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P Kopp

Publications and source records attributed to P Kopp.

At least 73 records · Page 4Linked to original sources
PubMed1996

Second zinc finger mutants of thyroid hormone receptor selectively preserve DNA binding and heterodimerization but eliminate transcriptional activation.

Transcriptional regulation by thyroid hormone is mediated through its nuclear receptors (TRs), which bind to target responsive elements as homodimers or as heterodimers with 9-cis retinoic acid receptors (RXRs). We examined the dimerization and functional properties of TRs containing mutations in the first and second zinc finger regions of the DNA binding domain. Interestingly, a mutation (R158G) in the loop of second zinc finger, or a chimeric mutant in which the second zinc finger of the glucocorticoid receptor (GR) was substituted for that of the TR, did not form homodimer, but still bound as a heterodimer with RXR alpha. Despite the presence of heterodimer formation, these mutants were functionally inactive in transfection assays. We conclude that sequences within the loop of the second zinc finger may play an important role in stability in vivo or transcriptional activation of the TR.

Amino Acid Sequence↗
PubMed1996

Sexually dimorphic transcriptional responses to gonadotropin-releasing hormone require chronic in vivo exposure to estradiol.

GnRH regulates secretion of the gonadotropins, LH and FSH, in a sexually dimorphic manner. In the present study, we examined GnRH regulation of the gonadotropin alpha-subunit promoter to assess whether sex-dependent hormonal effects are manifest at the transcriptional level. Primary cultures of male or female rat pituitary cells were transfected with a reporter gene containing the alpha-promoter linked to luciferase (-420 alpha-LUC) and then subjected to treatment with GnRH for 24 h. Basal alpha-LUC expression was 4.2-fold greater in pituitary cells from males than in those from females. alpha-LUC activity was stimulated 5.3-fold by GnRH in males, whereas GnRH induced a 148-fold increase in alpha-promoter activity in females. The GnRH responsiveness of the transfected alpha-promoter did not vary in pituitary cells isolated at different stages of the female reproductive cycle, suggesting that acute changes in the hormonal milieu are not sufficient to alter transcriptional responses to GnRH. In males, orchidectomy minimally influenced alpha-LUC activity, indicating that testosterone does not exert a suppressive effect on GnRH responsiveness. In ovariectomized females, basal expression of alpha-LUC increased 3.7-fold, and GnRH stimulation was reduced from 165- to 11-fold, suggesting that an ovarian factor suppresses basal activity and enhances GnRH stimulation. Treatment of ovariectomized females with estrogen suppressed basal activity and restored GnRH stimulation of alpha-LUC, but the estrogen effects required long term treatment (10 days). Addition of progesterone to estrogen or treatment with the progesterone antagonist, RU486, had little effect on GnRH responsiveness. We conclude that estrogen exerts dual effects to suppress basal expression and to dramatically enhance GnRH responsiveness of the alpha-promoter. This model reveals potent actions of estrogen at the level of transcription and should provide new insights into the mechanisms that control estrogen priming of gonadotrope cells.

Animals↗
PubMed1996

Constitutive activation of the Gs alpha protein-adenylate cyclase pathway may not be sufficient to generate toxic thyroid adenomas.

In toxic thyroid adenomas, mutations in the TSH receptor (TSH-R) gene or the gene encoding the alpha-subunit of the stimulatory guanine nucleotide-binding protein (Gs alpha) have been demonstrated to constitutively activate the cAMP cascade, which subsequently stimulates the growth and function of these tumors. However, the widely varying thyroid phenotypes in patients with TSH-R germline mutations, ranging from only slightly enlarged diffuse to multinodular goiters, suggest that additional mechanisms may be effective in the pathogenesis of toxic adenomas. We have investigated the levels of stimulatory and inhibitory G protein alpha-subunits together with basal and TSH-stimulated adenylate cyclase (AC) activity in toxic adenomas with or without activating mutations and in nodular and extranodular tissues of a toxic goiter due to a germline mutation in the TSH-R gene. Augmented expression of Gs alpha protein was detected in all toxic adenomas, independent of the presence of mutations, and in the nodular tissue of the toxic goiter, but not in the nonnodular hyperplastic tissue of the toxic goiter with the mutated TSH-R. Analogously, the expression of the alpha-subunit of the inhibitory G protein (Gi alpha) was also increased in all adenomas and the nodular tissue of the goiter, but, again, not in the hyperplastic goiter tissue. Basal AC activity was high in all tissues with mutations, but was only slightly increased in adenomas without detected mutations. No correlation was detectable between basal or TSH-stimulated AC activity and the levels of Gs alpha and Gi alpha. Our data suggest that mutational activation of the cAMP cascade may not be sufficient to generate toxic nodules and adenomas, but far more complex mechanisms, including alterations of G protein signaling, may be effective in the pathogenesis of these tumors.

