Osteopontin (OPN) is a secreted phosphoprotein that confers on cancer cells a migratory phenotype. We showed recently that nicotine, a major risk factor in pancreatic ductal adenocarcinoma (PDA), increases OPN expression in PDA cells. An OPN splice variant, OPNc, supports anchorage independence and maybe the most potent OPN isoform to convey metastatic behavior. In this study, we tested the effect of nicotine on OPNc expression, and analyzed the correlation between total OPN/OPNc levels and patients’ smoking history.
Real time PCR and UV-light-illumination of ethidium-bromide staining were used to examine the mRNA expression in tissue and in PDA cells treated with or without nicotine (3-300 nM). OPN and OPNc were localized by immunohisotchemistry, and ELISA was used to analyze OPN serum levels.
Nicotine treatment of PDA cells selectively induced denovo expression of OPNc. OPNc was found in 87% of invasive PDA lesions, of which 73% were smokers. The levels of OPNc correlated well with higher expression levels of total OPN in the tissue and serum from patients with invasive PDA.
Our data suggest that smoking and nicotine may contribute to PDA metastatic potential through promoting OPNc expression. Although the direct role of OPNc in PDA progression is not defined, OPNc may have value as a diagnostic and prognostic marker, especially in invasive PDA.