WNK1 Activates Large-Conductance Ca2+-Activated K+ Channels through Modulation of ERK1/2 Signaling

With no lysine (WNK) kinases are members of the serine/threonine kinase family. We previously showed that WNK4 inhibits renal large-conductance Ca2+-activated K+ (BK) channel activity by enhancing its degradation through a lysosomal pathway. In this study, we investigated the effect of WNK1 on BK channel activity. In HEK293 cells stably expressing the alpha subunit of BK (HEK-BK alpha cells), siRNA-mediated knockdown of WNK1 expression significantly inhibited both BK alpha channel activity and open probability. Knockdown of WNK1 expression also significantly inhibited BK alpha protein expression and increased ERK1/2 phosphorylation, whereas overexpression of WNK1 significantly enhanced BK alpha expression and decreased ERK1/2 phosphorylation in a dose-dependent manner in HEK293 cells. Knockdown of ERK1/2 prevented WNK1 siRNA-mediated inhibition of BK alpha expression. Similarly, pretreatment of HEK-BK alpha cells with the lysosomal inhibitor bafilomycin A1 reversed the inhibitory effects of WNK1 siRNA on BK alpha expression in a dose-dependent manner. Knock-down of WNK1 expression also increased the ubiquitination of BK alpha channels. Notably, mice fed a high-K+ diet for 10 days had significantly higher renal protein expression levels of BK alpha and WNK1 and lower levels of ERK1/2 phosphorylation compared with mice fed a normal-K+ diet. These data suggest that WNK1 enhances BK channel function by reducing ERK1/2 signaling-mediated lysosomal degradation of the channel.