Correlation of glucocorticoid receptor binding sites on MMTV proviral DNA with hormone inducible transcription

A redundant nuclear protein binding site contributes to negative regulation of the mouse mammary tumor virus long terminal repeat

The tissue specificity of mouse mammary tumor virus (MMTV) expression is controlled by regulatory elements in the MMTV long terminal repeat (LTR). These regulatory elements include the hormone response element, located approximately between -200 and -75, as well as binding sites for NF-1, Oct-1 (OTF-1), and mammary gland enhancer factors. Naturally occurring MMTV deletion variants isolated from T-cell and kidney tumors, transgenic-mouse experiments with MMTV LTR deletions, and transient transfection assays with LTR constructs indicate that there are additional transcription regulatory elements, including a negative regulatory element (NRE), located upstream of the hormone response element. To further define this regulatory region, we have constructed a series of BAL 31 deletion mutants in the MMTV LTR for use in transient transfection assays. These assays indicated that deletion of two regions (referred to as promoter-distal and -proximal NREs) between -637 and -201 elevated basal MMTV promoter activity in the absence of glucocorticoids. The region between -637 and -264 was surveyed for the presence of nuclear protein binding sites by gel retardation assays. Only one type of protein complex (referred to as NRE-binding protein or NBP) bound exclusively to sites that mapped to the promoter-distal and -proximal NREs identified by BAL 31 mutations. The promoter-proximal binding site was mapped further by linker substitution mutations and transfection assays. Mutations that mapped to a region containing an inverted repeat beginning at -287 relative to the start of transcription elevated basal expression of a reporter gene driven by the MMTV LTR. A 59-bp DNA fragment from the distal NRE also bound the NBP complex. Gel retardation assays showed that mutations within both inverted repeats of the proximal NRE eliminated NBP binding and mutations within single repeats altered NBP binding. Intriguingly, the NBP complex was detected in extracts from T cells and lung cells but was absent from mammary gland cells. These results suggest that a factor contributing to high-level expression of MMTV in the mammary gland is the lack of negative regulation by NBP.

The interaction of a c-Jun/Fos related protein factor with the U3 sequences of the mouse mammary tumor virus LTR

Using polyacrylamide gel mobility shift assay we have detected a nuclear factor (NF-S) in a mouse mammary tumor cell line (GR) that binds to an upstream sequence domain (-766 to -737) near the 5'-end of the mouse mammary tumor virus (MMTV) long terminal repeat (LTR). Antibodies to the products of the Jun and Fos oncogenes interfered with the binding potential of this factor, indicating that the factor shares antigenic determinants with c-Jun/AP-1. In vitro translated c-Jun and c-Fos were also found to bind to the NF-S binding domain consisting of the sequence TGA(A/G)TCA that are known to be recognized by c-Jun/AP-1. Our results raise the possibility that the MMTV-LTR sequence element-766 to -737 by interacting with a Jun/Fos related protein play a role in MMTV transcription and/or the activation of int protooncogenes that are associated with murine mammary tumorigenesis.

Immunohistochemical localization of metallothionein in human testicular embryonal carcinoma cells

The presence of high levels of metallothionein (MT) in developing mammalian cells is well documented. It has been suggested that the developmental profile and gene expression of MT is similar to that of the so-called oncodevelopmental gene products such as a-fetoprotein. In this study tissue sections of nine human embryonal carcinomas of the testis were tested by means of the avidin-biotin peroxidase complex for the presence of MT. The antigen was localized in variable amounts in the cytoplasm and nucleus in tumour cells in all cases. There was evidence that immunoreactivity was related to the histological growth pattern of tumour cells. These findings suggest that MT may be considered an oncodevelopmental product which could be useful as a tumour marker. In addition, the histology of these tumours might predict MT expression; this may prove of value in testing the hypothesis of MT-related emergence of drug-resistant cell lines in the course of treatment of tumours with metal-containing chemotherapeutic agents.

