Intersubunit interactions between mutant DEG/ENaCs induce synthetic neurotoxicity

Cell Death Differ. 2008 Nov;15(11):1794-803. doi: 10.1038/cdd.2008.114. Epub 2008 Aug 1.

Abstract

Ion channel hyperactivation can result in neuronal loss in injury, stroke and neurodegenerative disease. Acidosis-associated hyperactivation of the Degenerin/epithelial amiloride-sensitive Na(+) channel (DEG/ENaC) acid-sensing ion channel 1a (ASIC1a), a proton-gated channel expressed in the mammalian brain, contributes significantly to neuronal loss in ischemia. Analogously, in invertebrates, genetic hyperactivation of the Caenorhabditis elegans mechanosensory (MEC) channel (MEC-4(d)) of the DEG/ENaC ion channel superfamily induces neuronal necrosis. Similarly substituted MEC-10(d) mutant subunits of the same MEC channel are only marginally neurotoxic, and we therefore exploited the weak necrosis phenotype of mec-10(d) lines to screen for novel extragenic mutations that enhance neuronal death. Here, we report on one mec-10(d) necrosis enhancer, which we show is MEC-4 variant MEC-4(A149V). MEC-4(A149V) executes normal MEC-4 function in touch sensation and does not induce necrosis on its own, but rather combines with MEC-10(d) to create a strongly neurotoxic channel. The MEC-4(A149V)+MEC-10(d) channel conducts elevated Na(+) and Ca(2+) currents (with a disproportionate increase in Ca(2+) current) in the Xenopus oocyte expression system, and exhibits altered binding of the channel inhibitor amiloride. Our data document the first example of synergistically toxic intersubunit interactions in the DEG/ENaC channel class and provide evidence that Ca(2+) current levels may be decisive factors in tipping the balance between neuronal survival and necrosis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Caenorhabditis elegans / genetics
  • Caenorhabditis elegans / metabolism*
  • Caenorhabditis elegans Proteins / chemistry
  • Caenorhabditis elegans Proteins / metabolism*
  • Calcium / metabolism
  • Calreticulin / metabolism
  • Conserved Sequence
  • Epithelial Sodium Channels / chemistry
  • Epithelial Sodium Channels / metabolism*
  • Genes, Dominant
  • Genes, Helminth
  • Ion Channel Gating
  • Membrane Proteins / chemistry
  • Membrane Proteins / metabolism
  • Molecular Sequence Data
  • Mutant Proteins / chemistry
  • Mutant Proteins / metabolism*
  • Necrosis
  • Nerve Degeneration / metabolism*
  • Protein Binding
  • Protein Structure, Tertiary
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism*
  • Sensation
  • Sodium / metabolism
  • Sodium Channels / chemistry
  • Sodium Channels / metabolism*
  • Touch

Substances

  • Caenorhabditis elegans Proteins
  • Calreticulin
  • Deg-1 protein, C elegans
  • Epithelial Sodium Channels
  • Mec-4 protein, C elegans
  • Membrane Proteins
  • Mutant Proteins
  • Protein Subunits
  • Sodium Channels
  • MEC-10 protein, C elegans
  • Sodium
  • Calcium