CFTR modulators have revolutionized the treatment of individuals with cystic fibrosis (CF) by improving the function of existing protein. Unfortunately, almost half of the disease-causing variants in CFTR are predicted to introduce premature termination codons (PTC) thereby causing absence of full-length CFTR protein. We hypothesized that a subset of nonsense and frameshift variants in CFTR allow expression of truncated protein that might respond to FDA-approved CFTR modulators. To address this concept, we selected 26 PTC-generating variants from four regions of CFTR and determined their consequences on CFTR mRNA, protein and function using intron-containing minigenes expressed in 3 cell lines (HEK293, MDCK and CFBE41o-) and patient-derived conditionally reprogrammed primary nasal epithelial cells. The PTC-generating variants fell into five groups based on RNA and protein effects. Group A (reduced mRNA, immature (core glycosylated) protein, function <1% (n = 5)) and Group B (normal mRNA, immature protein, function <1% (n = 10)) variants were unresponsive to modulator treatment. However, Group C (normal mRNA, mature (fully glycosylated) protein, function >1% (n = 5)), Group D (reduced mRNA, mature protein, function >1% (n = 5)) and Group E (aberrant RNA splicing, mature protein, function > 1% (n = 1)) variants responded to modulators. Increasing mRNA level by inhibition of NMD led to a significant amplification of modulator effect upon a Group D variant while response of a Group A variant was unaltered. Our work shows that PTC-generating variants should not be generalized as genetic 'nulls' as some may allow generation of protein that can be targeted to achieve clinical benefit.

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variants primary nasal epithelial modulator treatment core glycosylated protein function modulators rna nmd cftr mrna protein diseasecausing nonsense absence of fulllength cftr premature termination codons frameshift

Neeraj Sharma,Taylor A Evans,Matthew J Pellicore,Emily Davis,Melis A Aksit,Allison F McCague,Anya T Joynt,Zhongzhu Lu,Sangwoo T Han,Arianna F Anzmann,Anh-Thu N Lam,Abigail Thaxton,Natalie West,Christian Merlo,Laura B Gottschalk,Karen S Raraigh,Patrick R Sosnay,Calvin U Cotton,Garry R Cutting,.Capitalizing on the heterogeneous effects of CFTR nonsense and frameshift variants to inform therapeutic strategy for cystic fibrosis.. 14 (11),.

Neeraj Sharma,Taylor A Evans,Matthew J Pellicore,Emily Davis,Melis A Aksit,Allison F McCague,Anya T Joynt,Zhongzhu Lu,Sangwoo T Han,Arianna F Anzmann,Anh-Thu N Lam,Abigail Thaxton,Natalie West,Christian Merlo,Laura B Gottschalk,Karen S Raraigh,Patrick R Sosnay,Calvin U Cotton,Garry R Cutting,"Capitalizing on the heterogeneous effects of CFTR nonsense and frameshift variants to inform therapeutic strategy for cystic fibrosis." 14

Neeraj Sharma,Taylor A Evans,Matthew J Pellicore,Emily Davis,Melis A Aksit,Allison F McCague,Anya T Joynt,Zhongzhu Lu,Sangwoo T Han,Arianna F Anzmann,Anh-Thu N Lam,Abigail Thaxton,Natalie West,Christian Merlo,Laura B Gottschalk,Karen S Raraigh,Patrick R Sosnay,Calvin U Cotton,Garry R Cutting,"Capitalizing on the heterogeneous effects of CFTR nonsense and frameshift variants to inform therapeutic strategy for cystic fibrosis."