title: Decrease in transient receptor potential melastatin 6 mRNA stability caused by rapamycin in renal tubular epithelial cells.
abstract: Rapamycin, an inhibitor of mammalian target of rapamycin (mTOR), is used in treatments for transplantation and cancer. Rapamycin causes hypomagnesemia, although precisely how has not been examined. Here, we investigated the effect of rapamycin on the expression of transient receptor potential melastatin 6 (TRPM6), a Mg2+ channel. Rapamycin and LY-294002, an inhibitor of phosphatidilinositol-3 kinase (PI3K) located upstream of mTOR, inhibited epidermal growth factor (EGF)-induced expression of the TRPM6 protein without affecting TRPM7 expression in rat renal NRK-52E epithelial cells. Both rapamycin and LY-294002 decreased EGF-induced Mg2+ influx. U0126, a MEK inhibitor, inhibited EGF-induced increases in c-Fos, p-ERK, and TRPM6 levels. In contrast, neither rapamycin nor LY-294002 inhibited EGF-induced increases in p-ERK and c-Fos levels. EGF increased p-Akt level, an effect inhibited by LY-294002 and 1L-6-hydroxymethyl-chiro-inositol2-[(R)-2-O-methyl-3-O-octadecylcarbonate] (Akt inhibitor). Akt inhibitor decreased TRPM6 level similar to rapamycin and LY-294002. These results suggest that a PI3K/Akt/mTOR pathway is involved in the regulation of TRPM6 expression. Rapamycin inhibited the EGF-induced increase in TRPM6 mRNA but did not inhibit human TRPM6 promoter activity. In the presence of actinomycin D, a transcriptional inhibitor, rapamycin accelerated the decrease in TRPM6 mRNA. Rapamycin decreased the expression and activity of a luciferase linked with the 3'-untranslated region of human TRPM6 mRNA. These results suggest that TRPM6 expression is up-regulated by a PI3K/Akt/mTOR pathway and rapamycin reduces TRPM6 mRNA stability, resulting in a decrease in the reabsorption of Mg2+.
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: Ayumi
authors.initials: A
authors.lastname: Sanada
authors.forename: Hayato
authors.initials: H
authors.lastname: Sawada
authors.forename: Chiaki
authors.initials: C
authors.lastname: Okude
authors.forename: Chie
authors.initials: C
authors.lastname: Tonegawa
authors.forename: Junko
authors.initials: J
authors.lastname: Sugatani
mesh_terms: D000818:Animals; D002070:Butadienes / Q000494:pharmacology; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D015151:Immunoblotting; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007294:Inositol / Q000031:analogs & derivatives / Q000494:pharmacology; D007684:Kidney Tubules / Q000166:cytology; D009025:Morpholines / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D020871:RNA Stability / Q000187:drug effects*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D050053:TRPM Cation Channels / Q000235:genetics*
chemical_list: D002070:Butadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D007166:Immunosuppressive Agents; D007294:Inositol; D009025:Morpholines; D009570:Nitriles; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D050053:TRPM Cation Channels; C477931:1L-6-hydroxymethyl-chiro-inositol 2(R)-2-O-methyl-3-O-octadecylcarbonate; C459082:TRPM6 protein, human; C507531:TRPM6 protein, rat; C113580:U 0126; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C486584:Trpm7 protein, rat