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-alpha, microtubule-associated protein 2D, and the PKA type IIbeta 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-alpha, and vascular endothelial growth factor is dependent upon HIF-1 activity, because a dominant negative form of HIF-1alpha 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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Animals
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Cell Differentiation
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Chromones / pharmacology
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Cyclic AMP-Dependent Protein Kinase RIIbeta Subunit
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Cyclic AMP-Dependent Protein Kinases / metabolism
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DNA-Binding Proteins / metabolism*
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Enzyme Activation
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Enzyme Inhibitors / pharmacology
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Female
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Follicle Stimulating Hormone / metabolism*
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Genes, Dominant
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Genes, Reporter
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Granulosa Cells / cytology
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Hypoxia-Inducible Factor 1
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Hypoxia-Inducible Factor 1, alpha Subunit
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Inhibins / metabolism
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Luciferases / metabolism
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Microtubule-Associated Proteins / metabolism
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Models, Biological
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Monomeric GTP-Binding Proteins / metabolism*
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Morpholines / pharmacology
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Neuropeptides / metabolism*
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Nuclear Proteins / metabolism*
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Phosphatidylinositol 3-Kinases / metabolism*
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Phosphorylation
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Protein Kinases / metabolism*
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Protein Serine-Threonine Kinases*
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Protein Structure, Tertiary
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Proto-Oncogene Proteins / metabolism*
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Proto-Oncogene Proteins c-akt
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Ras Homolog Enriched in Brain Protein
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Rats
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Rats, Sprague-Dawley
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Receptors, LH / metabolism
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Ribosomal Protein S6 Kinases, 70-kDa / metabolism
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Signal Transduction
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TOR Serine-Threonine Kinases
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Time Factors
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Transcription Factors*
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Transfection
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Up-Regulation
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ras Proteins / metabolism*
Substances
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Chromones
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Cyclic AMP-Dependent Protein Kinase RIIbeta Subunit
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DNA-Binding Proteins
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Enzyme Inhibitors
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Hif1a protein, rat
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Hypoxia-Inducible Factor 1
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Hypoxia-Inducible Factor 1, alpha Subunit
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Microtubule-Associated Proteins
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Morpholines
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Neuropeptides
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Nuclear Proteins
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Prkar2b protein, rat
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Proto-Oncogene Proteins
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Ras Homolog Enriched in Brain Protein
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Receptors, LH
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Rheb protein, rat
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Transcription Factors
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inhibin-alpha subunit
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2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
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Inhibins
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Follicle Stimulating Hormone
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Luciferases
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Protein Kinases
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mTOR protein, rat
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Akt1 protein, rat
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-akt
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Ribosomal Protein S6 Kinases, 70-kDa
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TOR Serine-Threonine Kinases
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Cyclic AMP-Dependent Protein Kinases
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Monomeric GTP-Binding Proteins
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ras Proteins