Follicle-stimulating Hormone Activation of Hypoxia-inducible Factor-1 by the Phosphatidylinositol 3-Kinase/AKT/Ras Homolog Enriched in Brain (Rheb)/Mammalian Target of Rapamycin (mTOR) Pathway Is Necessary for Induction of Select Protein Markers of Follicular Differentiation

Abstract

We sought to elucidate the role of AKT in folliclestimulating hormone (FSH)-mediated granulosa cell (GC) differentiation. Our results define a signaling pathway in GCs whereby the inactivating phosphorylation of tuberin downstream of phosphatidylinositol (PI) 3-kinase/AKT activity leads to Rheb (Ras homolog enriched in brain) and subsequent mTOR (mammalian target of rapamycin) activation. mTOR then stimulates translation by phosphorylating p70 S6 kinase and, consequently, the 40 S ribosomal protein S6. Activation of this pathway is required for FSH-mediated induction of several follicular differentiation markers, including luteinizing-hormone receptor (LHR), inhibin-␣, microtubuleassociated protein 2D, and the PKA type II␤ regulatory subunit. FSH also promotes activation of the transcription factor hypoxia-inducible factor-1 (HIF-1). FSHstimulated HIF-1 activity is inhibited by the PI 3-kinase inhibitor LY294002, the Rheb inhibitor FTI-277 (farnesyltransferase inhibitor-277), and the mTOR inhibitor rapamycin. Finally, we find that the FSH-mediated upregulation of reporter activities for LHR, inhibin-␣, and vascular endothelial growth factor is dependent upon HIF-1 activity, because a dominant negative form of HIF-1␣ interferes with the up-regulation of these genes. These results show that FSH enhances HIF-1 activity downstream of the PI 3-kinase/AKT/Rheb/mTOR pathway in GCs and that HIF-1 activity is necessary for FSH to induce multiple follicular differentiation markers.The anterior pituitary hormone follicle-stimulating hormone (FSH) 1 provides the key stimulus that promotes proliferation and differentiation of the ovarian follicle to the pre-ovulatory phenotype (1, 2 FSH signaling results in increased transcription of a number of characteristic follicular differentiation markers, including the steroidogenic enzymes side-chain cleavage cytochrome P-450 and aromatase cytochrome P-450 (12), the luteinizing hormone receptor (LHR) (3), inhibin-␣ (13), the signaling intermediates microtubule-associated protein 2D (MAP2D) (14), and the PKA type II␤ regulatory subunit (RII␤) (15). FSH also stimulates antrum formation and angiogenesis in the peripheral follicle thecal cells mediated in part by the vascular endothelial growth factor (VEGF) (16,17). Our investigation into the mechanisms by which two of these FSH targets, MAP2D and RII␤, are up-regulated in response to FSH revealed that their up-regulation at the protein level is blocked by the PI 3-kinase inhibitors LY294002 and wortmannin. FSH-mediated PI 3-kinase activation is also necessary for the expression of the cartilage link protein (8) in GCs and for optimal transferrin secretion and lactate production by Sertoli cells (9). In support of a role for PI 3-kinase/AKT activity in GC differentiation, insulin-like growth factor-1 (IGF-1), which activates the PI 3-kinase/AKT pathway via the IGF-1 receptor (18), synergizes with FSH in GCs to increase the expression of LHR (19), inhibin-␣ (20), and side-chain cleavage cytochrome P-450 and is sufficient for the expres...

Activation of the PI3K/AKT pathway mediates FSH-stimulated VEGF expression in ovarian serous cystadenocarcinoma

“…However, little was known about the mechanism of FSH stimulation on VEGF expression. Other studies showed HIF-1α and survivin may play a role in VEGF expression [7][8][9][10][13][14][15][16], and it had also been shown that FSH induces HIF-1α and survivin expression [37][38][39]. In this study, we showed that treatment with FSH also increased survivin and HIF-1α expression (Figure 2A and 2B).…”

“…FSH stimulated PI3K/AKT signal transduction in many cells, including granular cells, Sertoli cells, and oocytes [39][40][41]. FSH has also been shown to activate ERK and p38 mitogen-activated protein kinase (MAPK) in granulose cells [42,43].…”

The ‘beneficial’ adipokines in reproduction and fertility

“…74 The sequelae of this interaction are not yet known, but may be part of the mechanism by which FSH activates the Akt/PKB pathway. 75 Indeed, in rat granulosa cells, adiponectin provokes phosphorylation of Akt/PKB, 40 and in other tissues Evidence indicates that FSH can also interact with APPL1, presumably via the C-terminal intracellular domain, with the potential, and it is further known that FSH via unknown intermediates, induces phosphoinosital-3 kinase activation and thus the Akt or protein kinase B pathway. Insulin likewise functions through this mechanism, although direct interaction between the insulin receptor and APPL1 has not been shown.…”

TCR Engagement Increases Hypoxia-Inducible Factor-1α Protein Synthesis via Rapamycin-Sensitive Pathway under Hypoxic Conditions in Human Peripheral T Cells

“…In addition to this hypoxia-dependent mechanism, recent studies have demonstrated non-hypoxic pathways for regulation of HIF-1␣ activity (9,10) and multiple regulatory mechanisms of HIF-1␣ protein level, may enable cells to adapt to diverse alteration of environments and preserve homeostasis in a tissue-dependent manner. For example, receptor-mediated regulation of HIF-1␣ expression is thought to be cell and signal specific, and a number of reports have suggested that receptor-mediated factors such as growth factors, hormones, and cytokines induce HIF-1␣ protein expression through various signalings including PI3K/mammalian target of rapamycin (mTOR) pathway (11)(12)(13)(14)(15).…”