P-299 - Short-term regulation of Aquaporin-5 by combined phosphorylation and pH

Abstract

Aquaporin-5 (AQP5) is a membrane water channel widely distributed in human tissues that was found up-regulated in different tumors and considered implicated in carcinogenesis. AQP5 phosphorylation was reported to increase its expression and trafficking, resulting in increased membrane abundance. Interestingly, AQP5 is mostly found phosphorylated in tumor tissues. However, the effects of phosphorylation on channel activity as well as its sensitivity to extracellular acidification have not been investigated so far. In this work, using a yeast model of heterologous expression, we investigated the effect of protein phosphorylation and pH sensitivity as a mechanism of AQP5 short-term regulation. We observed that external acidification alone (pH 5) does not affect AQP5 activity. However, AQP5 phosphorylation induced by intracellular cAMP renders the protein channel prone to pH sensing, resulting in marked increase in water permeability when pH is raised to 7.4. The mechanism of gating may involve intracellular phosphorylation of AQP5 with consequent change in protein conformation and channel pore widening. In this new open configuration, deprotonation of residues occurring at pH 7.4 may support an increased water transport capacity of the AQP5 protein.