EXPRESSION OF FGFR1-IIIB INHIBITS PANCREATIC CANCER CELL GROWTH IN VITRO AND IN VIVO

Abstract

Fibroblast growth factors (FGFs) and their high affinity receptors (FGFRs) play important roles in many malignancies being involved in processes like angiogenesis and mitogenesis. Ligand binding specificities are determined predominantly by alternative mRNA splicing of the second half of Ig-like domain III of the FGFRs. Cells of epithelial origin mostly express IIIb and cells of mesenchymal origin more often the IIIc variants. We recently demonstrated that FGFR1-IIIc dramatically enhanced the transforming potential of TAKA-1 pancreatic ductal cells and that human pancreatic carcinoma tissue and cultured pancreatic cancer cells predominantly express FGFR1-IIIc. Presently only little is known about the recently cloned human FGFR1-IIIb. The aim of this study was to characterize possible functions and the transforming potential of human FGFR1-IIIb in pancreatic ductal cells. In-situ-hybridization demonstrated that FGFR1-IIIb localized in normal pancreatic acinar and ductal pancreatic cancer cells. Full-length human FGFR1-IIIb was stably expressed in TAKA-1 pancreatic ductal cells and PANC-1 pancreatic cancer cells next. FGFR1-IIIb was expressed as a glycosylated 110 kDa protein. Basal anchorage-dependent and-independent growth, determined by MTT and soft agar assays, respectively, was significantly inhibited by at least 35% and 75%, respectively. These effects were paralleled by a reduced phosphorylation of p44/42 MAPK and increased p38 MAPK and c-Jun-N-terminal kinase activity. Additionally, expression of FGFR1-IIIb in PANC-1 cells reduced single cell movement determined by time-lapse microscopy and invasion in the Boyden chamber assay. Xenograft formation was inhibited. Thus, only thirty of 40 sites injected with FGFR1-IIIb expressing PANC-1 cells developed tumors compared to 38 of 40 sites injected with control-transfected cells. The growth of the developing xenograft tumors and their KI-67 labeling index were further significantly reduced. Establishment of clones in MIA PaCa-2 cells showed inhibitory functions by FGFR1-IIIb expression and enhancement of proliferation by IIIc. In this study, for the first time, functions of human FGFR1-IIIb are described in the pancreas demonstrating inhibition of transformation in contrast to FGFR1-IIIc in vitro and in vivo. Our results suggest that exon switching of FGFR1 from IIIc to IIIb may significantly influence the transforming potential of pancreatic cancer cells.