Die humane IIIb-mRNA-Splicevariante des FGFR1 ist ein funktionsfähiger Tyrosinkinaserezeptor und hemmt das Wachstum von Pankreaskarzinomzellen

Abstract

Background: Fibroblast growth factors (FGFs) and their high-affinity FGF receptors (FGFR) are involved in various biological processes including angiogenesis and mitogenesis. Several FGFs are overexpressed in human pancreatic cancer and high FGF expression correlates with poor prognosis. FGFs act by binding to specific FGFRs. Additional to the existence of 4 FGFRs several mRNA splice variants have been described exhibiting distinct ligand-binding properties. We have recently demonstrated that the IIIc variant of FGFR1 has transforming capacities after expression in normal TAKA-1 pancreatic ductal cells which do not express endogenous FGFR1. However, nothing is presently known about the human IIIb variant which has been recently subcloned. The aim of this study was to characterize the effect of FGFR1 IIIb expression in pancreatic ductal cells. Methods: The full-length human FGFR1-IIIb cDNA was expressed in a stable manner in TAKA-1 normal pancreatic ductal cells and PANC-1 human pancreatic cancer cells. Clones were selected by G418 and screened using immunoblot and Northern blot analysis. Cell counting, MTT assays and soft agar were used to assess the effect of FGFR-1 IIIb expression on cell growth and colony formation. Immunoprecipitation, p42/p44 and p38 MAP kinase assays were used to investigate the effect of FGFs on intracellular signalling. Results: FGFR1-IIIb was expressed in a stable manner in TAKA-1 and PANC-1 cells. The growth of TAKA-1 cells expressing IIIb was significantly enhanced by FGF-1, FGF-2 and FGF-4 while no effect was seen in wild-type or control transfected TAKA-1 cells. FGF-1 and FGF-2 enhanced tyrosine phosphorylation of fibroblast growth factor receptor substrate-2 (FRS2) and p42/p44 and p38 kinase activity. In comparison to control transfected clones the basal growth of TAKA-1 and PANC-1 clones expressing FGFR1-IIIb was inhibited. In addition, the colony formation was significantly reduced after expression of IIIb in these cells. Conclusion: The human IIIb-mRNA splice variant of FGFR1 is a functional fibroblast growth factor receptor. In contrast to the IIIc variant of FGFR1 the IIIb variant inhibits the transforming ability of human pancreatic cancer cells.