Intracellular receptors use a common mechanism to interpret signaling information at response elements.

Abstract

The glucocorticoid receptor (GR) activates transcription in certain glucocorticoid response element (GRE) contexts, and represses or displays no activity in others. We isolated point mutations in one GRE, plfG, at which GR activated transcription under conditions in which the wild-type element was inactive or conferred repression, implying that GREs may carry signals that are interpreted by bound receptors. Consistent with this notion, we identified a mutant rat GR, K461A, which activated transcription in all GRE contexts tested, implying that this residue is important in interpretation of GRE signals. In a yeast screen of 60,000 GR mutants for strong activation from plfG, all 13 mutants isolated contained substitutions at K461. This lysine residue is highly conserved in the zinc-binding region (ZBR) of the intracellular receptor (IR) superfamily; when it was mutated in MR and RARP, the resulting receptors similarly activated transcription at response elements that their wild-type counterparts repressed or were inactive. We suggest that IR response elements serve in part as signaling components, and that a critical lysine residue serves as an allosteric "lock" that restricts IRs to inactive or repressing configurations except in response element contexts that signal their conversion to transcriptional activators. Therefore, mutation of this residue produces altered receptors that activate in many or all response element contexts.[Key Words: Glucocorticoid receptor; transcriptional repression; DNA-binding domain; context-dependent activity; intracellular receptor] Received January 1, 1996; accepted in revised form March 27, 1996.Regulation of transcription typically commences with the specific binding of a regulatory protein to a response element close to the target promoter; the regulator also interacts with other regulatory factors, with the transcription machinery andlor chromatin components, therefore modulating the rate of transcription initiation (for review, see Sheldon and Reinberg 1995;Hori and Carey 1994; Tjian and Maniatis 1994). Numerous regulators have been shown to activate transcription in certain cell types and at certain promoters, and to repress in other settings (Meyer et al. 1980;Keleher et al. 1988;Pedersen et al. 1991). Therefore, it is apparent that the precise activity of a regulator can be determined largely by its context-cell type, promoter, response element, and extracellular signals. The mechanisms by which regulators sense and interpret their contexts and thereby display distinct activities in different settings remain to be determined.The glucocorticoid receptor (GR) is a member of the intracellular receptor (IR) superfamily, which encompasses a large group of transcriptional regulators (Tsai Present addresses: 2Department

Glucocorticoid receptor heterozygosity combined with lack of receptor auto-induction causes glucocorticoid resistance in Jurkat acute lymphoblastic leukemia cells

“…To the contrary, there was even a slight increase in luciferase expression suggesting that the mutant might paradoxically induce, rather than repress, this (and perhaps other) promoter(s), as has been reported for the rat K461A mutation that is located next to the fourth cystein in the first Zn finger. 28,29 Thus, the R477H mutation markedly impaired the ability of GR to transactivate and to transrepress gene expression.…”

Cross-talk between glucocorticoid receptor and AP-1

“…. Although GR mutants di erently acting on the composite element of the proliferin gene have been screened for in yeast (Starr et al, 1996); the tethering cross-talk could not be reconstructed in yeast (our unpublished data) suggesting the lack of a co-factor.…”

“…The hypothesis that the DNA element or its arrangement in¯uences the structure of a transcription factor and even of those relevant here, is not without precedent: AP-1, RAR-RXR and TR have been shown to alter their conformation and function upon binding to DNA (Patel et al, 1990;Ikeda et al, 1996;Mangelsdorf et al, 1991;Chen and Evans, 1995). Conformational changes of the GR upon interaction with GRE-like elements can be concluded both, from the detection of mutations which arrest the GR in one conformation, and from structural analyses (Starr et al, 1996;van Tiborg et al, 2000).…”

Multiple mutations contribute to repression by the v-Erb A oncoprotein

“…The collagenase AP-1 site-luciferase and pRSV-c-Jun constructs were previously described (Sharif and Privalsky, 1992;Starr et al, 1996).…”