title: The phosphatase calcineurin PP2BAβ mediates part of mineralocorticoid receptor transcriptional activity.
abstract: 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 PP2BAβ but not via PP2BAα. Altered PP2BAβ expression, elevated cytosolic Ca(2+), 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 PP2BAβ independent of MR activation but dependent on HSP90. Activated MR alters the subcellular distribution of PP2BAβ, 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 PP2BAβ, 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.
authors.affiliation: Julius-Bernstein-Institut für Physiologie, Universität Halle-Wittenberg, Magdeburger Strasse 6, 06112 Halle (Saale), Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Seiferth
authors.forename: Stefanie
authors.initials: S
authors.lastname: Ruhs
authors.forename: Sigrid
authors.initials: S
authors.lastname: Mildenberger
authors.forename: Michael
authors.initials: M
authors.lastname: Gekle
authors.forename: Claudia
authors.initials: C
authors.lastname: Grossmann
mesh_terms: D019703:Calcineurin / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors; D006801:Humans; D050778:NFATC Transcription Factors / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D018161:Receptors, Mineralocorticoid / Q000187:drug effects / Q000502:physiology*
chemical_list: C115163:CREB1 protein, human; D017362:Cyclic AMP Response Element-Binding Protein; D018841:HSP90 Heat-Shock Proteins; D050778:NFATC Transcription Factors; D034741:RNA, Small Interfering; D018161:Receptors, Mineralocorticoid; D019703:Calcineurin