Investigations on the role of Hsp90 in the pathogenic glucocorticoid resistance of corticotroph pituitary adenomas

The main function of glucocorticoids in corticotroph cells is to suppress proopiomelanocortin, the precursor of the stress hormone adrenocorticotropin (ACTH). Cushing?s disease is a rare but severe neuroendocrine condition caused by partially glucocorticoid resistant corticotroph adenomas, which consequently secrete excessive amounts of ACTH in an uncontrolled fashion. The patients suffer from chronic hypercortisolism due to excessive stimulation of the adrenal glands by ACTH to produce glucocorticoids. Impairing mutations of the glucocorticoid receptor (GR) only sporadically explain the reduced glucocorticoid sensitivity in the adenomas ? the molecular mechanism behind the partial resistance is poorly understood. The function of GR depends on direct interactions with the molecular chaperone Hsp90. Both the reduction and overexpression of Hsp90 impedes GR activity in different experimental settings. Therefore, the expression of the inducible Hsp90\ensuremath{α} isoform was determined in biopsy specimens of corticotroph pituitary adenomas from patients with Cushing?s disease. Its strong overexpression compared to normal human pituitary cells paved the way to study its role in the function of corticotroph adenomas using small molecules which target Hsp90. The three distinct Hsp90 inhibitors 17?AAG, Novobiocin and Silibinin showed antiproliferative effects in AtT?20 cells through the degradation of the oncogenic client kinase Cdc2, a hallmark of pharmacologic inhibition of Hsp90. Surprisingly, only the N?terminal Hsp90 inhibitor 17?AAG caused the degradation of GR, as was reported also for other Geldanamycin?based Hsp90 inhibitors. Neither Silibinin nor the C?terminal Hsp90 inhibitor Novobiocin affected GR protein levels. These converging effects led to the assumption that both compounds bind to the same domain in Hsp90. It was shown here that Novobiocin displaces Silibinin from the C?terminal domain of Hsp90, and that these compounds dissociate mature GR from Hsp90 at the biochemical level. As a result, increased levels of mature receptor were present in the cell able to bind glucocorticoids with high affinity. This novel molecular mechanism proved to potentiate GR transcriptional activity in AtT?20 cells. The potentiation in GR activity also led to enhanced suppression of ACTH elicited by low concentrations of Dexamethasone in AtT?20 cells and in primary cultures of human corticotroph adenomas from patients with Cushing?s disease. In contrast, Silibinin did not show effects on rat normal pituitary cells. Finally, Silibinin reduced tumor growth, partially reverted hormonal alterations, and alleviated symptoms in a mouse allograft model for Cushing?s disease. These results suggest that the regulation of GR sensitivity by overexpressed Hsp90 may represent a pharmacologically reversible mechanism in the pathogenesis of this disease. Together, a proof of principle is provided that the clinically safe Hsp90 inhibitor Silibinin potentially restores glucocorticoid sensitivity in corticotroph adenomas in vitro and in vivo, and that it might be used to treat Cushing?s patients in the future

Investigations on the role of Hsp90 in the pathogenic glucocorticoid resistance of corticotroph pituitary adenomas

