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Mechanistic basis for LQT1 caused by S3 mutations in the KCNQ1 subunit of IKs.

ABSTRACT: Long QT interval syndrome (LQTS) type 1 (LQT1) has been reported to arise from mutations in the S3 domain of KCNQ1, but none of the seven S3 mutations in the literature have been characterized with respect to trafficking or biophysical deficiencies. Surface channel expression was studied using a proteinase K assay for KCNQ1 D202H/N, I204F/M, V205M, S209F, and V215M coexpressed with KCNE1 in mammalian cells. In each case, the majority of synthesized channel was found at the surface, but mutant I(Ks) current density at +100 mV was reduced significantly for S209F, which showed approximately 75% reduction over wild type (WT). All mutants except S209F showed positively shifted V(1/2)'s of activation and slowed channel activation compared with WT (V(1/2) = +17.7 +/- 2.4 mV and tau(activation) of 729 ms at +20 mV; n = 18). Deactivation was also accelerated in all mutants versus WT (126 +/- 8 ms at -50 mV; n = 27), and these changes led to marked loss of repolarizing currents during action potential clamps at 2 and 4 Hz, except again S209F. KCNQ1 models localize these naturally occurring S3 mutants to the surface of the helices facing the other voltage sensor transmembrane domains and highlight inter-residue interactions involved in activation gating. V207M, currently classified as a polymorphism and facing lipid in the model, was indistinguishable from WT I(Ks). We conclude that S3 mutants of KCNQ1 cause LQTS predominantly through biophysical effects on the gating of I(Ks), but some mutants also show protein stability/trafficking defects, which explains why the kinetic gain-of-function mutation S209F causes LQT1.

SUBMITTER: Eldstrom J

PROVIDER: S-EPMC2860592 | biostudies-literature | 2010 May

REPOSITORIES: biostudies-literature

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Mechanistic basis for LQT1 caused by S3 mutations in the KCNQ1 subunit of IKs.

Eldstrom Jodene J Xu Hongjian H Werry Daniel D Kang Congbao C Loewen Matthew E ME Degenhardt Amanda A Sanatani Shubhayan S Tibbits Glen F GF Sanders Charles C Fedida David D

The Journal of general physiology 20100501 5

Long QT interval syndrome (LQTS) type 1 (LQT1) has been reported to arise from mutations in the S3 domain of KCNQ1, but none of the seven S3 mutations in the literature have been characterized with respect to trafficking or biophysical deficiencies. Surface channel expression was studied using a proteinase K assay for KCNQ1 D202H/N, I204F/M, V205M, S209F, and V215M coexpressed with KCNE1 in mammalian cells. In each case, the majority of synthesized channel was found at the surface, but mutant I( ...[more]

PMID: 20421371

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Project description:AimsLong QT syndrome 1 (LQT1) mutations in KCNQ1 that decrease cardiac IKs (slowly activating delayed rectifier K(+) current) underlie ventricular arrhythmias and sudden death. LQT1 mutations may suppress IKs by preventing KCNQ1 assembly, disrupting surface trafficking, or inhibiting gating. We investigated mechanisms underlying how three LQT1 mutations in KCNQ1 C-terminus assembly domain (R555H/G589D/L619M) decrease IKs in heterologous cells and cardiomyocytes.Methods and resultsIn Chinese hamster ovary (CHO) cells, mutant KCNQ1 + KCNE1 channels either produced no currents (G589D/L619M) or displayed markedly reduced IKs with a right-shifted voltage-dependence of activation (R555H). When co-expressed with wild-type (wt) KCNQ1, the mutant KCNQ1s displayed varying intrinsic dominant-negative capacities that were affected by auxiliary KCNE1. All three mutant KCNQ1s assembled with wt KCNQ1 as determined by fluorescence resonance energy transfer (FRET). We developed an optical quantum dot labelling assay to measure channel surface density. G589D/R555H displayed substantial reductions in surface density, which were either partially (G589D) or fully (R555H) rescued by wt KCNQ1. Unexpectedly, L619M showed no trafficking defect. In adult rat cardiomyocytes, adenovirus-expressed homotetrameric G589D/L619M + KCNE1 channels yielded no currents, whereas R555H + KCNE1 produced diminished IKs with a right-shifted voltage-dependence of activation, mimicking observations in CHO cells. In contrast to heterologous cells, homotetrameric R555H channels showed no trafficking defect in cardiomyocytes.ConclusionDistinct LQT1 mutations in KCNQ1 assembly domain decrease IKs using unique combinations of biophysical and trafficking mechanisms. Functional deficits in IKs observed in heterologous cells are mostly, but not completely, recapitulated in adult rat cardiomyocytes. A 'methodological chain' combining approaches in heterologous cells and cardiomyocytes provides mechanistic insights that may help advance personalized therapy for LQT1 mutations.

Dataset Information

Mechanistic basis for LQT1 caused by S3 mutations in the KCNQ1 subunit of IKs.

Publications

Mechanistic basis for LQT1 caused by S3 mutations in the KCNQ1 subunit of IKs.

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