Type 1 pseudohypoaldosteronism (PHA1), a primary form of mineralocorticoid resistance, is due to inactivating mutations of the NR3C2 gene, coding for the mineralocorticoid receptor (MR).

The objective of the study was to assess whether different NR3C2 mutations have distinct effects on the pattern of MR-dependent transcriptional regulation of aldosterone-regulated genes.

Four MR mutations affecting residues in the ligand binding domain, identified in families with PHA1, were tested. MR proteins generated by site-directed mutagenesis were analyzed for their binding to aldosterone and were transiently transfected into renal cells to explore the functional effects on the transcriptional activity of the receptors by cis-trans-cotransactivation assays and by measuring the induction of endogenous gene transcription.

Binding assays showed very low or absent aldosterone binding for mutants MR_877Pro, MR_848Pro, and MR_947stop and decreased affinity for aldosterone of MR_843Pro. Compared with wild-type MR, the mutations p.Leu843Pro and p.Leu877Pro displayed half-maximal aldosterone-dependent transactivation of reporter genes driven by mouse mammary tumor virus or glucocorticoid response element-2 dependent promoters, whereas MR_848Pro and MR_947stop nearly or completely lost transcriptional activity. Although MR_848Pro and MR_947stop were also incapable of inducing aldosterone-dependent gene expression of endogenous sgk1, GILZ, NDRG2, and SCNN1A, MR_843Pro retained complete transcriptional activity on sgk1 and GILZ gene expression, and MR_877Pro negatively affected the expression of sgk1, NDRG2, and SCNN1A.

Our data demonstrate that MR mutations differentially affect individual gene expression in a promoter-dependent manner. Investigation of differential gene expression profiles in PHA1 may allow a better understanding of the molecular substrate of phenotypic variability and to elucidate pathogenic mechanisms underlying the disease.