Abstract 424: PKA Regulates HERG Synthesis and Interaction with HSP70
Chronically altered autonomic regulation is a common contributor to cardiovascular diseases and β-adrenergic receptors are frequently the target for medical therapy. Acute changes in β-adrenergic stimulation produce effects through cAMP and protein kinase A (PKA). PKA phosphorylation of ion channel proteins can alter their gating behavior within seconds. HERG K+channels can be acutely regulated by PKA phosphorylation of the channel protein and by direct binding of cAMP. We examined the response of the HERG channel to prolonged cAMP/PKA signaling in a stable expression system. Sustained elevation of cAMP increased HERG protein abundance by 2–5-fold in 24 hours, with measurable difference as early as four hours. The cAMP-induced augmentation was not due to altered transcription and was specific to HERG in that other stable K+channel cell lines (Kv1.4, Kv1.5, Kir2.1 and KvLQT1) did not show comparable changes. Direct PKA phosphorylation of the HERG protein at 3 of its 4 PKA-consensus sites was responsible for the cAMP-induced changes. The elevation of HERG protein was seen in ER, Golgi and plasma membrane with concomitant enhancement of K+current density. The cAMP-augmented HERG abundance was primarily due to acceleration of synthesis rates with minor effect on protein stability. Analysis of chaperone interactions indicates that the PKA-phosphorylation state of HERG alters its interaction with Hsp70. These results provide evidence for a novel mechanism whereby regulated phosphorylation of a nascent protein dictates its rate of synthesis through control of heat shock protein binding kinetics.