Endocrine Abstracts

The mammalian Forkhead Box O (FoxO) transcription factors, FoxO1, FoxO3a and FoxO4 are emerging as an important family of proteins that modulate the expression of genes involved in cell cycle regulation, induction of apoptosis, DNA damage repair and response to oxidative stress. Their transcriptional activity is tightly regulated by the action of several regulatory co-factors, and a series of post-translational modifications controlling a shuttling system, that confines them either to the nucleus or the cytoplasm. We show that GnRH receptor signalling targets the phosphorylation and acetylation status of FoxOs, and utilize several FoxO-driven promoter luciferase constructs to demonstrate that GnRH targets FoxO transcriptional activity. We have examined the impact of two apparently inter-dependent signalling pathways that utilize PI3K/Akt and IKK as primary mediators, on the phosphorylation, cellular localization, and transcriptional activity of FoxOs in response to GnRH. The GnRH-induced nuclear accumulation of beta-catenin, a known FoxO co-factor, has previously been reported. In the present study, we assess the action of beta-catenin in regulating GnRH-mediated FoxO transcriptional activity. Finally, quantitative RT-PCR studies have revealed the regulation of several cell cycle and apoptotic related FoxO-driven genes in response to GnRH. The anti-proliferative and apoptotic effects of GnRH on tumour cells are well-documented, and our studies highlight a potential role for FoxO activity in mediating these effects, in addition to a variety of normal physiological and pathological cellular processes in the reproductive system.