprints and methylation interference patterns are similar to those reported with highly purified rabbit progesterone receptors, suggesting that both human and rabbit receptors recognize similar features in the hormone response element. More importantly, these patterns suggest that if other factors are associated with unpurified nuclear receptor, they do not alter the contacts made by receptor nor do they make contacts themselves with MMTV DNA in a manner detected by DNase I or methylation interference assays. The sites of interaction of receptors bound with the clinically important progestin antagonist, RU 486, are comparable to those observed with an agonist-receptor complex. These results suggest that the antagonist prevents receptor action at a step after its recognition and binding to specific sites on a hormone-responsive enhancer element.

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.

Heterogeneity and properties of transformation of corticosteroid receptors in spinal cord and hippocampus

The central nervous system contains two classes of corticoid receptors, named types I and II following terminology accepted for the kidney. Phenotypically, type I sites are differentiated into a corticosterone (CORT)-preferring species (Ia) and a mineralocorticoid receptor (Ib). These populations were tentatively compared in the spinal cord and hippocampus. Using [3H]dexamethasone (DEX) and selective blockage of sites, we have observed that type II receptors were comparable in both tissues, while Ia was almost exclusive of the hippocampus. Saturation analysis using [3H]DEX demonstrated that type Ia was a low affinity receptor (Kd approximately equal to 2-5 nM) while type II was a higher affinity site (KdII less than KdI). Using [3H]CORT, or [3H]aldosterone (ALDO), as ligand, preferential labeling of type I sites was achieved, always showing higher concentrations in the hippocampus. Therefore, [3H]DEX seems a ligand of choice to visualize types Ia and II receptors. Another difference noted between the spinal cord and hippocampus, pertained to the sensitivity towards the enzyme RNAse A, which increases heat-induced transformation of the bound receptor, according to the results of DNA cellulose affinity chromatography. In these experiments, type I sites of both spinal cord and hippocampus, plus type II of hippocampus, showed sensitivity toward the enzyme, whereas type II of the spinal cord was refractory to RNAse A enhancement of transformation. These results indicate that the dynamics of transformation is different among receptors showing similar affinity and competition, suggesting further heterogeneity due to receptors themselves, or to tissue factors regulating their biochemical properties.

tRNA(Tyr) genes of Drosophila melanogaster: expression of single-copy genes studied by S1 mapping

Six Drosophila melanogaster tRNA(Tyr) genes have been isolated and sequenced. They contained introns of different sequences and two size classes: 20 or 21 base pairs (bp) (five genes) and 113 bp (one gene). However, the sequences coding for the mature tRNA(Tyr) were identical in all six genes. The 113-bp intron-containing gene was a single-copy gene. Hence, its primary transcript could be traced by S1 mapping. The gene was turned on during embryogenesis and continually expressed to various degrees during the following developmental stages. Thus, S1 mapping is a feasible method to follow the transcriptional activity of individual genes with identical mature products, provided that their primary transcripts are unique. The six genes were organized in two clusters of three and two genes, respectively (each containing a 20- or a 21-bp intron; cytological localization, 85A), and a single-copy gene (113-bp intron; cytological localization, 28C). We show that four of the six tRNA(Tyr) genes characterized were localized in putative 5' control regions of developmentally controlled genes transcribed by polymerase II.

Glucocorticoid receptor activation in isolated perfused rat hearts

The formation of unactivated and activated glucocorticoid receptor complexes was studied in intact, isolated, perfused rat hearts in the presence of [3H]triamcinolone acetonide. Receptor activation, as quantified by the DNA-cellulose-binding assay, began to increase within 30 s of perfusion and reached a final steady-state level (t 1/2 = 4.6 min) with 46% of the steroid-receptor complexes bound to DNA-cellulose. With the use of a linear potassium phosphate (KP) gradient (5-400 mM), unactivated receptors eluted from DEAE-cellulose anion exchange columns at approximately 250 mM KP. Two activated receptor forms appeared, which eluted either in the wash fraction (binder IB) or between 50 and 100 mM KP (binder II) and occurred with half times of 1.3 and 2.7 min, respectively. Postperfusion cytosol preparation did not markedly influence the results as receptor binding was reduced by 10% or less when a 100-fold excess of unlabeled triamcinolone acetonide was included in the homogenizing buffer. We conclude from these results that glucocorticoids are able to exert a direct effect on the heart through binding to their own receptor in the absence of endogenous hormones. The time dependency of receptor activation supports a physiological role for this process. However, activation rates, determined from conformational changes associated with altered DEAE-cellulose elution profiles and appearance of activated receptor forms, occur earlier and may not be coordinated with the rate of activation as quantified by DNA-cellulose binding.

