Insulin‐like growth factor I regulation of FOXO1 in gonadotropes (1012.7)

Abstract

The transcription factor FOXO1 is important for several aspects of reproductive function, including endometrial decidualization, ovarian follicular maturation, and spermatogenesis. We have previously reported that in pituitary gonadotropes FOXO1 functions as a repressor of both luteinizing hormone beta (Lhb) and follicle stimulating hormone beta (Fshb) transcription, which are critical for reproduction. Insulin‐like growth factor I (IGFI) is a negative regulator of FOXO1 transcriptional activity. Given that FOXO1 can repress Lhb and Fshb transcription and that IGFI stimulation of gonadotrope cells enhances Lhb and Fshb synthesis, we investigated how IGFI regulates FOXO1 activity in gonadotropes in the current study. In LβT2 gonadotrope cells, we determined by western analyses that IGFI induced Ser256 FOXO1 phosphorylation, causing FOXO1 inhibition and cytoplasmic localization as identified by immunofluorescence microscopy. In addition, inhibition of components of the IGFI signaling pathway, such as PI3K or AKT, blocked IGFI‐induced phosphorylation of FOXO1. As the in vivo gonadotrope hormone milieu includes GnRH along with IGFI, we next investigated the effect of GnRH on FOXO1 phosphorylation and subcellular localization. Stimulation of LβT2 cells with GnRH alone induced moderate cytoplasmic localization of FOXO1, although GnRH did not induce phosphorylation of FOXO1 Ser256. Moreover, the GnRH‐induced shuttling of FOXO1 to the cytoplasm was not blocked by inhibition of PI3K activity. We are currently investigating the effects of IGFI and GnRH co‐treatment.Grant Funding Source: Supported by NIH Grants T32 HD007203 and F32 HD074414 to DVS; R01 HD067448 and U54 HD012303 to VGT.