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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Regulation of the voltage-gated K⁺ channels KCNQ2/3 and KCNQ3/5 by serum- and glucocorticoid-regulated kinase-1

¹School of Biomedical Sciences and Queensland Brain Institute, University of Queensland, Brisbane, Queensland; and ²Hanson Institute, Institute of Medical and Veterinary Sciences, Adelaide, South Australia, Australia

Submitted 13 March 2008 ; accepted in final form 29 April 2008

The voltage-gated KCNQ2/3 and KCNQ3/5 K⁺ channels regulate neuronal excitability. We recently showed that KCNQ2/3 and KCNQ3/5 channels are regulated by the ubiquitin ligase Nedd4-2. Serum- and glucocorticoid-regulated kinase-1 (SGK-1) plays an important role in regulation of epithelial ion transport. SGK-1 phosphorylation of Nedd4-2 decreases the ability of Nedd4-2 to ubiquitinate the epithelial Na⁺ channel, which increases the abundance of channel protein in the cell membrane. In this study, we investigated the mechanism(s) of SGK-1 regulation of M-type KCNQ channels expressed in Xenopus oocytes. SGK-1 significantly upregulated the K⁺ current amplitudes of KCNQ2/3 and KCNQ3/5 channels 1.4- and 1.7-fold, respectively, whereas the kinase-inactive SGK-1 mutant had no effect. The cell surface levels of KCNQ2-hemagglutinin/3 were also increased by SGK-1. Deletion of the KCNQ3 channel COOH terminus in the presence of SGK-1 did not affect the K⁺ current amplitude of KCNQ2/3/5-mediated currents. Coexpression of Nedd4-2 and SGK-1 with KCNQ2/3 or KCNQ3/5 channels did not significantly alter K⁺ current amplitudes. Only the Nedd4-2 mutant ^S448ANedd4-2 exhibited a significant downregulation of the KCNQ2/3/5 K⁺ current amplitudes. Taken together, these results demonstrate a potential mechanism for regulation of KCNQ2/3 and KCNQ3/5 channels by SGK-1 regulation of the activity of the ubiquitin ligase Nedd4-2.

KCNQ channel; M current; potassium channel; ubiquitin ligase; Xenopus oocyte