GPCR-Based Regulation of the hERG Potassium Channel Biosynthesis and Function

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DESCRIPTION (provided by applicant): Mutations in the hERG (human ether-a-go-go related gene) potassium channel are linked to the hereditary Long QT syndrome (LOTS, locus LQT2). Patients with the hereditary LOTS or drug-induced LOTS are susceptible to fatal tachyarrhythmias. HERG channels are regulated by several intracellular signaling pathways that together contribute to the overall modulation of the potassium current IKr in normal and disease states. Previous studies have established the acute regulation of HERG current and gating though the p-adrenergic system via direct phosphorylation of the HERG channel. Recent studies show that acute treatment of HERG-expressing Xenopus oocyteswith phorbol esters, a broad PKC activator, leads to a shift in the voltage dependence of activation of HERG. Chronic effects of adrenergic stimulation on the HERG channel have not been studied. Our experiments show that 24-hour stimulation with increased intracellular cAMP levels ((3-adrenergicpathway) or phorbol esters (a-adrenergic pathway) result in distinct increases in HERG protein abundance which are not transcriptionally mediated. The goal of the proposed research is to elucidate the mechanisms by which the P- and a-adrenergic pathways (via PKA and PKC) modulate changes in HERG protein abundance. We hypothesize that chronic p-and a-adrenergic receptor stimulation specifically enhances the rate of HERG synthesis through mechanisms involving PKA and the PKC isoforms which ultimately lead to translational up-regulation. We propose to determine the roles of PKA and PKC during translation of HERG using polysomal profiling with quantitative real-time PCR and in-vitro translation methods with radioisotope labeling. We also propose to dissect the upstream adrenergic signaling pathways leading to increases in HERG abundance by using pharmacological and biochemical methods in a heterologous expression system. PUBLIC HEALTH RELEVANCE: Long-term increases in the circulating levels of the hormones epinephrine and norepinephrine are consistently observed in patients with chronic heart disease and this may put them at an increased risk for abnormal heart rhythms. Our research is designed to examine the molecular pathways between the long-term hormonal stimulation and changes in the cardiac HERG ion-channel, which normally helps to maintain the heart rhythm. This work may identify potential targets for therapy in the prevention of rhythm disturbances accompanying chronic heart disease.