The mineralocorticoid receptor and its coregulators.

The mineralocorticoid receptor (MR) is a member of the nuclear receptor superfamily and is essential for controlling sodium transport in epithelial tissues such as the kidney and colon. Moreover, it is also present in other non-epithelial tissues and is capable of activation by both mineralocorticoids and glucocorticoids. A challenge in understanding transcriptional regulation by the MR and other nuclear receptors is to determine how tissue- and ligand-specificity is achieved. Over the past decade, it has become clear that a heterogeneous group of non-receptor proteins termed as coregulators are required to either enhance or repress nuclear receptor-mediated transactivation of target genes. A subset of these coregulators may be expected to confer specificity to MR-mediated responses by virtue of their variable tissue expression and selectivity for different ligands. Specific coregulator-MR interactions may be a suitable target in the rational design of tissue-specific MR modulators as has been described for other steroid receptors. However, the number of coregulators identified to date for the MR is very limited compared with other nuclear receptors. Understanding the full complement of MR coregulators is essential for unraveling the complexity of MR signaling pathways and will facilitate the development of selective MR modulators.