Electrophysiological Characteristics of the LQT2 Syndrome Mutation KCNH2-G572S and Regulation by Accessory Protein KCNE2

Abstract

Mutations in <i>hERG</i> cause long QT syndrome type 2 which is characterized by a prolonged QT interval on electrocardiogram and predisposition to life-threatening ventricular tachyarrhythmia, syncope, and sudden death. <i>hERG-G572S</i> induces trafficking defects of <i>hERG</i> channel protein from Golgi to the plasma membrane and results in a dominant negative suppression of <i>hERG</i> current density. As an accessory β subunit, <i>KCNE2</i> promotes <i>hERG</i> migration from Golgi to cellular membrane. In this study, we investigated the rescue effect of <i>KCNE2</i> in a <i>G572S</i> mutation of <i>hERG</i>. Transfection was performed into HEK293 cells. Patch clamp technique, western blotting analyses and confocal microscopic examination were used. Results showed that <i>KCNE2</i> had a significantly enhanced effect on <i>G572S</i> mutation current. The increase of current was largest at <i>KCNH2</i>:<i>KCNE2</i> of 1:3. Confocal images showed co-expressing <i>G572S</i> and <i>KCNE2</i> could cause a substantial up-regulated membrane protein (155 kDa) expression. Expression of membrane protein accumulated markedly with increasing ratio of <i>KCNH2</i>:<i>KCNE2</i>. <i>G572S</i> defective mutant could be restored by both <i>KCNE2</i> and lower temperature (27°C), which suggested that the lower temperature could be the favorable circumstances for the rescue function of <i>KCNE2</i>. In this study, we successfully set up "the action potential" on the HEK 293 cells by genetically engineered to express Kir2.1, Nav1.5, and Kv11.1, wherein on reaching over an excitation threshold by current injection. The results suggested that <i>KCNE2</i> could shorten action potential duration which was prolonged by <i>G572S</i>. These findings described electrophysiological characteristics of the LQT2 syndrome mutation <i>KCNH2-G572S</i> and regulation by accessory protein <i>KCNE2</i>, and provided a clue about LQT2 and relative rescue mechanism.