Previous immunohistochemical studies have demonstrated enhanced appearance of FGF-1 and nitrotyrosine, a footprint of reactive nitrogen species peroxynitrite (ONOO-), in human pancreatic adenocarcinoma. We have examined the consequences of constitutive exposure to FGF-1 in nontumorigenic rat ductal epithelial cells (ARIP). ARIP cells were transduced with either a secreted chimera of FGF-1, ARIP(FGF-1), or a control plasmid, 65 RIP(βg). These cells were evaluated for alteration in growth and morphology, responses to ONOO- (protein tyrosine nitration/phosphorylation), and in vivo tumor formation. ARIP(FGF-1) cells, in contrast to 65 RIP(βg), demonstrated a transformed morphology, a 2-fold increased growth rate, and enhanced protein tyrosine phosphorylation. Treatment with 150 μM ONOO- resulted in 86 and 7% (p < .01) death of ARIP(βg) and ARIP(FGF-1), respectively. Exposure of 65 RIP(βg) cells to ONOO- enhanced tyrosine phosphorylation and tyrosine nitration of several polypeptides. Cell signaling by FGF-1 enhanced both phosphorylation and nitration of tyrosine residues in target proteins modified by ONOO-. ARIP(βg) cells failed to exhibit tumor formation in nude mice, but at d 7 in vivo cells were TUNEL and nitrotyrosine positive and FGF-1 negative. ARIP(FGF-1) cells readily formed tumor nodules, exhibiting features of pancreatic adenocarcinoma and demonstrating FGF-1-positive, nitrotyrosine-positive, and TUNEL-negative epithelium. These results suggest an interdependent role between FGF-1 and ONOO- during the development and progression of pancreatic adenocarcinoma. © 2001 Elsevier Science Inc.