Sequence requirements for regulated RNA splicing of the human fibroblast growth factor receptor-1 α exon

Progression of astrocytes from a benign to a malignant phenotype is accompanied by a change in the RNA processing of the fibroblast growth factor receptor 1 (FGFR-1) gene. The level of a high affinity form of the FGFR-1 is dramatically elevated as a result of α-exon skipping during RNA splicing. In this paper we have been able to duplicate this tumor-specific RNA processing pathway by transfection of a chimeric minigene containing a 4-kilobase fragment of the human FGFR-1 gene (including the α-exon) into a variety of cell lines. In a transfected human astrocytoma cell line, α-exon skipping was consistently observed for RNA transcripts derived from both the chimeric minigene and endogenous gene expression. This exon skipping phenotype was dependent on the size of the flanking intron as deletions which reduced the introns to less than 350 base pairs resulted in enhanced α-exon inclusion. Increased exon inclusion was not sequence-specific as exon skipping could be restored with insertion of nonspecific sequence. Cell-specific exon recognition was maintained with a 375-nucleotide sequence inclusive and flanking the α-exon, provided that intron size was maintained. These results identify the minimal cis-regulatory sequence requirements for exclusion of FGFR-1 α-exon in astrocytomas.