The phosphatase calcineurin PP2BAβ mediates part of mineralocorticoid receptor transcriptional activity

Recently it was shown that the mineralocorticoid receptor (MR) may exert part of its transcriptional activity by mediation of calcineurin (PP2B). Here we investigated the mechanism of interaction of MR with calcineurin and provide a new MR signaling pathway with potential physiological and pathophysiological relevance. MR -> calcineurin crosstalk was assessed in a heterologous expression system (human embryonic kidney cells), which provides the opportunity for detailed mechanistic investigation. SiRNA knockdown experiments show that activated MR, but not GR, reduces CREB-and enhances NFaT-mediated transcriptional activation via the catalytic calcineurin subunit PP2BA beta but not via PP2BA alpha. Altered PP2BA beta expression, elevated cytosolic Ca2+, activation of mitogen-activated kinase [p38, extracellular signal-regulated kinase (ERK) 1/2], or protein kinase C do not seem to be involved, whereas inhibition of the chaperone heat-shock protein 90 (HSP90) abrogated the effect of MR. Coimmunoprecipitation indicates the existence of protein complexes harboring MR and PP2BA beta independent of MR activation but dependent on HSP90. Activated MR alters the subcellular distribution of PP2BA beta, enhancing its nuclear fraction, and reduces mRNA expression of the endogenous inhibitor CAIN (calcineurin inhibitor) but not of RCAN1 (regulator of calcineurin). Overall, transcriptional relevant MR -> calcineurin crosstalk occurs via the catalytic subunit PP2BA beta, enables glucocorticoid response element-independent genomic signaling of MR, and is of potential pathophysiological relevance. Mechanistically, the crosstalk results from HSP90-mediated cytosolic protein complex formation, altered subcellular distribution, and altered endogenous inhibitor expression.-Seiferth, A., Ruhs, S., Mildenberger, S., Gekle, M., Grossmann, C. The phosphatase calcineurin PP2BA beta mediates part of mineralocorticoid receptor. FASEB J. 26, 2327-2337 (2012). www.fasebj.org