Multi-physiopathological consequences of the c.1392G>T CFTR mutation revealed by clinical and cellular investigations

This study combines a clinical approach and multiple level cellular analyses to determine the physiopathological consequences of the c.1392G>T (p.Lys464Asn) CFTR exon 10 mutation, detected in a CF patient with a frameshift deletion in trans and a TG(11)T(5) in cis. Minigene experiment, with different TG(m)T(n) alleles, and nasal cell mRNA extracts were used to study the impact of c.1392G>T on splicing in both in cellulo and in vivo studies. The processing and localization of p.Lys464Asn protein were evaluated, in cellulo, by western blotting analyses and confocal microscopy. Clinical and channel exploration tests were performed on the patient to determine the exact CF phenotype profile and the CFTR chloride transport activity. c.1392G>T affects exon 10 splicing by inducing its complete deletion and encoding a frameshift transcript. The polymorphism TG(11)T(5) aggravates the effects of this mutation on aberrant splicing. Analysis of mRNA obtained from parental airway epithelial cells confirmed these in cellulo results. At the protein level the p.Lys464Asn protein showed neither maturated form nor membrane localization. Furthermore, the in vivo channel tests confirmed the absence of CFTR activity. Thus, the c.1392G>T mutation alone or in association with the TG repeats and the poly T tract revealed obvious impacts on splicing and CFTR protein processing and functionality. The c.[T(5); 1392G>T] complex allele contributes to the CF phenotype by affecting splicing and inducing a severe misprocessing defect. These results demonstrate that the classical CFTR mutations classification is not sufficient: in vivo and in cellulo studies of a possible complex allele in a patient are required to provide correct CFTR mutation classification, adequate medical counseling, and adapted therapeutic strategies.