Enhanced Ca2+ entry due to Orai1 plasma membrane insertion increases IL-8 secretion by cystic fibrosis airways

Cystic fibrosis (CF) is caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR). The most common mutation, Delta F508, causes retention of CFTR in the endoplasmic reticulum (ER). Some CF abnormalities can be explained by altered Ca2+ homeostasis, although it remains unknown how CFTR influences calcium signaling. This study examined the novel hypothesis that store-operated calcium entry (SOCE) through Orai1 is abnormal in CF. The significance of Orai1-mediated SOCE for increased interleukin-8 (IL-8) expression in CF was also investigated. CF and non-CF human airway epithelial cell line and primary cells (obtained at lung transplantation) were used in Ca2+ imaging, electrophysiology, and fluorescence imaging experiments to explore differences in Orai1 function in CF vs. non-CF cells. Protein expression and localization was assessed by Western blots, cell surface biotinylation, ELISA, and image correlation spectroscopy (ICS). We show here that store-operated Ca2+ entry (SOCE) is elevated in CF human airway epithelial cells (hAECs; similar to 1.8- and similar to 2.5-fold for total Ca-i(2+) increase and Ca2+ influx rate, respectively, and similar to 2-fold increase in the I-CRAC current) and is caused by increased exocytotic insertion (similar to 2-fold) of Orai1 channels into the plasma membrane, which is normalized by rescue of Delta F508-CFTR trafficking to the cell surface. Augmented SOCE in CF cells is a major factor leading to increased IL-8 secretion (similar to 2-fold). CFTR normally down-regulates the Orai1/stromal interaction molecule 1 (STIM1) complex, and loss of this inhibition due to the absence of CFTR at the plasma membrane helps to explain the potentiated inflammatory response in CF cells.-Balghi, H., Robert, R., Rappaz, B., Zhang, X., Wohlhuter-Haddad, A., Evagelidis, A., Luo, Y., Goepp, J., Ferraro, P., Romeo, P., Trebak, M., Wiseman, P. W., Thomas, D. Y., Hanrahan, J. W. Enhanced Ca2+ entry due to Orai1 plasma membrane insertion increases IL-8 secretion by cystic fibrosis airways. FASEB J. 25, 4274-4291 (2011). www.fasebj.org