Prostaglandin E2 drives cyclooxygenase-2 expression via cyclic AMP response element activation in human pancreatic...

Cyclooxygenase-2 (COX-2) is constitutively expressed in most human primary carcinomas and with its synthesized product, prostaglandin E2 (PGE2), appears to play important roles in tumor invasion, angiogenesis, resistance to apoptosis and suppression of host immunity. However, the molecular mechanisms that control COX-2 expression are unclear. The purpose of this study was to clarify the mechanism of basal and PGE2-mediated COX-2 expression in the highly metastatic L3.6pl human pancreatic cancer cell line. Using RNA interference to disrupt the expression of CREB and the NF-kappaB p65 subunit, we found that both are involved in maintaining basal COX-2 expression in L3.6pl cells. We also demonstrated that PGE2 increased the cyclic AMP concentration, thereby activating protein kinase A (PKA), which in turn phosphorylated the cyclic AMP response element binding protein (CREB), leading to interaction with the cyclic AMP response element in the promoter region of the COX-2 gene. Immunocytochemical analysis confirmed that PGE2 stimulated the translocation of PKA to the nucleus and increased the immuno-reactivity of phosphorylated CREB. Pretreatment with the PKA selective inhibitor H 89 and the E-prostanoid receptor 2 inhibitor AH 6809 reduced COX-2 upregulation by PGE2. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay results further suggested a role for CREB in COX-2 transcriptional control. Understanding the pathways that control COX-2 expression may lead to a better understanding of its dysregulation in pancreatic carcinomas and facilitate the development of novel therapeutic approaches.