Adrenergic Regulation of the HERG Potassium Channel Biosynthesis and Function

Abstract

The HERG (human ether-a-go-go related gene) potassium channel is linked to the hereditary Long QT Syndrome (LQTS, locus LQT2) and is a drug binding target in the acquired LQTS. HERG channels are regulated by several intracellular signaling pathways that together contribute to the overall modulation of the cardiac potassium current IKr in normal and disease states. Previous studies have established the acute regulation of HERG current though the beta-adrenergic pathway with an increase in cellular cAMP levels, activation of protein kinase A (PKA) and direct phosphorylation of the HERG channel. Regulation by the alpha-adrenergic system involving protein kinase C (PKC) activity has been less well characterized. Chronic effects of adrenergic stimulation on the HERG channel have not been studied. We have found that 24-hour stimulation with increased intracellular cAMP levels or phorbol esters result in distinct increases in HERG protein abundance. This increase in protein levels is not transcriptionally mediated as shown by qRT-PCR and corresonds more to increased production rather than reduced degradation of channel protein. We are currently investigating the underlying mechanism of this kinase-responsive enhancement of steady-state HERG protein levels. We have found that PKA activity can be co-precipitated with HERG, as they exist in a complex. We are using a cell-free in-vitro translation system to isolate and determine the contribution of signaling components such as PKA and PKC during HERG synthesis at the ER. We have found that addition of ATP and purified PKA together accelerates generation of new HERG protein, indicating a direct regulation of translation rate. Ongoing studies using this system will allow us to dissect the molecular mechanisms that regulate HERG channel synthesis.