title: Syntrophin mutation associated with long QT syndrome through activation of the nNOS-SCN5A macromolecular complex.
abstract: Mutations in 11 genes that encode ion channels or their associated proteins cause inherited long QT syndrome (LQTS) and account for approximately 75-80% of cases (LQT1-11). Direct sequencing of SNTA1, the gene encoding alpha1-syntrophin, was performed in a cohort of LQTS patients that were negative for mutations in the 11 known LQTS-susceptibility genes. A missense mutation (A390V-SNTA1) was found in a patient with recurrent syncope and markedly prolonged QT interval (QTc, 530 ms). SNTA1 links neuronal nitric oxide synthase (nNOS) to the nNOS inhibitor plasma membrane Ca-ATPase subtype 4b (PMCA4b); SNTA1 also is known to associate with the cardiac sodium channel SCN5A. By using a GST-fusion protein of the C terminus of SCN5A, we showed that WT-SNTA1 interacted with SCN5A, nNOS, and PMCA4b. In contrast, A390V-SNTA1 selectively disrupted association of PMCA4b with this complex and increased direct nitrosylation of SCN5A. A390V-SNTA1 expressed with SCN5A, nNOS, and PMCA4b in heterologous cells increased peak and late sodium current compared with WT-SNTA1, and the increase was partially inhibited by NOS blockers. Expression of A390V-SNTA1 in cardiac myocytes also increased late sodium current. We conclude that the A390V mutation disrupted binding with PMCA4b, released inhibition of nNOS, caused S-nitrosylation of SCN5A, and was associated with increased late sodium current, which is the characteristic biophysical dysfunction for sodium-channel-mediated LQTS (LQT3). These results establish an SNTA1-based nNOS complex attached to SCN5A as a key regulator of sodium current and suggest that SNTA1 be considered a rare LQTS-susceptibility gene.
authors.affiliation: Department of Medicine, University of Wisconsin, Madison, WI 53792, USA.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Ueda
authors.forename: Carmen
authors.initials: C
authors.lastname: Valdivia
authors.forename: Argelia
authors.initials: A
authors.lastname: Medeiros-Domingo
authors.forename: David J
authors.initials: DJ
authors.lastname: Tester
authors.forename: Matteo
authors.initials: M
authors.lastname: Vatta
authors.forename: Gianrico
authors.initials: G
authors.lastname: Farrugia
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ackerman
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Makielski
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics*; D002460:Cell Line; D004789:Enzyme Activation; D005260:Female; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D015640:Ion Channel Gating; D008133:Long QT Syndrome / Q000201:enzymology* / Q000235:genetics*; D046911:Macromolecular Substances / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000473:pathology; D062554:NAV1.5 Voltage-Gated Sodium Channel; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism*; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000378:metabolism; D015222:Sodium Channels / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009124:Muscle Proteins; D050505:Mutant Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; C568320:SCN5A protein, human; C568321:Scn5a protein, mouse; D015222:Sodium Channels; C091825:syntrophin alpha1; D052248:Nitric Oxide Synthase Type I; C507517:ATP2B4 protein, human; D053499:Plasma Membrane Calcium-Transporting ATPases