Nicotine promotes gastric tumor growth and neovascularization by activating extracellular signal-regulated kinase and cyclooxygenase-2.
Early studies revealed that cigarette smoke promotes gastric cancer growth through the induction of cyclooxygenase-2 (COX-2). Nicotine, one of the active ingredients in cigarette smoke, has detrimental effects in the stomach. To date, there is no direct evidence to validate the effect of nicotine on gastric tumor growth and its carcinogenic mechanism(s). We therefore investigated whether nicotine could promote tumor growth and neovascularization in vivo, and the biological mechanism(s) in connection with the signaling cascade involving COX-2 and extracellular signal-regulated protein kinase (ERK). Athymic nude mice, with gastric cancer cells (AGS) orthotopically implanted into the gastric wall, treated with nicotine (50 or 200 microg/ml) in their drinking water for 3 months developed larger tumor areas than mice in the control group. Nicotine further increased proliferating cellular nuclear antigen (PCNA) staining and microvessel density by 70 and 30%, respectively, with concomitant activation of ERK phosphorylation, COX-2 and vascular endothelial growth factor (VEGF) expression in the tumors. Intraperitoneal administration of a selective COX-2 inhibitor (SC-236, 2 mg/kg) prevented the nicotine-induced tumor growth and neovascularization dose-dependently. Consistent with our animal model, an in vitro study also demonstrated that incubation with nicotine (50-200 microg/ml) for 5 h stimulated cell proliferation dose-dependently and increased COX-2 expression, prostaglandin E(2) (PGE(2)) and VEGF release, as well as activation of ERK phosphorylation. Pre-treatment with specific mitogen-activated protein kinase kinase (MEK) inhibitors (U0126 or PD98059) attenuated COX-2 expression and subsequent PGE(2) release by nicotine. Furthermore, the stimulatory action of nicotine on cancer cell growth and angiogenic factor VEGF production was suppressed by inhibitors of MEK (U0126) and COX-2 (SC-236). These findings reveal a direct promoting action of nicotine on the growth of gastric tumor and neovascularization through sequential activation of the ERK/COX-2/VEGF signaling pathway, which can be targeted for chemoprevention of gastric cancer, particularly in cigarette smokers.
Shin
Vivian Y
VY
Department of Pharmacology, Faculty of Medicine, The University of Hong Kong, Hong Kong, HKSAR, China.
Wu
William K K
WK
Ye
Yi-Ni
YN
So
Wallace H L
WH
Koo
Marcel W L
MW
Liu
Edgar S L
ES
Luo
Jiing-Chyuan
JC
Cho
Chi-Hin
CH
D000230:Adenocarcinoma / Q000098:blood supply / Q000378:metabolism / Q000473:pathology; D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D051546:Cyclooxygenase 2; D015232:Dinoprostone / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005731:Ganglionic Stimulants / Q000633:toxicity*; D007527:Isoenzymes / Q000378:metabolism*; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009389:Neovascularization, Pathologic / Q000473:pathology*; D009538:Nicotine / Q000633:toxicity*; D010766:Phosphorylation / Q000187:drug effects; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D015398:Signal Transduction; D013274:Stomach Neoplasms / Q000098:blood supply / Q000378:metabolism / Q000473:pathology; D014183:Transplantation, Heterologous; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
D004791:Enzyme Inhibitors; D005731:Ganglionic Stimulants; D007527:Isoenzymes; D018809:Proliferating Cell Nuclear Antigen; D042461:Vascular Endothelial Growth Factor A; D009538:Nicotine; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D015232:Dinoprostone