Stereochemical complementary of DNA and steroid agonists and antagonists

Modelling studies in our laboratories over the past decade have demonstrated that a variety of natural products exhibit stereochemical complementarity with nucleic acids. In the case of steroid hormones, the basic cyclopentanophenanthrene skeleton fits between base pairs in partially unwound double stranded DNA; heteroatoms on the steroids form stereospecific donor/acceptor linkages to hydrogen bonding heteroatoms on the DNA. Each of the hormones appears to fit best in the site, i.e. 5'-dTdG-3'.5'dCdA-3'; the pattern of donor/acceptor linkages is unique for each type of hormonal activity. Steroid hormone agonists fit into the same site as the parent hormone; degree of fit correlates with degree of hormonal activity. Steroid hormone antagonists (e.g. RU 486; tamoxifen; anandron) fit into the same site as the agonists but possess different donor/acceptor linkages than the parent hormone; these linkages occur within the site between the base pairs or along the outside surface of the DNA helix in the major or minor grooves. A chronological review of the underlying concepts and observations leading to these discoveries is presented. Work in progress and some potential implications of the emerging technology are also discussed.

DNA sequence and RNA transcription through a site of recombination in a non-neurovirulent herpes simplex virus intertypic recombinant

RE6 is a herpes simplex type-1 (HSV-1) X herpes simplex type-2 (HSV-2) intertypic recombinant that cannot replicate in the adult mouse nervous system. In the accompanying report, we have shown that HSV-1 sequences between 0.698 and 0.721 map units can restore a partial neurovirulent phenotype to RE6. In this report, we have used comparative DNA sequence analysis of RE6, 17syn+ (HSV-1) and HG52 (HSV-2) to demonstrate that this region contains a site of recombination between HSV-1 and HSV-2 sequences in RE6. High resolution transcription analysis has demonstrated that three readily detected transcripts are present in this region of the genome. In addition, the 5' end of a low abundance 5 kb transcript was also located in the right-hand portion of this region. All the transcripts encoded by HSV-1 and HSV-2 in this region of the genome are expressed by the RE6 recombinant. This and our sequence data suggest that the lack of neurovirulence in RE6 is not due to a simple loss in the expression of a transcript or to a defect in a protein encoded by a gene at the site of recombination.

Physiological relationships among stress, viruses, and cancer in experimental animals

Anxiety-induced psychoneural stimulation, via the hypothalamic-pituitary axis, activates the adrenal cortex to release corticosteroids, which elicit various alterations of corticoid-sensitive cell-mediated immunologic processes. Stress sensitive murine tumor-host experimental models have been utilized to demonstrate various effects of stress upon aspects of tumor development. Although many of the observed anxiety-induced alterations of tumor-related parameters can be interpreted in terms of corticoid-induced modifications of immune functions, other observations are more difficult to interpret, and may be caused in part by corticosteroid-independent modulation of lymphocyte functions. In the case of tumors induced by oncogenic viruses, anxiety-induced plasma corticoid elevations may also act independently of the immune system to stimulate tumor development via hormone binding sites on proviral DNA. Rigorously controlled environmental and experimental conditions are fundamental for the demonstration and interpretation of stress-related phenomena. Technical prerequisites include protective animal facilities, special handling procedures, the use of nontraumatic stressors, and the recognition of vital psychosocial, coping and timing factors. Various biologic factors, such as sex, genetic substrain differences and common interfering viral infections, must also be controlled or taken into consideration.

Effects of dehydroepiandrosterone and its sulfate on brain tissue in culture and on memory in mice

Low concentrations of dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) enhanced neuronal and glial survival and/or differentiation in dissociated cultures of 14-day mouse embryo brain. Posttrial intracisternal injection into the brains of mice undergoing active avoidance training alleviated amnesia and enhanced long-term memory. By minimizing degenerative changes in injured nerve tissue and facilitating plastic changes, DHEA and DHEAS may be of use in treatment of neurodegenerative and memory disorders in man.

Steroid-dependent interaction of transcription factors with the inducible promoter of mouse mammary tumor virus in vivo

We have used exonuclease protection in vivo as an assay to detect interaction of nuclear factors with the steroid-inducible promoter of mouse mammary tumor virus. Binding of two factors is detected uniquely at the steroid-activated promoter, and results in protection of sequences between -82 and approximately +12 One factor is identified as the murine homolog of nuclear factor 1. The second (designated factor i) binds downstream of nuclear factor 1 and protects sequences extending over the cap site. Binding activities associated with both factors can be detected in crude nuclear extracts; their apparent concentrations are unaffected by hormone treatment of the cells. These results demonstrate that glucocorticoid induction of transcription results from receptor-mediated establishment of a transcription factor complex at the promoter rather than activation of a preexisting complex.

