C-terminal HERG (LQT2) mutations disrupt IKr channel regulation through 14-3-3epsilon.
Beta-adrenergic receptor-mediated cAMP or protein kinase A (PKA)-dependent modulation of cardiac potassium currents controls ventricular action potential duration (APD) at faster heart rates. HERG (KCNH2) gene mutations are associated with congenital long-QT syndrome (LQT2) and affect IKr activity, a key determinant in ventricular repolarization. Physical activity or emotional stress often triggers lethal arrhythmias in LQT2 patients. Beta-adrenergic stimulation of HERG channel activity is amplified and prolonged in vitro by the adaptor protein 14-3-3epsilon. In LQT2 families, we identified three novel heterozygous HERG mutations (G965X, R1014PfsX39, V1038AfsX21) in the C-terminus that led to protein truncation and loss of a PKA phosphorylation site required for binding of 14-3-3epsilon. When expressed in CHO cells, the mutants produced functional HERG channels with normal kinetic properties. We now provide evidence that HERG channel regulation by 14-3-3epsilon is of physiological significance in humans. Upon co-expression with 14-3-3epsilon, mutant channels still bound 14-3-3epsilon but did not respond with a hyperpolarizing shift in voltage dependence as seen in wild-type channels. Co-expression experiments of wild-type and mutant channels revealed dominant-negative behavior of all three HERG mutations. Simulations of the effects of sympathetic stimulation of HERG channel activity on the whole-cell action potential suggested a role in rate-dependent control of APD and an impaired ability of mutant cardiac myocytes to respond to a triggered event or an ectopic beat. In summary, the attenuated functional effects of 14-3-3epsilon on C-terminally truncated HERG channels demonstrate the physiological importance of coupling beta-adrenergic stimulation and HERG channel activity.
Choe
Chi-un
CU
Institute for Neural Signal Transduction, ZMNH, Department of Pediatrics, University Hospital Hamburg-Eppendorf, Hamburg, Germany.
Schulze-Bahr
Eric
E
Neu
Axel
A
Xu
Jun
J
Zhu
Zheng I
ZI
Sauter
Kathrin
K
Bähring
Robert
R
Priori
Silvia
S
Guicheney
Pascale
P
Mönnig
Gerold
G
Neapolitano
Carlo
C
Heidemann
Jan
J
Clancy
Colleen E
CE
Pongs
Olaf
O
Isbrandt
Dirk
D
D048948:14-3-3 Proteins / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics* / Q000378:metabolism*; D008297:Male; D008955:Models, Cardiovascular; D009154:Mutation; D032383:Myocytes, Cardiac / Q000378:metabolism; D010375:Pedigree; D015221:Potassium Channels / Q000378:metabolism*; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D048948:14-3-3 Proteins; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D015221:Potassium Channels; D021122:Protein Subunits; D011994:Recombinant Proteins; C482983:YWHAE protein, human