Overexpressed glucocorticoid receptor negatively regulates gene expression under conditions that favour accumulation of non-hormone-binding forms of the receptor (original) (raw)
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Proceedings of the National Academy of Sciences, 1981
Activated glucocorticoid receptor protein, purified to 40-60% homogeneity from rat liver extracts, binds selectively in vitro to a cloned fragment of murine mammary tumor virus (MTV) DNA. The DNA fragment tested contains about half of the sequences present in intact MTV DNA, and its rate of transcription, like that of the intact viral element, is strongly stimulated by glucocorticoids when it is introduced into the genome of a receptor-containing cell. In contrast, the receptor fails to bind selectively to DNA restriction fragments from E. coli plasmids pBR322 and RSF2124 or from bacteriophages A and T4. Preliminary experiments to localize regions within MTV DNA responsible for selective binding have revealed thus far one subfragment that fails to bind the receptor and one selectively bound subfragment that maps far downstream from the 5' terminus ofthe normal RNA transcript. These studies are consistent with the notion that steroid receptors may modulate rates of transcription by recognizing specific DNA sequences within or near the regulated genes.
Functional dissection of the hormone and DNA binding activities of the glucocorticoid receptor
The EMBO Journal, 1987
We have identified two separate regions of the 795 amino acid rat glucocorticoid receptor that interact with hormonal ligands and DNA respectively. The functional regions were defined by direct assays of segments of the receptor coding sequence translated in vitro. Hormone affinity measurements suggested that residues near the receptor C-terminus are the primary determinants of ligand binding, whereas sequence-specific DNA binding activity resides between amino acids 440 and 546. DNA binding efficiency was stimulated only modestly by prior hormone binding. The receptor regions identified in these in vitro studies correspond to those that mediate ligand-dependent transcriptional enhancement in vivo.
Autoregulation of glucocorticoid receptor gene expression
Steroids, 1991
Glucocorticoid receptors are members of a highly conservedfamily of steroid receptor proteins, which are ligand-dependent transcription j;lctors. Previous studies huve shown that the presence offunctional glucocorticoid receptors is N prerequisitefor manifestation of cellular responses to hormone. Glucocorticoid receptors undergo down-regulation following treutment with glucocorticoids. To define the molecular mechanisms that are involved in this process n'e have analyzed the down-regulation of glucocorticoid receptors both in HeLa cells, which contain endogenous receptors, and in cells containing receptors that have been introduced by DNA transfection. Our results show that cells that contain glucocorticoid receptors-either endogenous or trrmsfected-undergo down-regulation of steroid-binding capabilities, us well NS reductions in receptor protein rend mRNA levels, in a remarkably similar fashion. DNA sequences in the coding region of the humrrn glucocorticoid receptor cDNA appear to be sufJicient to uccount jtir down-regulution of receptor. This novel jinding suggests that unique mechanisms are involved in controlling glucocorticoid receptor homeostcrsis.
Mechanism of gene expression by the glucocorticoid receptor: Role of protein-protein interactions
BioEssays, 1997
The glucocorticoid receptor belongs to an important class of transcription factors that alter the expression of target genes in response to a specific hormone signal. The glucocorticoid receptor can function at least at three levels: (1) recruitment of the general transcription machinery; (2) modulation of transcription factor action, independent of DNA binding, through direct proteinprotein interactions; and (3) modulation of chromatin structure to allow the assembly of other gene regulatory proteins and/or the general transcription machinery on the DNA. This review will focus on the multifaceted nature of protein-protein interactions involving the glucocorticoid receptor and basal transcription factors, coactivators and other transcription factors, occurring at Accepted these different levels of regulation.
The Journal of biological chemistry, 1991
Gel retardation analysis with full-and half-palindromic sequences using partially purified glucocorticoid receptor (GR) resulted in GR-glucocorticoid response element (GRE) species of identical mobilities, suggesting that formation of the dimeric GR protein complex is not catalyzed by DNA binding. These results are in contrast to the behavior of the isolated DNA binding domain of the glucocorticoid receptor where dimerization occurred on the GRE. Density gradient centrifugation of cytosolic GR resulted in two forms, a 4 S peak characteristic of the monomeric GR and a fraction which sediments at 6 S which is consistent with the observed size of the dimeric GR. These two forms were found to differ in their ability to bind to specific DNA sequences with the 6 S species having a higher affinity for a GRE. Taken together our results are consistent with a two-step model for hormoneinduced transformation of GR: dissociation of the multimeric untransformed complex and dimerization of the GR to yield a high affinity DNA binding species.
Cloning and regulation by glucocorticoid receptor ligands of a rat hsp90
The Journal of Steroid Biochemistry and Molecular Biology, 1992
mWe have isolated a full length eDNA that encodes a heat shock protein, hsp90, from a rat brain library and present the nucleotide sequence and deduced amino acid sequence. Comparison of the entire nueleotide sequence with mouse hsp84 and human hsp90fl cDNAs reveal sequence similarities of 92 and 87%, respectively. The coding region of 2172 nucleotides corresponds to a polypeptide chain of 724 amino acids. Comparison with mouse hsp84 and human hsp90fl amino acid sequences indicates a similarity of 97%, respectively. Characterization of the constitutive expression of this eDNA both by RNA blot hybridization and immunoblotting, reveals that it is expressed in all rat tissues examined. Hsp90 has been shown to form a transient complex with steroid hormone receptors. In order to further elucidate the role of hspg0 in the endocrine response of cells, we have examined the effects of dexamethasone and RU38486 on the level of hsp90 mRNA in a system in which glucocorticoids down-regulate glucocorticoid receptor mRNA levels. In this system, a subtle but reproducible approx. 2-fold decrease in hspg0 mRNA levels is observed after 48 h treatment with dexamethasone.
The Glucocorticoid Receptor: Rapid Exchange with Regulatory Sites in Living Cells
Science, 2000
Steroid receptors bind to site-specific response elements in chromatin and modulate gene expression in a hormone-dependent fashion. With the use of a tandem array of mouse mammary tumor virus reporter elements and a form of glucocorticoid receptor labeled with green fluorescent protein, targeting of the receptor to response elements in live mouse cells was observed. Photobleaching experiments provide direct evidence that the hormone-occupied receptor undergoes rapid exchange between chromatin and the nucleoplasmic compartment. Thus, the interaction of regulatory proteins with target sites in chromatin is a more dynamic process than previously believed.