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

水通道蛋白-2 （Aquaporin-2, AQP2）是一种膜水通道蛋白，在肾脏水分重吸收中起重要作用。AQP2通过血清加压素的作用在胞内囊泡和质膜之间进行转运。本研究利用磷酸化的AQP2特异性抗体检测丝氨酸256和丝氨酸269磷酸化对AQP2亚细胞分布的影响。结果表明，当抗利尿激素水平较低时，丝氨酸269不被磷酸化，AQP2留在细胞内。当加压素水平升高时，269丝氨酸迅速磷酸化，AQP2在质膜上积累。抗利尿激素拮抗剂抑制抗利尿素作用导致aqp2返回细胞内，丝氨酸269被迅速去磷酸化。这些结果表明丝氨酸269磷酸化的AQP2倾向于停留在质膜上。另一方面，丝氨酸256的磷酸化被认为对aqp2转运到质膜起主导作用，但对其亚细胞分布并不是很重要。

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.