Involvement of osteopontin in the matrix-degrading and proangiogenic changes mediated by nicotine in pancreatic cancer cells

Abstract

Background: Substantial evidence indicates that exposure to cigarette smoke is associated with an elevated risk of pancreatic ductal adenocarcinoma (PDA). However, the mechanisms underlying the effects of nicotine on the development or progression of PDA remain to be investigated. Previously, we showed that nicotine promotes the expression of osteopontin c (OPNc), an isoform of OPN protein that confers on cancer cells a migratory phenotype. In this study, we explored the potential prometastatic role of nicotine in PDA through studying its effect on the expression of matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor (VEGF) and evaluated the role of OPN in mediating these effects.

Materials and methods: MMP-9 and VEGF mRNA and protein were analyzed in PDA cells treated with or without nicotine (3-300 nM). Transient transfection and luciferase-labeled promoter studies evaluated the effects of OPNc and OPN protein on the transcription and translation of MMP-9 and VEGF. Real-time PCR and immunohistochemistry were used to analyze the mRNA expression levels and localization of OPN, MMP-9, and VEGF proteins in matched invasive human PDA and surrounding nonmalignant tissues.

Results and discussion: Nicotine significantly enhanced the expression of MMP-9 and VEGF mRNA and protein in PDA cells. Blocking OPN with siRNA or OPN antibody prevented the nicotine-mediated increase of both MMP-9 and VEGF. Transient transfection of OPNc gene in PDA cells or their treatment with recombinant OPN protein significantly (p < 0.05) increased MMP-9 and VEGF mRNA expression levels and induced their promoter activities. In invasive PDA lesions, MMP-9 mRNA levels were significantly (p < 0.005) higher in smokers vs. nonsmokers. VEGF protein co-localized with MMP-9 and OPN in the malignant ducts and correlated well with their higher levels in invasive PDA lesions.

Conclusions: Our data show for the first time that cigarette smoking and nicotine may contribute to PDA metastasis through inducing MMP-9 and VEGF and suggest that OPN plays a central role in mediating these effects. The presence of OPN as a downstream effector of nicotine that is capable of mediating its prometastatic effects in PDA cells is novel and could provide a unique therapeutic target to control pancreatic cancer aggressiveness, especially in the cigarette-smoking population.