Steroid hormone receptor localization in the nuclear matrix: interaction with acceptor sites

The nuclear matrix is a conceptually attractive candidate for the site in the nucleus where steroid hormone-receptor complexes might interact to modulate DNA structure and function. We have demonstrated that in sex steroid target tissues a major proportion (50-100%) of the high affinity and steroid-specific receptors that become associated with the nucleus following hormonal stimulation are localized in the nuclear matrix. Direct cell-free binding assays confirm that this localization is due to the presence of specific acceptor sites in the matrix to which steroid-receptor complexes bind with high affinity and tissue specificity, and is not the result of spurious binding. The nuclear matrix appears to be a major site of hormone receptor binding in the nucleus, and this situation is consistent with the known ability of steroid hormones to stimulate gene transcription, a process which also appears to occur in association with the nuclear matrix.

Structure and function of the glucocorticoid receptor

The glucocorticoid receptor protein is a transcriptional regulatory protein that interacts with specific enhancer sequences. A stoichiometric analysis of the interaction indicates an equimolar relationship between the receptor protein and the specific enhancer sequences. The activity of the receptor protein is itself regulated by the binding of glucocorticoids. The two functional domains (DNA-binding and steroid-binding) are adjacent and lie within the C-terminal half of the receptor protein. The N-terminal half of the protein appears to modulate the interaction with DNA but does not have any role in the binding of the steroid. The functional domains have also been defined at the sequence level.

In situ hybridization detection of estradiol-induced changes in ribosomal RNA levels in rat brain

In this study, quantitative assessment of estradiol (E2)-induced changes in levels of ribosomal RNA within brain regions concentrating the hormone was accomplished by in situ hybridization with nick-translated tritiated ribosomal DNA probes and use of a computer-based image analysis system. Ovariectomized rats were either implanted with estradiol capsules for 6 h, 24 h, or 15 days, or sham-implanted under the same time course to serve as controls. The mean number of grains, somal area, and grain density of neurons within three E2-concentrating brain regions, the ventrolateral portion of the ventromedial and the arcuate nuclei of the hypothalamus (VL-VMN and ARC, respectively) and the corticomedial nucleus of the amygdala (AMY) were determined. In the VL-VMN and ARC, levels of rRNA were significantly increased after 6 h of E2 treatment (70% and 30%, respectively) and after 24 h of E2 treatment (60% and 62%, respectively). However, these effects on rRNA levels in VL-VMN and ARC were not observed after prolonged exposure of 15 days to the hormone. Neuronal hypertrophy was present only after 24 h of E2 treatment in the VL-VMN and ARC (32% and 14%, respectively). No changes were found in the AMY. As an additional internal control, measurements were also collected from the dorsomedial portion of the VMN (DM-VMN), a region with few E2-concentrating neurons. No changes in any of the parameters were found in DM-VMN at any time after exposure to the hormone. By extending the in situ hybridization technique to the quantitative level, these findings demonstrate differential estrogenic regulation of a known gene product, rRNA, in rat brain that is temporally and regionally specific.

Glucocorticoid receptor binding and activation of a heterologous promoter by dexamethasone by the first intron of the human growth hormone gene

In this study DNA-binding and gene transfer experiments were performed to examine a potential glucocorticoid regulatory element (GRE) in the human growth hormone gene. As assayed by nitrocellulose filter binding, only two regions of the human growth hormone gene, the 5'-flanking sequences and a fragment containing part of the first intron, were retained preferentially by purified glucocorticoid-receptor complexes. The relative binding by the transcribed sequences was three times greater than the relative binding by the 5'-flanking sequences, but less than the relative binding by a fragment containing the human metallothionein-IIA gene GRE. The intron, but not the 5'-flanking sequences, generated a "footprint" when the receptor complex was used to protect the segments against exonuclease III digestion; the protected sequence spanned nucleotides +86 to +115 in the first intron and contained a structure homologous in 14 of 16 nucleotides to a 16-nucleotide consensus GRE. The hexanucleotide 5'-TGTCCT-3', thought to be important for GRE activity, not only was found in this sequence and in the 5'-flanking region, but also was present twice in the 3' end of the gene that did not show specific receptor binding. The latter results suggest that the hexanucleotide alone is not sufficient to generate specific receptor binding tight enough to be assayed in this way. To test the biological activity of the intron binding site, a fragment containing these sequences was fused 5' to the human metallothionein-IIA gene promoter depleted of its GRE and linked to the structural sequences of the herpes simplex virus thymidine kinase (TK) gene. When this hybrid gene was transfected into Rat 2 TK- cells, its expression was induced threefold by the glucocorticoid dexamethasone, as assessed by transfection efficiency and RNA blotting analyses. Expression of the same gene without the human growth hormone gene segment was not affected by the steroid, whereas the wild-type human metallothionein-IIA gene promoter containing its GRE responded to the hormone by a sixfold increase in thymidine kinase mRNA. These results indicate that the human growth hormone gene contains a structure within its first intron that can function as a GRE.

