Differential regulation of human ether-à-go-go-related gene (HeRG) current and expression by activation of protein kinase C

The human ether-à-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 (D2-354 hERG) or 1-136 of the N terminus (DN 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 D2-354 hERG and DN136 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.