Hypomagnesemia with Secondary Hypocalcemia due to a Missense Mutation in the Putative Pore-forming Region of TRPM6

• Published in: The Journal of biological chemistry 2007-03, Vol.282 (10), p.7656-7667
• Main Authors: Chubanov, Vladimir, Schlingmann, Karl P., Wäring, Janine, Heinzinger, Jolanta, Kaske, Silke, Waldegger, Siegfried, Schnitzler, Michael Mederos y, Gudermann, Thomas
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Cells, Cultured; Humans; Hypocalcemia - etiology; Hypocalcemia - genetics; Magnesium - blood; Magnesium Deficiency - etiology; Magnesium Deficiency - genetics; Molecular Sequence Data; Mutation, Missense; Protein-Serine-Threonine Kinases; TRPM Cation Channels - chemistry; TRPM Cation Channels - genetics; TRPM Cation Channels - physiology; Xenopus
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M611117200

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, TRPM6P1017R 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, TRPM6P1017R 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.