| Abstrakt: |
We have previously demonstrated that prostaglandin F2α(PGF2α) induces a rapid and transient expression of Nur77 in luteal cells. We have shown that Nur77 plays an important role in ovarian physiology by mediating the PGF2αinduction of 20α-HSD, a steroidogenic enzyme involved in the catabolism of progesterone. In this report we established, using luteinized granulosa cells, that PGF2αstimulates in vitro nur77expression in a time- and dose-dependent manner. Serial 5′-deletion of thenur77promoter revealed that the necessary and sufficient elements for PGF2αinduction of Nur77 promoter activity are located between the nucleotides −86 and −33 upstream of the transcription start site, this region containing two AP1 elements. JunD binds to these AP1 sites, but its binding is not stimulated by PGF2α. However, mutation of the AP1 sites as well as a dominant-negative JunD abolished nur77induction by PGF2α. PGF2αinduces phosphorylation of JunD bound to the nur77promoter. Stimulation ofnur77expression and JunD phosphorylation were prevented by inhibitors of calcium, calmodulin, or ERK1/2 kinase. PGF2α-induced ERK1/2 phosphorylation was prevented by calcium/calmodulin inhibitors. We conclude that activation of JunD through a calmodulim-dependent activation of ERK1/2 mediates nur77induction by PGF2α. Finally, we demonstrated that this molecular mechanism also mediates20α-hsdinduction. |
