Regulation of COX-2 gene expression in rat uterus in vivo and in vitro

Prostaglandins are involved in mediating several important processes in mammalian reproduction, including the initiation of parturition. In the present study, we examined the expression in the rat uterus of two-rate limiting enzymes involved in prostaglandin production, cyclooxygenase (COX) 1 and 2. Expression of the COX-2 gene in the pregnant rat uterus gave rise to a single mRNA transcript of approximately 4.4 kb. COX-2 mRNA levels increased 3.5 fold between day 7 of pregnancy and the onset of parturition on day 22. In contrast, COX-1 mRNA levels remained constant during the same period. To investigate factors involved in mediating the regulation of COX-1 and COX-2 gene expression, rat endometrial stromal and epithelial cell lines, were used. In the stroma-derived cell line, CUS-V2, COX-2 gene expression was demonstrated by reverse transcriptase/polymerase chain reaction (RT-PCR) and by immunocytochemistry. In these cells, COX-2 gene expression was inducible by the cytokines interleukin-1 β and tumor necrosis factor α, but not by interleukin-6. The two former cytokines also induced prostaglandin F_2α production. In contrast, COX-1 gene expression was constitutive in this cell line. In the endometrial epithelium-derived cell line, CUE-P both COX-1 and COX-2 genes were expressed in a constitutive fashion. In conclusion, the present in vivo and in vitro data indicate that decidual COX-2, but not COX-1, gene expression is regulated during pregnancy and implicate specific cytokines as possible inducers within the decidua.