The main function of glucocorticoids in corticotroph cells is to suppress proopiomelanocortin, the precursor of the stress hormone adrenocorticotropin (ACTH). Cushing’s disease is a rare but severe neuroendocrine condition caused by partially glucocorticoid resistant corticotroph adenomas, which consequently secrete excessive amounts of ACTH in an uncontrolled fashion. The patients suffer from chronic hypercortisolism due to excessive stimulation of the adrenal glands by ACTH to produce glucocorticoids. Impairing mutations of the glucocorticoid receptor (GR) only sporadically explain the reduced glucocorticoid sensitivity in the adenomas – the molecular mechanism behind the partial resistance is poorly understood. The function of GR depends on direct interactions with the molecular chaperone Hsp90. Both the reduction and overexpression of Hsp90 impedes GR activity in different experimental settings. Therefore, the expression of the inducible Hsp90α isoform was determined in biopsy specimens of corticotroph pituitary adenomas from patients with Cushing’s disease. Its strong overexpression compared to normal human pituitary cells paved the way to study its role in the function of corticotroph adenomas using small molecules which target Hsp90. The three distinct Hsp90 inhibitors 17–AAG, Novobiocin and Silibinin showed antiproliferative effects in AtT–20 cells through the degradation of the oncogenic client kinase Cdc2, a hallmark of pharmacologic inhibition of Hsp90. Surprisingly, only the N–terminal Hsp90 inhibitor 17–AAG caused the degradation of GR, as was reported also for other Geldanamycin–based Hsp90 inhibitors. Neither Silibinin nor the C–terminal Hsp90 inhibitor Novobiocin affected GR protein levels. These converging effects led to the assumption that both compounds bind to the same domain in Hsp90. It was shown here that Novobiocin displaces Silibinin from the C–terminal domain of Hsp90, and that these compounds dissociate mature GR from Hsp90 at the biochemical level. As a result, increased levels of mature receptor were present in the cell able to bind glucocorticoids with high affinity. This novel molecular mechanism proved to potentiate GR transcriptional activity in AtT–20 cells. The potentiation in GR activity also led to enhanced suppression of ACTH elicited by low concentrations of Dexamethasone in AtT–20 cells and in primary cultures of human corticotroph adenomas from patients with Cushing’s disease. In contrast, Silibinin did not show effects on rat normal pituitary cells. Finally, Silibinin reduced tumor growth, partially reverted hormonal alterations, and alleviated symptoms in a mouse allograft model for Cushing’s disease. These results suggest that the regulation of GR sensitivity by overexpressed Hsp90 may represent a pharmacologically reversible mechanism in the pathogenesis of this disease. Together, a proof of principle is provided that the clinically safe Hsp90 inhibitor Silibinin potentially restores glucocorticoid sensitivity in corticotroph adenomas in vitro and in vivo, and that it might be used to treat Cushing’s patients in the future

Analysis and comparison of the Antarctic Oscillation in reanalysis and climate model data

Die Antarktische Oszillation ist bekannt als das dominante atmosphärische Variabilitätsmuster in außertropischen Regionen der Südhemisphäre und ist gekennzeichnet durch eine entgegengesetzte Schwankung von troposphärischen Luftdruckanomalien zwischen mittleren und höheren Breiten. Dieses großräumige Muster atmosphärischer Variabilität steht in engem Zusammenhang mit diversen beobachteten klimatischen Entwicklungen der jüngeren Vergangenheit auf der südlichen Erdhälfte. Aus diesem Grund wird die folgende Arbeit zunächst die zeitlichen Entwicklungen der letzten Jahrzehnte und die räumlichen Muster der Antarktischen Oszillation in der Troposphäre sowie in der Stratosphäre in Reanalysedaten untersuchen. Daraufhin werden verschiedene, um das Atmosphärenmodell ECHAM aufgebaute Modellkonfigurationen daraufhin untersucht, inwiefern sie in der Lage sind, die aus den Reanalysedaten abgeleiteten Charakteristiken zu reproduzieren

Investigations on the role of Hsp90 in the pathogenic glucocorticoid resistance of corticotroph pituitary adenomas

