Cyclooxygenase-2 and alpha-methylacyl-CoA racemase in prostate cancer

Understanding the molecular mechanisms underlining the initiation and progression of prostate cancer (PCa) would provide helpful information for the prevention, diagnosis and therapy of this disease. This dissertation research has focused on the involvement of two enzymes in PCa, namely Cyclooxygenase-2 (COX-2) and α-methylacyl-CoA racemase (AMACR). COX-2 is the inducible isoform of the rate limiting enzymes that convert arachidonic acid to pro-inflammatory prostaglandins and is the primary target for non-steroidal anti-inflammatory drugs (NSAIDs). Accumulating evidence suggests that up-regulation of COX-2 is associated with carcinogenesis in multiple organ systems. In this study, immunohistochemistry and RT-PCR were used to evaluate the expression of COX-2 in clinical prostate tissue specimens at different stages of PCa development. Furthermore, the variable ability of PCa cell lines to induce COX-2 expression and the contributions of promoter methylation to this variation were characterized. In contrast to several previous reports, our results uncovered the consistent overexpression of COX-2 in areas of proliferative inflammatory atrophy (PIA), but not in established PCa or in high-grade prostatic intraepithelial neoplasia (PIN) as compared to adjacent normal prostate tissue. These results suggest that if NSAIDs are indeed chemopreventive and/or chemotherapeutic for PCa, their effects are likely to be mediated by modulating COX-2 activity in non-adenocarcinoma cells, or by affecting a COX-2 independent pathway. AMACR is an enzyme involved in β-oxidation of branched-chain fatty acids and bile acid intermediates. Recent work identified AMACR as a new diagnostic marker for PCa. An extensive investigation of the function and transcriptional regulation of AMACR was performed. The results suggest that AMACR is functionally important for the optimal growth of PCa cells in vitro. Enzyme activity of AMACR is increased ∼4 fold in PCa in comparison with normal prostate. Small interference RNA (siRNA) against AMACR reduced the expression of AMACR and significantly impaired the proliferation of the androgen responsive PCa cell line LAPC-4. Further study suggests that the function and expression of AMACR are independent from androgen receptor (AR) mediated signaling. Simultaneous inhibition of both AMACR and androgen signaling by means of androgen withdrawal further suppressed the growth of LAPC-4 cells than either treatment alone. Taken together, these data suggest that AMACR is essential for the growth of PCa cells in vitro and has the potential to be a complementary target with androgen ablation for PCa treatment.