Polypyrimidine tract-binding protein represses splicing of a fibroblast growth factor receptor-2 gene alternative exon through exon sequences

The fibroblast growth factor receptor (FGFR)-2 gene contains two mutually e xclusive exons, K-SAM and BEK. We made a cell line designed to become drug- resistant on repression of BEK exon splicing. One drug-resistant derivative of this line carried an insertion within the BEK exon of a sequence contai ning at least two independent splicing silencers. One silencer was a pyrimi dine-rich sequence, which markedly increased binding of polypyrimidine trac t-binding protein to the BEK exon. The BEK exon binds to polypyrimidine tra ct-binding protein even in the silencer's absence. Several exonic pyrimidin e runs are required for this binding, and they are also required for overex pression of polypyrimidine tract-binding protein to repress BEK exon splici ng. These results show that binding of polypyrimidine tract-binding protein to exon sequences can repress splicing. In epithelial cells, the K-SAM exo n is spliced in preference to the BEK exon, whose splicing is repressed. Mu tation of the BEK exon pyrimidine runs decreases this repression. If this m utation is combined with the deletion of a sequence in the intron upstream from the BEK exon, a complete switch from K-SAM to BEK exon splicing ensues . Binding of polypyrimidine tract binding protein to the BEK exon thus part icipates in the K-SAM/BEK alternative splicing choice.