Protein kinase A-dependent biophysical phenotype for V227F-KCNJ2 mutation in catecholaminergic polymorphic ventricular tachycardia.
BACKGROUND
KCNJ2 encodes Kir2.1, a pore-forming subunit of the cardiac inward rectifier current, I(K1). KCNJ2 mutations are associated with Andersen-Tawil syndrome and catecholaminergic polymorphic ventricular tachycardia. The aim of this study was to characterize the biophysical and cellular phenotype of a KCNJ2 missense mutation, V227F, found in a patient with catecholaminergic polymorphic ventricular tachycardia.


RESULTS
Kir2.1-wild-type (WT) and V227F channels were expressed individually and together in Cos-1 cells to measure I(K1) by voltage clamp. Unlike typical Andersen-Tawil syndrome-associated KCNJ2 mutations, which show dominant negative loss of function, Kir2.1WT+V227F coexpression yielded I(K1) indistinguishable from Kir2.1-WT under basal conditions. To simulate catecholamine activity, a protein kinase A (PKA)-stimulating cocktail composed of forskolin and 3-isobutyl-1-methylxanthine was used to increase PKA activity. This PKA-simulated catecholaminergic stimulation caused marked reduction of outward I(K1) compared with Kir2.1-WT. PKA-induced reduction in I(K1) was eliminated by mutating the phosphorylation site at serine 425 (S425N).


CONCLUSIONS
Heteromeric Kir2.1-V227F and WT channels showed an unusual latent loss of function biophysical phenotype that depended on PKA-dependent Kir2.1 phosphorylation. This biophysical phenotype, distinct from typical Andersen-Tawil syndrome mutations, suggests a specific mechanism for PKA-dependent I(K1) dysfunction for this KCNJ2 mutation, which correlates with adrenergic conditions underlying the clinical arrhythmia.
Department of Medicine, University of Wisconsin, Madison, Wisconsin 53792, USA.
Amanda L
AL
Vega
David J
DJ
Tester
Michael J
MJ
Ackerman
Jonathan C
JC
Makielski
D000328:Adult; D000704:Analysis of Variance; D050030:Andersen Syndrome / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D019556:COS Cells / Q000378:metabolism; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004562:Electrocardiography; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D020125:Mutation, Missense; D010641:Phenotype; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics*; D017180:Tachycardia, Ventricular / Q000235:genetics* / Q000378:metabolism; D014162:Transfection
C489457:KCNJ2 protein, human; D024661:Potassium Channels, Inwardly Rectifying; D017868:Cyclic AMP-Dependent Protein Kinases