Oncoprotein fos activation in epithelial-cells induces an epitheliomesenchymal conversion and changes the receptor encoded by the fgfr-2 messenger-RNA from k-sam to bek.

Activation of c-Fos, by using an inducible c-Fos estrogen receptor fusion protein, triggers the epitheliofibroblastoid cell conversion of mouse mammary epithelial cells. We show that this change in phenotype is accompanied by a definitive switch of the fibroblast growth factor receptor 2 from K-SAM to BEK. This splicing switch occurs a few hours after estrogen stimulation. Our data suggest that Fos proteins could be important in modulating the FGFR-2 splicing choice. Moreover, these observations reinforce previous evidence that the BEK/K-SAM choice is strictly tissue-specific: the K-SAM exon is expressed exclusively in epithelial cells, the BEK exon in cells of the fibroblastic type.