*2.3. Cells*

The following cell cultures were employed: CFBE41o- and Fischer rat thyroid (FRT) cells with stable expression of F508del-CFTR (F508del-CBFE41o- and F508del-FRT, respectively) as well as CFBE41o- cells expressing a wild-type CFTR (wt-CFBE41o-) [29]. CFBE41o- cells were cultured in minimal essential medium (MEM), and FRT cells were cultured in Coon's modified Ham's F-12 medium (Sigma-Aldrich, St. Luis, MO, USA), both supplemented with 10% fetal calf serum, 2 mM L-glutamine, and antibiotics (0.1 mg/mL of penicillin and streptomycin), at 37 ◦C and 5% CO2 in 75 cm<sup>2</sup> flasks. Stable expression is maintained by adding puromycin (0.5 μg/mL or 2 μg/mL for wt-CBFE41o- or F508del-CBFE41o-, respectively) and 0.6 mg/mL zeocin for FRT cell line to the complete culture medium. CF and non-CF primary bronchial cells were from the University of Pittsburgh CF center cell culture core facility. They were cultured in flasks and maintained at air–liquid interface (ALI) until being fully differentiated as polarized cells for experiments.
