Ligand activation of alternatively spliced fibroblast growth factor receptor-1 modulates pancreatic adenocarcinoma cell malignancy.

Pancreatic adenocarcinoma continues to be a devastating tumor (28,000 new cases per year in the United States; 10% 2-year survival). Pancreatic adenocarcinoma frequently (90% of the time) overexpresses fibroblast growth factor ligands (FGF-1 and FGF-2) and alternatively spliced high-affinity receptors (FGFR-1beta) (FGFR-1alpha was previously found in normal pancreatic tissue). To study the significance of this observation in vitro, PANC-1 cells were stably transfected via the pMEXneo vector containing FGFR-1alpha (PANC-1alpha) or FGFR-1beta (PANC-1beta) isoforms. Cells were treated with 1 mg/ml of 5-fluorouracil. Cells were evaluated for growth inhibition, apoptosis (propidium iodide staining and flow cytometry, caspase 3 activation) and for Bcl-x(L)/BAX expression (by Western blot analysis). In vivo, 7 x 10(6) cells of each isoform were injected into nude Balb/c mice for xenograft formation (N = 10). Compared to PANC-1beta (9%) in vitro, 5-fluorouracil-induced death was significantly (P < 0.05) increased in PANC-1alpha (20%) at 24 hours. Increased cell death in PANC-1alpha was mediated by activated caspase 3 and was correlated with decreased expression of Bcl-x(L)/BAX. In vivo, PANC-1beta readily demonstrated formation of tumor xenograft at 2 weeks, whereas PANC-1alpha did not form tumors. Alternative splicing of FGFR-1 to the beta isoform appears to correlate with pancreatic adenocarcinoma cell growth in vivo and resistance to chemotherapy. Inhibition of FGFR-1 splicing or overexpression of FGFR-1alpha inhibits pancreatic adenocarcinoma cell growth in vivo and restores cytotoxic responses to chemotherapy, thereby suggesting the basis of rational interventional strategies for this devastating tumor.