Interleukin 1 Upregulates Ovarian Prostaglandin Endoperoxide Synthase-2 Expression: Evidence for Prostaglandin-Dependent/Ceramide-Independent Transcriptional Stimulation and for Message Stabilization

Abstract

We have recently documented a marked dependence of ovarian prostaglandin endoperoxide synthase (PGS)-2 transcripts, proteins, and activity on interleukin (IL) 1, a putative intermediary in the ovulatory cascade. The purpose of the present study was to characterize the cellular and molecular mechanisms underlying the ability of IL-1β to upregulate the steady-state levels of ovarian transcripts corresponding to PGS-2. Results of studies designed to enrich or deplete nitric oxide strongly suggest that the stimulatory effect of IL-1β on ovarian PGS-2 expression is independent of nitric oxide. Utilization of a series of agents designed to simulate or enhance transduction via the sphingomyelin ceramide cycle suggests that the long-term stimulatory effect of IL-1β on ovarian PGS-2 gene expression is independent of ceramide. In contrast, inhibition of prostaglandin biosynthesis with a series of distinct inhibitors suggests that the ability of IL-1β to upregulate ovarian PGS-2 transcripts is due, if only in part, to the generation of endogenous prostaglandin estradiol-17β (E₂). Inhibition of protein biosynthesis suggested that the IL-1β-induced PGS-2 gene expression required de novo protein biosynthesis. Our findings revealed substantial IL-1β-mediated stabilization of PGS-2 transcripts, as assessed by a threefold increase in the half-life of the message. We have also observed the ability of IL-1β to upregulate the transcription of PGS-2 promoter constructs subjected to transient transfection into whole-ovarian dispersates (twofold increase as assessed by activation of the luciferase reporter gene). Taken together, these findings suggest that the stimulatory effect of IL-1β on PGS-2 expression is 1) independent of nitric oxide as well as ceramide, 2) dependent on prostaglandin E₂, 3) contingent on de novo protein biosynthesis, and 4) accounted for by both increased transcription and message stabilization. These observations provide indirect support for the hypothesis that IL-1β, acting in part through PGS-2 (an obligatory ovulatory principal), may constitute a key intermediary in the ovulatory cascade.