A distinct modulating domain in glucocorticoid receptor monomers in the repression of activity of the transcription factor AP-1.

Abstract

Steroid receptors activate and repress genes. An important class of genes that they repress is controlled by the transcription factor AP‐1. The activity of AP‐1 is inhibited by the receptor, a mechanism exploited for the therapy of various forms of pathological hyperproliferation in humans. We show here by point mutations in the DNA binding domain and by the choice of steroid ligands that repression of AP‐1 activity and transactivation functions of the glucocorticoid receptor (GR) are separable entities. While DNA binding and activation of glucocorticoid‐regulated promoters require GR dimerization, we present data that suggest that repression is a function of GR monomers.

How Do Corticosteroids Work in Asthma?

“…Because corticosteroids bind to the same glucocorticoid receptors, this seems at first to be an unlikely possibility, but while DNA binding involved a glucocorticoid receptor homodimer, interaction with transcription factors AP-1 and NF-B and coactivators involves only a single glucocorticoid receptor (22). A separation of transactivation and transrepression has been demonstrated by using reporter gene constructs in transfected (see Glossary) cells using selective mutations of the glucocorticoid receptor (71). In addition, in mice with glucocorticoid receptors that do not dimerize, there is no transactivation, but transrepression seems to be normal (21,28).…”

Nontranscriptional actions of the glucocorticoid receptor

“…Transcriptional activation by GR requires homodimerization through two different dimerization interfaces. A five amino acid sequence (D loop) in the second zinc-finger of the DBD mediates cooperative DNA-binding to the palindromic motive of the GRE, and mutations in the D loop abrogate transactivation by GR [36,37]. In addition, dimerization requires reciprocal interactions of two hydrophobic amino acids in the LBD.…”

Selective glucocorticoid receptor agonists (SEGRAs): Novel ligands with an improved therapeutic index

“…The introduction of a point mutation in the dimerization domain of the GR was used to demonstrate in vitro that dimerization of the GR is a prerequisite for transactivation function (Heck et al, 1994). In mice carrying a dimerization-deficient GR the induction of several liver specific genes was strongly reduced (Reichardt et al, 1998).…”

“…This mechanism is fully functional with dimerization-defective GR (Heck at al., 1994, Reichardt et al, 1998Tuckermann et al, 1999) and is therefore thought to occur through GR monomers. The transcription factors to which the GR is tethered include activator protein 1 (AP-1), nuclear factor-κB (NF-κB) and interferon regulatory factor 3 (IRF3) (Reily et al, 2006;Ogawa et al, 2005).…”

“…This concept is based on studies with a mutant GR, where the exchange of a single amino acid residue in the dimerization domain of the receptor molecule abrogated dimerization and transactivation activities of the GR without affecting the ability of the receptor to repress AP-1 regulated genes (Heck et al, 1994). Further studies with genetically modified mice carrying this dimerization deficient GR (GR dim/d im ) demonstrated a similar phenotype.…”