Characterization of a novel mutant KCNQ1 channel subunit lacking a large part of the C-terminal domain.
A mutation of KCNQ1 gene encoding the alpha subunit of the channel mediating the slow delayed rectifier K(+) current in cardiomyocytes may cause severe arrhythmic disorders. We identified KCNQ1(Y461X), a novel mutant gene encoding KCNQ1 subunit whose C-terminal domain is truncated at tyrosine 461 from a man with a mild QT interval prolongation. We made whole-cell voltage-clamp recordings from HEK-293T cells transfected with either of wild-type KCNQ1 [KCNQ1(WT)], KCNQ1(Y461X), or their mixture plus KCNE1 auxiliary subunit gene. The KCNQ1(Y461X)-transfected cells showed no delayed rectifying current. The cells transfected with both KCNQ1(WT) and KCNQ1(Y461X) showed the delayed rectifying current that is thought to be mediated largely by homomeric channel consisting of KCNQ1(WT) subunit because its voltage-dependence of activation, activation rate, and deactivation rate were similar to the current in the KCNQ1(WT)-transfected cells. The immunoblots of HEK-293T cell-derived lysates showed that KCNQ1(Y461X) subunit cannot form channel tetramers by itself or with KCNQ1(WT) subunit. Moreover, immunocytochemical analysis in HEK-293T cells showed that the surface expression level of KCNQ1(Y461X) subunit was very low with or without KCNQ1(WT) subunit. These findings suggest that the massive loss of the C-terminal domain of KCNQ1 subunit impairs the assembly, trafficking, and function of the mutant subunit-containing channels, whereas the mutant subunit does not interfere with the functional expression of the homomeric wild-type channel. Therefore, the homozygous but not heterozygous inheritance of KCNQ1(Y461X) might cause major arrhythmic disorders. This study provides a new insight into the structure-function relation of KCNQ1 channel and treatments of cardiac channelopathies.
Laboratory for Neural Information Technology, Graduate School of Sciences and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.
Katsuya
K
Kimoto
Koshi
K
Kinoshita
Tomoki
T
Yokoyama
Yukiko
Y
Hata
Takuto
T
Komatsu
Eikichi
E
Tsushima
Kohki
K
Nishide
Yoshiaki
Y
Yamaguchi
Koichi
K
Mizumaki
Toshihide
T
Tabata
Hiroshi
H
Inoue
Naoki
N
Nishida
Kenkichi
K
Fukurotani
D000328:Adult; D019943:Amino Acid Substitution; D057809:HEK293 Cells; D006801:Humans; D051657:KCNQ1 Potassium Channel / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D008133:Long QT Syndrome / Q000235:genetics; D008297:Male; D021122:Protein Subunits / Q000235:genetics
D051657:KCNQ1 Potassium Channel; D021122:Protein Subunits
(FLAG-)WT(+E1) cell; (FLAG-)YX(+E1) cell; (FLAG-)YX/WT(+E1) cell; Arrhythmia; IsK; K(V)7.1; K(V)LQT1; KCNQ1(WT); KCNQ1(Y461X); LQT1; cell transfected with (FLAG-fused) KCNQ1(WT) (and KCNE1); cell transfected with (FLAG-fused) KCNQ1(WT) and KCNQ1(461X) (plus KCNE1); cell transfected with (FLAG-fused) KCNQ1(Y461X) and (and KCNE1); minK; mutant KCNQ1 producing a subunit truncated at tyrosine 461; wild-type KCNQ1