Vol. 62, Issue 6, 1306-1313, December 2002

11-Hydroxyprogesterone Acts as a Mineralocorticoid Agonist in Stimulating Na⁺ Absorption in Mammalian Principal Cortical Collecting Duct Cells

Marie-Edith Rafestin-Oblin, Jerome Fagart, Anny Souque, Cendrine Seguin, Marcelle Bens, and Alain Vandewalle

Institut National de la Santé et de la Recherche Médicale U478, Institut Fédératif de Recherche 02, Faculté de Médecine Xavier Bichat, Paris, France

The binding of mineralocorticoid hormones to the mineralocorticoid receptor is the first step in a cascade of events leading to the stimulation of Na⁺ reabsorption by renal cortical collecting duct (CCD) principal cells. The agonist properties of mineralocorticoid hormones are linked to contacts between their 21-hydroxyl group and Asn770, a residue of the ligand-binding domain of the human mineralocorticoid receptor (hMR). Here, we investigate whether the presence of a hydroxyl group at position 11, 17, or 20 could also alter the activity of progesterone (P), a mineralocorticoid antagonist without the 21-hydroxyl group. Both 17-hydroxyprogesterone (17OHP) and 20-hydroxyprogesterone (20OHP) antagonized the aldosterone-induced trans-activation activity (IC₅₀: 17OHP, 10⁷ M; 20OHP, 10⁸ M) of the hMR transiently expressed in COS-7 cells lacking steroid receptors. In cultured mouse mpkCCD_cl4 principal cells, 17OHP and 20OHP also prevented the aldosterone-stimulated amiloride-sensitive component of the short-circuit current (Ams I_sc), reflecting Na⁺ absorption mediated by the epithelial Na⁺ channel (ENaC). In contrast, 11-hydroxyprogesterone (11OHP) activated the transiently expressed hMR in COS-7 cells in a dose-dependent manner (ED₅₀: 10⁸ M) and, like aldosterone, stimulated Ams I_sc in mpkCCD_cl4 cells. Docking 11OHP within the hMR-ligand-binding domain homology model revealed that the agonist activity of 11OHP is caused by contacts between its 11-hydroxyl group and Asn770. Furthermore, 11OHP was unable to activate the mutant hMR/N770A, in which Ala is substituted for Asn at position 770. These findings demonstrate that in the absence of the 21-hydroxyl group, the 11-hydroxyl group can produce the contact with the hMR-Asn770 required for the hMR activation leading to stimulated Na⁺ absorption.