Altered splicing of FGFR1 is associated with high tumor grade and stage and leads to increased sensitivity to FGF1 in bladder cancer.
Fibroblast growth factor receptors (FGFRs) play key roles in proliferation, differentiation, and tumorigenesis. Previously, we demonstrated that FGFR1 expression is increased in urothelial carcinoma cell lines and tumors, which promotes proliferation and survival via activation of the mitogen-activated protein kinase (MAPK) pathway. Here we examined splice variants of FGFR1 in both urothelial carcinoma cell lines and tumors. Two known FGFR1 IIIc splice variants (FGFR1α and FGFR1β) were expressed. FGFR1β lacks exon 3 of FGFR1α, removing the first Ig loop of the extracellular domain. Both isoforms were expressed at similar levels in normal urothelial cells, but FGFR1β was expressed at higher levels in most tumor cell lines. In tumor tissues, expression levels were higher than in controls, and the FGFR1β:FGFR1α ratio was significantly increased in association with tumor stage and grade. When FGFR1α and FGFR1β were expressed in urothelial cells, no differences in signaling were observed. FGFR1-induced proliferation paralleled MAPK pathway activation. The relative activation of FGFR1β and FGFR1α by all known mammalian FGFs was examined. Both isoforms were activated by the same FGFs, but the level of activation differed. FGFR1β showed higher affinity for low concentrations of FGF1, leading to enhanced signaling and increased proliferation. An FGFR1α-to-FGFR1β isoform switch and increased FGF1-induced activation of FGFR1β may result in a proliferative advantage that plays a key role during bladder tumor progression.
Tomlinson
Darren C
DC
Cancer Research UK Clinical Centre, Leeds Institute of Molecular Medicine, St James's University Hospital, Leeds, LS9 7TF, UK.
Knowles
Margaret A
MA
D002460:Cell Line; D016220:Fibroblast Growth Factor 1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D020033:Protein Isoforms / Q000235:genetics* / Q000378:metabolism; D012326:RNA Splicing; D051496:Receptor, Fibroblast Growth Factor, Type 1 / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D001749:Urinary Bladder Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology*
D020033:Protein Isoforms; D016220:Fibroblast Growth Factor 1; C496348:FGFR1 protein, human; D051496:Receptor, Fibroblast Growth Factor, Type 1