Distinct sequence elements involved in the glucocorticoid regulation of the mouse mammary tumor virus promoter identified by linker scanning mutagenesis

In the proviral DNA of mouse mammary tumor virus (MMTV), sequences up to approximately equal to 200 base-pairs from the RNA start site are required for stimulation of transcription by glucocorticoid hormones in cultured cells. A total of 26 mutant plasmids with clustered point mutations or small deletions in the hormone control region of the MMTV long terminal repeat were constructed, linked to the coding portion of the Herpes simplex virus thymidine kinase gene, and introduced by transfection into LTK- cells. Transcription from mutant DNA in the presence or absence of hormone was quantified by S1 nuclease protection assays. Our analysis revealed the presence of at least three control elements that affect the extent of transcription stimulation by glucocorticoid hormones: (1) a distal element, between -181 and -172 base-pairs from the RNA initiation site. Linker scanning mutants in this segment have a reduction of up to 20-fold in the hormone response with respect to wild type. (2) An element around position -120, defined by a mutation of 4 base-pairs between -121 and -117, which causes a fivefold reduction. (3) An element from approximately equal to -78 to -70, defined by a mutant with also a roughly fivefold lower stimulation. The first two are included in areas that have been shown by others to interact in vitro with hormone-receptor complexes; the last one overlaps the in vitro binding site of a nuclear protein factor. A mutant lacking all three elements (-193 to -70) is completely non-inducible by glucocorticoids. Together with earlier results obtained with 5' deletion mutants, the data show that the largest contribution to the stimulatory response is made by the distal element, which however does require the presence of both more-proximal ones for the response to be maximal. In the absence of the distal one, the two proximal elements together produce a residual stimulation in the order of 5 to 10% of wild type, while the -70 element alone is ineffective. In addition, we show that a functional TATA homology is required for maximum stimulation. It appears that transcriptional regulation of MMTV by glucocorticoid hormones is achieved by the concerted action of multiple sequence modules, not all of which correspond to receptor binding sites in vitro.

Differential expression of endogenous mouse mammary tumor virus genes during development of the BALB/c mammary gland

Expression of endogenous mouse mammary tumor virus sequences varied over the course of development of the mammary gland during primary pregnancy and lactation in virus-free BALB/c mice. Although RNA from all regions of the genome was detected, both the level and temporal regulation of expression were different for long terminal repeat-, env-, and gag-pol-specific RNAs. Analysis of the methylation status of proviral DNA indicated differential accessibility of the three endogenous units during development. The results demonstrated noncoordinate regulation of mouse mammary tumor virus expression with respect to provirus template utilized and specific transcripts accumulated.

The stereochemical complementarity of DNA and reproductive steroid hormones correlates with biological activity

Modeling studies revealed that progesterone, testosterone, and estradiol are stereochemically complementary to the cavity formed between base pairs in the DNA sequence, 5'-dTdG-3' X 5'-dCdA-3'. Each steroid aligned precisely with the topography of the cavity and formed 2 stereospecific hydrogen bonds linking phosphate oxygens on adjacent DNA strands. Hydrogen bonding donor-acceptor relationships were different for each hormone. The remarkable stereochemical specificity of the hormone-DNA complexes was demonstrated by the lack of complementarity of steroid enantiomers and steroid analogs having alternate ring systems and/or changes in the position of functional groups. Fit of molecules into DNA in the manner of the parent hormone correlated with biological activity. Antagonists also fit into the cavity but differed from agonists in their hydrogen bonding linkages to DNA and/or extended out of the cavity beyond the helix. Unlike flat intercalating agents which form stable complexes with DNA, wedge shaped steroids may thus be capable of forming reversible sequence-specific complexes with DNA. We conclude that the stereochemistry of DNA can be used to predict hormonal activity.

