Follicle-Stimulating Hormone Increases Tuberin Phosphorylation and Mammalian Target of Rapamycin Signaling through an Extracellular Signal-Regulated Kinase-Dependent Pathway in Rat Granulosa Cells

Abstract

FSH-mediated regulation of mammalian target of rapamycin (mTOR) signaling in proliferating granulosa cells and the effect of dihydrotestosterone (DHT) on this pathway were examined. Inhibiting mTOR activation using rapamycin significantly reduced the FSH-mediated increase in cyclin D2 mRNA expression, suggesting that mTOR plays a role in the FSH-mediated increase in granulosa cell proliferation. FSH treatment of granulosa cells showed a 2-fold increase in phosphorylation of p70S6 kinase (p70S6K), the downstream target of mTOR. The increase in p70S6K phosphorylation by FSH treatment was abolished by prior exposure to DHT, suggesting that DHT inhibits FSH-mediated activation of mTOR signaling in cultured granulosa cells. The effect of FSH and DHT treatment on tuberin (TSC2), the upstream regulator of mTOR, was then examined. FSH treatment increased TSC2 phosphorylation, and pretreatment with DHT for 24 h reduced this stimulation. These results indicate that reduced p70S6K phosphorylation observed in DHT-treated cells might be the result of reduced TSC2 phosphorylation. Because Akt is the upstream activator of TSC2 phosphorylation, the effect of Akt inhibition was examined to test whether FSH-mediated TSC2 phosphorylation proceeds through an Akt-dependent pathway. Our results show that inhibiting Akt phosphorylation did not block FSH-stimulated TSC2 phosphorylation, whereas ERK inhibition reduced FSH-mediated stimulation. These results demonstrate the involvement of ERK rather than Akt in FSH-mediated TSC2 phosphorylation in granulosa cells. Based on these observations, we conclude that in granulosa cells, FSH uses a protein kinase A-/ERK-dependent pathway to stimulate TSC2 phosphorylation and mTOR signaling, and DHT treatment significantly reduces this response.

Stimulatory Effect of Insulin on 5α-Reductase Type 1 (SRD5A1) Expression through an Akt-Dependent Pathway in Ovarian Granulosa Cells

“…Previous studies from our laboratory have shown that 5␣-DHT inhibits FSH-mediated mitogenic signals in immature rat GCs leading to cell cycle arrest (6,31). Although the role of insulin as a regulator of growth and steroidogenesis in ovarian tissues is well documented, the undesirable consequences of insulin's stimulatory action have not been previously examined.…”

AKT is involved in granulosa cell autophagy regulation via mTOR signaling during rat follicular development and atresia

“…The PI3K/AKT pathway may therefore also be involved in the regulation of granulosa cell autophagy via control of mTOR activity during follicular development and atresia, as gonadotropin is known to suppress granulosa cell autophagy in follicular development (Choi et al 2010). However, there is also a report suggesting that mTOR activation by gonadotropin may not be controlled by the PI3K/AKT pathway in rat granulosa cells (Kayampilly & Menon 2007), and there is no direct evidence of the involvement of the PI3K/AKT pathway through mTOR in granulosa cell autophagy regulation.…”

mTORC1 et sirolimus

“…Chez la rate, la voie mTOR activée stimule la prolifé-ration (induite par la FSH) des cellules de la granulosa [22] et celle des cellules de la thèque (induite par la LH) [23]. L'inhibition de mTORC1 dans des cultures primaires de cellules de la thèque induit une baisse d'expression des marqueurs de prolifération, tels que PCNA (proliferating cell nuclear antigen) ou la cycline D3, et ce malgré l'induction de la prolifération par de l'hCG (human chorionic gonadotropin) qui mime l'effet de la LH [23].…”