Protein Kinase A-Dependent Biophysical Phenotype for V227F-KCNJ2 Mutation in Catecholaminergic Polymorphic Ventricular Tachycardia

Abstract

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. Methods and 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.

Phenotypic Manifestations of Mutations in Genes Encoding Subunits of Cardiac Potassium Channels

“…46,55 A specific KCNJ2 mutation, V227F, was identified in a patient with a typical catecholaminergic polymorphic VT phenotype. 56 Heterologous expression with the COS cell line showed that heterozygous wild-type/V227F channels were identical to wild-type channels in function, but stimulation by cAMP-dependent protein kinase A significantly downregulated heterozygous mutant Kir2.1 and not wild-type Kir2.1 currents. 56 This particular type of loss of function explained why the proband displayed the catecholaminergic polymorphic VT phenotype, in which typical bidirectional or polymorphic VT is provoked by exercise.…”

“…56 Heterologous expression with the COS cell line showed that heterozygous wild-type/V227F channels were identical to wild-type channels in function, but stimulation by cAMP-dependent protein kinase A significantly downregulated heterozygous mutant Kir2.1 and not wild-type Kir2.1 currents. 56 This particular type of loss of function explained why the proband displayed the catecholaminergic polymorphic VT phenotype, in which typical bidirectional or polymorphic VT is provoked by exercise. Most recently, a mutation in KCNJ5 was reported to result in a loss of function of I K-ACh responsible for LQT13, 54 although the precise role of I K-ACh in the ventricle is still unknown.…”

“…137 Even after successful expression in membrane, alterations in channel function (steps 7 through 9 in Figure 3) induced by mutations are also pathological: those in potassium permeation (step 7), voltage gating (step 8), and modulation by various physiological stimulations, including protein kinase A and membrane phosphoinositide phosphatidylinositol 4,5-bisphosphate (PIP2). 51,56,138,139 Finally, endocytosis of channel proteins (step 10 in Figure 3) regulates its degradation apart from the plasma membrane. More recently, cholesterol has been shown to regulate Kv1.5 channel expression by modulating its trafficking through the Rab11-associated recycling endosome.…”

Epidemiology of Arrhythmias and Sudden Cardiac Death in Asia

“…89 Although the finding has been considered a benign ECG manifestation, Haissaguerre et al first reported that the ER pattern In addition, a third variant of CPVT was reported to result from a mutation in KCNJ2, which encodes Kir2.1, a subunit for inward-rectifier potassium channels. 102 In 50 Japanese CPVT probands, mutations in RYR2, CASQ, and KCNJ2 were identified in 28 (56%), 1 (2%), and 1 (2%), respectively. 103 CPVT is a rare disease with an estimated prevalence of 1/10,000, but has become recognized as a significant cause of SCD in children and young adults.…”

A Novel KCNJ2 Nonsense Mutation, S369X, Impedes Trafficking and Causes a Limited Form of Andersen-Tawil Syndrome

“…14 Recently, KCNJ2 mutations were reported not only in patients with ATS, but also in patients with catecholaminergic polymorphic ventricular tachycardia. 20 In the present study, we identified a novel nonsense KCNJ2 mutation, S369X, in a 13-year-old boy who had a prominent QU prolongation and mild muscle weakness but lacked dysmorphic features and examined its functional characterization by using electrophysiological and subcellular distribution analyses.…”