Enhanced cell-surface stability of rescued ΔF508 cystic fibrosis transmembrane conductance regulator (CFTR) by pharmacological chaperones

Misfolded proteins destined for the cell surface are recognized and degraded by the ERAD [ER (endoplasmic reticulum) associated degradation] pathway. TS (temperature-sensitive) mutants at the permissive temperature escape ERAD and reach the cell surface. In this present paper, we examined a TS mutant of the CFTR [CF (cystic fibrosis) transmembrane conductance regulator], CFTR Delta F508, and analysed its cell-surface trafficking after rescue [r Delta F508 (rescued Delta F508) CFTR]. We show that r Delta F508 CFTR endocytosis is 6-fold more rapid (similar to 30% per 2.5 min) than WT (wild-type, similar to 5% per 2.5 min) CFTR at 37 degrees C in polarized airway epithelial cells (CFBE41o(-)). We also investigated r Delta F508 CFTR endocytosis under two further conditions: in culture at the permissive temperature (27 degrees C) and following treatment with pharmacological chaperones. At low temperature, r Delta F508 CFTR endocytosis slowed to WT rates (20% per 10 min), indicating that the cell-surface trafficking defect of r Delta F508 CFTR is TS. Furthermore, r Delta F508 CFTR is stabilized at the lower temperature; its half-life increases from <2 h at 37 degrees C to >8 h at 27 degrees C. Pharmacological chaperone treatment at 37 degrees C corrected the r Delta F508 CFTR internalization defect, slowing endocytosis from similar to 30% per 2.5 min to similar to 5% per 2.5 min, and doubled Delta F508 surface half-life from 2 to 4 h. These effects are Delta F508 CFTR-specific, as pharmacological chaperones did not affect WT CFTR or transferrin receptor internalization rates. The results indicate that small molecular correctors may reproduce the effect of incubation at the permissive temperature, not only by rescuing Delta F508 CFTR from ERAD, but also by enhancing its cell-surface stability.