Translational regulation of myelin protein synthesis by steroids

Various steroids, including glucocorticoids, were observed to exert a direct effect on the rates of translation of several myelin-protein specific transcripts in a cell-free, reticulocyte lysate system. Hydrocortisone caused a twofold stimulation in the translation of mRNAs of myelin basic protein and proteolipid protein. It inhibited the translation of 2',3'-cyclic nucleotide 3'-phosphodiesterase mRNA by 50%, and had no effect on the translation of a number of other mRNAs. The data suggest that steroid-mediated translational regulation may serve as a novel mechanism to modulate the expression of myelin protein genes at the translational level.

RNA-induced transformation of the estrogen receptor detected by a monoclonal antibody which recognizes the activated receptor

The effect of RNA and polyribonucleotides on the estrogen receptor from fetal guinea pig uterus was studied through the analysis of the sedimentation properties of this receptor and its interaction with the monoclonal antibody D547. Different exogenous RNAs (calf thymus RNA, yeast RNA and rabbit liver transfer RNA) were able to induce a transformation of the 9S native receptor to 4.5-7S sedimenting forms in low salt sucrose density gradients, as activating factors such as temperature and time do. This transformation was prevented by 20mM sodium molybdate. Moreover, the RNA treated receptor was partially recognized by the monoclonal antibody D547. This antibody, as was demonstrated previously, selectively reacts with the activated form of this receptor. When different homo-polyribonucleotides were tested, the effect depended on their composition. In contrast, DNA did not affect either the sedimentation properties of the receptor or its reaction with the antibody. These observations suggest that RNA induces a dissociation of the 9S receptor and that at least one of the resulting forms is the activated receptor. However, RNA and polyribonucleotides inhibited the receptor binding to DNA-cellulose apparently by competing with DNA. The data suggest a role of RNA in estrogen receptor activation.

Genes coding for RNA polymerase beta subunit in bacteria. Structure/function analysis

The nucleotide sequence of the rpoB gene of Salmonella typhimurium has been determined in this work. It was compared with known sequences of the gene from other sources and the conservative regions were detected. This allowed some interesting conclusions to be made about the distribution of the functional domains in bacterial RNA polymerase and about the three-dimensional structure of its beta subunit.

Comparison of in vivo and in vitro glucocorticoid sensitivity in depression: relationship to the dexamethasone suppression test

The effect of in vivo (1 mg) and in vitro (10(-7)-10(-10) M) dexamethasone administration on mitogen-induced lymphocyte proliferation was examined in drug-free depressed patients, nondepressed psychiatric patients, as well as normal controls, and was related to the results of a standard overnight Dexamethasone Suppression Test (DST). The effect of oral dexamethasone administration was also examined for its effect on lymphocyte cytosolic glucocorticoid receptor content. Oral dexamethasone administration significantly decreased both phytohemagglutinin (PHA) and concanavalin A (Con-A) induced lymphocyte proliferation, as well as glucocorticoid receptor number in suppressors, whereas dexamethasone failed to decrease these responses in nonsuppressors. Nonsuppressors had significantly lower serum dexamethasone levels compared to suppressors at both 8:00 AM and 4:00 PM. However, when differences in serum dexamethasone levels were covaried out, there were still significant differences between suppressors and nonsuppressors on the dexamethasone-induced mitogen changes, but the changes in glucocorticoid receptor content were no longer significant. In vitro incubation of lymphocytes with dexamethasone produced a dose-related decrease in mitogenesis, which was not different between the depressed and nondepressed groups. However, at physiologically relevant concentrations of dexamethasone (10(-9)-10(-10) M), nonsuppressors as compared to suppressors were more resistant to the immunosuppressive effects of in vitro dexamethasone on the Con-A response. The inhibitory effect of in vitro dexamethasone on Con-A-stimulated lymphocytes was positively correlated with basal 4:00 PM cortisol values. In conclusion, in vitro techniques are useful probes to assess glucocorticoid sensitivity in depression. The present results also further support the hypothesis that glucocorticoid insensitivity is associated with DST nonsuppression.

