DEVELOPMENTAL GENETICS 21:109-115 (1997) Regulation of Cyclooxygenase Gene Expression in Rat Endometrial Stromal Cells: The Role of Epidermal Growth Factor BRENT M. BANY* AND THOMAS G. KENNEDY Departments of Physiology and Obstetrics and Gynaecology, The University of Western Ontario, London, Canada ABSTRACT Epidermal growth factor stimulates prostaglandin production and cyclooxygenase activity in endometrial stromal cells isolated from the uteri of ovariectomized rats sensitized for the decidual reaction. The present study examined the effect of epidermal growth factor on cyclooxygenase-1 and cyclooxygenase-2 mRNA and protein levels in these cells. Treatment with epidermal growth factor (40 ng/ml) for 24 hr increased steady-state cyclooxygenase-1 and cyclooxygenase-2 mRNA and protein levels in the cells as determined by Northern and Western analyses. Dexamethasone inhibited the epidermal growth factor induced increases in steady-state mRNA levels for cyclooxygenase-2, but not for cyclooxygenase-1. Finally, the effects of epidermal growth factor and dexamethasone on steady-state cyclooxygenase-1 and cyclooxygenase-2 mRNA levels paralleled the changes in the levels of immunocytochemical staining for these enzymes in the cells. This showed that the changes in cyclooxygenase-1 and -2 protein levels were due to generalized changes in most cells, and not to changes in a subpopulation of stromal cells. The results of this study suggest that epidermal growth factor causes an increase in cyclooxygenase-1 and cyclooxygenase-2 gene expression in endometrial stromal cells isolated from the uteri of rats which have been sensitized for decidualization, and that the previously reported transcriptional- and translational- dependent increases in cyclooxygenase activity in these cells in response to epidermal growth factor were likely due to its effect on cyclooxygenase- 1 and cyclooxygenase-2 gene expression. Dev. Genet. 21:109-115, 1997. © 1997 Wiley-Liss, Inc. Key words: Epidermal growth factor; cyclooxygen- ase; uterus; endometrium INTRODUCTION Cyclooxygenase (COX) is believed to be a rate-limiting enzyme in the production of prostaglandins [PGs; DeWitt, 1991]. COX converts arachidonic acid sequentially to prostaglandin G 2 and then to prostaglandin H 2 (PGH 2 ) through bis-oxygenase and peroxidase activities, respectively [Smith et al., 1991]. PGH 2 is © 1997 WILEY-LISS, INC. Contract grant sponsor: Medical Research Council of Canada; Contract grant number: MA-10414. *Correspondence to: Brent M. Bany, Department of Physiology, The University of Western Ontario, M223 Medical Sciences Building, London, Ontario, N6A 5C1. Received for publication 6 February 1997; accepted 24 March 1997. then the direct precursor of the biologically active 2-series PGs and thromboxanes. In several cell types, agonist-induced increases in PG production is accompanied by an increase in COX gene expression [DeWitt, 1991; Herschman, 1994]. The level of COX gene expression may be important for prolonged elevated PG production since COX is a suicide enzyme [Egan et al., 1976] and must be replaced to sustain PG production. Recently, it has been realized that two isozymes of COX exist. Two separate human [Hla and Neilson, 1992; Takahashi et al., 1992], mouse [DeWitt et al., 1991; Kujubu et al., 1991], and rat [Feng et al., 1993] COX genes have been cloned and are called cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). The 4.1 kb COX-2 mRNA is much larger than the 2.8 kb COX-1 mRNA, mainly because of the presence of a large T-untranslated region in COX-2. The most striking difference between these two isoforms is the presence of this large T-untranslated region in COX-2 containing a large number of Shaw-Kamen sequences which are known to confer selective mRNA degradation on other transcripts [Shaw and Kamen, 1986]. Despite the differences in transcript sizes, the COX-1 and COX-2 genes encode proteins of almost identical molecular mass which share approximately 75% sequence identity within species. PGs, particularly of the E-series, play an important role in blastocyst implantation and decidualization in many animals [reviewed by Kennedy, 1990; Smith, 1991]. PG levels are higher in the endometrium. at implantation sites compared to interimplantation sites in many species. Inhibition of endometrial PG production prevents or delays implantation and decidualization in many species, effects which can be prevented by the administration of exogenous PGs. Although essen