Abstract 10189: Dominant-Negative Control of cAMP-Dependent IKs Upregulation in Human Long-QT Syndrome Type 1
Introduction: The mutation A341V in the S6 transmembrane segment of KCNQ1, the α-subunit of the slowly-activating delayed-rectifier K+ (IKs) channel, predisposes to an unusually severe long-QT1 syndrome with sympathetic-triggered ventricular tachyarrhythmias and sudden cardiac death. Several genetic risk-modifiers have been identified in A341V patients, but the molecular mechanisms underlying the pronounced repolarization phenotype, particularly during β-adrenergic receptor stimulation, remain unclear. We aimed to elucidate these mechanisms and provide new insights into control of cAMP-dependent modulation of IKs.
Methods: We characterized the effects of the LQT1 mutations A341V, G589D, and the substitutions S27A, S27D on the IKs macromolecular channel complex in transfected Chinese-hamster ovary (CHO) cells.
Results: A341V caused a dominant-negative suppression of cAMP-dependent Yotiao-mediated IKs upregulation on top of a dominant-negative reduction in basal current (Figure). The phosphomimetic substitution KCNQ1-S27D rescued this loss of upregulation only when Yotiao was present. Western blot analysis showed reduced phosphorylation of KCNQ1 at S27, even for heterozygous A341V, suggesting that impaired phosphorylation of some (mutant) KCNQ1 subunits can abolish IKs upregulation. Heterozygous KCNQ1 WT:G589D (an LQT1 mutant with impaired Yotiao binding) and heterozygous KCNQ1 WT:S27A (a phosphorylation-inert substitution) also showed dominant-negative suppression of cAMP-dependent upregulation (Figure).
Conclusions: Our results indicate the involvement of the KCNQ1-S6 region at or around A341 in cAMP-dependent stimulation of IKs, a process which is under strong dominant-negative control, suggesting that tetrameric KCNQ1-S27 phosphorylation is required. Specific long-QT1 mutations, including A341V, disable this regulation, thereby creating a ‘homozygous phenotype’ in heterozygous conditions.
- © 2011 by American Heart Association, Inc.