Deletion of CFTR translation start site reveals functional isoforms of the protein in CF patients.
OBJECTIVE
Mutations in the CFTR gene cause Cystic Fibrosis (CF) the most common life-threatening autosomal recessive disease affecting Caucasians. We identified a CFTR mutation (c.120del23) abolishing the normal translation initiation codon, which occurs in two Portuguese CF patients. This study aims at functionally characterizing the effect of this novel mutation.


METHODS
RNA and protein techniques were applied to both native tissues from CF patients and recombinant cells expressing CFTR constructs to determine whether c.120del23 allows CFTR protein production through usage of alternative internal codons, and to characterize the putative truncated CFTR form(s).


RESULTS
Our data show that two shorter forms of CFTR protein are produced when the initiation translation codon is deleted indicating usage of internal initiation codons. The N-truncated CFTR generated by this mutation has decreased stability, very low processing efficiency, and drastically reduced function. Analysis of mutants of four methionine codons downstream to M1 (M82, M150, M152, M156) revealed that each of the codons M150/M152/M156 (exon 4) can mediate CFTR alternative translation.


CONCLUSIONS
The CFTR N-terminus has an important role in avoiding CFTR turnover and in rendering effective its plasma membrane traffic. These data correlate well with the severe clinical phenotype of CF patients bearing the c.120del23 mutation.
Ramalho
Anabela S
AS
University of Lisboa, Centre for Biodiversity, Functional and Integrative Genomics, Lisboa, Portugal.
Lewandowska
Marzena A
MA
Farinha
Carlos M
CM
Mendes
Filipa
F
Gonçalves
Juan
J
Barreto
Celeste
C
Harris
Ann
A
Amaral
Margarida D
MD
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002648:Child; D018387:Codon, Initiator; D006224:Cricetinae; D003550:Cystic Fibrosis / Q000235:genetics*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D005091:Exons; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D010641:Phenotype; D014176:Protein Biosynthesis; D020033:Protein Isoforms / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D017384:Sequence Deletion; D014162:Transfection
D018387:Codon, Initiator; D020033:Protein Isoforms; D012333:RNA, Messenger; D019005:Cystic Fibrosis Transmembrane Conductance Regulator