Endocrine Abstracts

Apoptosis is crucial in regulating many aspects of the reproductive system. Since mitogen-activated-protein-kinases (MAPKs) and phosphatidylinositol-3′-kinase (PI3K)-dependent signaling systems play important roles in apoptosis regulation, we undertook to study their involvement in the induction of apoptosis in the reproductive system.

Two pro-apoptotic stimulants were investigated in two corresponding cell lines. One of them was prostaglandin F2α (PGF2α), which is known to be the principal physiologic luteolytic factor in mammals. It was found to exert direct apoptosis in human luteinized granulosa cells, and thereby studied in SVOG-4O cell line. The second stimulant was gonadotropin-releasing-hormone-analog (GnRH-a), which is known to induce direct apoptotis in many malignancies, benign diseases and various cell lines. As a model system we used the mouse pituitary cell line, αT3-1, which was found here to undergo apoptosis upon GnRH-a treatment.

We report that PGF2α and GnRH-a directly induces apoptosis in SVOG-4O and αT3-1 cell lines respectively in a dose and time dependent manner. The apoptotic effect of PGF2α and GnRH-a is mediated by JNK and inhibited by the PI3K-PKB pathway. PKC activation induces the assembly of the catalytic and regulatory subunits of PP2A, thus activating it. Activated PP2A binds to PKB causing its dephosphorylation. Furthermore, PKC activation induces inhibition of PI3K activity. Altogether, the reduction of PKB activity releases PKB-induced inhibition of MLK3, thus further stimulates JNK activity and accelerates PGF2α and GnRH-a apoptotic effect.

We conclude that both PGF2α and GnRH-a exert pro-apoptotic effect via similar signal transduction pathways. Our results support a potential use of GnRH-a for the treatment of various diseases and suggest that the outcome of this treatment can be amplified by using PI3K-PKB inhibitors. Finally, revealing the signal transduction pathways governing apoptosis in luteinized human granulosa cells may help both in the diagnosis and treatment of various reproductive abnormalities, using specific signal transduction modulators.