Overexpression of Platelet-type 12-Lipoxygenase Promotes Tumor Cell Survival by Enhancing

Arachidonic acid metabolism leads to the generation of biologically active metabolites that regulate cell growth and proliferation, as well as survival and apoptosis. We have demonstrated previously that platelettype 12-lipoxygenase (LOX) regulates the growth and survival of a number of cancer cells. In this study, we show that overexpression of platelettype 12-LOX in prostate cancer PC3 cells or epithelial cancer A431 cells significantly extended their survival and delayed apoptosis when cultured under serum-free conditions. These effects were shown to be a result of enhanced surface integrin expression, resulting in a more spread morphology of the cells in culture. PC3 cells transfected with 12-LOX displayed increased v 3 and v 5 integrin expression, whereas other integrins were unaltered. Transfected A431 cells did not express v 3; however, v 5 integrin expression was increased. Treatment of both transfected cell lines with monoclonal antibody to v 5 (and in the case of PC3 cells, antiv 3) resulted in significant apoptosis. In addition, treatment with 100 nM 12(S)-hydroxy-eicosatetraenoic acid, the end product of platelet-type 12-LOX, but not other hydroxy-eicosatetraenoic acids, enhanced the survival of wild-type PC3 and A431 cells and resulted in increased expression of v 5. Furthermore, Baicalein or N-benzyl-Nhydroxy-5-phenylpentamide, specific 12-LOX inhibitors, significantly decreased v 5-mediated adhesion and survival in 12-LOX-overexpressing cells. The results show that 12-LOX regulates cell survival and apoptosis by affecting the expression and localization of the vitronectin receptors, v 3 and v 5, in two cancer cell lines.