Control of BEK and K-SAM splice sites in alternative splicing of the fibroblast growth factor receptor 2 pre-mRNA.

Abstract

The fibroblast growth factor receptor 2 gene pre-mRNA can be spliced by using either the K-SAM exon or the BEK exon. The exon chosen has a profound influence on the ligand-binding specificity of the receptor obtained. Cells make a choice between the two alternative exons by controlling use of both exons. Using fibroblast growth factor receptor 2 minigenes, we have shown that in cells normally using the K-SAM exon, the BEK exon is not used efficiently even in the absence of the K-SAM exon. This is because these cells apparently express a titratable repressor of BEK exon use. In cells normally using the BEK exon, the K-SAM exon is not used efficiently even in the absence of a functional BEK exon. Three purines in the K-SAM polypyrimidine tract are at least in part responsible for this, as their mutation to pyrimidines leads to efficient use of the K-SAM exon, while mutating the BEK polypyrimidine tract to include these purines stops BEK exon use.Multiple alternative splicing events lead to synthesis from the fibroblast growth factor (FGF) receptor 2 (FGFR-2) gene of a family of receptors differing in defined parts of their extra-and intracellular domains (reviewed in references 19 and 21). In its first described version, FGFR-2 contains an extracellular domain made up of three immunoglobulin-like domains (Ig domains), with a stretch of consecutive acidic residues, the acid box, separating the first two Ig domains. A particularly interesting alternative splice concerns sequences of the mRNA coding for the carboxy-terminal half of the third Ig domain, as this region of the receptor appears to be part of the ligand-binding site. Two alternative exons (K-SAM and BEK) code for this part of FGFR-2 (4,20,29,40). Use of the K-SAM exon results in synthesis of a high-affinity receptor for acidic FGF and keratinocyte growth factor (KGF), while use of the BEK exon yields a high-affinity receptor for acidic FGF and basic FGF (16,29,40). Correct control of the BEK-K-SAM splicing choice appears important, since this choice can influence a cell's response to growth factors that it produces itself as well as to those present in its environment. Consistent with this view, we and others have shown that a given cell line uses predominantly one of the two alternative exons, use of the other exon being sufficiently rare that it cannot be detected in a reverse transcriptase (RT)-polymerase chain reaction (PCR) analysis (4, 29). Thus, epithelial cells express the K-SAM form of FGFR-2 but do not produce KGF, an epithelial cell-specific growth factor, while fibroblasts, which secrete KGF, express the BEK form. The consequences of a "wrong" choice can be disastrous: forced expression of the K-SAM receptor form in fibroblasts producing KGF leads to transformation (30).We are interested in determining the mechanisms involved in discrimination between the BEK and K-SAM exons. Pre-mRNA sequence elements representing potential targets for control of splicing include the 5' and 3' splice sites, the branch point sequence, and the associated polypy...

Fibroblast growth factor-5 stimulates mitogenic signaling and is overexpressed in human pancreatic cancer: evidence for autocrine and paracrine actions

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Re‐programming of expression of the KGFR and bek variants of fibroblast growth factor receptor 2 during limb regeneration in newts (Notophthalmus viridescens)

“…These observations suggest that the dorsoventral gradients of the FGFR2 variants in both embryonic development and limb regeneration are governed by the same homeotic genes. Interestingly, Gilbert et al (1993) showed, using FGFR2 minigenes, that cells normally using exon IIIb apparently express a titratable repressor which excludes the splicing of exon IIIc. It was further proposed that in the absence of the repressor, exon IIIc is preferred over exon IIIb due to the three purines in the exon IIIb poly- These are adjacent sections taken from the same limb.…”

Alternative splicing in fibroblast growth factor receptor 2 is associated with induced epithelial-mesenchymal transition in rat bladder carcinoma cells.

“…The fact that some cells still expressed a mesenchymal phenotype after 4 d of KGF treatment ( Figures 1B and 8B) can probably be explained by the relative heterogeneity of the NBT-II cells. As seen in Figure 7 and Figure 8, the RNA switch is not total, and some cells probably express enough FGFR2b/KGFR to remain induced and maintain (Gilbert et al, 1993). During embryonic development, a linkage between FGFR expression and differentiation process involving phenotype transition may also occur.…”