Up-Regulation of Kir2.1 (KCNJ2) by the Serum & Glucocorticoid Inducible SGK3

Abstract

Background/Aims: The serum & glucocorticoid inducible kinase SGK3, an ubiquitously expressed serine/threonine kinase, regulates a variety of ion channels. It has previously been shown that SGK3 upregulates the outwardly rectifying K+ channel KV11.1, which is expressed in cardiomyocytes. Cardiomyocytes further express the inward rectifier K+ channel Kir2.1, which contributes to maintenance of resting cell membrane potential. Loss-of-function mutations of KCNJ2 encoding Kir2.1 result in Andersen-Tawil syndrome with periodic paralysis, cardiac arrhythmia and dysmorphic features. The present study explored whether SGK3 participates in the regulation of Kir2.1. Methods: cRNA encoding Kir2.1 was injected into Xenopus oocytes with and without additional injection of cRNA encoding wild type SGK3, constitutively active S419DSGK3 or inactive K191NSGK3. Kir2.1 activity was determined by two-electrode voltage-clamp and Kir2.1 protein abundance in the cell membrane by immunostaining and subsequent confocal imaging or by chemiluminescence. Results: Injection of 10 ng cRNA encoding wild type SGK3 and S419DSGK3, but not K191NSGK3 significantly enhanced Kir2.1-mediated currents. SGK inhibitor EMD638683 (50 µM) abrogated S419DSGK3-induced up-regulation of Kir2.1. Moreover, wild type SGK3 enhanced the channel protein abundance in the cell membrane. The decay of Kir2.1-mediated currents following inhibition of channel insertion into the cell membrane by brefeldin A (5 µM) was similar in oocytes coexpressing Kir2.1 and SGK3 as in oocytes expressing Kir2.1 alone, suggesting that SGK3 influences channel insertion into rather than channel retrieval from the cell membrane. Conclusions: SGK3 is a novel regulator of Kir2.1.

Keywords

• KCNJ2
• SGK3
• Cell membrane potential
• Neurons
• Cardiomyocytes
• Heart