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M Danielsen

Publications and source records attributed to M Danielsen.

At least 19 recordsLinked to original sources
PubMed2001

Describing the pumping heart as a pressure source.

The pumping heart is described by a new mathematical approach which considers the heart as a pressure source depending on time, volume and flow. This new approach allows a separation between isovolumic (non-ejecting) and ejecting heart properties. The computed results cover most of the features of the human ventricle during normal and altered vascular conditions. It is shown that the time-varying elastance concept is disqualified as an independent description of the heart, it follows from isovolumic heart properties and an ejection effect which consists of positive and negative effects of ventricular blood ejection.

Animals↗
PubMed2000

Effects of antiandrogens on chromatin remodeling and transcription of the integrated mouse mammary tumor virus promoter.

Inhibition of the ligand-activated androgen receptor (AR) by antiandrogens plays an important role in the treatment of various hyperandrogenic disorders including prostate cancer. However, the molecular mechanisms of antiandrogen activity in vivo remain unclear. In this study we analyzed the effects of cyproterone acetate (CPA), flutamide (F), and hydroxyflutamide (OHF) on transcriptional activation and chromatin remodeling of the genomically integrated mouse mammary tumor virus (MMTV) promoter. This promoter has provided an excellent model system to study the impact of steroid hormones on transcriptional activation in the context of a defined chromatin structure. The MMTV hormone response element is positioned on a phased nucleosome, which becomes remodeled in response to steroids. We utilized this model system in mouse L-cell fibroblasts that contain a stably integrated MMTV promoter. In these cells, dihydrotestosterone (DHT) induced a large increase of AR protein levels that correlated with transcriptional activation and chromatin remodeling of the MMTV promoter. Coadministration of DHT and CPA or DHT and OHF in these cells inhibited the increase of AR levels, which resulted in a strong blockage of transcriptional activation and chromatin remodeling of the MMTV promoter. In contrast, F had no significant influence on these activities. We conclude that a major portion of the antiandrogenic effects of CPA and OHF in vivo are mediated by the reduction of AR levels.

Androgen Antagonists↗
PubMed2000

The frequency of mutators in populations of Escherichia coli.

Owing to occasional spontaneous mutations in genes encoding DNA repair, any population of a reasonable size is expected to harbor a sub-population of genetic mutators. Using a genetically modified strain of Escherichia coli K-12, we have estimated the frequency of mutators to be about 3x10(-5). By and large, this corresponds to a mutation rate from non-mutators to mutators of 5x10(-6) per bacterium per generation. Using a mutS∷Tn10 derivative as representative for mutators, we estimated the increase in mutation rates in mutators to be 19- to 82-fold, depending on the test-mutation under consideration. The load associated with this increase in mutation rate resulted in a growth inhibition of 1%. From these data, we estimated that the rate of detrimental mutations in the non-mutators to be 2x10(-4)-8x10(-4). The situations where adaptive mutations may result in an increase in the frequency of mutators are discussed.

Adenosine Triphosphatases↗
PubMed2000

The left ventricular ejection effect.

A recently developed model of the left ventricle, based on experimental data, has been shown to exhibit the main features of the heart's ability to pump. Two special cases during blood ejection, termed pressure deactivation and hyperactivation, were identified. This study proposes an 'ejection effect' correction to the model that addresses deactivation, hyperactivation and adjusts the shape of the computed ventricular ejection curve in late systole. Also, a new approach based on new animal experiments is proposed to identify the ejection effect mechanism(s).

Animals↗
PubMed1999

Inhibition of histone deacetylation augments dihydrotestosterone induction of androgen receptor levels: an explanation for trichostatin A effects on androgen-induced chromatin remodeling and transcription of the mouse mammary tumor virus promoter.

