Regulation of the water channel Aquaporin-2 by Cullin E3 ubiquitin ligases.

Aquaporin 2 (AQP2) is a vasopressin (VP) regulated water channel in the renal collecting duct. Phosphorylation and ubiquitylation of AQP2 play essential roles in controlling the cellular abundance of AQP2 and its accumulation on the plasma membrane in response to VP. Cullin-RING ubiquitin ligases (CRLs) are multi-subunit E3 ligases involved in ubiquitylation and degradation of their target proteins, eight of which are expressed in the collecting duct. Here, we utilized an established cell model of the collecting duct (mpkCCD14 cells) to study the role of Cullins in modulating AQP2. Western blotting identified Cul-1 to -5 in mpkCCD14 cells. Treatment of cells for 4 h with a pan-cullin inhibitor (MLN4924) decreased AQP2 abundance, prevented a VP-induced reduction in AQP2 Ser