There is little understanding of the effect that reactive oxygen metabolites have on cellular behavior during the processes of invasion and metastasis. These oxygen metabolites could interact with a number of targets modulating their function such as enzymes involved in basement membrane dissolution, adhesion molecules involved in motility or receptors involved in proliferation. We investigated the effect of increased scavenging of superoxide anions on the expression of the urokinase receptor (uPAR) in PC-3M human prostate cancer cells. Urokinase receptor is a GPIlinked cell surface molecule which mediates multiple functions including adhesion, proliferation and pericellular proteolysis. Addition of the superoxide scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (TEMPOL) to PC-3M cultures stimulated expression of uPAR protein peaking between 48 and 72 hours. Cell surface expression of the uPAR was also increased. Surprisingly, uPAR transcript levels increased only slightly and this mild increase did not coincide with the striking degree of protein increase. This disparity indicates that the TEMPOL effect on uPAR occurs through a post-transcriptional mechanism. TEMPOL presence in PC-3M cultures reduced intracellular superoxide-type species by 75% as assayed by NBT dye conversion; however this reduction significantly diminished within hours following TEMPOL removal. The time gap between TEMPOL treatment and peak uPAR protein expression suggests that reduction of reactive oxygen metabolites in prostate cancer cells initiates a multistep pathway which requires several hours to culminate in uPAR induction. These findings reveal a novel pathway for uPAR regulation involving reactive oxygens such as superoxide anion. FindingsReactive oxygen species (ROS) are becoming increasingly associated with several aspects of cancer progression including not only carcinogenesis but also tumor cell proliferation and invasion [1]. In prostate cancer, oxygen radicals are reported to arise from several sources within the cells including the NADPH oxidase [1], mitochondrial glycerophosphate-dependent ROS [2], xanthine oxidase and nitric oxide synthases [3]. The cell's net redox state is a balance between oxygen radical synthesis and breakdown, and net ROS metabolism in prostate cancer arises via activities of the scavenger enzyme systems catalase, superoxide dismutase I (Zn2+/Cu2+ SOD) and II (MN-SOD), and glutathione peroxidase [3].

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