The mineralocorticoid receptor (MR) is a member of the steroid hormone receptor family. It acts as an inducible transcription factor and plays an important role in epithelial tissue to regulate water- and salt homeostasis. Additionally in the renocardiovascular system activated MR induces pathophysiological changes like endothelial dysfunction, vascular remodeling and heart failure. Besides controlling gene expression, the activated MR is able to interfere with signaling pathways in the cytosol. As a possible mechanism for mediating pathophysiological effects we focused on the interaction of acitviated MR with the cAMP/CREB signaling pathway. Previously, we reported on the crosstalk of MR and the phosphatase Calcineurin PP2B with the cAMP/CREB signaling pathway. MR activation by aldosterone inhibits forskolin-stimulated cAMP/CREB-signaling in connection with an increase of calcineurin activity and CREB dephosphorylation (1). Here we focused on the analysis of PP2B as a potent phosphatase that dephosphorylates CREB and thereby inhibiting cAMP/CREB-signaling in HEK cells, transfected with MR. We performed knockdown of the catalytic subunits of calcineurin, PP2BA-a and PP2BA-ß, using siRNA. CRE-SEAP reporter gene assays revealed that a knockdown of PP2BA-ß, but not of PP2BA-a, reduced inhibition of cAMP/CREB-signaling by MR. On the basis of co-immunoprecipitation analysis we demonstrated that MR interacts with PP2BA-ß. Furthermore we focus on the changes of subcellular localization of PP2BA elicited by activated MR using immunofluorescence analysis. We observed a shift of PP2BA localisation by activated MR from cytosol into the nucleus. Overall these results indicate PP2BA-ß as the relevant PP2B isoform that interacts with MR and consequently inhibits forskolin-stimulated cAMP/CREB-signaling.¹Grossmann C, Wuttke M, Ruhs S, Seiferth A, Mildenberger S., Rabe S, Schwerdt, G, Gekle M. FASEB J. 2010 Jun; 24(6):2010–9).