INDUCTION OF AQUAPORIN-3 BY CORTICOSTEROID IN A HUMAN AIRWAY EPITHELIAL-CELL LINE

Although aquaporin 3 (AQP3) is expressed in many tissues in the kidney , gastrointestinal tract, lung, and other organs, its physiological si gnificance in the body still remains to be clarified. To determine whe ther AQP3 expression is regulated by dexamethasone in human airway epi thelium, we studied mRNA expression, protein expression, and water per meability of the eel membrane in a human airway epithelial cell line ( A549 cells). Expression of AQP3 mRNA and protein was studied by Northe rn blot analysis and immunoblot analysis, and osmotic water permeabili ty (P-f) was measured by a stopped-flow light-scattering method. Expre ssion of AQP3 mRNA and protein was detectable in A549 cells and was st imulated by dexamethasone. P-f in A549 cells after incubation with dex amethasone was similar to 2.5-fold greater than that without dexametha sone. Moreover, this dexamethasone-induced increase in P-f was inhibit ed after treatment with HgCl2. In conclusion, the present study shows that A549 cells express AQP3 and that dexamethasone upregulates the ex pression of AQP3 and increases the water permeability of the cell memb rane. Dexamethasone-regulated AQP3 expression might be important in ce rtain forms of pulmonary diseases accompanied by airway hypersecretion that are treated by corticosteroid administration.