Cellular and viral splicing factors can modify the splicing pattern of CFTR transcripts carrying splicing mutations

Variable levels of aberrantly spliced cystic fibrosis transmembrane conduct ance regulator (CFTR) transcripts were suggested to correlate with variable cystic fibrosis (CF) severity. We studied the effect of the cellular splic ing factors, hnRNP A1 and ASF/SF2, and their adenoviral analogues, E4-ORF6 and E4-ORF3, that promote exon skipping and/or exon inclusion, on the splic ing pattern of the CFTR mutation 3849+10 kb C --> T and the 5T allele, Thes e mutations can lead to cryptic exon inclusion and exon skipping, respectiv ely, Overexpression of the cellular factors promoted exon skipping of pre-m RNA transcribed from minigenes carrying the mutation (p5T or p3849M), This led to a substantial decrease in the level of correctly spliced mRNA transc ribed from p5T and generated correctly spliced mRNA transcribed from p3849M that was not found without overexpression of the factors. The viral factor , E4-ORF3, promoted exon inclusion and led to a substantial increase of the correctly spliced mRNA transcribed from the p5T, The factor, E4-ORF6, acti vated exon skipping and generated correctly spliced mRNA transcribed from p 3849M, Thus, overexpression of alternative splicing factors can modulate th e splicing pattern of CFTR alleles carrying splicing mutations. These resul ts are important for understanding the mechanism underlying phenotypic vari ability in CF and other genetic diseases.