Abstract: TH-OR24
Role of WNK1 and WNK4 in Sensing Extracellular Potassium in Principal Cells to Modulate mTORC2-Dependent Activation of Epithelial Sodium Channel
Session Information
- Fluid, Electrolyte, and Acid-Base Disorders: Basic and Clinical Research
November 04, 2021 | Location: Simulive, Virtual Only
Abstract Time: 04:30 PM - 06:00 PM
Category: Fluid, Electrolyte, and Acid-Base Disorders
- 901 Fluid, Electrolyte, and Acid-Base Disorders: Basic
Authors
- Saha, Bidisha, University of California San Francisco, San Francisco, California, United States
- Shabbir, Waheed, University of California San Francisco, San Francisco, California, United States
- Takagi, Enzo, University of California San Francisco, San Francisco, California, United States
- Sorensen, Mads Vaarby, Aarhus Universitet, Aarhus, Midtjylland, Denmark
- Leite-Dellova, Deise C A, University of California San Francisco, San Francisco, United States
- Pearce, David, University of California San Francisco, San Francisco, California, United States
Background
mTORC2 phosphorylation of SGK1 and consequent activation of ENaC is essential in the regulation of ion transport by principal cells (PCs) of the distal tubular system. We recently demonstrated that local K+ concentration could be sensed by PCs to activate ENaC through mTORC2-SGK1 signaling, and suggested a role for WNK1 in this mechanism. However, the mechanistic basis of this regulation has not been explored. In DCT, WNK4 modulates NCC activity in response to extracellular K+ in a kinase-dependent manner. Here we have explored the role of WNK1 and 4 in local sensing of extracellular K+ and ENaC regulation in the mpkCCD cultured PC model.
Methods
We used CRISPR to generate WNK1-/- and WNK4 -/- mpkCCD cells. WT and KO cells were grown on Transwell filters and adapted to 1 or 3 mM [K+] on the basolateral side, followed by raising [K+] to 5 mM in the presence or absence of WNK kinase inhibitor. Amiloride-sensitive current was measured by volt-ohmmeter as well as by patch clamp. Cells were processed for co-IP and immunoblot analysis.
Results
In WT mpkCCD cells, extracellular K+ stimulated ENaC current concomitant with mTORC2-dependent SGK1 phosphorylation, Nedd4-2 phosphorylation and expression of cleaved ENaC. In WT cells, inhibition of WNK kinase activity by WNK463 had no significant effect on K+-stimulated ENaC current or SGK1 phosphorylation, although SPAK phosphorylation was markedly reduced. In contrast, WNK1 deletion blocked the effect of extracellular K+ on ENaC and SGK1 phosphorylation. Transfection of WNK1-/- mpkCCD cells with either WT or kinase-dead WNK1 restored K+-stimulated SGK1 phosphorylation and ENaC activity. Furthermore, this effect was accompanied by greater association of SGK1 with both mTORC2 and WNK1 (WT or kinase-dead). WNK4 deletion and the recovery of WNK4 expression, had similar effects to WNK1 on SGK1 phosphorylation and ENaC current.
Conclusion
Our data support a scaffolding role for WNK1 and 4 that promotes mTORC2-SGK1 interaction and hence phosphorylation through a mechanism that does not require its kinase activity. Extracellular K+, which has a well-established role to inhibit WNK-dependent SPAK phosphorylation, stimulates WNK1/4-SGK1 interaction, and assembly of an mTORC2-SGK1-WNK complex, resulting in enhanced SGK1 activity and ENaC activation in PCs
Funding
- NIDDK Support