Characterisation of the Cullin‐3 mutation that causes a severe form of familial hypertension and hyperkalaemia

Deletion of exon 9 from Cullin‐3 ( CUL 3, residues 403–459: CUL 3 Δ403–459 ) causes pseudohypoaldosteronism type IIE ( PHA 2E), a severe form of familial hyperkalaemia and hypertension ( FHH t). CUL 3 binds the RING protein RBX 1 and various substrate adaptors to form Cullin‐ RING ‐ubiquitin‐ligase complexes. Bound to KLHL 3, CUL 3‐ RBX 1 ubiquitylates WNK kinases, promoting their ubiquitin‐mediated proteasomal degradation. Since WNK kinases activate Na/Cl co‐transporters to promote salt retention, CUL 3 regulates blood pressure. Mutations in both KLHL 3 and WNK kinases cause PHA 2 by disrupting Cullin‐ RING ‐ligase formation. We report here that the PHA 2E mutant, CUL 3 Δ403–459 , is severely compromised in its ability to ubiquitylate WNK s, possibly due to altered structural flexibility. Instead, CUL 3 Δ403–459 auto‐ubiquitylates and loses interaction with two important Cullin regulators: the COP 9‐signalosome and CAND 1. A novel knock‐in mouse model of CUL 3 WT /Δ403–459 closely recapitulates the human PHA 2E phenotype. These mice also show changes in the arterial pulse waveform, suggesting a vascular contribution to their hypertension not reported in previous FHH t models. These findings may explain the severity of the FHH t phenotype caused by CUL 3 mutations compared to those reported in KLHL 3 or WNK kinases.