Cyclooxygenase-2 (COX-2) plays an important role in tumor development and progression. Inconsistent reports on the expression of COX-2 in early versus advanced prostate cancer raised the question on whether COX-2 inhibition affects prostate carcinogenesis. Evidence from recent studies indicates that prostate carcinogenesis depends on the altered expression of several factors including androgen receptor signaling, proinflammatory, and cell cycle regulatory genes. Very often, the outcome of androgen ablation treatment is not effective and, eventually, the cancer becomes androgen independent followed by activation of several survival genes and transcription factors. Most importantly, the extent of the influence of COX-2 on the regulation of the androgen receptor, cyclin D1, and other factors involved in cancer growth is not known. Using RNA interference-mediated COX-2 inhibition in metastatic prostate cancer cells, this study has shown that the silencing of COX-2 at the mRNA level can induce cell growth arrest and down-regulate androgen receptor and cyclin D1. We have further shown for the first time that COX-2 knockdown prostate cancer cells depict morphologic changes associated with enhanced expression of differentiation markers, particularly the neuronal protein synaptophysin along with activation of p21((Waf1/Cip1)) and p27((Kip1)). In summary, our findings determined the role of COX-2 in prostate carcinogenesis and its control on COX-2-independent targets. Second, abrogation of COX-2 and activation of synaptophysin provide evidence for the control of COX-2 on the expression of a neuronal protein. Finally, our findings provide evidence of COX-2-independent targets promoting cell growth arrest and differentiation in cells lacking COX-2 expression at the mRNA level.