Determinants of promoter-specific activity by glucocorticoid receptor.

Abstract

Glucocorticoid receptor (GR) is expressed at essentially equal levels in almost all tissues and cell types. Remarkably, glucocorticoids themselves regulate transcription in vivo in both a promoter- and tissue-specific manner. Thus, specific systems must be in place to regulate receptor action within certain cells and at certain promoters. To address two specific aspects of these systems, we have analyzed promoter-specific activity of GR using two different, well studied promoters (termed simple and composite promoters) from which GR activates transcription. The simple promoter depends only on the receptor for glucocorticoid-responsive transcriptional activation, while GR activity at the composite promoter depends on additional transcription factors. We have compared the action of several GR ligands at these promoters and demonstrate fundamental differences in the activities of these ligands on receptor activity. Furthermore, these compounds induce unique conformational changes in receptor, resulting in promoter-specific receptor function. We have identified critical amino acid residues within GR which, when mutated, genetically distinguish the action of GR at these promoters. Taken together, the data indicate that the presence of only the receptor and the ligand is not sufficient to allow activation of transcription. An additional system of regulation influences receptor action in both a tissue- and promoter-selective fashion, suggesting that multiple, regulated surfaces of the receptor respond to the cellular environment and determine the spectrum of GR activities. These functional surfaces may be induced or regulated by ligand binding, by the DNA sequence to which receptor is bound, or by the nonreceptor factors resident at the promoter or in the tissue.

Negative Response Elements in Keratin Genes Mediate Transcriptional Repression and the Cross-talk among Nuclear Receptors

“…[33][34][35]. For example, studies by Lefstin and Yamamoto included a variety of positive GREs and suggested that REs may act as "ligands for regulators" (34).…”

Anti-inflammatory functions of glucocorticoid-induced genes

“…Although GR alone has low affinity for sites that diverge from the GRE consensus, high affinity binding and transcriptional activation can be restored in the presence of multiple sub-optimal GR binding sites such as half GREs (Lechner et al, 1997) or adjacent binding sites for other transcription factors (Guido et al, 1996;Morin et al, 2000;Stafford et al, 2001;Strahle et al, 1988). Recruitment to such sites is thought to be mediated by both protein-DNA interactions and protein-protein interactions of GR with other transcription factors.…”

Allosteric Effects of Dexamethasone and RU486 on Glucocorticoid Receptor-DNA Interactions

“…The agonist dexamethasone enhances GR-DNA binding severalfold, whereas antagonists including RU486 have no effect on GR-DNA binding. However, this observation is contested by a report that also implements gelshift methods with a palindromic GRE substrate but uses in vitro transcribed GR (13). This work shows that dexamethasone and RU486 predominantly affect the mobility of GR-DNA complex in a gel and only modestly affect the affinity of GR for DNA (13).…”

“…However, this observation is contested by a report that also implements gelshift methods with a palindromic GRE substrate but uses in vitro transcribed GR (13). This work shows that dexamethasone and RU486 predominantly affect the mobility of GR-DNA complex in a gel and only modestly affect the affinity of GR for DNA (13). Therefore, although ligands clearly regulate GRmediated transcriptional activity, a direct effect of these ligands on specific GR-DNA interactions is controversial.…”

“…In general, studies indicate that hormones are not required for stable GR binding to DNA in vitro (11)(12)(13)(14)(15)(16). Specifically, complexes of agonist triamcinolone acetonide and antagonist RU486 bound to GR have a comparable affinity for glucocorticoid response elements from different promoters (14 -16).…”