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Cullin-RING ligases are a family of E3 ubiquitin ligases that control cellular processes through regulated degradation. Cullin 3 targets with-no-lysine kinase 4 (WNK4), a kinase that activates the Na(+)-Cl(−) cotransporter (NCC), the main pathway for Na(+) reabsorption in the distal convoluted tubule (DCT). Mutations in the cullin 3 gene lead to familial hyperkalemic hypertension by increasing WNK4 abundance. The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) regulates the activity of cullin-RING ligases by removing the ubiquitin-like protein neural precursor cell expressed developmentally downregulated protein 8. Genetic deletion of the catalytically active CSN subunit, Jab1, along the nephron in mice (KS-Jab1(−/−)) led to increased WNK4 abundance; however, NCC abundance was substantially reduced. We hypothesized that the reduction in NCC resulted from a cortical injury that led to hypoplasia of the segment, which counteracted WNK4 activation of NCC. To test this, we studied KS-Jab1(−/−) mice at weekly intervals over a period of 3 wk. The results showed that NCC abundance was unchanged until 3 wk after Jab1 deletion, at which time other DCT-specific proteins were also reduced. The kidney injury markers kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin demonstrated kidney injury immediately after Jab1 deletion; however, the damage was initially limited to the medulla. The injury progressed and expanded into the cortex 3 wk after Jab1 deletion coinciding with loss of the DCT. The data indicate that nephron-specific disruption of the cullin-RING ligase system results in a complex progression of tubule injury that leads to hypoplasia of the DCT. NEW & NOTEWORTHY Cullin 3 (CUL3) targets with-no-lysine-kinase 4 (WNK4), which activates Na(+)-Cl(−) cotransporter (NCC) in the distal convoluted tubule (DCT) of the kidney. Renal-specific genetic deletion of the constitutive photomorphogenesis 9 signalosome, an upstream regulator of CUL3, resulted in a reduction of NCC due to DCT hypoplasia, which coincided with cortical kidney injury. The data indicate that nephron-specific disruption of the cullin-RING ligase system results in a complex progression of tubule injury leading to hypoplasia of the DCT. |
