10.25376/hra.7800926.v1 Mohammed Zubaerul Ferdaus Mohammed Zubaerul Ferdaus Lauren N. Miller Lauren N. Miller Larry N. Agbor Larry N. Agbor Turgay Saritas Turgay Saritas Jeffrey D. Singer Jeffrey D. Singer Curt D. Sigmund Curt D. Sigmund James A. McCormick James A. McCormick Mutant Cullin 3 causes familial hyperkalemic hypertension via dominant effects Health Research Alliance 2019 Cullin 3 familial hyperkalemic hypertension Nephrology and Urology 2019-03-05 00:08:54 Journal contribution https://hra.figshare.com/articles/journal_contribution/Mutant_Cullin_3_causes_familial_hyperkalemic_hypertension_via_dominant_effects/7800926 Mutations in the ubiquitin ligase scaffold protein Cullin 3 (CUL3) cause the disease familial hyperkalemic hypertension (FHHt). In the kidney, mutant CUL3 (CUL3-Δ9) increases abundance of With-No-Lysine [K] Kinase 4 (WNK4), with excessive activation of the downstream Sterile 20 (STE20)/SPS-1–related proline/alanine-rich kinase (SPAK) increasing phosphorylation of the Na<sup>+</sup>-Cl<sup>–</sup> cotransporter (NCC). CUL3-Δ9 promotes its own degradation via autoubiquitination, leading to the hypothesis that <i>Cul3</i> haploinsufficiency causes FHHt. To directly test this, we generated <i>Cul3</i> heterozygous mice (CUL3-Het), and <i>Cul3</i> heterozygotes also expressing CUL3-Δ9 (CUL3-Het/<br>Δ9), using an inducible renal epithelial–specific system. Endogenous CUL3 was reduced to 50% in both models, and consistent with autoubiquitination, CUL3-Δ9 protein was undetectable in CUL3-Het/Δ9 kidneys unless primary renal epithelia cells were cultured. Abundances of WNK4<br>and phosphorylated NCC did not differ between control and CUL3-Het mice, but they were elevated in CUL3-Het/Δ9 mice, which also displayed higher plasma [K<sup>+</sup>] and blood pressure. Abundance of phosphorylated Na<sup>+</sup>-K<sup>+</sup>-2Cl<sup>–</sup> cotransporter (NKCC2) was also increased, which may contribute to the severity of CUL3-Δ9–mediated FHHt. WNK4 and SPAK localized to puncta in NCC-positive<br>segments but not in NKCC2-positive segments, suggesting differential effects of CUL3-Δ9. These results indicate that <i>Cul3</i> haploinsufficiency does not cause FHHt, but dominant effects of CUL3-Δ9 are required.