Progesterone receptor interaction in the 5'-flanking regulatory region of the ovalbumin gene

Highly purified hen oviduct progesterone receptor A subunit has been found to interact preferentially with the 5'-flanking region of the chicken ovalbumin gene. Saturation kinetics showed that 2-fold less receptor was required for half-maximal binding to ovalbumin gene flanking sequences than to plasmid pBR322 sequences. Studies of selective binding were facilitated by a preferential adsorption assay involving gel electrophoretic analysis of [32P]DNA restriction fragments eluted from receptor-DNA complexes isolated on nitrocellulose filters. Approximately 10-fold difference in binding was observed at 37 degrees C for a 1.7 Kb ovalbumin DNA insert compared to binding of receptor to a 3.6 Kb plasmid pBR322 fragment. Selective receptor A binding was dramatically reduced when assayed at 4 degrees C. In addition to temperature dependence, preferential binding required the presence of glycerol or dimethyl sulfoxide during binding. Divalent cations and ionic strength had no apparent effect on the relative sequence selectivity but did alter the total DNA binding observed. Binding data from a variety of different restriction digests suggest receptor A interacts between -135 and -249 bp (upstream) from the start of ovalbumin transcription. Preferential binding to a DNA fragment containing the sequence -16 to -247 compared to an adjacent upstream fragment or plasmid DNA fragment confirm this assignment. This binding site lies within the regulatory sequence required for progesterone induction of a transfected fusion gene in primary chicken oviduct cells.

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.

Mechanisms of glucocorticoid hormone action

This report summarizes our studies, in context with the results of other laboratories, of the molecular mechanisms of glucocorticoid hormone action. The receptors for these steroids are comprised of single polypeptide chains of about 90,000 molecular weight. Binding of agonist steroids to the receptor induces a conformational change to an active receptor form that is followed by a second change in the glucocorticoid-receptor complex, termed activation, that alters the charge of the complex and results in its binding to specific sites on the DNA termed glucocorticoid regulatory elements (GREs). The GRE on the human metallothionein-IIA gene is located in the 5'-flanking DNA. It can function independently of the gene's promoter, and when ligated upstream from the herpes simplex virus (HSV) thymidine kinase (TK) gene promoter, can activate it. The binding of the glucocorticoid-receptor complex to the GRE probably alters chromatin structure over a limited span to facilitate RNA polymerase action. The regulation by glucocorticoids of growth hormone gene expression is more complex. The steroid appears to elicit both transcriptional and posttranscriptional influences that are also affected by thyroid hormone. Also the glucocorticoid influences appear to be exerted in part through DNA structures located downstream from the transcriptional initiation site. A GRE has been defined in intron A of the hGH gene through gene transfer and DNA binding experiments. Finally, gene transfer experiments suggest that pituitary-specific factors influence the ability of glucocorticoids to affect GH gene expression.

Glucocorticoid receptor binding and activation of a heterologous promoter by dexamethasone by the first intron of the human growth hormone gene

In this study DNA-binding and gene transfer experiments were performed to examine a potential glucocorticoid regulatory element (GRE) in the human growth hormone gene. As assayed by nitrocellulose filter binding, only two regions of the human growth hormone gene, the 5'-flanking sequences and a fragment containing part of the first intron, were retained preferentially by purified glucocorticoid-receptor complexes. The relative binding by the transcribed sequences was three times greater than the relative binding by the 5'-flanking sequences, but less than the relative binding by a fragment containing the human metallothionein-IIA gene GRE. The intron, but not the 5'-flanking sequences, generated a "footprint" when the receptor complex was used to protect the segments against exonuclease III digestion; the protected sequence spanned nucleotides +86 to +115 in the first intron and contained a structure homologous in 14 of 16 nucleotides to a 16-nucleotide consensus GRE. The hexanucleotide 5'-TGTCCT-3', thought to be important for GRE activity, not only was found in this sequence and in the 5'-flanking region, but also was present twice in the 3' end of the gene that did not show specific receptor binding. The latter results suggest that the hexanucleotide alone is not sufficient to generate specific receptor binding tight enough to be assayed in this way. To test the biological activity of the intron binding site, a fragment containing these sequences was fused 5' to the human metallothionein-IIA gene promoter depleted of its GRE and linked to the structural sequences of the herpes simplex virus thymidine kinase (TK) gene. When this hybrid gene was transfected into Rat 2 TK- cells, its expression was induced threefold by the glucocorticoid dexamethasone, as assessed by transfection efficiency and RNA blotting analyses. Expression of the same gene without the human growth hormone gene segment was not affected by the steroid, whereas the wild-type human metallothionein-IIA gene promoter containing its GRE responded to the hormone by a sixfold increase in thymidine kinase mRNA. These results indicate that the human growth hormone gene contains a structure within its first intron that can function as a GRE.

