title: Hypomagnesemia with secondary hypocalcemia due to a missense mutation in the putative pore-forming region of TRPM6.
abstract: Hypomagnesemia with secondary hypocalcemia is an autosomal recessive disorder caused by mutations in the TRPM6 gene. Current experimental evidence suggests that TRPM6 may function in a specific association with TRPM7 by means of heterooligomeric channel complex formation. Here, we report the identification and functional characterization of a new hypomagnesemia with secondary hypocalcemia missense mutation in TRPM6. The affected subject presented with profound hypomagnesemia and hypocalcemia caused by compound heterozygous mutation in the TRPM6 gene: 1208(-1)G > A affecting the acceptor splice site preceding exon 11, and 3050C > G resulting in the amino acid change (P1017R) in the putative pore-forming region of TRPM6. To assess the functional consequences of the P1017R mutation, TRPM6(P1017R) and wild-type TRPM6 were co-expressed with TRPM7 in Xenopus oocytes and HEK 293 cells, and currents were assessed by two-electrode voltage clamp and whole cell patch clamp measurements, respectively. Co-expression of wild-type TRPM6 and TRPM7 resulted in a significant increase in the amplitude of TRPM7-like currents. In contrast, TRPM6(P1017R) suppressed TRPM7 channel activity. In line with these observations, TRPM7, containing the corresponding mutation P1040R, displayed a dominant-negative effect upon co-expression with wild-type TRPM7. Confocal microscopy and fluorescence resonance energy transfer recordings demonstrated that the P1017R mutation neither affects assembly of TRPM6 with TRPM7, nor co-trafficking of heteromultimeric channel complexes to the cell surface. We conclude that a functional defect in the putative pore of TRPM6/7 channel complexes is sufficient to impair body magnesium homeostasis.
authors.affiliation: Institute for Pharmacology and Toxicology, Philipps-University Marburg, Karl-von-Frisch-Strasse 1, 35033 Marburg, Germany.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Chubanov
authors.forename: Karl P
authors.initials: KP
authors.lastname: Schlingmann
authors.forename: Janine
authors.initials: J
authors.lastname: Wäring
authors.forename: Jolanta
authors.initials: J
authors.lastname: Heinzinger
authors.forename: Silke
authors.initials: S
authors.lastname: Kaske
authors.forename: Siegfried
authors.initials: S
authors.lastname: Waldegger
authors.forename: Michael
authors.initials: M
authors.lastname: Mederos y Schnitzler
authors.forename: Thomas
authors.initials: T
authors.lastname: Gudermann
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D006801:Humans; D006996:Hypocalcemia / Q000209:etiology / Q000235:genetics*; D008274:Magnesium / Q000097:blood; D008275:Magnesium Deficiency / Q000209:etiology / Q000235:genetics*; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D017346:Protein Serine-Threonine Kinases; D050053:TRPM Cation Channels / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D014981:Xenopus
chemical_list: D050053:TRPM Cation Channels; C459082:TRPM6 protein, human; D017346:Protein Serine-Threonine Kinases; C486583:TRPM7 protein, human; D008274:Magnesium