Characterization of the nontransformed and transformed androgen receptor and heat shock protein 90 with high-performance hydrophobic-interaction chromatography

The hydrophobicity of the nontransformed and transformed androgen receptor from rat submandibular gland and heat shock protein 90 (hsp90) from rat submandibular gland and liver was characterized by using high-performance hydrophobic-interaction chromatography on TSK gel Ether-5PW. In the absence of molybdate, cytosol [3H]R1881-androgen receptor complexes were mainly eluted in the 1.3 M region (Peak 1) with a small peak in the 0.8 M region (Peak 2) of a descending salt gradient (2 to 0 M) of ammonium sulfate. In the presence of molybdate, Peak 2 was predominant. When labeled-cytosol was applied after being heated at 25 degrees C for 30 min, a third peak (Peak 3) at around 0.64 M ammonium sulfate was newly observed. Peaks 2 and 3 were observed, while Peak 1 completely disappeared with the labeled-cytosol precipitated at 40% saturated ammonium sulfate. The Stokes radius of Peak 1 was 7 nm, and of Peak 2 was 8 nm. Both peaks were retained poorly by DNA-cellulose but bound rather well to DEAE-cellulose. These results suggest that these two peaks represent the nontransformed receptor, indicating that there are isoforms of the nontransformed androgen receptor which are distinguished by their hydrophobic properties and Stokes radii. Peak 3 had a Stokes radius of 5 nm and preferentially bound to DNA-cellulose, suggesting that this peak corresponds to the transformed receptor. These results indicated that the transformation of the androgen receptor accompanies the enrichment of the hydrophobicity of the receptor molecule. Hsp90 purified from rat livers and hsp90 in the cytosol both from livers and submandibular glands were eluted from Ether-5PW at 0.8 M ammonium sulfate, at almost the same position as Peak 2. This finding suggests that the enrichment of hydrophobicity on transformation is due to dissociation of hsp90 from the nontransformed androgen receptor.

tRNA(Tyr) genes of Drosophila melanogaster: expression of single-copy genes studied by S1 mapping

Six Drosophila melanogaster tRNA(Tyr) genes have been isolated and sequenced. They contained introns of different sequences and two size classes: 20 or 21 base pairs (bp) (five genes) and 113 bp (one gene). However, the sequences coding for the mature tRNA(Tyr) were identical in all six genes. The 113-bp intron-containing gene was a single-copy gene. Hence, its primary transcript could be traced by S1 mapping. The gene was turned on during embryogenesis and continually expressed to various degrees during the following developmental stages. Thus, S1 mapping is a feasible method to follow the transcriptional activity of individual genes with identical mature products, provided that their primary transcripts are unique. The six genes were organized in two clusters of three and two genes, respectively (each containing a 20- or a 21-bp intron; cytological localization, 85A), and a single-copy gene (113-bp intron; cytological localization, 28C). We show that four of the six tRNA(Tyr) genes characterized were localized in putative 5' control regions of developmentally controlled genes transcribed by polymerase II.

Nonactivated and activated glucocorticoid receptor complexes from human salivary gland adenocarcinoma cell line