Events in glucocorticoid hormone action. A correlation of histone H1 variant pattern changes, hormone binding to cell nuclei, and induction of mouse mammary tumor virus RNA

To approach experimentally changes of chromatin structure introduced by glucocorticoids, the histone H1 compositions of hormone-treated and non-treated mouse mammary tumor cells of the GR line [Ringold, G., Lasfargues, E. Y., Bishop, J. M. and Varmus, H. E. (1975) Virology 65, 135-147] were compared. To define the biologically important hormone concentration range, the cells were exposed to different concentrations of triamcinolone, a synthetic glucocorticoid. The induction of mouse mammary tumor virus (MMTV) RNA was measured by cDNA excess hybridization, and the amount of hormone bound to nuclei was determined by a filter-binding assay. Between 0.3 nM and 30 nM triamcinolone the relative increase in nuclear bound hormone corresponded well with the relative induction of MMTV RNA. The half-life of triamcinolone in nuclei of growing cells was 1 h, as measured by a pulse-chase experiment. Reversed-phase high-performance liquid chromatography of histone H1 resulted in its separation into four subfractions. The treatment of cells with biologically active glucocorticoid, 3 nM or 30 nM triamcinolone or 1 microM dexamethasone, resulted in changes in the relative amounts of two subfractions and to a positional shift of two subfractions as compared to untreated cells. No changes were observed after exposure to 3 nM dexamethasone, a concentration which does not induce MMTV RNA [Ringold, G. M., Yamamoto, K. R., Tomkins, G. M., Bishop, J. M. and Varmus, H. E. (1975) Cell 6, 299-305].

Binding of the glucocorticoid receptor complex to the nucleosomal core in the P1798 mouse lymphosarcoma

Binding of the glucocorticoid receptor complex to nucleosomes has been studied using the mouse P1798 lymphosarcoma. Cells were incubated with [3H]triamcinolone acetonide (TA), and nuclei prepared and digested with 3 different concentrations of micrococcal nuclease. After fractionation with EDTA and NaCl, it was observed that [3H]TA bound with similar specific radioactivity to mononucleosomes containing both core and linker DNA, of 183 +/- 5, and 168 +/- 4 base pair lengths, respectively, as well as to core size DNA, of 148 +/- 3 base pair length, suggesting that the glucocorticoid receptor bound to the core portion of the nucleosome. Steroid binding was found to be associated with regions of the nucleosome that were depleted in histone H1 and enriched in high mobility group (HMG) proteins 1 and 2; only negligible binding was noted in nucleosomes enriched in histone H1 and depleted in HMG proteins. In addition to binding to core nucleosomes, the glucocorticoid receptor complex was also shown to bind to a fraction sedimenting at 5-6 S on sucrose gradients characterized by subnucleosome and mononucleosome size DNA, as well as by core histones. While binding of the steroid receptor complex to linker regions of the nucleosome cannot be ruled out, this data would appear to present the first concrete evidence that glucocorticoid binding, at least in the P1798 lymphosarcoma, is to core nucleosomes. Some caution in interpretation of the results is indicated, however, on 2 points: (1) receptor redistribution during nuclease digestion cannot be ruled out; (2) only the binding of a small proportion of the steroid receptor complex may be physiologically relevant.