Adenoma↗
PubMed1996

Syndrome of resistance to thyroid hormone: insights into thyroid hormone action.

Thyroid hormones (T3, T4) exert multiple cellular effects through nuclear thyroid hormone receptors (TR alpha, TR beta). Thyroid hormone receptors are transcription factors that act by altering patterns of gene expression. Resistance to thyroid hormone (RTH) is a rare disorder caused by mutations in the TR beta gene. Biochemically, the syndrome is defined by elevated circulating levels of free thyroid hormones due to reduced target tissue responsiveness and normal, or elevated, levels of thyroid-stimulating hormone (TSH). This "inappropriate" TSH elevation contrasts with the situation in hyperthyroidism, where the pituitary secretion of TSH is suppressed. Patients with RTH usually present with goiter and an euthyroid or mildly hypothyroid metabolic state. Thus, pituitary resistance results in hypersecretion of TSH, which compensates, at least in part, for hormone resistance in peripheral tissues. Despite this compensation, clinical effects of RTH can include short stature, delayed bone maturation, hyperactivity, learning disabilities, and hearing defects, as well as variable features of hyper- and hypothyroidism. With the exception of a single sibship, which harbored a deletion of the entire coding sequence of the TR beta gene and a recessive pattern of inheritance, all other cases of RTH have been inherited in an autosomal dominant manner or have been de novo heterozygous mutations of the TR beta gene. The dominant pattern of inheritance is explained by the functional properties of the mutant receptors which act in a dominant negative manner to block the activity of normal TR alpha and TR beta receptors. Now that a large number of different RTH mutations have been identified, it is striking that the mutations are clustered within restricted domains in the carboxyterminal region of the receptor. Mutations in these regions have been shown to preserve critical receptor functions such as dimerization and DNA binding, while inactivating other activites such as T3 binding and transcriptional activation. The examination of patients with RTH and their mutated receptors has provided important insights into the mechanisms of thyroid hormone action, the structure-function relationship of the receptors, and the molecular mechanisms of dominant negative activity.

Amino Acid Sequence↗
PubMed1995

Thyroid hormone (T3) inhibits ciprofibrate-induced transcription of genes encoding beta-oxidation enzymes: cross talk between peroxisome proliferator and T3 signaling pathways.

Peroxisome proliferators cause rapid and coordinated transcriptional activation of genes encoding peroxisomal beta-oxidation system enzymes by activating peroxisome proliferator-activated receptor (PPAR) isoform(s). Since the thyroid hormone (T3; 3,3',5-triiodothyronine) receptor (TR), another member of the nuclear hormone receptor superfamily, regulates a subset of fatty acid metabolism genes shared with PPAR, we examined the possibility of interplay between peroxisome proliferator and T3 signaling pathways. T3 inhibited ciprofibrate-induced luciferase activity as well as the endogenous peroxisomal beta-oxidation enzymes in transgenic mice carrying a 3.2-kb 5'-flanking region of the rat peroxisomal enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase gene fused to the coding region of luciferase. Transfection assays in hepatoma H4-II-E-C3 and CV-1 cells indicated that this inhibition is mediated by TR in a ligand-dependent fashion. Gel shift assays revealed that modulation of PPAR action by TR occurs through titration of limiting amounts of retinoid X receptor (RXR) required for PPAR activation. Increasing amounts of RXR partially reversed the inhibition in a reciprocal manner; PPAR also inhibited TR activation. Results with heterodimerization-deficient TR and PPAR mutants further confirmed that interaction between PPAR and TR signaling systems is indirect. These results suggest that a convergence of the peroxisome proliferator and T3 signaling pathways occurs through their common interaction with the heterodimeric partner RXR.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1995

A comparison of techniques used to estimate the amount of resuspended soil on plant surfaces.