[3H]Triamcinolone acetonide glucocorticoid receptor complexes from human salivary gland adenocarcinoma cells (HSG cells) were shown to be activated with an accompanying decrease in molecular weight in intact cells, as analyzed by gel filtration, DEAE chromatography, the mini-column method and glycerol gradient centrifugation. Glucocorticoid receptor complexes consist of steroid-binding protein (or glucocorticoid receptor) and non-steroid-binding factors such as the heat-shock protein of molecular weight 90,000. To determine whether the steroid-binding protein decreases in molecular weight upon activation, affinity labeling of glucocorticoid receptor in intact cells by incubation with [3H]dexamethasone 21-mesylate, which forms a covalent complex with glucocorticoid receptor, was performed. Analysis by gel filtration and a mini-column method indicated that [3H]dexamethasone 21-mesylate-labeled receptor complexes can be activated under culture conditions at 37 degrees C. SDS-polyacrylamide gel electrophoresis of [3H]dexamethasone 21-mesylate-labeled steroid-binding protein resolved only one specific 92 kDa form. Furthermore, only one specific band at 92 kDa was detected in the nuclear fraction which was extracted from the cells incubated at 37 degrees C. These results suggest that there is no change in the molecular weight of steroid-binding protein of HSG cell glucocorticoid receptor complexes upon activation and that the molecular weight of nuclear-binding receptor does not change, although the molecular weight of activated glucocorticoid receptor complexes does decrease. Triamcinolone acetonide induced an inhibitory effect on DNA synthesis in HSG cells. Dexamethasone 21-mesylate exerted no such effect and blocked the action of triamcinolone acetonide on DNA synthesis. These results suggests that dexamethasone 21-mesylate acts as antagonist of glucocorticoid in HSG cells. The fact that dexamethasone 21-mesylate-labeled receptor complexes could be activated and could bind to DNA or nuclei as well as triamcinolone acetonide-labeled complexes suggests that dexamethasone 21-mesylate-labeled complexes can not induce specific gene expression after their binding to DNA.

Dehydroepiandrosterone sulfate improves memory in aging mice

Middle-aged (18 month old) and old (24 month old) mice showed poorer retention of footshock active avoidance training (FAAT) than young mice (2 month old). Immediate post-training subcutaneous injection of dehydroepiandrosterone sulfate (DHEAS) improved retention of FAAT in middle-aged and old mice to the high levels observed in young mice. DHEAS, a major naturally occurring adrenal steroid that decreases in blood serum with age, could be rate-limiting in achievement of retention of learning.

Dehydroepiandrosterone and its sulfate enhance memory retention in mice

Dehydroepiandrosterone (DHEA) and its sulfate (DHEAS), major naturally occurring precursors of both androgenic and estrogenic steroids, were shown in the present study to have convincing memory enhancing effects in mice. Post-training intracerebroventricular (i.c.v.) administration of DHEA in dimethylsulfoxide (2 microliters) prevented the amnesia for footshock active avoidance training (FAAT) caused by the same volume of dimethylsulfoxide alone. DHEAS significantly enhanced retention of FAAT in weakly trained mice whether injected i.c.v. or s.c. immediately post-training or given in the drinking water for a 2-week period. In the latter instance DHEAS was shown to facilitate retention of FAAT without enhancing acquisition. The maximally effective doses were: i.c.v., 162 ng/mouse; s.c., 700 micrograms/mouse; and oral, 1.45 mg/mouse/day. DHEAS administered i.c.v. occluded the amnestic effects of anisomycin (inhibitor of protein synthesis) and scopolamine (muscarinic cholinergic antagonist). There was a time-dependence of the facilitatory effects of post-training i.c.v. administration of DHEAS on retention of FAAT, significant enhancement of retention being observed when it was given either immediately (within 2 min) or at 30 and 60 min after training, but not at 90 or 120 min. DHEAS given i.c.v. also improved retention for step-down passive avoidance. In all instances, dose-dependent inverted U curves were obtained in a manner typical for memory enhancing substances. At a practical level, these experiments open new possibilities for the development of substances that may help in alleviating amnesic disorders in man.

Dexamethasone inhibition of interleukin 1 beta production by human monocytes. Posttranscriptional mechanisms

Dexamethasone is known to have an inhibitory effect on IL-1 production. To determine the mechanism(s) of this inhibition, adherent human blood monocytes were stimulated with Escherichia coli lipopolysaccharide (LPS) (10 micrograms/ml) in the presence of dexamethasone. Nuclear transcription run-off assays showed that LPS induced IL-1 beta gene transcription two- to fourfold and that this induction was unaffected by dexamethasone exposure (10(-5) M). The lack of dexamethasone's transcriptional effects was further supported by the absence of any significant change in IL-1 beta mRNA accumulation between LPS-stimulated monocytes exposed or unexposed to dexamethasone, as determined by Northern blot analysis. Posttranscriptionally, dexamethasone was found to have multiple effects: slight prolongation of IL-1 beta mRNA half-life, moderate inhibition of translation of the IL-1 beta precursor, and profound inhibition of the release of IL-1 beta into the extracellular fluid. The data indicate that IL-1 beta is first translated as the 33,000-D pro-IL-1 beta protein, the predominant intracellular form, and the processed to a 17,500-D IL-1 beta protein before or during extracellular transport. The major inhibitory effects of dexamethasone appear to be directed at the translational and posttranslational steps involved in these events.