The integrated mouse mammary tumor virus (MMTV) promoter has provided an excellent model system with which to study the impact of steroid hormones on transcriptional activation in the context of a defined chromatin structure. The hormone response element (HRE) of this promoter is positioned on a phased nucleosome which becomes remodeled in response to steroids. One possible mechanism of chromatin remodeling by steroid receptors could involve recruitment of coactivators which alter the histone acetylation status of the HRE nucleosome. To examine how the androgen receptor (AR) influences transcription and chromatin remodeling and to assess whether changes in histone acetylation are involved in these effects, we determined whether the specific histone deacetylase inhibitor trichostatin A (TSA) influenced basal- and androgen-mediated transcriptional activation of the integrated MMTV promoter in the mouse L-cell fibroblast cell line 29+. These cells harbor the MMTV promoter integrated in the genome and express only one steroid hormone receptor subtype, i.e., the AR. Surprisingly, we found that treatment of the cells with TSA alone had virtually no effect on transcription and chromatin remodeling of the MMTV promoter nor on AR levels. However, pretreatment with TSA augmented the DHT effects on all three parameters. These results suggest that histone acetylation changes at the MMTV B nucleosome per se are not alone sufficient to induce chromatin remodeling and subsequent induction of MMTV transcription. Rather, the histone deacetylase inhibitor TSA exerts a portion of its effect on MMTV chromatin remodeling and transcriptional activation indirectly through increases in AR levels.

Acetylation↗
PubMed1999

Comparison of chromatin remodeling and transcriptional activation of the mouse mammary tumor virus promoter by the androgen and glucocorticoid receptor.

We examined the interaction between the androgen (AR) and glucocorticoid receptor (GR) at the transcriptional level using mouse fibroblast cell lines harboring an integrated mouse mammary tumor virus (MMTV) promoter. We found that the AR, after induction with dihydrotestosterone (DHT), caused a progressive increase in MMTV-CAT reporter activity over 72 h which was correlated to an increase in chromatin remodeling of the MMTV promoter in the vicinity of the hormone response element (HRE). In contrast, stimulation of the GR by the synthetic glucocorticoid dexamethasone (Dex) caused a transient increase in MMTV transcriptional activity which returned to basal levels after 72 h. These changes were correlated to a transient increase in chromatin remodeling in the region of the HRE. Neither cotreatment nor pretreatment with Dex affected the DHT response. In fact, there was a more than additive effect of the two hormones on transcription at early time points. This suggests that the inability of GR to remodel chromatin, after 24 h of hormone treatment, is most likely related to changes in the GR itself and not the chromatin remodeling process. Consistent with this, nuclear GR levels dropped by greater than 50% after Dex treatment whereas the AR was induced fourfold after 24 h of DHT treatment. We conclude that a promoter with an ordered chromatin structure can still respond to androgens even after its glucocorticoid responsiveness is lost. This may be one mechanism cells utilize to establish target gene specificity for nuclear receptors that recognize identical DNA sequences.

Animals↗
PubMed1999

The glucocorticoid receptor gene as a candidate for gene therapy in asthma.

Glucocorticoids (GC) are commonly used as anti-inflammatory drugs in asthma, but can produce serious secondary effects and, moreover, be inefficient in corticoresistant asthmatics. After binding to the glucocorticoid receptor (GR), they repress the synthesis of proinflammatory cytokines via inhibition of the transcription factors AP-1 and NF-kappa B. Since qualitative and quantitative defects of the GR have been reported in corticoresistant patients, the transfer of the GR gene in the lung epithelium, the primary site of inflammation in asthma, may restore sensitivity to GC in these patients. As a prerequisite to in vivo studies, we have transfected A549 human lung epithelial cells with a GR expression vector. Using AP-1 and NF-kappa B-dependent reporter gene assays and an immunoassay for the pro-inflammatory cytokine RANTES, we show that the over-expressed GR significantly repressed AP-1 and NF-kappa B activities in the absence of hormone and that the GC dexamethasone produced an additive inhibitory effect. The GC-independent repression of AP-1 and NF-kappa B activities was further demonstrated by overexpressing a ligand-binding deficient GR mutant. Our data suggest that delivery of the GR gene in vivo may reduce inflammation without recourse to GC and may constitute an alternative therapeutic approach for corticoresistant asthma.

Animals↗
PubMed1998

Differential regulation of androgen and glucocorticoid receptors by retinoblastoma protein.

