X-linked inhibitor of apoptosis protein activates the phosphatidylinositol3-kinase/Akt pathway in rat granulosa cells during follicular development

X-linked inhibitor of apoptosis protein (XIAP) in granulosa cells is regula ted by gonadotropins during follicular development, although the current un derstanding of the mechanisms by which XIAP suppressed granulosa cell apopt osis is incomplete. In the present study, we investigated the possible invo lvement of the phosphatidylinositol 3-kinase (P1wI-K) survival pathway in t he regulation of granulosa cell fate. Using a fully characterized in vivo m odel to study the induction of follicular development and atresia in immatu re rats, we have demonstrated that gonadotropin treatment increased granulo sa cell XIAP and phospho-Akt protein contents and suppressed apoptosis. In addition, gonadotropin withdrawal [equine CG (eCG)-primed rats treated with an anti-eCG antibody] induced granulosa cell apoptosis and significantly d ecreased ovarian weight. The increased apoptosis was accompanied by marked decreases in XIAP expression and phosphorylation of Akt protein. Infection of granulosa cells from eCG-primed rats with adenoviral sense XIAP [lacZ as a control; multiplicity of infection, 1-5] resulted in XIAP overexpression and increased phospho-Akt content, whereas XIAP antisense expression (mult iplicity of infection, 10-40) decreased granulosa cell phospho-Akt level an d induced apoptosis. Addition of the specific PI 3-K inhibitor LY294002 to the granulosa cell cultures decreased Akt phosphorylation and induced apopt osis in a dose-dependent manner. Taken together, these results demonstrate for the first time the importance and regulation of the PI 3-K survival pat hway by XIAP in the control granulosa cell apoptosis.