Apoptosis of granulosa cells (GC) contributes to
ovarian follicular atresia, and has been implicated
to depend on the oxidant status of GC within follicles.
Here, we investigated the effects of cAMP and
prostaglandin E
2 (PGE
2) on sensitivity to oxidative
stress using 4B2 cells with cAMP-dependent,
steroidogenic and differentiated properties. This
cell line was isolated from mouse GC co-transfected
with genes for SV40 large T antigen and
Ad4BP/SF1 transcription factor (Kamei et al.
2005). Treatment of serum-starved cells with 8-BrcAMP
caused 30 to 40% of the cells to become
polygonal within 2 h through actin rearrangement.
Interestingly, H
2O
2 treatment showed that these
polygonal cells were vulnerable to oxidative
stress that led to cell death, which was inhibited by
pretreatment with phalloidin, an F-actin stabilizing
agent. Although PGE
2 alone had no effect, cotreatment
with PGE
2 and 8-Br-cAMP completely
inhibited the effects of 8-Br-cAMP on cell shape
change and oxidative stress vulnerability through
phosphatidylinositol 3-kinase (PI3K)-dependent
manner. Notably, PGE
2 and 8-Br-cAMP cooperated
additively to increase progesterone secretion.
These data suggest that cAMP signaling in GC may
enhance oxidative stress risk through actin
rearrangement, and PGE
2 may reduce such risk
through activating PI3K, while cooperating with
cAMP signaling in steroidogenesis.
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