Regulation der Fibroblastenwachstumsfaktorenrezeptor-1 III-mRNA-Splicevarianten in Pankreaskarzinomzellen

Background: Fibroblast growth factors (FGFs) are mitogenic polypeptides signalling via trans-membrane FGF receptors (FGFRs). Alterations in their expression profile can result in significant changes of the effects on the target cells. In our previous work we characterized the effects of the Ig-domain III mRNA splice variants of FGFR1 (FGFR1-IIIb and FGFR1-IIIc) in regard to the transforming potential on ductal pancreatic cells. Overexpression of FGFR1-IIIc transformed TAKA-1 pancreatic ductal cells enhanced the malignant phenotype of pancreatic cancer cells. In contrast, overexpression of FGFR1-IIIb inhibited the transformed phenotype of pancreatic cancer cells. Nothing is presently known about the regulation of the expression of the splice variants in pancreatic cancer cells. Aim: We investigated the expression and regulation of the human FGFR1-IIIb and FGFR1-IIIc mRNA splice variants in cultured pancreatic cancer cells. Methods: Expression of FGFR1 was determined by immunoblot and Northern blot analysis, while the expression of the specific splice variants was characterized by RT-PCR in relation to cell density and growth factor stimulation. Results: Cultured pancreatic cancer cells (ASPC-1, BxPC-3, COLO-357, Mia PaCa-2, PANC-1, T3M4) showed a coexpression of both variants. FGFR1-IIIc was the predominant receptor in all cell lines. CAPAN-1 cells only expressed very low levels of FGFR1-IIIc and no FGFR1-IIIb. At high cell density, FGFR1-IIIc expression remained constant, while FGFR1-IIIb mRNA expression was downregulated. Incubation of Mia PaCa-2 and PANC-1 cells with EGF, IGF-I or FGF-2 resulted in a strong induction of FGFR1- IIIc expression. FGFR1-IIIb expression was not altered by EGF or IGF-I. In contrast to EGF and IGF-I and to its effect on FGFR1-IIIc, FGF-2 significanlty inhibited FGFR1-IIIb expression in both cell lines. Similar effects on FGFR1-IIIb were achieved by FGF-5. Conclusion: Besides its direct effects on cell proliferation and angiogenesis FGF-2 is able to enhance the expression of FGFR1-IIIc and reduce the expression of FGFR1-IIIb enhancing the malignant phenotype of pancreatic cancer cells.