Transformation in vitro and covalent modification with biotin of steroid-affinity-purified rat-liver glucocorticoid-hormone-receptor complex

The molybdate-stabilized rat liver glucocorticoid receptor complex was purified 9000-fold with a 46% yield by steroid-affinity chromatography and DEAE-Sephacel ion-exchange chromatography. The purified glucocorticoid receptor was identified as a 90-92-kDa protein by SDS/polyacrylamide gel electrophoresis. Raising the temperature to 25 degrees C in the absence of molybdate resulted in increased binding of the receptor complex to DNA-cellulose or nuclei, similar to the effect on the cytosolic complex. The purified complex has a sedimentation coefficient of 9-10 S before and after heat treatment in the absence of molybdate. The appearance of smaller 3-4-S species was unrelated to the extent of DNA-cellulose binding of the complex. The process termed 'transformation', i.e. increasing the affinity for DNA, is not concomitant with subunit dissociation or loss of RNA. Highly purified glucocorticoid receptor could be covalently modified with biotin to retain its steroid-binding activity but with a 50% decrease in nuclear binding capacity. The biotin-modified complex reacts with streptavidin in solution without losing its steroid.

The actions of interferon and antiinflammatory agents of induction of indoleamine 2,3-dioxygenase in human peripheral blood monocytes

Interferon substantially induced indoleamine 2,3-dioxygenase and increased L-tryptophan metabolism in human peripheral blood monocytes. The induction of dioxygenase by gamma-interferon was significantly higher than that observed with alpha-interferon. This cytokine-dependent induction of the enzyme was markedly and differentially altered by antiinflammatory drugs (i.e., acetaminophen, 3-deazaadenosine, indomethacin and dexamethasone). Dexamethasone potentiated the effect of gamma-interferon and resulted in "super-induction" of the enzyme. This is the first demonstration of the interferon-elicited induction of the dioxygenase in the cells of the immune system and of a novel mechanism for regulating tryptophan metabolism in the cells.

Ultrastructural localization of glucocorticoid receptor (GR) in hypothalamic paraventricular neurons synthesizing corticotropin releasing factor (CRF)

Corticotropin releasing factor (CRF) synthesizing neurons, located in the hypothalamic paraventricular nucleus (PVN), are the main central regulators of the pituitary-adrenal cortex endocrine axis. The hormone production and release of CRF-synthesizing neurons is regulated by neuronal messages and feedback action(s) of glucocorticoids secreted by the adrenal gland. In order to characterize the latter mechanism, glucocorticoid receptor (GR)-immunoreactive (IR) sites were studied in hypothalamic paraventricular neurons of intact, long-term adrenalectomized, and adrenalectomized plus glucocorticoid treated animals, by means of ultrastructural immunocytochemical labelling. In intact animals, glucocorticoid receptor immunoreactivity was found predominantly in the nuclei of parvocellular neurons. Following adrenalectomy GR-immunoreactivity was localized in the cytoplasm of the cells, and there was a concomitant disappearance of the label from the nuclei. After corticosterone administration to adrenalectomized animals, GR-IR sites were again concentrated within the cell nuclei. Immunocytochemical double labelling studies performed on adrenalectomized plus corticosterone-replaced animals demonstrated glucocorticoid receptor-IR sites in the cell nuclei of parvocellular paraventricular neurons that expressed CRF-immunoreactivity in their cytoplasm. These ultrastructural data indicate that the intracellular location of glucocorticoid receptor is dependent on the availability of glucocorticoids by the neurons. The simultaneous expression of GR- and CRF-immunoreactivity in parvocellular paraventricular neurons supports the concept of a direct feedback action of glucocorticoids upon CRF-synthesizing neurons.