Molecular and functional characterization of CBAVD-causing mutations located in CFTR nucleotide-binding domains.

ABSTRACT

BACKGROUND: About 98% of male affected with cystic fibrosis (CF [MIM 219700]) are infertile due to bilateral absence of vas deferens (CBAVD [MIM 277180]), which makes up 1-2 % of all cases with male infertility. A previous screening of the entire coding region of the cystic fibrosis transmembrane conductance regulator gene (CFTR [MIM 602421]) in CBAVD patients identified three novel mutations P439S is located in the first nucleotide binding domain (NBD1) of CFTR, whereas P1290S and E1401K are located in NBD2. METHODS: We analysed the effects of these novel mutations on CFTR processing and chloride (Cl(-)) channel activity. RESULTS: Although maturation patterns were not affected, total amounts of mature P439S-CFTR and P1290S-CFTR were reduced. Confocal microscopy showed correct membrane localisation of E1401K-CFTR, whereas P439S-CFTR and P1290S-CFTR mutants were located mainly in the cytoplasm. Iodide influx assay and whole-cell patch clamp demonstrated significantly reduced cAMP-dependent anion conductances for all three mutants. CONCLUSION: Dysfunction of CFTR is caused by either defective CFTR trafficking (P439S and P1290S) or/and Cl- channel function (P1290S and E1401K). Thus reduced Cl- conductance caused by the three CFTR mutations affects normal development of vas deferens and leads to CBAVD, but the remaining function is sufficient to prevent other typical CF symptoms.