The androgen receptor (AR) plays a major role in the development and maintenance of male primary and secondary sexual characteristics. The growth promoting effects of androgens are clearly seen in prostate cancer where treatment by androgen ablation usually leads to tumor regression, followed sometime later, by growth of tumor cells that are resistant to endocrine therapy. We have found that the level of pRB in cells controls AR activity. Overexpression of pRB leads to increased transcriptional activity of the AR. This is similar to the previously reported potentiation of glucocorticoid receptor activity by pRB. In contrast, loss of pRB activity inhibits AR but not glucocorticoid receptor activity. This inhibition correlates with the unique ability of the AR to form a protein-protein complex with pRB in vitro. The site of interaction with pRB lies within the N-terminal domain of the AR and co-localizes with the region of the AR that specifies a requirement for pRB. Thus, the AR has a novel requirement for pRB raising the possibility that the growth promoting activity of AR is due to its direct interaction with pRB. Furthermore, loss of pRB activity during progression of prostate cancer may directly result in a decreased response to androgens.

Binding Sites↗
PubMed1998

Identification of glucocorticoid receptor domains necessary for transcriptional activation of the mouse mammary tumor virus promoter integrated in the genome.

It has previously been determined that the mouse mammary tumor virus (MMTV) promoter when integrated in the genome assumes a defined chromatin structure which is disrupted upon addition of glucocorticoids. In contrast, a transiently introduced MMTV promoter has a random nucleoprotein structure. To reveal glucocorticoid receptor (GR) domains necessary for transcriptional activation of the MMTV promoter we compared the effects of mutations of the GR on transcriptional activation of the stably integrated versus transiently introduced MMTV promoter. For this purpose we generated a GR-negative cell line which has an MMTV promoter/reporter construct integrated in the genome and studied the transcriptional activation of this construct by different GR mutants introduced into the cells. Transcriptional activation of the integrated and transiently introduced promoter was achieved by the wild-type GR or a chimeric receptor in which the MR hormone-binding domain (HBD) replaced the GR HBD. In contrast, we found that deletion of the HBD of the GR or replacement of this region with the equivalent domain of the estrogen receptor produced receptors that were unable to activate the MMTV promoter integrated in the genome although these receptors efficiently activated the transiently introduced MMTV promoter. The HBD was not the sole determinant of MMTV transcriptional activation when integrated in the genome. Chimeric receptors which harbored the MR amino terminal domain or the wild-type MR were also unable to activate the integrated MMTV promoter. Taken together, these data indicate a rigid requirement for sequences in both the GR amino and the carboxy terminal domains for transcriptional activation of a hormone response element in the defined chromatin context of the MMTV promoter.

Aldosterone↗
PubMed1998

The Nuclear Receptor Resource: a growing family.

Last year, the original Glucocorticoid Receptor Resource was expanded into a comprehensive project: the Nuclear Receptor Resource (NRR, http:// nrr.georgetown.edu/nrr/nrr.html ). The NRR has since been offering comprehensive information on nuclear receptor structure and function, as well as general facts of interest to the scientific community on meetings, funding and employment opportunities. The project now includes individual resources as part of a network which integrates information on glucocorticoid, androgen, mineralocorticoid, thyroid hormone, Vitamin D and peroxisome-proliferator activated receptors. Many investigators have joined the NRR network by filling the Who is who? form available in the NRR home page. This has facilitated communication among scientists in the field and dissemination of data nor otherwise published. Because several investigators have contacted NRR authors over the past few months asking for advice and materials for educational purposes, we have recently decided to include in our project an educational resource on nuclear receptors termed the 'Graphics Library'. The input and suggestions of NRR users do shape the future direction of the project, so we encourage user to give us feedback.

Computer Communication Networks↗
PubMed1997

The Nuclear Receptor Resource Project.

We have expanded the original Glucocorticoid Receptor Resource (GRR) database to include several individual resources as part of a larger project called the Nuclear Receptor Resource (NRR). In addition to the GRR, the NRR currently features the Thyroid Hormone Receptor Resource, the Androgen Receptor Resource, the Mineralocorticoid Receptor Resource, the Vitamin D Receptor Resource, and the Steroid Receptor Associated Proteins Resource. The goal of the NRR project is to provide a comprehensive resource for information on the nuclear receptor superfamily, and to provide a forum for the dissemination and discussion of both published and unpublished material on these proteins. Although the individual resources are managed from different servers, all the files are integrated and can be accessed through the project's Home Page, housed at http://nrr. georgetown.edu/nrr.html. In the near future, we hope to expand the project to contain information on other nuclear receptors and to better our electronic publication system. To accomplish this, we encourage the involvement of nuclear receptor investigators in the NRR.

Amino Acid Sequence↗
PubMed1996

The glucocorticoid receptor resource.

