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*
- Hena Alam‡,
- Evelyn T. Maizels‡,
- Youngkyu Park‡,
- Shail Ghaey‡,
- Zachary J. Feiger‡,
- Navdeep S. Chandel§ and
- Mary Hunzicker-Dunn‡¶
- Departments of ‡Cell and Molecular Biology and §Medicine, Northwestern University, Feinberg School of Medicine, Chicago, Illinois 60611
- ¶ To whom correspondence should be addressed: 303 E. Chicago Ave., Chicago, IL 60611. Tel.: 312-503-8940; Fax: 312-503-0566; E-mail: mhd{at}northwestern.edu.
Abstract
We sought to elucidate the role of AKT in follicle-stimulating 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-α, microtubule-associated protein 2D, and the PKA type IIβ regulatory subunit. FSH also promotes activation of the transcription factor hypoxia-inducible factor-1 (HIF-1). FSH-stimulated 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 up-regulation of reporter activities for LHR, inhibin-α, and vascular endothelial growth factor is dependent upon HIF-1 activity, because a dominant negative form of HIF-1α 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.
Footnotes
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↵1 The abbreviations used are: FSH, follicle-stimulating hormone; CREB, cAMP-response element-binding protein; 8-CPT-cAMP, 8-chlorophenylthio-cyclic adenosine monophosphate; ERK, extracellular signal-regulated kinase; FTI-277, farnesyltransferase inhibitor-277; 4EBP1, 4E binding protein-1; GC, granulosa cell; HIF-1, hypoxia-inducible factor-1; HRE, hypoxia response element; IGF-1, insulin-like growth factor-1; LHR, luteinizing hormone receptor; Luc, luciferase; MAP2D, microtubule-associated protein 2D; mTOR, mammalian target of rapamycin; p70S6k, p70 S6 kinase; PI 3-kinase, phosphatidylinositol-3-kinase; PKA, protein kinase A; PMSG, pregnant mare serum gonadotropin; Rheb, ras homolog enriched in brain; RIIβ, PKA type IIβ regulatory subunit; SF-1, steroidogenic factor-1; TK, thymidine kinase; VEGF, vascular endothelial growth factor.
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↵* This work was supported by National Institutes of Health Grants PO1-HD-21921 (to M. H. D.), GM60472-05, and P01-HL071643, American Heart Association Grant 0350054N (to N. S. C.), and National Institutes of Health Training Program in Reproductive Biology Grant T32 HD 07086. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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- Received February 4, 2004.
- Revision received February 20, 2004.
- The American Society for Biochemistry and Molecular Biology, Inc.
