Abstract
The human ether-à-go-go-related gene (hERG) encodes the channel that conducts the rapidly activating delayed rectifier potassium current (IKr) in the heart. Reduction in IKr 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 IKr in isolated neonatal rat ventricular myocytes. Acute activation of PKC by PMA (30 nM, 30 minutes) reduced both hERG current (IhERG) and IKr Chronic activation of PKC by PMA (30 nM, 16 hours) increased IKr in cardiomyocytes and the expression level of hERG proteins; however, chronic (30 nM, 16 hours) PMA treatment decreased IhERG, which became larger than untreated control IhERG after PMA removal for 4 hours. Deletion of amino acid residues 2-354 (Δ2-354 hERG) or 1-136 of the N terminus (ΔN 136 hERG) abolished acute PMA (30 nM, 30 minutes)-mediated IhERG reduction. In contrast to wild-type hERG channels, chronic activation of PKC by PMA (30 nM, 16 hours) increased both Δ2-354 hERG and ΔN136 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.