title: Down-regulation of TRPM6-mediated magnesium influx by cyclosporin A.
abstract: Transient receptor potential melastatin 6 (TRPM6) is distributed along the apical membrane of the renal tubular cells and is involved in the reabsorption of magnesium. In this study, we show that TRPM6 expression is suppressed by cyclosporin A (CsA) via a down-regulation of c-Fos expression. TRPM6 was expressed in NRK-52E, but not in Madin-Darby canine kidney cells. In contrast, its homolog, TRPM7, was equally expressed in both cells. In NRK-52E cells, CsA dose-dependently decreased TRPM6 expression without affecting TRPM7 expression. Magnesium load measurements revealed the rise in the intracellular free magnesium concentration ([Mg2+]i) to be inhibited by CsA. The transfection of TRPM6 siRNA decreased TRPM6 expression without affecting TRPM7 expression and inhibited the elevation of [Mg2+]i. CsA did not affect the intracellular distribution of nuclear factor of activated T cells (NFATc). Furthermore, TRPM6 expression was not changed by a NFATc inhibitor. Next, we examined the effect of CsA on the transcription factors c-Fos and c-Jun. CsA decreased c-Fos expression without affecting c-Jun expression. The transfection of c-Fos siRNA suppressed TRPM6 expression without affecting TRPM7 expression. We suggest that CsA decreases TRPM6 expression mediated by inhibition of c-Fos transcription, resulting in a decrease of renal Mg2+ reabsorption.
authors.affiliation: Department of Pharmaco-Biochemistry, School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, 422-8526, Japan. ikari@u-shizuoka-ken.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Ikari
authors.forename: Chiaki
authors.initials: C
authors.lastname: Okude
authors.forename: Hayato
authors.initials: H
authors.lastname: Sawada
authors.forename: Tadanobu
authors.initials: T
authors.lastname: Takahashi
authors.forename: Junko
authors.initials: J
authors.lastname: Sugatani
authors.forename: Masao
authors.initials: M
authors.lastname: Miwa
mesh_terms: D000818:Animals; D002460:Cell Line; D016572:Cyclosporine / Q000008:administration & dosage / Q000494:pharmacology*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000494:pharmacology*; D007668:Kidney / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D050778:NFATC Transcription Factors / Q000187:drug effects / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D050053:TRPM Cation Channels / Q000187:drug effects* / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
chemical_list: D007166:Immunosuppressive Agents; D050778:NFATC Transcription Factors; D016760:Proto-Oncogene Proteins c-fos; D034741:RNA, Small Interfering; D050053:TRPM Cation Channels; C507531:TRPM6 protein, rat; D016572:Cyclosporine; C486584:Trpm7 protein, rat; D008274:Magnesium