The C-Terminal PDZ-Binding Motif in the Kv1.5 Potassium Channel Governs its Modulation by the Na+/H+ Exchanger Regulatory Factor 2

Kv1.5 belongs to the family of voltage-gated potassium (Kv) channels and contains a N- and a C-terminal PDZ-binding motif that might be recognized by PDZ domains on the scaffold proteins NHERF1 and NHERF2. Expression studies in Xenopus oocytes demonstrated that NHERF1 and NHERF2 activate Kv1.5, an effect requiring the C-terminal PDZ-binding motif on Kv1.5. NHERF2 enhances Kv1.5 activity and cell surface expression as determined by electrophysiology and immunoassays. NHERF2 elevates Kv1.5 abundance at the plasma membrane by decreasing channel internalization as proven by Brefeldin A experiments. Kv1.5 is stimulated by the serum and glucocorticoid inducible kinase SGK1, a kinase known to interact with the second PDZ domain of NHERF2. This study aims to identify if SGK1 and NHERF2 synergize to increase Kv1.5 currents. Expression of NHERF2 potentiated SGK1-mediated Kv1.5 activation, which was significantly attenuated by deletion of the second PDZ domain in NHERF2. Specificity of observed effects was verified by evaluating the influence of NHERFs on Kv1.3, a known SGK1 target that contains an internal PDZ binding motif. In summary, our results suggest that NHERFs might participate in the regulation of electrical excitability in part by controlling Kv1.5 surface abundance and by clustering signal transduction molecules to the channel.