The Ligand-Dependent Interaction of Mineralocorticoid Receptor with Coactivator and Corepressor Peptides Suggests Multiple Activation Mechanisms

Abstract

We investigated the coregulator (coactivator and corepressor) interactions with the mineralocorticoid receptor (MR) that lead to activation and inhibition of the receptor in the presence of agonist and/or antagonist. Our results indicate that MR ligand binding domain (LBD) interacts strongly with only a few specific coactivator peptides in the presence of the agonist aldosterone and that these interactions are blocked by the antagonist eplerenone. We also discovered that cortisol, the preferred physiological ligand for the glucocorticoid receptor in humans, is a partial MR agonist/antagonist, providing a possible molecular explanation of the tissue-selective effects of glucocorticoids on MR. However, when we examined the coactivator and corepressor peptide interactions in the presence of cortisol, we found that MR bound with cortisol or aldosterone interacted with the same set of peptides. Thus, the partial agonism shown by cortisol is unlikely to be the result of differential interaction with known coactivators and corepressors. On the other hand, we have identified coactivator binding groove mutations that are critical for cortisol activation but not for aldosterone activation, suggesting that the two steroids induce different MR LBD conformations. In addition, we also show that cortisol becomes full agonist when S810L mutation is introduced in the LBD of MR. Interestingly, MR antagonists, such as eplerenone and progesterone, become partial agonist/antagonist of S810L but are still able to recruit LXXLL peptides to the mutant receptor. Together, these findings suggest a model to explain the MR activation by various ligands.

Coactivation of the N-terminal Transactivation of Mineralocorticoid Receptor by Ubc9

“…These results suggest that Ubc9 contributes to MR-dependent transcriptional activation at least partly by binding SRC-1 and recruiting it to cellular transcriptional machinery. Because recent reports (56) showed that relatively few coactivators, including SRC-1, strongly interact with MR in the presence of aldosterone, these findings are consistent with our data that Ubc9 and SRC-1 cooperatively function as coactivators of MR.…”

Mechanisms of Mineralocorticoid Action

“…20 Specific mutations in the MR-LBD can also dissociate the effects of aldosterone and cortisol on coactivator interactions. 25 These observations together with studies of other steroid receptors indicate an unexpected degree of plasticity in the receptor allowing the conformation to be in part dictated by the ligand.…”

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Evolution of the mineralocorticoid receptor: sequence, structure and function

“…Figure 5 also shows the α-helices on the MR as determined by X-ray crystallography (Bledsoe et al 2005, Fagart et al 2005, Edman et al 2015 and amino acids that have been found to be important in either steroid binding or transcriptional activation of the MR or CR (Fagart et al 1998, Geller et al 2000, Bledsoe et al 2005, Hultman et al 2005, Bridgham et al 2006, Shibata et al 2013, Edman et al 2015, Jimenez-Canino et al 2016, Mani et al 2016 or the GR (Bledsoe et al 2002, He et al 2014, Edman et al 2015, Mani et al 2016. A striking feature, discussed in more detail below, is the strong conservation of amino acids among the CR, MR, GR, PR and AR, including lamprey PR and CR.…”

“…9). Differences in the conformation of AF2 may be important in selective binding of coactivators to MR and GR (Hultman et al 2005, Hu & Funder 2006, Baker et al 2007, Yang & Young 2009, Fuller et al 2012, Baker et al 2013). …”