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Published on: May 26, 2017
Antagonistic regulation of ROMK by long and kidney-specific WNK1 isoforms
Ahmed Lazrak1, Zhen Liu, Chou-Long Huang
1Department of Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390-8856, USA.
Abstract:
WNK kinases are serine-threonine kinases with an atypical placement of the catalytic lysine. Intronic deletions with increased expression of a ubiquitous long WNK1 transcript cause pseudohypoaldosteronism type 2 (PHA II), characterized by hypertension and hyperkalemia. Here, we report that long WNK1 inhibited ROMK1 by stimulating its endocytosis. Inhibition of ROMK by long WNK1 was synergistic with, but not dependent on, WNK4. A smaller transcript of WNK1 lacking the N-terminal 1-437 amino acids is expressed highly in the kidney. Whether expression of the KS-WNK1 (kidney-specific, KS) is altered in PHA II is not known. We found that KS-WNK1 did not inhibit ROMK1 but reversed the inhibition of ROMK1 caused by long WNK1. Consistent with the lack of inhibition by KS-WNK1, we found that amino acids 1-491 of the long WNK1 were sufficient for inhibiting ROMK. Dietary K(+) restriction decreases ROMK abundance in the renal cortical-collecting ducts by stimulating endocytosis, an adaptative response important for conservation of K(+) during K(+) deficiency. We found that K(+) restriction in rats increased whole-kidney transcript of long WNK1 while decreasing that of KS-WNK1. Thus, KS-WNK1 is a physiological antagonist of long WNK1. Hyperkalemia in PHA II patients with PHA II mutations may be caused, at least partially, by increased expression of long WNK1 with or without decreased expression of KS-WNK1.
Insights
Long WNK1 inhibits ROMK1, contributing to hypertension and hyperkalemia in pseudohypoaldosteronism type 2 (PHA II). Kidney-specific WNK1 (KS-WNK1) acts as an antagonist, suggesting its altered expression contributes to PHA II.
Area of Science:
- Molecular Biology
- Renal Physiology
- Endocrinology
Background:
- WNK kinases are serine-threonine kinases involved in ion transport.
- Pseudohypoaldosteronism type 2 (PHA II) is characterized by hypertension and hyperkalemia, linked to WNK1 gene mutations.
- The regulation of ROMK1 channels by WNK1 isoforms is not fully understood.
Purpose of the Study:
- To investigate the role of different WNK1 transcripts in regulating ROMK1 channel activity.
- To elucidate the mechanism by which WNK1 affects ROMK1 endocytosis.
- To determine the physiological relevance of WNK1 isoforms in potassium homeostasis.
Main Methods:
- In vitro studies using cell lines expressing WNK1 isoforms and ROMK1.
- Analysis of ROMK1 endocytosis stimulated by WNK1.
- In vivo studies in rats involving dietary potassium restriction.
- Quantitative analysis of WNK1 transcript levels in response to dietary changes.
Main Results:
- Long WNK1 inhibits ROMK1 by promoting its endocytosis, an effect synergistic with WNK4.
- Kidney-specific WNK1 (KS-WNK1) does not inhibit ROMK1 but reverses long WNK1-mediated inhibition.
- Dietary potassium restriction alters the expression of WNK1 isoforms, increasing long WNK1 and decreasing KS-WNK1.
- Amino acids 1-491 of long WNK1 are sufficient for ROMK1 inhibition.
Conclusions:
- KS-WNK1 acts as a physiological antagonist to long WNK1 in regulating ROMK1.
- Altered expression of WNK1 isoforms, specifically increased long WNK1 and/or decreased KS-WNK1, may contribute to hyperkalemia in PHA II.
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