Generation of glucocorticoid-responsive Moloney murine leukemia virus by insertion of regulatory sequences from murine mammary tumor virus into the long terminal repeat

The glucocorticoid-regulatory sequences from the murine mammary tumor virus long terminal repeat (MMTV LTR) were introduced into the LTR of Moloney murine leukemia virus (M-MuLV) by recombinant DNA techniques. The site of insertion was in the M-MuLV LTR U3 region at -150 base pairs with respect to the RNA cap site. Infectious M-MuLVs carrying the altered LTRs (Mo + MMTV M-MuLVs) were recovered by transfection of proviral clones into NIH-3T3 cells. The Mo + MMTV M-MuLVs were hormonally responsive in that infection was 3 logs more efficient when performed in the presence of dexamethasone, irrespective of the orientation of the inserted MMTV sequences. However, even in the presence of hormone, the Mo + MMTV M-MuLVs were less infectious than wild-type M-MuLV. In contrast to the large effect on infectivity, dexamethasone induced virus-specific RNA levels in chronically Mo + MMTV M-MuLV-infected cells only two- to fourfold. Fusion plasmids between the altered LTRs and the bacterial chloramphenicol acetyltransferase gene allowed the investigation of LTR promoter strength by the transient chloramphenicol acetyltransferase expression assay. The chloramphenicol acetyltransferase assays indicated that the insertion of MMTV sequences into the M-MuLV LTR reduced promoter activity in the absence of glucocorticoids but that promoter activity could be induced two- to fivefold by dexamethasone. The Mo + MMTV M-MuLVs were also tested for the possibility that viral DNA synthesis or integration during initial infection was enhanced by dexamethasone. However, no significant difference was detected between cultures infected in the presence or absence of hormone. The insertion of MMTV sequences into an M-MuLV LTR deleted of its enhancer sequences did not yield infectious virus or active promoters, even in the presence of dexamethasone.

Hormonal response region in the mouse mammary tumor virus long terminal repeat can be dissociated from the proviral promoter and has enhancer properties

The proviral DNA of mouse mammary tumor virus (MMTV) contains a regulatory region closely associated with its promoter, which subjects transcription to the control of glucocorticoid hormones. Delimitation analysis of a chimeric MMTV long terminal repeat-thymidine kinase gene (LTR-tk) has shown that the hormonal regulation sequence is confined to 202 nucleotides preceding the LTR-specific RNA initiation site. A second RNA initiation site (tk-specific mRNA) placed close to the regulatory MMTV sequence by in vitro recombination is also subjected to hormonal stimulation in transfected cells. A series of plasmids with deletions around the LTR cap site progressing from 3' to 5' was made and functionally tested. In vitro deletion of MMTV LTR sequences comprising the RNA initiation sequence and the "TATA" box do not effect hormonal regulation at the tk-specific mRNA start site. Nucleotides up to position -59 from the LTR initiation site could be deleted without influence on the glucocorticoid regulation, whereas deletions to position -65 abolished the hormonal effect on the tk gene transcription. A short MMTV LTR segment containing nucleotides -236 to -52 from the LTR initiation site was recombined with the tk gene or the alpha-globin gene. This fragment confers hormonal inducibility onto the heterologous genes over distances of 0.4 or 1.1 kilobases. The hormonal response region functions when it is placed either 5' or 3' of the regulated gene in both of the possible orientations and is reminiscent of an enhancer sequence.

Pretranslational regulation of tyrosine aminotransferase and phosphoenolpyruvate carboxykinase (GTP) synthesis by glucagon and dexamethasone in adult rat hepatocytes

The regulation of synthesis of the gluconeogenic cytosolic enzyme phosphoenolpyruvate carboxykinase (PEPCK) and of tyrosine aminotransferase (TAT) by glucagon and glucocorticoid hormones was studied in hepatocytes maintained in suspension culture for 7 h. Specific antibodies were used to measure relative rates of enzyme synthesis after pulse-labelling of the cells with [3H]leucine or [35S]methionine. Concomitantly, amounts of mRNA were quantified after translation in vitro in a reticulocyte lysate and specific immunoprecipitation of the proteins. Glucagon stimulated the rate of synthesis of PEPCK by 4-6-fold and that of TAT by 6-8-fold in 2h. In contrast, dexamethasone had little effect on PEPCK synthesis, whereas it increased TAT synthesis by 5-9-fold. When used in combination, the two hormones displayed additive effects on TAT synthesis, whereas the glucocorticoid hormone strongly potentiated stimulation of PEPCK synthesis by glucagon. In every instance, changes in rates of synthesis of the two enzymes were totally accounted for by increases in amounts of the corresponding functional mRNA, suggesting a pretranslational site of action for both glucagon and dexamethasone.

