Carcinogenesis Advance Access published online on January 3, 2008
Carcinogenesis, doi:10.1093/carcin/bgm274
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Platelet-type 12-lipoxygenase accelerates tumor promotion of mouse epidermal cells through enhancement of cloning efficiency
1 Division of Genetics, Cancer Research Institute
2 Department of Pharmacology, Graduate School of Medicine, Kanazawa University, Kanazawa, 920-0934 Japan
3 Department of Physiology and Pathophysiology
4 Department of Hematology, Medical College, Yanbian University, Yanji, Jilin, China
5 Department of Clinical Pharmacology, Faculty of Pharmaceutical Sciences, Hokuriku University, Kanazawa 920-1181 Japan
To whom correspondence should be addressed: Masanobu Oshima, Division of Genetics, Cancer Research Institute, Kanazawa University, 13-1 Takara-machi, Kanazawa, 920-0934 Japan. Phone/FAX: +81-76-265-2721/+81-76-234-4519, E-mail: oshimam{at}kenroku.kanazawa-u.ac.jp
Accumulating evidence suggests that platelet-type 12-lipoxygenase (p12-LOX) plays an important role in tumor development. However, how p12-LOX contributes to tumorigenesis is still not understood yet. The role of p12-LOX was therefore examined in tumor promotion using mouse epidermal JB6 P+ cells that are sensitive to TPA-induced transformation. The expression of p12-LOX was significantly higher in JB6 P+ cells than in JB6 P– cells that were resistant to transformation, and its expression was further increased by tumor necrosis factor (TNF)-
. Importantly, the inhibition of p12-LOX in JB6 P+ cells by baicalein, a specific inhibitor or siRNA significantly suppressed TPA-induced transformation. Moreover, treatment with 12(S)-HETE, a metabolite of p12-LOX, enhanced TPA-induced neoplastic transformation either in the presence or absence of baicalein. These results indicate that p12-LOX is required for tumor promotion of epidermal cells and that 12(S)-HETE functions as a rate-limiting factor. Notably, treatment with baicalein significantly suppressed the proliferation of JB6 P+ cells when cells were seeded at a low density in a culture plate. Moreover, the cloning efficiency of JB6 P+ cells was dramatically decreased by inhibition of p12-LOX. In contrast, baicalein treatment did not affect the cloning efficiency of most malignant cancer cells. These results indicate that p12-LOX is induced by the inflammatory cytokine TNF- in the early stage of tumorigenesis, and is required for tumor promotion through enhancing efficient proliferation of a small number of initiated cells. The present results suggest that the p12-LOX pathway may be an effective target of chemoprevention for skin carcinogenesis.
Key Words: lipoxygenase • tumor promotion • chemoprevention • JB6
Received July 10, 2007; revised October 29, 2007; accepted November 24, 2007.