The objectives of this study were to compare four common techniques used to estimate soil mass loadings on plant surfaces and to assess the need to account for particle-size distributions of both the soil tracer and contaminant of concern within the soil. Soil loadings (g soil kg-1 dried plant) from split samples collected in a pasture near Chernobyl were estimated using soil tracers of plutonium analyzed via alpha spectroscopy (mean +/- standard error; 1.0 +/- 0.2), titanium analyzed with an inductive coupled plasma spectrometer; (3.6 +/- 0.6), and neutron activation analysis for scandium (8.1 +/- 1.6), as well as simply washing the soil off the vegetation (34.1 +/- 5.6) Differences were significant at p < 0.001. We also found that soil loading estimates from any one technique varied by a factor of 10 depending on the soil particle size used in the calculations. This was because soil loadings decreased when smaller-sized soil fractions dominated the resuspension process. However, the percent of the plant's total contamination attributable to soil loading increased with smaller soil particles. Smaller soil particles apparently contribute less to the mass of soil loading (g soil kg-1 dry plant), but more to the total plant contamination (Bq) because of the higher concentration of contaminant found in the smaller-sized soil fractions. Differences in mass loading estimates due to the technique chosen (a factor of 10), or due to differences in elemental concentration as a result of the soil particle size used in the calculation (also a factor of 10), were greater than the natural variability observed in the field (2.5).

Alpha Particles↗
PubMed1995

The thyrotropin (TSH) receptor transmembrane domain mutation (Pro556-Leu) in the hypothyroid hyt/hyt mouse results in plasma membrane targeting but defective TSH binding.

The hyt/hyt mouse is hypothyroid because of a mutation in the TSH receptor (TSH-R). In this report, we confirm the presence of a Pro to Leu mutation in amino acid 556 of the fourth transmembrane domain (TM4) of the TSH-R. This Pro is highly conserved in members of the G protein-coupled seven-transmembrane family of receptors. Insertion of this mutation into the wild-type rat receptor eliminated TSH binding and receptor function in transfected 293 and COS cells. Wild-type TSH-R conferred a 7.4-fold increase in cAMP and a 2.3-fold stimulation of a cAMP-responsive reporter gene. The P556L mutant receptor elicited no increase in cAMP or the reporter gene. Cells transfected with wild-type receptor bound TSH with a Kd of 3.3 x 10(-10) M, whereas no TSH binding was detected with the P556L mutant. Because the P556L mutation occurs in a receptor region (TM4) that is not expected to alter the binding of TSH, additional studies were performed to examine receptor processing and cellular localization. Mutant receptors from solubilized membranes also failed to bind TSH, indicating that the absence of binding to intact cells was not accounted for intracellular trapping of the mutant receptor. Western blot analyses demonstrated that the mutant and wild-type receptors were processed through a similar series of precursors and that a mature 95-kilodalton form of the mutant TSH-R was produced, consistent with its insertion into the plasma membrane. Immunofluorescence studies confirmed expression of the P556L mutant on the cell surface of transfected cells and in thyroid tissue from hyt/hyt mice. Although the extracellular domain of the TSH-R is sufficient for high affinity binding of TSH, we conclude that the hyt mutation in the fourth transmembrane domain eliminates TSH binding. These results suggest interactions between the extracellular and transmembrane domains of the TSH-R and indicate that this highly conserved proline is required for normal receptor structure and function.

Amino Acid Sequence↗
PubMed1994

Age-associated changes of rat brain neuronal and astroglial poly(ADP-ribose) polymerase activity.

Nuclear poly(ADP-ribose) polymerase levels as well as the DNA strand break levels of whole-brain neuronal and astroglial cells were investigated. Three- and 30-month-old rats were used. Low-molecular-weight neurofilaments and glutamine synthetase served as neuronal and astroglial markers, respectively. A large increase in the poly(ADP-ribose) polymerase activity was observed in the neurons (threefold) and astrocytes (3.7-fold) derived from 30-month-old rats. Similarly, the amount of poly(ADP-ribose) polymerase, evaluated per milligram of DNA, increased approximately 3.5-fold in neurons and 3.9-fold in astrocytes prepared from 30-month-old rats. Whether the increase in the poly(ADP-ribose) polymerase activity was due to an enhanced rate of DNA strand break was investigated by determining the rate of DNA unwinding. A significant increase in DNA unwinding rate was detected in the neurons (2.7-fold), although a lower increase was observed in the astroglia (1.3-fold) of aged animals.