Interaction of high temperature and Salmonella pullorum antigen concentration on serum agglutinin and corticosteroid responses in white rock chickens

In three experiments, 6- to 7-week-old chickens were exposed to one or two standard heating episodes and were injected immediately afterward with different concentrations of heat-killed Salmonella pullorum antigen (Ag) or phosphate-buffered saline. The standard heat episode consisted of three .5-hr exposures of 44 to 46 C with .5-hr periods of 22 C between exposures. Nonheated chickens were maintained at 22 C. When two heating episodes were used, there was a 12-hr interval between episodes. Sera from blood collected at 0 through 15 days postimmunization (PI) were titrated for total agglutinins and assayed for corticosteroids in all three experiments. Additionally, in Experiment 3, sera were titrated for 2-mercaptoethanol-resistant (2-MER) antibody. Total agglutinins were suppressed from 5 through 13 days PI by one heating episode in birds receiving lower doses of Ag but not in those receiving higher doses. When birds were exposed to two heat episodes, 12 hr apart, total agglutinin titers were suppressed in birds receiving the low Ag dose during the induction phase (4 to 5 days PI) only. During the declining phase (7 to 14 days PI), the effect was reversed, and titers were significantly lower in heated birds receiving the higher dosage. These results are similar to those previously obtained with ACTH (adrenocorticotropin). Determination of 2-MER antibody indicated that IgM was probably suppressed during the induction of the immune response but that IgG was suppressed during the declining phase of the response. Serum corticosteroid concentrations were significantly increased immediately after exposure to high temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Reversible and persistent changes in chromatin structure accompany activation of a glucocorticoid-dependent enhancer element

A derivative of mouse mammary tumor virus (MTV) DNA, LTL, was constructed in vitro and introduced into the genome of mouse L cells. Transcription of LTL was stimulated by dexamethasone, a glucocorticoid hormone. Two features of LTL chromatin structure are altered upon hormone treatment. First, "moderate" DNAase I sensitivity of the entire LTL element increases following addition of dexamethasone; this alteration persists after hormone withdrawal, when LTL transcription is shut off. Second, a discrete DNAase I-hypersensitive region is induced with a time course that closely parallels the rate of increasing transcription from the MTV promoter; this structure disappears upon hormone removal. The induced hypersensitive region coincides with a segment of the MTV long terminal repeat sequence that specifically binds purified glucocorticoid receptor in vitro and functions as a hormone-dependent enhancer element in vivo. We suggest that specific glucocorticoid receptor-DNA interactions may alter the configuration of DNA or chromatin in the vicinity of the binding sites, thereby creating an active transcriptional enhancer.

Functional analysis of the steroid hormone control region of mouse mammary tumor virus

Gene fusions between the mouse mammary tumor virus long terminal repeat and the E. coli lacZ gene have been shown to exhibit hormone dependent expression of beta-galactosidase activity. These constructions were used in transient expression experiments to assess the effects of specific modifications introduced into the region upstream of the transcription initiation site. 5' deletions demonstrate that sequences sufficient for wild-type promoter function are contained downstream of residue -64 relative to the initiation site. Other deletions define a region of approximately 80 base pairs between -220 and -140 which contains sequences essential for hormonal control. Between this control region and the promoter lie sequences dispensable for both functions.

DNA binding properties of glucocorticosteroid receptors bound to the steroid antagonist RU-486

RU-486 is an anti-fertility steroid which also has anti-glucocorticosteroid effects. RU-486 is shown to be a strong antagonist of the glucocorticosteroid-induced cytolytic response of the murine thymoma lines W7TB and T1M1b , and of the induction of mouse mammary tumor virus (MMTV) mRNA in T1M1b cells. The glucocorticosteroid receptor of W7 cells has high affinity for RU-486 (Kd = 3 X 10(-9) M) but the complex formed has low nuclear transfer capacity. Binding of RU-486, as compared with the glucocorticosteroid agonist triamcinolone acetonide, to mouse receptor results in a decreased affinity for DNA in general and a reduced specific recognition of a site in the promoter region of MMTV proviral DNA. The RU-486 complex formed with rat liver receptor exhibits the same behavior; in addition, it is shown that only a fraction of these complexes are activated by temperature and these form highly salt-sensitive interactions with DNA. These results indicate that the binding of RU-486 to glucocorticosteroid receptors mimics pharmacologically the properties of a class of receptor variants (nt-) which are non-functional and have reduced nuclear transfer and altered DNA binding capacity. These results substantiate the importance of DNA binding in receptor function.