WNK4 kinase inhibits Maxi K channel activity by a kinase-dependent mechanism

• Authors: Jieqiu Zhuang, Department of Nephrology, The Second Affiliated Hospital, Wenzhou Medical College and Departments of Medicine; Xuemei Zhang, Department of Pharmacology, School of Pharmacy, Fudan University and Departments of Medicine; Dexuan Wang, Department of Nephrology, The Second Affiliated Hospital, Wenzhou Medical College and Departments of Medicine; Juan Li, Physiology; Bo Zhou, Departments of Medicine; Zhen Shi, Department of Nephrology, The Second Affiliated Hospital, Wenzhou Medical College; Dingying Gu, Department of Nephrology, The Second Affiliated Hospital, Wenzhou Medical College; Donald D. Denson, Emory University; Douglas C Eaton, Emory University; Hui Cai, Emory University
• Journal Title: American Journal of Physiology - Renal Physiology
• Volume: Volume 301, Number 2
• Publisher: American Physiological Society | 2011-08, Pages F410-F419
• Type of Work: Article | Post-print: After Peer Review
• Publisher DOI: http://doi.org/10.1152/ajprenal.00518.2010
• Subjects: Biology, Physiology
• Keywords: protein expression; lysosomal degradation

Abstract

WNK [with no lysine (k)] kinase is a serine/threonine kinase subfamily. Mutations in two of the WNK kinases result in pseudohypoaldosteronism type II (PHA II) characterized by hypertension, hyperkalemia, and metabolic acidosis. Recent studies showed that both WNK1 and WNK4 inhibit ROMK activity. However, little is known about the effect of WNK kinases on Maxi K, a large-conductance Ca2+ and voltage-activated potassium (K) channel. Here, we report that WNK4 wild-type (WT) significantly inhibits Maxi K channel activity in HEK αBK stable cell lines compared with the control group. However, a WNK4 dead-kinase mutant, D321A, has no inhibitory effect on Maxi K activity. We further found that WNK4 inhibits total and cell surface protein expression of Maxi K equally compared with control groups. A dominant-negative dynamin mutant, K44A, did not alter the WNK4-mediated inhibitory effect on Maxi K surface expression. Treatment with bafilomycin A1 (a proton pump inhibitor) and leupeptin (a lysosomal inhibitor) reversed WNK4 WT-mediated inhibition of Maxi K total protein expression. These findings suggest that WNK4 WT inhibits Maxi K activity by reducing Maxi K protein at the membrane, but that the inhibition is not due to an increase in clathrin-mediated endocytosis of Maxi K, but likely due to enhancing its lysosomal degradation. Also, WNK4's inhibitory effect on Maxi K activity is dependent on its kinase activity.