Platelet-type arachidonate 12-lipoxygenase (12-LOX) is highly expressed in many types of cancers and plays an important role in cancer pathophysiology. Arachidonic acid metabolism by 12-LOX results in the stable end product 12(S)-hydroxy eicosatetraenoic acid (12(S)-HETE), which is a signaling molecule with effects on cell proliferation, motility, invasiveness, angiogenesis, and inhibition of apoptosis. The myriad biological activities manifested by 12(S)-HETE appear to be mediated, at least in part, by the activation of NF-kappaB. Overexpression of the 12-LOX in PC-3 prostate cancer cells resulted in the constitutive activation of the transcription factor. The enzymatic product of arachidonic acid metabolism, 12(S)-HETE, mediates the activation of NF-kappaB by the 12-LOX. 12(S)-HETE treatment of PC-3 cells induced the degradation of IkappaB by the S6 proteasomal pathway and the activated NF-kappaB translocated to the nucleus causing kappaB-induced transcription. Specificity of the NF-kappaB activation by 12(S)-HETE was established by the use of a 12-LOX-specific inhibitor and 13(S)-HODE, a known 12(S)-HETE antagonist. Considering the known involvement of MAP kinase pathway in NF-kappaB activation and that of 12(S)-HETE in MAP kinase pathway, 12-LOX present in prostate cancer tissues may contribute to the constitutive activation of NF-kappaB in prostate cancer cells.