Expression and regulation of nicotine receptor and osteopontin isoforms in human pancreatic ductal adenocarcinoma.

Osteopontin (OPN) is a secreted phospho-protein that confers on cancer cells a migratory phenotype. We have recently shown that nicotine, a risk factor in pancreatic ductal adenocarcinoma (PDA), induces an alpha7-nicotine acetylcholine receptor (α7-nAChR)-mediated increase of OPN in PDA cells. In this study, we tested nicotine's effect on the expression of OPN splice variants (OPNa, b, c) in PDA cells. We also analyzed the correlation between patients' smoking history with OPN and α7-nAChR levels. RT-PCR and UV-light-illumination of ethidium-bromide staining were used to examine the mRNA expression in tissue and PDA cells treated with or without nicotine (3-300 nM). Localization of total OPN, OPNc and α7-nAChR was analyzed by immunohistochemistry, and their mRNA tissue expression levels were correlated with the patients' smoking history. PDA cells expressed varying levels of OPNa, OPNb, and α7-nAChR. Nicotine treatment selectively induced denovo expression of OPNc and increased α7-nAChR expression levels. In PDA tissue, OPNc was found in 87% of lesions, of which 73% were smokers. OPNc and total OPN levels were correlated in the tissue from patients with invasive PDA. Nicotine receptor was expressed in the invasive and premalignant lesions without clear correlation with smoking history. We show here for the first time that α7-nAChR is expressed in PDA cells and tissues and is regulated by nicotine in PDA cells. This, together with our previous findings that α7-nAChR mediates the metastatic effects of nicotine in PDA, suggest that combined targeting of α7-nAChR and OPNc could be a valid novel therapeutic strategy for invasive PDA, especially in the smoking population.

Expression of a prometastatic splice variant of osteopontin, OPNC, in human pancreatic ductal adenocarcinoma.

BACKGROUND: Osteopontin (OPN) is a secreted phosphoprotein that confers on cancer cells a migratory phenotype. We demonstrated 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. METHODS: Real-time polymerase chain reaction and ultraviolet 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 nmol/L). OPN and OPNc were localized by immunohistochemistry, and an enzyme-linked immunosorbent assay was used to analyze OPN serum levels. RESULTS: Nicotine treatment of PDA cells selectively induced de novo expression of OPNc. OPNc was found in 87% of invasive PDA lesions, of which 73% were found in smokers. The levels of OPNc correlated well with higher expression levels of total OPN in the tissue and serum from patients with invasive PDA. CONCLUSION: 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.

Induction of osteopontin expression by nicotine and cigarette smoke in the pancreas and pancreatic ductal adenocarcinoma cells.

Pancreatic ductal adenocarcinoma (PDA) is a lethal disease with etiological association with cigarette smoking. Nicotine, an important component of cigarettes, exists at high concentrations in the bloodstream of smokers. Osteopontin (OPN) is a secreted phosphoprotein that confers on cancer cells a migratory phenotype and activates signaling pathways that induce cell survival, proliferation, invasion, and metastasis. Here, we investigated the potential molecular basis of nicotine's role in PDA through studying its effect on OPN. Nicotine significantly (p < 0.02) increased OPN mRNA and protein secretion in PDA cells through activation of the OPN gene promoter. The OPN mRNA induction was inhibited by the nicotinic acetylcholine receptor antagonist, mechamylamine. Further, the tyrosine kinase inhibitor genistein inhibited the nicotine-mediated induction of OPN, suggesting that mitogen activated protein kinase signaling mechanism is involved. Nicotine activated the phosphorylation of ERK1/2, but not p38 or c-Jun NH2-terminal MAP kinases. Inhibition of ERK1/2 activation reduced the nicotine-induced OPN synthesis. Rats exposed to cigarette smoke showed a dose-dependent increase in pancreatic OPN that paralleled the rise of pancreatic and plasma nicotine levels. Analysis of cancer tissue from invasive PDA patients, the majority of whom were smokers, showed the presence of significant amounts of OPN in the malignant ducts and the surrounding pancreatic acini. Our data suggest that nicotine may contribute to PDA pathogenesis through upregulation of OPN. They provide the first insight into a nicotine-initiated signal transduction pathway that regulates OPN as a possible tumorigenic mechanism in PDA.