The glucocorticoid receptor resource focuses on the structure-function relationships of the glucocorticoid receptor. As well as links to sequence and bibliographic databases via the World Wide Web, the database contains sequence comparisons of receptors from different species and source information for glucocorticoid receptor clones, probes, cell lines and antibodies. The resource allows the electronic publication of essays, unpublished data and reviews on steroid receptors. These publications will not be reviewed or edited and should allow the rapid dissemination of information to the scientific community. The resource can be reached at: http://biochem1.basic- sci.georgetown.edu/grr/grr.html.

Computer Communication Networks↗
PubMed1996

GRBase, a database linking information on proteins involved in gene regulation.

The Gene Regulation Database (GRBase) is a compendium of information on the structure and function of proteins involved in the control of gene expression in eukaryotes. These proteins include transcription factors, proteins involved in signal transduction, and receptors. GRBase is now accessible via the World Wide Web (http://www.access.digex.net/regulate). A key feature of this database is the linking of each entry to data in other databases. The database is also available by anonymous ftp (URL ftp://ftp.trevigen.com/pub/Tfactors/) in both text and Filemaker pro formats.

Computer Communication Networks↗
PubMed1996

Role of the C terminus of the glucocorticoid receptor in hormone binding and agonist/antagonist discrimination.

The glucocorticoid receptor (GR) is a hormone-inducible intracellular modulator of specific gene transcription. Both glucocorticoids and progestins bind to the GR, and some progestins are able to activate the receptor. We have characterized a mutation of the mouse GR that restricts transcriptional activation, but not hormone binding, to glucocorticoids. This mutation, Y77ON, is located 13 amino acids from the C terminus of the mouse GR and helps define a region of the receptor that is important for transcriptional specificity. To further characterize this region of the GR, we have constructed a series of chimeric receptors between the glucocorticoid, progesterone, and androgen receptors. We find that the C-terminal 14 amino acids of the GR can be replaced by the equivalent region of the progesterone or androgen receptors with little alteration in either hormone-binding specificity or transcriptional response to agonists and antagonists. The region is required for hormone binding, however, since C-terminal deletions yield inactive receptors. We conclude that even though mutation of the C-terminal 14 amino acids of the GR can lead to alterations in hormone binding specificity and agonist potential, the differential hormone-binding capacities of the glucocorticoid, progesterone, and androgen receptors are not encoded in this region.

Amino Acid Sequence↗
PubMed1995

Effects of 12-O-tetradecanoylphorbol-13-acetate on estrogen receptor activity in MCF-7 cells.

The effects of long term treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) on estrogen receptor (ER) expression in the human breast cancer cell line, MCF-7, were studied. This study demonstrates that treatment of cells with the phorbol ester blocked estrogen receptor activity. Treatment of cells with 100 nM TPA resulted in an 80% decrease in the level of ER protein and a parallel decrease in ER mRNA and binding capacity. Following removal of TPA from the medium, the level of ER protein and mRNA returned to control values; however, the receptor failed to bind estradiol. These cells also failed to induce progesterone receptor in response to estradiol. In addition, TPA treatment blocked transcription from an estrogen response element in transient transfection assays and inhibited ER binding to its response element in a DNA mobility shift assay. The estrogen receptor in treated cells was recognized by two monoclonal anti-ER antibodies and was not quantitatively different from ER in control cells. RNase protection analysis failed to detect any qualitative changes in the ER mRNA transcript. Mixing experiments suggest that TPA induces/activates a factor which interacts with the ER to block binding of estradiol. The effects of TPA on ER levels and binding capacity were concentration-dependent. Low concentrations of TPA inhibited estradiol binding without a decrease in the level of protein, whereas higher concentrations were required to decrease the level of ER protein. The effects of TPA appear to be mediated by activation of protein kinase C since the protein kinase C inhibitors, H-7 and bryostatin, block the effects of TPA on estradiol induction of progesterone receptor. TPA treatment had no effect on the level or binding capacity of the glucocorticoid receptor, indicating that the effects are not universal for steroid receptors. These data demonstrate that activation of the protein kinase C signal transduction pathway modulates the estrogen receptor pathway. The long term effect of protein kinase C activation is to inhibit estrogen receptor function through induction/activation of a factor which interacts with the receptor.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