Agonist-Activated Glucocorticoid Receptor Inhibits Binding of Heat Shock Factor 1 to the Heat Shock Protein 70 Promoterin Vivo

Abstract

We have previously shown that activation of glucocorticoid receptor (GR) signaling in stressed cells will cause inhibition of the heat shock response as mediated by heat shock transcription factor 1 (HSF1). In that work, a full-length human heat shock protein 70 (Hsp70) promoter was used to measure HSF1 transactivity, and the data suggested inhibition of HSF1 through the transactivation or transrepressive properties of GR. Here, we show that the inhibitory effect of glucocorticoid agonist (dexamethasone) upon Hsp70 promoter activity is rapid, occurring within 1 h of hormone addition. Moreover, addition of hormone during the first hour of recovery from stress was sufficient to inhibit HSF1. Thus, dexamethasone is able to rapidly reverse HSF1 transactivity, suggesting a transrepressive mode of action for GR. Yet, GR transrepression of HSF1 by analysis of putative negative glucocorticoid response elements in the Hsp70 promoter was not found. To further investigate the in vivo nature of this fast-acting mechanism, we used the chromatin immunoprecipitation assay with primers specific to the human Hsp70 promoter. Dexamethasone inhibited HSF1 binding at the Hsp70 promoter in response to heat or chemical shock (sodium arsenite). Moreover, dexamethasone also blocked promoter binding by a constitutively active mutant of HSF1 (hHSF1-E189) expressed under nonstress conditions. In all cases, inhibition of HSF1 recruitment to the promoter by dexamethasone was blocked by the GR antagonist RU486, a result that was consistent with promoter activity based on chloramphenicol acetyl transferase gene expression. The ability of dexamethasone to prevent HSF1 recruitment to the promoter was fast acting (occurring in as little as 15 min), and the hormone also caused release of HSF1 already bound to the promoter. Although these results suggest GR can effectively prevent HSF1 binding to Hsp promoters, fractionation and Western blot experiments showed that stress-activated HSF1 was not released from the nucleus in response to hormone. Thus, this effect of dexamethasone is either specific to the Hsp70 promoter or causes shunting of HSF1 to other high-affinity nuclear sites. These observations provide evidence of a novel mechanism for attenuation of the heat shock response by glucocorticoids: prevention or reversal of HSF1 recruitment to Hsp promoters through the rapid actions of GR.

Compound A, a Selective Glucocorticoid Receptor Modulator, Enhances Heat Shock Protein Hsp70 Gene Promoter Activation

“…However, the involvement of GR does not coincide with a recruitment of GR to the HSPA1A gene promoter, suggesting that GR might act as a mediator rather than an effector. Interestingly, it has been described that GCs can repress heat shock-induced Hsp70 gene expression [64], [65], via the interference of GC-activated GR with the recruitment of the transcription factor HSF1 to the proximal HSE-elements in the Hsp70 promoter [65]. These reports provide the context for the observed DEX-mediated recruitment of GR to the HSPA1A gene promoter (Figure 9C).…”

Electrophilic Lipid Mediator 15-Deoxy-Δ12,14-Prostaglandin J2 Modifies Glucocorticoid Signaling via Receptor SUMOylation

“…ATF4 is also involved in cellular antioxidant protection (40), and its expression has been shown to be repressed by glucocorticoids (41). HSF1 is essential for organisms to survive during acute stress (42), and, interestingly, activation of GR signaling in stressed cells inhibits binding of HSF1 to the heat shock protein 70 promoter (43). In good agreement with the transcriptome data, the alleviation of GRmediated repression of HSF1 by 15d-PGJ 2 in GR SUMOylationcompetent cells resulted in robust expression of HSF1 target genes HSPA1A and HSPA1B.…”

Functions of the Hsp90-Binding FKBP Immunophilins

“…Thus, heterozygous fkbp52-deficient mice (52+/-) were generated to determine the in vivo roles for FKBP52 in GR-mediated physiology. 52+/-mice displayed phenotypes associated with reduced GR signaling including increased susceptibility to high-fat diet-induced hepatic steatosis, hyperglycemia, hyperinsulinemia, and behavioral alterations under basal and chronic stress conditions (Wadekar et al 2004;Warrier et al 2010).…”