Hypomagnesemia with secondary hypocalcemia due to a missense mutation in the putative pore-forming region of TRPM6

J Biol Chem. 2007 Mar 9;282(10):7656-67. doi: 10.1074/jbc.M611117200. Epub 2006 Dec 29.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 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

Substances

  • TRPM Cation Channels
  • TRPM6 protein, human
  • Protein-Serine-Threonine Kinases
  • TRPM7 protein, human
  • Magnesium