Role of cytoplasmic termini in sorting and shuttling of the aquaporin-2 water channel.

In mammals, the regulation of water homeostasis is mediated by the aquaporin-1 (AQP1) water channel, which localizes to the basolateral and apical membranes of the early nephron segment, and AQP2, which is translocated from intracellular vesicles to the apical membrane of collecting duct cells after vasopressin stimulation. Because a similar localization and regulation are observed in transfected Madin-Darby Canine Kidney (MDCK) cells, we investigated which segments of AQP2 are important for its routing to forskolin-sensitive vesicles and the apical membrane through analysis of AQP1-AQP2 chimeras. AQP1 with the entire COOH tail of AQP2 was constitutively localized in the apical membrane, whereas chimeras with shorter COOH tail segments of AQP2 were localized in the apical and basolateral membrane. AQP1 with the NH2 tail of AQP2 was constitutively localized in both plasma membranes, whereas AQP1 with the NH2 and COOH tail of AQP2 was sorted to intracellular vesicles and translocated to the apical membrane with forskolin. These data indicate that region N220-S229 is essential for localization of AQP2 in the apical membrane and that the NH2 and COOH tail of AQP2 are essential for trafficking of AQP2 to intracellular vesicles and its shuttling to and from the apical membrane.