Over-activation of cAMP signaling increases vulnerability to hydrogen peroxide via actin rearrangement, which is inhibited by prostaglandin E2 in a mouse granulosa cell line

Apoptosis of granulosa cells (GC) contributes toovarian follicular atresia, and has been implicatedto depend on the oxidant status of GC within follicles.Here, we investigated the effects of cAMP andprostaglandin E2 (PGE2) on sensitivity to oxidativestress using 4B2 cells with cAMP-dependent,steroidogenic and differentiated properties. Thiscell line was isolated from mouse GC co-transfectedwith genes for SV40 large T antigen andAd4BP/SF1 transcription factor (Kamei et al.2005). Treatment of serum-starved cells with 8-BrcAMPcaused 30 to 40% of the cells to becomepolygonal within 2 h through actin rearrangement.Interestingly, H2O2 treatment showed that thesepolygonal cells were vulnerable to oxidativestress that led to cell death, which was inhibited bypretreatment with phalloidin, an F-actin stabilizingagent. Although PGE2 alone had no effect, cotreatmentwith PGE2 and 8-Br-cAMP completelyinhibited the effects of 8-Br-cAMP on cell shapechange and oxidative stress vulnerability throughphosphatidylinositol 3-kinase (PI3K)-dependentmanner. Notably, PGE2 and 8-Br-cAMP cooperatedadditively to increase progesterone secretion.These data suggest that cAMP signaling in GC mayenhance oxidative stress risk through actinrearrangement, and PGE2 may reduce such riskthrough activating PI3K, while cooperating withcAMP signaling in steroidogenesis.