Aging↗
PubMed1994

The use of a high-purity germanium detector for routine measurements of 125I in radiation workers.

A high-purity germanium detector was calibrated for the assessment of 125I uptake in the thyroid gland of radiation workers. A cylindrical water phantom (perspex walls) with high flexibility for position and size of the thyroid was constructed. Within a massive shielding chamber built for a whole-body counter, an activity of 2.2 Bq was detectable (MDA). This is well below the very restrictive limiting value of 20 Bq for inhalation specified by Austrian law. An activity of 128 Bq was measured with a statistical uncertainty of 5% in a counting period of 10 min. Various parameters influencing the result are investigated as well as the performance of two other measurement geometries outside the shielding chamber.

Gamma Rays↗
PubMed1994

Polyclonal and monoclonal thyroid nodules coexist within human multinodular goiters.

Although somatic mutations have been identified in a subset of thyroid nodules, the pathogenesis of nodules in multinodular goiters remains unclear. Clonal analysis indicates whether a nodule arises from the polyclonal proliferation of a group of cells or forms a clone from a genetically altered cell. Individual thyroid nodules have been shown to be of polyclonal or monoclonal origin. In this study we examined the clonality of several different nodules in patients with multinodular goiters. Clonality was established using the X-chromosomal probe M27 beta, which detects a multiallelic polymorphism at the locus DXS255 in 90% of females. Twenty-five nodules from 9 multinodular goiters were analyzed; 9 nodules were polyclonal, and 16 were monoclonal. Three goiters contained only polyclonal nodules, whereas 3 contained only monoclonal nodules. Polyclonal and monoclonal nodules coexisted in 3 goiters. In 2 goiters, the monoclonal nodules were shown to derive from different progenitor cells. We conclude that polyclonal and monoclonal nodules may coexist in multinodular goiters and that monoclonal nodules can originate from different cells. The coexistence of polyclonal and monoclonal nodules suggests that different pathogenic mechanisms occur simultaneously or that monoclonal nodules emerge secondarily from a polyclonal population due to a growth advantage from a genetically altered cell.

Adult↗
PubMed1991

Lung and blood superoxide dismutase activity in mercury vapor exposed rats: effect of N-acetylcysteine treatment.

Rats were exposed to mercury vapors (30 mg/m3) for either 1 or 2 h. Histological lesions like alveolar oedema, hyaline membranes and sometimes fibrosis were observed. The lesions were more significant after 2 h of exposure, with about 50% of the animals dying within 2 weeks. The mercury level and the superoxide dismutase activity in the blood and the lungs demonstrated differences according to the time of exposure. In the animals exposed for 2 h to mercury vapors, N-acetylcysteine treatment increased survival time and the percentage of living animals. The lung superoxide dismutase was lower than in the non-treated animals indicating an antioxidant effect. Mercury levels were decreased in blood and lung, suggesting some chelating effect of N-acetylcysteine. The exact mechanism of its action must be further elucidated.

Acetylcysteine↗
PubMed1991

Combined effects of ethanol and manganese on cultured neurons and glia.

Manganese is essential for normal development and activity of the nervous tissue. Mn2+ ions are involved in protein synthesis and may prevent free radical damage. Since it is now established that alcohol degradation may produce free radicals, we studied the effect of Mn2+ on ethanol induced alterations using cultured nerve cells as an experimental model of the central nervous system. Neurons and glial cells were cultured from rat brain cortex; a tumoral rat glial cell line (C6) was also examined. We measured enzymatic markers of nerve cell maturation (enolase, glutamine synthetase) and superoxide dismutase, a scavenger of free radicals; all these enzymes being activated by Mn2+ ions. Only for the glial cell types an alcohol antagonizing effect was found when Mn2+ was combined with ethanol. Neurons were not sensitive to that Mn2+ effect.

Animals↗
PubMed1990

Alcohol exposure before pregnancy: biochemical and behavioral effects on the offspring of rats.

