Abstract
Aquaporin-5 (AQP5) is selectively expressed in the apical membrane of exocrine glands, such as salivary, sweat, and submucosal airway glands, and plays important roles in maintaining their secretory functions. Because AQP5 is not regulated by gating, localization on the plasma membrane is important for its water-permeable function. Ezrin is an ezrin–radixin–moesin family protein that serves as a crosslinker between the plasma membrane and actin cytoskeleton network. It plays important roles in translocation of various membrane proteins to mediate vesicle trafficking to the plasma membrane. In this study, we examined the effects of ezrin inhibition on membrane trafficking of AQP5. Ezrin inhibition selectively suppressed an ionomycin-induced increase in AQP5 translocation to the plasma membrane of mouse lung epithelial cells (MLE-12) without affecting the steady-state level of plasma membrane AQP5. Taken together, our data suggest that AQP5 translocates to the plasma membrane through at least two pathways and that ezrin is selectively involved in a stimulation-dependent pathway.
Highlights
Aquaporins (AQPs) are water-selective channel proteins that allow rapid movement of water across the plasma membrane in secretory and adsorptive cells
We investigated the effect of ezrin-DN transfection on Ca2+ ionophore ionomycin-induced translocation of AQP5 from the intracellular space to plasma membrane
In empty vector- or ezrin-WT-transfected cells, ionomycin treatment changed the subcellular localization of AQP5 from the intracellular space to plasma membrane (Figure 1C), which suggests that this reagent stimulates plasma membrane trafficking of AQP5
Summary
Aquaporins (AQPs) are water-selective channel proteins that allow rapid movement of water across the plasma membrane in secretory and adsorptive cells. Cyclic AMP and a protein kinase A (PKA)-dependent pathway have been shown to increase translocation from the intracellular space to the plasma membrane of bronchial epithelial, salivary gland, and sweat gland cells. Ezrin and other ERM proteins have a C-terminal FERM domain, which interacts with the cytoplasmic domain of membrane and scaffolding proteins, such as Na+/H+ exchange regulatory factors, and an N terminal actin-binding domain that binds to F-actin [11,12] These proteins play important roles in membrane protein and vesicle trafficking [13]. We investigated the effects of ezrin inhibition on translocation of AQP5 from the intracellular space to plasma membrane as well as membrane water permeability in mouse lung epithelial cells
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