Differential interaction of RU486 with the progesterone and glucocorticoid receptors

Abstract

Steroid hormone receptor antagonists are widely used in clinical medicine, but their use is often complicated by the lack of receptor specificity to presently available drugs. We previously demonstrated an important role of a widely conserved helix 3 (H3)-helix 5 (H5) interaction in determining the sensitivity and specificity of steroid hormone receptors to receptor agonists. Intriguingly, the same H3 residues also play a crucial role in receptor antagonism; mutation of these residues alters the response of these receptors to antagonists. Given the close interaction of H3 and H5 residues at this site, we asked whether H5 residues might also play a role in the sensitivity of these receptors to antagonists. We demonstrate here that modification of H5 residues produces marked changes in the sensitivities of the glucocorticoid and progesterone receptor (PR) to RU486 antagonism. Moreover, while we confirm previous reports that alteration of the H3 residue, Gly 722 prevents RU486-mediated inhibition of the PR, we show that the corresponding substitution in the glucocorticoid receptor does not inhibit RU486-mediated receptor antagonism. Taken together, our data support the notion that RU486 binds differently to these two receptors, providing a potential target for the design of more specific antiglucocorticoid and antiprogestin drugs.

Helix 3–helix 5 interactions in steroid hormone receptor function

“…To better understand the effect of H3 and H5 substitutions on antagonist activity, we examined whether mutations at these positions would affect hGR sensitivity to RU486 as well. Although previous reports had suggested hGR containing a substitution of alanine for glycine at the H3 position, hGR G567A , is inactive [29], we found this receptor possessed significant transcriptional activity in the presence of dexamethasone and cortisol, albeit somewhat reduced from that of hGR WT [33], and furthermore, we found that the G567A mutation did not alter RU486 inhibition of hGR; as dexamethasone and cortisol induced activation of hGR G567A were inhibited at similar RU486 concentrations as hGR WT [33]. This stands in sharp contrast to hPR, in which the G722A mutation renders hPR entirely resistant to RU486.…”

“…We further showed, however, that alteration of the H5 position also renders hPR highly resistant to RU486, as 100-fold increased RU486 concentrations are required for receptor inhibition for receptors bearing alanine, glycine, or serine, but not leucine, at the H5 position compared to PR WT (Fig. 4A) [33]. Importantly, RU486 did not stimulate activity in the absence of progesterone in these receptors, indicating that this result is not due to RU486 acting as an agonist.…”

Influence of hormones and hormone metabolites on the growth of schwann cells derived from embryonic stem cells and on tumor cell lines expressing variable levels of neurofibromin

“…We found that the effect of the PR inhibitor RU486 was variable, ranging from significant inhibition of cell proliferation even below control levels in some cell types (SW10 and PNF) to no significant effect (ST, D3SC, SKOSC, DKOSC). RU486 is also an inhibitor of AR and the glucocorticoid receptor, which could also influence the results (Ghoumari et al,2003; Zhang et al,2006). However, because these cells were grown in hormone‐free medium with only P4 added, this influence should be minimal in these experiments.…”

Structure–function relationships in the mineralocorticoid receptor

“…Mineralocorticoid specificity in MR is thought to be provided partially by a hydrogen bond between asparagine-770 on helix 3 and the C 21 -OH group of the ligand (Zhang et al 2006). Geller et al (2000) identified a point mutation in the human MR, serine at 810 to leucine (S810L) in helix 5, which causes exacerbated hypertension during pregnancy.…”