PKA phosphorylation of HERG protein regulates the rate of channel synthesis

Departments of 1 Medicine and 2 Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York; and 3 Department of Pharmacology, Faculty of Medicine, National University of Singapore, Singapore Submitted 1 December 2008 ; accepted in final form 18 February 2009 Acute changes in cAMP and protein kinase A (PKA) signaling can regulate ion channel protein activities such as gating. Effects on channels due to chronic PKA signaling, as in stress or disease states, are less understood. We examined the effects of prolonged PKA activity on the human ether - a - go - go -related gene (HERG) K + channel in stably transfected human embryonic kidney (HEK)293 cells. Sustained elevation of cAMP by either chlorophenylthiol (CPT)-cAMP or forskolin increased the HERG channel protein abundance two- to fourfold within 24 h, with measurable difference as early as 4 h. The cAMP-induced augmentation was not due to changes in transcription and was specific for HERG compared with other cardiac K + channels (Kv1.4, Kv1.5, Kir2.1, and KvLQT1). PKA activity was necessary for the effect on HERG protein and did not involve other cAMP signaling pathways. Direct PKA phosphorylation of the HERG protein was responsible for the cAMP-induced augmentation. Enhanced abundance of HERG protein was detected in endoplasmic reticulum-enriched, Golgi, and plasma membrane without significant changes in trafficking rates or patterns. An increase in the K + current density carried by the HERG channel was also observed, but with a delay, suggesting that traffic to the surface is rate-limiting traffic. Acceleration of the HERG protein synthesis rate was the primary factor in the cAMP/PKA effect with lesser effects on protein stability. These results provide evidence for a novel mechanism whereby phosphorylation of a nascent protein dictates its rate of synthesis, resetting its steady-state abundance. adenosine 3',5'-cyclic monophosphate; human ether - a - go - go -related gene; potassium channel; protein kinase A Address for reprint requests and other correspondence: T. McDonald, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461 (e-mail: mcdonald{at}aecom.yu.edu )