Studies on the importance of quaporin-2 phosphorylation in its subcellular distribution and intracellular trafficking.

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Aquaporin-2 (AQP2) is a membrane water channel protein which plays an important role in water reabsorption in the kidney. AQP2 is trafficking between intracellular vesicles and the plasma membrane by the effect of serum vasopressin. In the present study, effects of the phosphorylation of serine 256 and serine 269 on subcellular distribution of AQP2 was examined by using phosphorylated AQP2-specific antibodies. It was shown that serine 269 is unphosphorylated and AQP2 remains intracellularly when the vasopressin level is low. Upon the elevation of vasopressin level, serine 269 was rapidly phosphorylated and AQP2 was accumulated on the plasma membrane. Inhibition of the vasopressin effect by its antagonist caused AQP2-returning to the intracellular compartment as serine 269 was rapidly dephosphorylated. These results suggested that serine 269-phosphorylated AQP2 tends to stay in the plasma membrane. On the other, phosphorylation of serine 256, which has been believed to have a dominant effect on AQP2-trafficking to the plasma membrane, was found not to be very important for its subcellular distribution.