Differential regulation of 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. Reductions in I Kr causes long QT syndrome (LQTS), 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. Here, we investigated effects of PKC activation using phorbol 12-myristate 13-acetate (PMA) on hERG channels expressed in HEK293 cells and I Kr in isolated neonatal rat ventricular myocytes. Acute activation of PKC by PMA (30 nM, 30 min) reduced both hERG current (I hERG ) and I Kr . Chronic activation of PKC by PMA (30 nM, 16 h) increased I Kr in cardiomyocytes and the expression level of hERG proteins. However, chronic (16 h, 30 nM) PMA treatment decreased I hERG , which became larger than untreated control I hERG after PMA removal for 4 h. Deletion of amino acid residues 2-354 (Δ2-354 hERG) or 1-136 of the N-terminus (ΔN136 hERG) abolished acute PMA (30 nM, 30 min) mediated I hERG reduction. In contrast to WT hERG channels, chronic activation of PKC by PMA (30 nM, 16 h) 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.