SciCombinator

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Concept: Selective glucocorticoid receptor agonist

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A newly discovered negative glucocorticoid response element (nGRE) mediates DNA-dependent transrepression by the glucocorticoid receptor (GR) across the genome and has a major role in immunosuppressive therapy. The nGRE differs dramatically from activating response elements, and the mechanism driving GR binding and transrepression is unknown. To unravel the mechanism of nGRE-mediated transrepression by the GR, we characterized the interaction between GR and an nGRE in the thymic stromal lymphopoietin (TSLP) promoter. We show using structural and mechanistic approaches that nGRE binding is a new mode of sequence recognition by human GR and that nGREs prevent receptor dimerization through a unique GR-binding orientation and strong negative cooperativity, ensuring the presence of monomeric GR at repressive elements.

Concepts: Immune system, Transcription factor, Nuclear receptor, Glucocorticoid receptor, Selective glucocorticoid receptor agonist, Response element, Hormone response element, Transrepression

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Dexamethasone is a synthetic glucocorticoid that is widely used as an adipogenic inducer in both murine and human in vitro models. Glucocorticoids have been shown to regulate early transcriptional events in adipogenesis. MicroRNAs (miRNAs) have been also implicated in the regulation of preadipocyte differentiation; however, the effects of glucocorticoids on miRNA expression levels during this process have not been studied. In this study we investigated the effects of glucocorticoids on the expression levels of miR-155 in differentiating 3T3-L1 preadipocytes. We found that miR-155 levels were up-regulated (2.4-fold) by glucocorticoids in differentiating 3T3-L1 preadipocytes, and this enhancement was abolished in the presence of RU486, a glucocorticoid receptor antagonist. In contrast, treatment with rosiglitazone, another adipogenic inducer decreased the expression levels of miR-155 in these cells. Further, our data show that endogenous miR-155 is unlikely to be involved in adipogenesis as we show that both dexamethasone and rosiglitazone induced adipogenesis to similar levels. Furthermore, using miR-155 inhibitor, we showed that the dexamethasone mediated miR-155 enhancement did not alter adipogenesis. Our data show that dexamethasone but not rosiglitazone increases miR-155 expression and that the increased expression of miR-155 is not involved in the dexamethasone-mediated adipogenesis in the 3T3-L1 model.

Concepts: Gene, Gene expression, MicroRNA, Receptor, Cortisol, Receptor antagonist, Glucocorticoid receptor, Selective glucocorticoid receptor agonist

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Chronic stress or prolonged administration of glucocorticoids suppresses proliferation and/or survival of newborn cells in adult rat dentate gyrus. Earlier we showed that administration of the glucocorticoid receptor antagonist mifepristone during the final 4 days of a 21 days period of corticosterone treatment fully normalized the number of newborn cells. Here we aimed to better understand how mifepristone achieves this effect and questioned whether an even shorter (single day) mifepristone treatment (instead of 4 days) also suffices to normalize neurogenesis.

Concepts: Receptor, Cortisol, Dentate gyrus, Neurogenesis, Receptor antagonist, Entorhinal cortex, Glucocorticoid receptor, Selective glucocorticoid receptor agonist