The transcription of a mammalian voltage-gated potassium channel is regulated by cAMP in a cell-specific manner

Abstract

The transcript of Kv1.5, a Shaker-like delayed rectifier K+ channel cloned in our laboratory, is regulated in both tissue and developmentally specific manners. In this study we characterized the 5'-flanking region of the Kv1.5 gene. The gene lacks a canonical TATA box, has several transcription start sites, and the 5'-noncoding sequence is intronless. A cAMP response element (CRE) consensus signal was identified in the 5'-noncoding region. cAMP regulates the expression of Kv1.5 gene in a cell-specific manner. In primary cardiac cells, cAMP induces a 6-fold increase in the steady state levels of Kv1.5 transcript. However, in GH3 cells cAMP induces a 5-6-fold decrease in steady state levels of Kv1.5 transcript. The half-life of Kv1.5 transcript is 37 min and is not affected by cAMP. Nuclear run-on experiments show that in GH3 cells, cAMP reduces the transcription rate of Kv1.5 gene. Transient transfection assays using 5'-deletion mutations of Kv1.5 5'-flanking sequences revealed that the CRE located at +636 can confer the cAMP inducibility to Kv1.5 reporter gene constructs and binds to CRE-binding protein (CREB) and CRE modulator protein (CREM) in electromobility gel shift assays. Furthermore, KCl-induced depolarization can increase the steady state levels of Kv1.5 transcript in primary atrial cells and decrease it in GH3 cells. We conclude that cAMP and depolarization play an important role in regulating K+ channel expression and thus may induce long term effects on the pattern of electrical activity of excitable cells.