Differential Regulation of Human Ether-a-Go-Go-Related Gene (hERG) Current and Expression by Activation of Protein Kinase C

The human ether-a-go-go-related gene (hERG) encodes the channel that conducts the rapidly activating delayed rectifier potassium current (I-Kr) in the heart. Reduction in I-Kr causes long QT syndrome, which can lead to fatal arrhythmias triggered by stress. One potential link between stress and hERG function is protein kinase C (PKC) activation; however, seemingly conflicting results regarding PKC regulation of hERG have been reported. We investigated the effects of PKC activation using phorbol 12-myristate 13-acetate (PMA) on hERG channels expressed in human embryonic kidney cell line 293 (HEK293) cells and I-Kr in isolated neonatal rat ventricular myocytes. Acute activation of PKC by PMA (30 nM, 30 minutes) reduced both hERG current (I-hERG) and I-Kr. Chronic activation of PKC by PMA (30 nM, 16 hours) increased I-Kr in cardiomyocytes and the expression level of hERG proteins; however, chronic (30 nM, 16 hours) PMA treatment decreased I-hERG, which became larger than untreated control I-hERG after PMA removal for 4 hours. Deletion of amino acid residues 2-354 (Delta 2-354 hERG) or 1-136 of the N terminus (Delta N 136 hERG) abolished acute PMA (30 nM, 30 minutes)-mediated I-hERG reduction. In contrast to wild-type hERG channels, chronic activation of PKC by PMA (30 nM, 16 hours) increased both Delta 2-354 hERG and Delta N136 hERG expression levels and currents. The increase in hERG protein was associated with PKC-induced phosphorylation (inhibition) of Nedd4-2, an E3 ubiquitin ligase that mediates hERG degradation. We conclude that PKC regulates hERG in a balanced manner, increasing expression through inhibiting Nedd4-2 while decreasing current through targeting a site(s) within the N terminus.