The effect of maternal alcohol exposure before mating was investigated in the offspring over a period of 6 months concerning some specific aspects of energy metabolism in the brain and the liver. The following biochemical parameters were analyzed: superoxide dismutase (involved in elimination of free radicals produced during ethanol oxidation), enolase isoenzymes (markers of nerve cell maturation), and alcohol and aldehyde dehydrogenase (the main alcohol degradating enzymes). These enzymatic activities were measured at their subcellular level. In these animals never directly exposed to alcohol, superoxide dismutase activity was decreased mainly in the liver cytosol. Only the nonneuronal form of enolase activity was modified. Alcohol dehydrogenase was decreased in the liver as well as in the brain. Aldehyde dehydrogenase was also decreased in the liver and in the brain, mainly in the mitochondria. Behavioral observations showed decreased emotional reactivity as well as an increase in locomotor activity. Our results suggest that long-lasting biochemical and behavioral effects of alcohol may occur in the offspring starting at the earliest stage of development.

Animals↗
PubMed1989

[2 cases of acute sickle cell crisis in subjects with sickle cell trait following high altitude exposure].

We present two patients with sickle cell trait (HbAS) who developed acute sickle cell crisis after passive exposure to high altitude on the Jungfraujoch (3454 meters, 11,333 ft). Both suffered splenic infarction and the first patient also presented with acute renal failure. Splenic infarction is known to be a complication of altitude exposure in carriers of the trait, whereas acute renal failure due to altitude exposure alone has as far as we know never been described in the literature. These forms of high altitude complications are totally unusual in Switzerland.

Adult↗
PubMed1989

An experimental study of fetal alcohol syndrome in the rat: biochemical modifications in brain and liver.

Maternal alcohol consumption produces various abnormalities in the offspring, termed fetal alcohol syndrome. We investigated various biochemical modifications occurring in the brain and the liver of pups born to alcohol-consuming rats. The parameters analysed were: superoxide dismutase, a protector against free radicals injury, enolase isoenzymes as markers of nerve cell maturation, glutamine synthetase involved in ammonia detoxification, alcohol and aldehyde deshydrogenases in order to evaluate the contribution of acetaldehyde teratogenicity and ATPase activities involved in ion and neurotransmitter transport. Activities of all these enzymes were decreased in the brain even when alcohol was withdrawn from the mother diet either during pregnancy or lactation. Activities were also decreased in the liver, except enolase and alcohol deshydrogenase activities, which were increased, suggesting possible adaptative events in the presence of alcohol. It seems likely that the multiple alterations observed in experimental fetal alcohol syndrome may be caused by free radicals following decreased superoxide dismutase activity in addition to the toxicity of alcohol and its metabolites.

Adenosine Triphosphatases↗
PubMed1988

Levels and sub-cellular distribution of physiologically important metal ions in neuronal cells cultured from chick embryo cerebral cortex.

Mg2+, Ca2+, Mn2+, Zn2+, and Cu content of neurons from chick embryo cortex cultivated in chemically defined serum free growth medium was determined by energy dispersive X-ray fluorescence and atomic absorption spectroscopy. The intracellular volume of cultured neurons was determined to be 2.73 microliters/mg. Intracellular Mn2+, Fe2+, Zn2+, and Cu2+ in the cultivated neurons were 100-200 times the concentrations in the growth medium: Mg2+ and Ca2+ were 0.9 and 1.7 mM respectively, around 20 fold higher than in growth medium. Mg2+, Fe2+, Cu2+ and Zn2+ concentrations in neurons were in the range of ca. 300-600 microM, approximately 2-3 times the values previously reported in glial cells; Ca2+ and Mn2+ content of the neurons were higher by 5 and 10 fold respectively compared to glial cells. In neurons, the subcellular distribution of Fe2+, Cu2+, and Mn2+ follows the rank order: cytosol greater than microsomes greater than mitochondria; for Zn2+ the distribution differs as following: cytosol greater than mitochondria greater than microsomes. Determination of the superoxide dismutase activities in the cultivated neurons indicated that the Mn2+ linked activity predominates whereas, the Cu-Zn dependent enzyme is dominant in glial cells. Enrichment of the culture medium with Mn2+ to 2.5 microM enhanced the Mn-SOD by approximately 33% but the Cu2+-Zn2+ enzyme activity was not modified. The high Mn2+ content, the capacity to accumulate Mn2+, and the predominancy of the Mn-SOD form observed in neurons is in accord with a fundamental functional role for this metal ion in this type of brain cells.

Animals↗