KCNQ1 is internalized by activation of α1 adrenergic receptors.

KCNQ1 (Kv7.1 or KvLQT1) plays important physiological roles in various tissues forming potassium channels with KCNE subunits. Among the channels formed by KCNQ1 and KCNE subunits, the best studied is the slow delayed rectifier potassium channel in the heart, the IKs (KCNQ1/KCNE1) channel, which is critical for repolarization of cardiac action potential. The KCNQ1 channel is internalized by Nedd4/Nedd4-like ligase-dependent ubiquitination. It is also reported that phosphorylation of KCNE1 by PKC results in internalization of the KCNQ1/KCNE1 channel. Because we have observed down-regulation of KCNQ1/KCNE1 currents by activation of the α1-adrenergic receptor (α1AR) that activates PKC, this study investigated whether α1AR causes internalization of the KCNQ1 protein. We fused HaloTag to the extracellular region of KCNQ1 (Halo-KCNQ1) and co-expressed it with α1ARs in HEK293 cells. The KCNQ1 protein on the cell surface was selectively labeled with membrane-impermeable HaloTag ligands, and changes in its localization were monitored by confocal fluorescence microscopy. Activation of α1AAR and α1BAR caused marked internalization of KCNQ1, which was not KCNE1-dependent. Internalization of KCNQ1 by α1AR activation was inhibited by disruption of the PY motif or the YXXΦ motif in the C-terminus. Double staining for the receptor and the channel revealed that KCNQ1 internalization was independent of α1AR internalization. Our results suggest that α1AR-mediated direct internalization of KCNQ1 is AP2/clathrin-dependent and may be triggered by ubiquitination of KCNQ1 via the AMP dependent kinase (AMPK)/Nedd4-2 pathway. When phenylephrine was applied to rat neonatal cardiomyocytes transfected with KCNQ1 and α1AR, the KCNQ1 protein was internalized. The internalization of KCNQ1 by α1AR would affect pathophysiology in a variety of tissues expressing KCNQ1, which merits further in vivo study.

Insulin treatment augments KCNQ1/KCNE1 currents but not KCNQ1 currents, which is associated with an increase in KCNE1 expression.

Diabetes mellitus affects ion channel physiology. We have previously reported that acute application of insulin suppresses the KCNQ1/KCNE1 currents that play an important role in terminating ventricular action potential. In this study, we investigated the effect of long-term insulin treatment on KCNQ1/KCNE1 currents using the Xenopus oocyte expression system. Insulin treatment with a duration longer than 6 h had an opposite effect to acute insulin application, that is, it augmented the KCNQ1/KCNE1 currents. Inhibitors of PI3K, wortmannin and LY294002, and a MEK inhibitor, U0126, abolished the potentiating effect of long-term insulin treatment. The long-term treatment with insulin had no effect on KCNQ1 currents indicating an essential role of KCNE1 in the insulin effect, which is similar to the acute insulin effect. Cycloheximide, an inhibitor of protein synthesis, and brefeldin A, an inhibitor of protein transport from endoplasmic reticulum, suppressed the long-term insulin effect. Western blotting analysis combined with these pharmacological data suggest that long-term insulin treatment augments KCNQ1/KCNE1 currents by increasing KCNE1 protein expression.