The main function of glucocorticoids in corticotroph cells is to suppress proopiomelanocortin, the precursor of the stress hormone adrenocorticotropin (ACTH). Cushing’s disease is a rare but severe neuroendocrine condition caused by partially glucocorticoid resistant corticotroph adenomas, which consequently secrete excessive amounts of ACTH in an uncontrolled fashion. The patients suffer from chronic hypercortisolism due to excessive stimulation of the adrenal glands by ACTH to produce glucocorticoids. Impairing mutations of the glucocorticoid receptor (GR) only sporadically explain the reduced glucocorticoid sensitivity in the adenomas – the molecular mechanism behind the partial resistance is poorly understood. The function of GR depends on direct interactions with the molecular chaperone Hsp90. Both the reduction and overexpression of Hsp90 impedes GR activity in different experimental settings. Therefore, the expression of the inducible Hsp90α isoform was determined in biopsy specimens of corticotroph pituitary adenomas from patients with Cushing’s disease. Its strong overexpression compared to normal human pituitary cells paved the way to study its role in the function of corticotroph adenomas using small molecules which target Hsp90. The three distinct Hsp90 inhibitors 17–AAG, Novobiocin and Silibinin showed antiproliferative effects in AtT–20 cells through the degradation of the oncogenic client kinase Cdc2, a hallmark of pharmacologic inhibition of Hsp90. Surprisingly, only the N–terminal Hsp90 inhibitor 17–AAG caused the degradation of GR, as was reported also for other Geldanamycin–based Hsp90 inhibitors. Neither Silibinin nor the C–terminal Hsp90 inhibitor Novobiocin affected GR protein levels. These converging effects led to the assumption that both compounds bind to the same domain in Hsp90. It was shown here that Novobiocin displaces Silibinin from the C–terminal domain of Hsp90, and that these compounds dissociate mature GR from Hsp90 at the biochemical level. As a result, increased levels of mature receptor were present in the cell able to bind glucocorticoids with high affinity. This novel molecular mechanism proved to potentiate GR transcriptional activity in AtT–20 cells. The potentiation in GR activity also led to enhanced suppression of ACTH elicited by low concentrations of Dexamethasone in AtT–20 cells and in primary cultures of human corticotroph adenomas from patients with Cushing’s disease. In contrast, Silibinin did not show effects on rat normal pituitary cells. Finally, Silibinin reduced tumor growth, partially reverted hormonal alterations, and alleviated symptoms in a mouse allograft model for Cushing’s disease. These results suggest that the regulation of GR sensitivity by overexpressed Hsp90 may represent a pharmacologically reversible mechanism in the pathogenesis of this disease. Together, a proof of principle is provided that the clinically safe Hsp90 inhibitor Silibinin potentially restores glucocorticoid sensitivity in corticotroph adenomas in vitro and in vivo, and that it might be used to treat Cushing’s patients in the future

Creak in the Rain: Phonation in Oregon English

No abstract

On the linkage between future Arctic sea ice retreat, Euro-Atlantic circulation regimes and temperature extremes over Europe

The question to what extent Arctic sea ice loss is able to affect atmospheric dynamics and climate extremes over mid-latitudes still remains a highly debated topic. In this study we investigate model experiments from the Polar Amplification Model Intercomparison Project (PAMIP) and compare experiments with future sea ice loss prescribed over the entire Arctic, as well as only locally over the Barents and Kara seas, with a present-day reference experiment. The first step is to perform a regime analysis and analyze the change in occurrence frequencies of five computed Euro-Atlantic winter circulation regimes. Forced by future Arctic sea ice conditions, most models show more frequent occurrences of a Scandinavian blocking pattern in at least 1 winter month, whereas there is an overall disagreement between individual models on the sign of frequency changes of two regimes that, respectively, resemble the negative and positive phase of the North Atlantic Oscillation. Focusing on the ECHAM6 PAMIP experiments, we subsequently employ a framework of conditional extreme-event attribution. It demonstrates how detected regime frequency changes can be used to decompose sea-ice-induced frequency changes of European temperature extremes into two different contributions: one “changed-regime” term that is related to dynamical changes in regime occurrence frequencies and another more thermodynamically motivated “fixed-regime” contribution that is related to increased surface temperatures during a specific circulation regime. We show how the overall fixed-regime warming effect and also an increased Scandinavian blocking pattern frequency under future sea ice reductions can equally contribute to and shape the overall response signal of European cold extremes in midwinter. We also demonstrate how a decreased occurrence frequency of an anticyclonic regime over the eastern Atlantic dynamically counteracts the fixed-regime warming response and results in no significant changes in overall January warm-extreme occurrences. However, when compared to other characteristics of future climate change, such as the thermodynamical impact of globally increased sea surface temperatures, the effects of Arctic sea ice loss on European temperature extremes are of secondary relevance