Abstract
Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disorder that occurs upon mutation of either the TSC1 or TSC2 genes, which encode the protein products hamartin and tuberin, respectively. Here, we show that hamartin and tuberin function together to inhibit mammalian target of rapamycin (mTOR)-mediated signaling to eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) and ribosomal protein S6 kinase 1 (S6K1). First, coexpression of hamartin and tuberin repressed phosphorylation of 4E-BP1, resulting in increased association of 4E-BP1 with eIF4E; importantly, a mutant of TSC2 derived from TSC patients was defective in repressing phosphorylation of 4E-BP1. Second, the activity of S6K1 was repressed by coexpression of hamartin and tuberin, but the activity of rapamycin-resistant mutants of S6K1 were not affected, implicating mTOR in the TSC-mediated inhibitory effect on S6K1. Third, hamartin and tuberin blocked the ability of amino acids to activate S6K1 within nutrient-deprived cells, a process that is dependent on mTOR. These findings strongly implicate the tuberin-hamartin tumor suppressor complex as an inhibitor of mTOR and suggest that the formation of tumors within TSC patients may result from aberrantly high levels of mTOR-mediated signaling to downstream targets.
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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Adaptor Proteins, Signal Transducing
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Amino Acids / metabolism
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Carrier Proteins / antagonists & inhibitors
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Carrier Proteins / chemistry
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Carrier Proteins / metabolism
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Cell Cycle Proteins
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Cell Line
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Humans
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In Vitro Techniques
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Insulin / pharmacology
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Models, Biological
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Phosphatidylinositol 3-Kinases / metabolism
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Phosphoproteins / antagonists & inhibitors
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Phosphoproteins / chemistry
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Phosphoproteins / metabolism
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Phosphorylation
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Point Mutation
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Protein Kinases / genetics
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Protein Kinases / metabolism*
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Proteins / genetics
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Proteins / metabolism*
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Repressor Proteins / genetics
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Repressor Proteins / metabolism*
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Ribosomal Protein S6 Kinases / antagonists & inhibitors
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Ribosomal Protein S6 Kinases / metabolism
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Signal Transduction
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TOR Serine-Threonine Kinases
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Tuberous Sclerosis / genetics
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Tuberous Sclerosis / metabolism
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Tuberous Sclerosis Complex 1 Protein
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Tuberous Sclerosis Complex 2 Protein
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Tumor Suppressor Proteins
Substances
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Adaptor Proteins, Signal Transducing
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Amino Acids
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Carrier Proteins
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Cell Cycle Proteins
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EIF4EBP1 protein, human
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Insulin
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Phosphoproteins
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Proteins
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Repressor Proteins
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TSC1 protein, human
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TSC2 protein, human
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Tuberous Sclerosis Complex 1 Protein
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Tuberous Sclerosis Complex 2 Protein
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Tumor Suppressor Proteins
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Protein Kinases
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MTOR protein, human
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Ribosomal Protein S6 Kinases
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TOR Serine-Threonine Kinases