Mineralocorticoid receptor splice variants in different human tissues.

The mineralocorticoid receptor (MR), a member of the steroid receptor family, acts as a transcription factor and mediates both aldosterone and cortisol effects. Aldosterone specificity in some tissues results from the inactivation of competing cortisol into cortisone by 11beta-hydroxysteroid dehydrogenase. In other tissues MR and the glucocorticoid receptor show overlapping physiological effects or may act together by forming a heterodimer. An additional MR splice variant (MR+4) has been found in different mRNA samples from rat tissues and human white blood cells, thereby implying additional modes of MR-regulated effects. We therefore looked for the presence of these two MR-mRNA isoforms in human classical aldosterone target tissues and various other tissues. MR-mRNA was found in all samples investigated, thereby showing the expression of MR to be more abundant than has been observed thus far. In addition, the MR+4-mRNA variant was also found in all the tissues examined.