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

Jieqiu Zhuang1, Xuemei Zhang, Dexuan Wang

  • 1Department of Nephrology, The Second Affiliated Hospital, Wenzhou Medical College, Zhejiang, China.

American Journal of Physiology. Renal Physiology
|May 27, 2011
PubMed

Insights

WNK4 kinase inhibits Maxi K channel activity by reducing its protein levels, likely through enhanced lysosomal degradation. This inhibition requires WNK4

Area of Science:

  • Molecular Biology
  • Physiology
  • Biochemistry

Background:

  • WNK (with no lysine) kinases are serine/threonine kinases.
  • Mutations in WNK kinases cause pseudohypoaldosteronism type II (PHA II).
  • WNK1 and WNK4 inhibit ROMK channels, but their effect on Maxi K channels is unknown.

Purpose of the Study:

  • Investigate the effect of WNK4 on Maxi K (large-conductance Ca(2+)-activated K+) channel activity.
  • Determine the mechanism by which WNK4 affects Maxi K channel expression and function.

Main Methods:

  • HEK αBK stable cell lines were used to study WNK4 and Maxi K interactions.
  • WNK4 wild-type (WT) and a dead-kinase mutant (D321A) were employed.
  • Protein expression levels (total and cell surface) were assessed.
  • Effects of dynamin, bafilomycin A1, and leupeptin on Maxi K expression were evaluated.

Main Results:

  • WNK4 WT significantly inhibited Maxi K channel activity.
  • WNK4's dead-kinase mutant (D321A) did not inhibit Maxi K activity, indicating kinase dependence.
  • WNK4 reduced both total and cell surface Maxi K protein expression.
  • Inhibition of Maxi K surface expression was independent of clathrin-mediated endocytosis.
  • Lysosomal degradation inhibitors (bafilomycin A1, leupeptin) reversed the reduction in total Maxi K protein.

Conclusions:

  • WNK4 kinase activity is essential for inhibiting Maxi K channel activity.
  • WNK4 reduces Maxi K protein at the cell surface.
  • The primary mechanism involves enhanced lysosomal degradation of Maxi K, not altered endocytosis.
  • WNK4 represents a novel regulator of Maxi K channel function.

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