Mineralocorticoid receptor transcriptional activity is affected by planar progesterone derivatives

MOLINARI, AM, MAZAIRA GI, PIWIEN PILIPUK, G, ERLEJMAN, AG, GALIGNIANA, MD

Edinburgh

Congreso; 14th Intl. Congress on Steroid Receptors, Steroid Hormones & Cancer.; 2010

EMBO

Introduction: We have previously postulated that the mineralocorticoid response is favored by the planar conformation of the steroid. Accordingly, the synthetic 21-deoxypreganesteroid 11,19-oxidoprogesterone (11-OP) shows equivalent Na+-retaining activity to natural mineralocorticoids, and also potentiates aldosterone effect. Dihydroderivatives of progesterone show biphasic action, i.e., increased antinatriuresis followed by a complete reversion of the effect at higher doses. Inasmuch as plasma concentration of the flat conformer 5á-dihydroprogesterone (5á-diH-P) increases over 20-fold at the end of pregnancy, we asked whether this natural steroid possesses analogous action to 11-OP on the MR-dependent response. Results: Relative binding affinities for MR were equivalent for both progesterone derivatives (30±5 nM for 5á-diH-P and 40±5 nM for 11-OP, versus 2±1 nM for aldosterone). GFP-MR was similarly translocated to the nucleus by each steroid alone or by combined mixtures of them. While cells transfected with the MMTV-Luc reporter gene showed a 20-fold maximum induction of luciferase activity with 1 nM aldosterone, a suboptimal concentration of 10 pM aldosterone mixtured with an inactive concentration of 1 pM 11-OP resulted in a strong potentiation of luciferase expression from 5- to 70-fold induction. Surprisingly, a fully inactive concentration of 10 pM 5á-diH-P inhibited luciferase induction for the entire range of aldosterone concentrations (from pM to µM). To explore whether these effects are related to coactivator recruitment, cells were cotransfected with CBP/p300. As expected, 1 pM 11-OP increased 300% the maximum effect of 1 nM aldosterone and its potentiating action on 10 pM aldosterone increased to 170-fold induction of luciferase activity. However, cotreatments with 10 pM 5á-diH-P and 1 nM aldosterone totally abolished the response of CBP/p300-transfected cells. Conclusions: We postulate that 5á-diH-P may regulate the MR-dependent effect in an allosteric-like manner via recruitment of cofactors, and also suggest that this reduced progesterone metabolite might play a role during the mineralocorticoid resistance syndrome.