Long-QT mutation p.K557E-Kv7.1: dominant-negative suppression of IKs, but preserved cAMP-dependent up-regulation.

ABSTRACT

AIMS: Mutations in KCNQ1, encoding for Kv7.1, the α-subunit of the IKs channel, cause long-QT syndrome type 1, potentially predisposing patients to ventricular tachyarrhythmias and sudden cardiac death, in particular, during elevated sympathetic tone. Here, we aim at characterizing the p.Lys557Glu (K557E) Kv7.1 mutation, identified in a Dutch kindred, at baseline and during (mimicked) increased adrenergic tone. METHODS AND RESULTS: K557E carriers had moderate QTc prolongation that augmented significantly during exercise. IKs characteristics were determined after co-expressing Kv7.1-wild-type (WT) and/or K557E with minK and Yotiao in Chinese hamster ovary cells. K557E caused IKs loss of function with slowing of the activation kinetics, acceleration of deactivation kinetics, and a rightward shift of voltage-dependent activation. Together, these contributed to a dominant-negative reduction in IKs density. Confocal microscopy and western blot indicated that trafficking of K557E channels was not impaired. Stimulation of WT IKs by 3'-5'-cyclic adenosine monophosphate (cAMP) generated strong current up-regulation that was preserved for K557E in both hetero- and homozygosis. Accumulation of IKs at fast rates occurred both in WT and in K557E, but was blunted in the latter. In a computational model, K557E showed a loss of action potential shortening during ß-adrenergic stimulation, in accordance with the lack of QT shortening during exercise in patients. CONCLUSION: K557E causes IKs loss of function with reduced fast rate-dependent current accumulation. cAMP-dependent stimulation of mutant IKs is preserved, but incapable of fully compensating for the baseline current reduction, explaining the long QT intervals at baseline and the abnormal QT accommodation during exercise in affected patients.