Intersubunit interactions between mutant DEG/ENaCs induce synthetic neurotoxicity.
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.
Zhang
W
W
Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, NJ 08854, USA.
Bianchi
L
L
Lee
W-H
WH
Wang
Y
Y
Israel
S
S
Driscoll
M
M
D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D037282:Calreticulin / Q000378:metabolism; D017124:Conserved Sequence; D053503:Epithelial Sodium Channels / Q000737:chemistry / Q000378:metabolism*; D005799:Genes, Dominant; D017238:Genes, Helminth; D015640:Ion Channel Gating; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism*; D009336:Necrosis; D009410:Nerve Degeneration / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism*; D012677:Sensation; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000737:chemistry / Q000378:metabolism*; D014110:Touch
D029742:Caenorhabditis elegans Proteins; D037282:Calreticulin; C094927:Deg-1 protein, C elegans; D053503:Epithelial Sodium Channels; C115871:Mec-4 protein, C elegans; D008565:Membrane Proteins; D050505:Mutant Proteins; D021122:Protein Subunits; D015222:Sodium Channels; C085942:MEC-10 protein, C elegans; D012964:Sodium; D002118:Calcium