Shank2E mediates dexamethasone‐induced increase in membrane CFTR in human airway cells

Abstract

Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR), which often leads to severely reduced CFTR membrane abundance. Thus, many therapeutic approaches aim to increase membrane CFTR. Dexamethasone (Dex) up‐regulates serum‐ and glucocorticoid‐induced protein kinase (SGK1) and has been previously reported to increase CFTR in the plasma membrane of Xenopus oocytes (Sato et al., 2007) and CFPAC‐1 cells (Caohuy et al., 2009). The goal of this study was to test if Dex also increases membrane wt‐CFTR in human airway cells and to elucidate the underlying mechanism. Dex (50nM, 4h) increased membrane wt‐CFTR by 139%, and increased SGK1 mRNA and protein by 171% and 708%, respectively. We found that SGK1 did not directly phosphorylate CFTR and identified Shank2E, a scaffold protein with two SGK1 phosphorylation sites, as a potential intermediate regulatory protein. siRNA‐mediated knockdown of endogenous Shank2E reduced the Dex‐mediated increase in membrane CFTR by 59%. While over‐expression of wt‐Shank2E slightly enhanced this Dexeffect, over‐expression of a Shank2E mutant without SGK1 consensus sites had a dominant‐negative effect and reduced the Dex‐induced increase in membrane CFTR by 43%. Our results suggest that Shank2E mediates the Dex‐induced increase in membrane CFTR and that this effect is dependent on SGK1 phosphorylation of Shank2E.