Up-regulation of Cyclooxygenase-2 Expression and Prostaglandin Synthesis in Endometrial Stromal Cells by Malignant Endometrial Epithelial Cells

We investigated the regulation of prostaglandin production in normal endometrial stromal cells (ESC) by malignant endometrial epithelial cells. We found that cyclooxygenase (COX)-2 mRNA and protein levels and prostaglandin (PG)E2production in ESC were significantly increased by Ishikawa malignant endometrial epithelial cell conditioned medium (MECM). By using transient transfection assays, we found that the −360/−218-bp region of the COX-2promoter gene was critical for MECM induction of promoter activity. This MECM-responsive region contained a variant nuclear factor (NF)-κB site at −222 to −213 that, when mutated, completely abolished COX-2promoter activation by MECM. Employing electrophoretic mobility shift assays, we further demonstrated that binding of NF-κB p65 to this NF-κB-binding site is, in part, responsible for the COX-2promoter activation by MECM. To investigate further the potential effects of MECM onCOX-2mRNA stability, ESC were treated with MECM in the absence or presence of actinomycin D, a general transcription inhibitor. We found that MECM significantly increased COX-2mRNA stability. Intriguingly, we found that PGE2was one of the major factors in MECM, which was responsible for up-regulating COX-2 expression in ESC. ECC-1 and HEC-1A malignant endometrial epithelial cell lines also produced significantly increased quantities of PGE2. In conclusion, malignant endometrial epithelial cells secrete PGE2that induces COX-2 expression in normal endometrial stromal cells in a paracrine fashion through activation of transcription and stabilization of COX-2mRNA.