Overexpression of 15-lipoxygenase-1 in PC-3 human prostate cancer cells increases tumorigenesis

The effect of overexpression of 15-lipoxygenase-1 (15-LO-1) was studied in the human prostate cancer cell line, PC-3. Stable PC-3 cell lines were gene rated by transfection with 15-LO-1-sense (15-LOS), 15-LO-1-antisense (15-LO AS) or vector (Zeo) and selection with Zeocin. After characterization by RT -PCR, western and HPLC, a PC3-15LOS clone was selected that possessed 10-fo ld 15-LO-1 enzyme activity compared with parental PC-3 cells. The PC3-15LOA S clone displayed little or no 15-LO-1 activity. These PC-3 cell lines were characterized for properties of tumorigenesis. The proliferation rates of the cell lines were as follows: PC3-15LOS > PC-3 = PC3-Zeo > PC3-15LOAS. Ad dition of a specific 15-LO-1 inhibitor, PD146176, caused a dose-dependent i nhibition of proliferation in vitro. Overexpression of 15-LO-1 also caused [IR]thymidine incorporation to increase by 4.0-fold (P < 0.01). Compared wi th parental and PC-3-Zeo cells, PC3-15LOS enhanced whereas PC3-15LOAS reduc ed the ability of PC-3 cells to grow in an anchorage-independent manner, as assessed by colony formation in soft agar. These data suggested a pro-tumo rigenic role for 15-LO-1 in PC-3 cells in vitro. Therefore, to clarify the role of 15-LO-1 in vivo, the effect of 15-LO-1 expression on the growth of tumors in nude mice was investigated. The PC-3 cell lines were inoculated s ubcutaneously into athymic nude mice. The frequency of tumor formation was increased and the sizes of the tumors formed were much larger in the PC3-15 LOS compared with PC3-15LOAS, parental PC-3 and PC-3-Zeo cells. Immunohisto chemistry for 15-LO-1 confirmed expression throughout the duration of the e xperiment. The expression of factor VIII, an angiogenesis marker, in tumor sections was increased in tumors derived from PC3-15LOS cells and decreased in those from PC3-15LOAS cells compared with tumors from parental or Zeo c ells. These data further supported the evaluation by ELISA of vascular endo thelial growth factor (VEGF) secretion by PC-3 cells in culture. Secretion of this angiogenic factor was elevated in PC3-15LOS cells compared with the other cell lines. These results support a role for 15-LO-1 in a novel grow th-promoting pathway in the prostate.