Roscovitine is a proteostasis regulator that corrects the trafficking defect of F 508del‐ CFTR by a CDK ‐independent mechanism

Background and Purpose The most common mutation in cystic fibrosis ( CF ), F 508del, causes defects in trafficking, channel gating and endocytosis of the CF transmembrane conductance regulator ( CFTR ) protein. Because CF is an orphan disease, therapeutic strategies aimed at improving mutant CFTR functions are needed to target the root cause of CF . Experimental Approach Human CF airway epithelial cells were treated with roscovitine 100 μ M for 2 h before CFTR maturation, expression and activity were examined. The mechanism of action of roscovitine was explored by recording the effect of depleting endoplasmic reticulum ( ER ) Ca 2+ on the F 508del‐ CFTR /calnexin interaction and by measuring proteasome activity. Key Results Of the cyclin‐dependent kinase ( CDK ) inhibitors investigated, roscovitine was found to restore the cell surface expression and defective channel function of F 508del‐ CFTR in human CF airway epithelial cells. Neither olomoucine nor ( S )‐ CR 8, two very efficient CDK inhibitors, corrected F 508del‐ CFTR trafficking demonstrating that the correcting effect of roscovitine was independent of CDK inhibition. Competition studies with inhibitors of the ER quality control ( ERQC ) indicated that roscovitine acts on the calnexin pathway and on the degradation machinery. Roscovitine was shown (i) to partially inhibit the interaction between F 508del‐ CFTR and calnexin by depleting ER Ca 2+ and (ii) to directly inhibit the proteasome activity in a Ca 2+ ‐independent manner. Conclusions and Implications Roscovitine is able to correct the defective function of F 508del‐ CFTR by preventing the ability of the ERQC to interact with and degrade F 508del‐ CFTR via two synergistic but CDK ‐independent mechanisms. Roscovitine has potential as a pharmacological therapy for CF.