Hyperkalemic hypertension–associated cullin 3 promotes WNK signaling by degrading KLHL3
James A. McCormick, … , Jeffrey D. Singer, David H. Ellison
James A. McCormick, … , Jeffrey D. Singer, David H. Ellison
Published September 24, 2014
Citation Information: J Clin Invest. 2014;124(11):4723-4736. https://doi.org/10.1172/JCI76126.
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Research Article Nephrology

Hyperkalemic hypertension–associated cullin 3 promotes WNK signaling by degrading KLHL3

Abstract

Familial hyperkalemic hypertension (FHHt) is a monogenic disease resulting from mutations in genes encoding WNK kinases, the ubiquitin scaffold protein cullin 3 (CUL3), or the substrate adaptor kelch-like 3 (KLHL3). Disease-associated CUL3 mutations abrogate WNK kinase degradation in cells, but it is not clear how mutant forms of CUL3 promote WNK stability. Here, we demonstrated that an FHHt-causing CUL3 mutant (CUL3 Δ403–459) not only retains the ability to bind and ubiquitylate WNK kinases and KLHL3 in cells, but is also more heavily neddylated and activated than WT CUL3. In cells, activated CUL3 Δ403–459 depleted KLHL3, preventing WNK degradation, despite increased CUL3-mediated WNK ubiquitylation; therefore, CUL3 loss in kidney should phenocopy FHHt in murine models. As predicted, nephron-specific deletion of Cul3 in mice did increase WNK kinase levels and the abundance of phosphorylated Na-Cl cotransporter (NCC). Over time, however, Cul3 deletion caused renal dysfunction, including hypochloremic alkalosis, diabetes insipidus, and salt-sensitive hypotension, with depletion of sodium potassium chloride cotransporter 2 and aquaporin 2. Moreover, these animals exhibited renal inflammation, fibrosis, and increased cyclin E. These results indicate that FHHt-associated CUL3 Δ403–459 targets KLHL3 for degradation, thereby preventing WNK degradation, whereas general loss of CUL3 activity — while also impairing WNK degradation — has widespread toxic effects in the kidney.

Authors

James A. McCormick, Chao-Ling Yang, Chong Zhang, Brittney Davidge, Katharina I. Blankenstein, Andrew S. Terker, Bethzaida Yarbrough, Nicholas P. Meermeier, Hae J. Park, Belinda McCully, Mark West, Aljona Borschewski, Nina Himmerkus, Markus Bleich, Sebastian Bachmann, Kerim Mutig, Eduardo R. Argaiz, Gerardo Gamba, Jeffrey D. Singer, David H. Ellison

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Figure 8

Kidney weight, plasma creatinine, cyclin E expression, and kidney morphology in control and KS-Cul3–/– mice.

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Kidney weight, plasma creatinine, cyclin E expression, and kidney morpho...
(A) Kidneys were significantly heavier and (B) plasma creatinine significantly higher in KS-Cul3–/– mice than in controls. (C) KS-Cul3–/– mice developed renal inflammation and fibrosis. Ovals denote glomeruli. Atrophic tubules (large arrows) and mononuclear inflammatory cells (small arrows) are illustrated. Inset shows a white cell cast (large arrow) and neutrophils (small arrows). Original magnification, ×400; ×200 (inset). (D) Cyclin E was increased in KS-Cul3–/– mice (P < 0.001), and there was a switch in apparent molecular size (blot quantified by Ponceau staining; see Supplemental Figure 9). (E) Simplified model of CUL3 effects. In WT cells, KLHL3 binds WNK kinases and CUL3, permitting ubiquitylation (ubiq) of WNK kinases, degrading WNK kinases, and restraining NCC. It also ubiquitylates cyclin E (via a different BTB protein). In Cul3-deficient cells, KLHL3 binds to WNK4, but cannot foster degradation as there is no CUL3, so WNK and pNCC increase. Disruption of Cul3 in the kidney also leads to kidney damage, possibly via increased expression of cyclin E. In CUL3-mediated FHHt, the mutant protein ubiquitylates KLHL3 strongly, leading to its degradation. Even though CUL3 retains the ability to ubiquitylate WNK kinases, this does not occur, as KLHL3 is missing and cannot complex CUL3 with WNK kinases. Several components and details of the CRL pathway are omitted for clarity.