Combined Kelch-like 3 and Cullin 3 Degradation is a Central Mechanism in Familial Hyperkalemic Hypertension in Mice
Yujiro Maeoka, Mohammed Z. Ferdaus, Ryan J. Cornelius, Avika Sharma, Xiao‐Tong Su, Lauren N. Miller, Joshua A. Robertson, Susan B. Gurley, Chao‐Ling Yang, David H. Ellison, James A. McCormick
Abstract
Background Mutations in the ubiquitin ligase scaffold protein Cullin 3 ( CUL3 ) gene cause the disease familial hyperkalemic hypertension (FHHt). In the kidney, mutant CUL3 ( CUL3-Δ9 ) increases abundance of With-No-Lysine (K) Kinase 4 (WNK4), inappropriately activating sterile 20/SPS-1–related proline/alanine-rich kinase (SPAK), which then phosphorylates and hyperactivates the Na + Cl – cotransporter (NCC). The precise mechanism by which CUL3-Δ9 causes FHHt is unclear. We tested the hypothesis that reduced abundance of CUL3 and of Kelch-like 3 (KLHL3), the CUL3 substrate adaptor for WNK4, is mechanistically important. Because JAB1, an enzyme that inhibits CUL3 activity by removing the ubiquitin-like protein NEDD8, cannot interact with CUL3-Δ9, we also determined whether Jab1 disruption mimicked the effects of CUL3-Δ9 expression. Methods We used an inducible renal tubule-specific system to generate several mouse models expressing CUL3-Δ9 , mice heterozygous for both CUL3 and KLHL3 ( Cul3+/−/Klhl3+/− ), and mice with short-term Jab1 disruption (to avoid renal injury associated with long-term disruption). Results Renal KLHL3 was higher in Cul3−/− mice, but lower in Cul3−/−/Δ9 mice and in the Cul3+/−/Δ9 FHHt model, suggesting KLHL3 is a target for both WT and mutant CUL3 . Cul3+/−/Klhl3+/− mice displayed increased WNK4-SPAK activation and phospho-NCC abundance and an FHHt-like phenotype with increased plasma [K + ] and salt-sensitive blood pressure. Short-term Jab1 disruption in mice lowered the abundance of CUL3 and KLHL3 and increased the abundance of WNK4 and phospho-NCC. Conclusions Jab1−/− mice and Cul3+/−/Klhl3+/− mice recapitulated the effects of CUL3-Δ9 expression on WNK4-SPAK-NCC. Our data suggest degradation of both KLHL3 and CUL3 plays a central mechanistic role in CUL3-Δ9–mediated FHHt.