Cell-specific regulation of L-WNK1 by dietary K⁺

Abstract

Flow-induced K+ secretion in the aldosterone-sensitive distal nephron is mediated by high-conductance Ca2+-activated K+ (BK) channels. Familial hyperkalemic hypertension (pseudohypoaldosteronism type II) is an inherited form of hypertension with decreased K+ secretion and increased Na+ reabsorption. This disorder is linked to mutations in genes encoding with-no-lysine kinase 1 (WNK1), WNK4, and Kelch-like 3/Cullin 3, two components of an E3 ubiquitin ligase complex that degrades WNKs. We examined whether the full-length (or “long”) form of WNK1 (L-WNK1) affected the expression of BK α-subunits in HEK cells. Overexpression of L-WNK1 promoted a significant increase in BK α-subunit whole cell abundance and functional channel expression. BK α-subunit abundance also increased with coexpression of a kinase dead L-WNK1 mutant (K233M) and with kidney-specific WNK1 (KS-WNK1), suggesting that the catalytic activity of L-WNK1 was not required to increase BK expression. We examined whether dietary K+ intake affected L-WNK1 expression in the aldosterone-sensitive distal nephron. We found a paucity of L-WNK1 labeling in cortical collecting ducts (CCDs) from rabbits on a low-K+ diet but observed robust staining for L-WNK1 primarily in intercalated cells when rabbits were fed a high-K+ diet. Our results and previous findings suggest that L-WNK1 exerts different effects on renal K+ secretory channels, inhibiting renal outer medullary K+ channels and activating BK channels. A high-K+ diet induced an increase in L-WNK1 expression selectively in intercalated cells and may contribute to enhanced BK channel expression and K+ secretion in CCDs.

An unexpected journey: conceptual evolution of mechanoregulated potassium transport in the distal nephron

“…These results are consistent with the notion that WNK4 enhances the routing of BK channels to lysosomes in a ubiquitin-dependent manner (260) that is also dependent on activation of MAPKs (250). In contrast to its effect on ROMK, L-WNK1 significantly increases BK␣ whole cell and functional expression in HEK293 cells (114,224). L-WNK1 expression reduced ERK phosphorylation, whereas knockdown of WNK1 increased the ubiquitination of BK␣, effects that are opposite to the effects seen with WNK4 (114).…”

“…L-WNK1 expression reduced ERK phosphorylation, whereas knockdown of WNK1 increased the ubiquitination of BK␣, effects that are opposite to the effects seen with WNK4 (114). Surprisingly, both KS-WNK1 and kinase dead L-WNK1 increased BK␣ whole cell expression in HEK293 cells, suggesting that WNK1 kinase activity is not required to enhance BK␣ expression (224).…”

“…WNK-1 expression in the CCD is low in rabbits fed a LK diet but is selectively upregulated in ␤ intercalated cells in HK-fed animals, where it is localized to the apical membrane and subapical region of this specific cell population (224). This finding has important implications regarding the adaptive response to K loading, where urinary flow rates are increased (12,23,52,193,215).…”

Renal Tubular Ubiquitin-Protein Ligase NEDD4-2 Is Required for Renal Adaptation during Long-Term Potassium Depletion

“…BK Channels Are Increased in Principal Cells of the CNT/CD in Nedd4L Pax8/LC1 Mice Because WNK1 is a positive regulator of BK channels, 42,43 we also assessed BK expression by Western blot, and found that the channel-forming BKa and BKb1 (but not BKb4) subunits were increased in total kidney extracts ( Figure 7, A and B). Immunostaining showed that BKa subunits were detectable in the CNT/CD despite active hypokalemia, and their expression was enhanced by about 30% in the CNT/CCD of Nedd4L Pax8/LC1 mice ( Figure 7, C and D).…”

Intercalated cell BKα subunit is required for flow-induced K+ secretion

“…thus, independent of ENaC, presumably reflecting the recruitment of a non-PC-mediated pathway for K + secretion into the urine (30); (c) dietary K + loading of rabbits leads to an increase in ICs of immunodetectable apical BKα and the long isoform of with-no-lysine kinase 1 (L-WNK1), a kinase that increases BKα abundance and functional channel expression in heterologous expression systems (31,32); (d) the apical membrane of the IC is depolarized relative to that of the PC (26,33,34), suggesting that there exists a favorable driving force for K + efflux across this membrane; and (e) increases in tubular fluid flow rate lead to increases in the intracellular Ca 2+ concentration ([Ca 2+ ] i ) in both ICs and PCs (35)(36)(37), and only a modest increase in [Ca 2+ ] i is necessary to open BK channels (26).…”