Abstract
The TSC1-TSC2/Rheb/Raptor-mTOR/S6K1 cell growth cassette has recently been shown to regulate cell autonomous insulin and insulin-like growth factor I (IGF-I) sensitivity by transducing a negative feedback signal that targets insulin receptor substrates 1 and 2 (IRS1 and -2). Using two cell culture models of the familial hamartoma syndrome, tuberous sclerosis, we show here that Raptor-mTOR and S6K1 are required for phosphorylation of IRS1 at a subset of serine residues frequently associated with insulin resistance, including S307, S312, S527, S616, and S636 (of human IRS1). Using loss- and gain-of-function S6K1 constructs, we demonstrate a requirement for the catalytic activity of S6K1 in both direct and indirect regulation of IRS1 serine phosphorylation. S6K1 phosphorylates IRS1 in vitro on multiple residues showing strong preference for RXRXXS/T over S/T,P sites. IRS1 is preferentially depleted from the high-speed pellet fraction in TSC1/2-deficient mouse embryo fibroblasts or in HEK293/293T cells overexpressing Rheb. These studies suggest that, through serine phosphorylation, Raptor-mTOR and S6K1 cell autonomously promote the depletion of IRS1 from specific intracellular pools in pathological states of insulin and IGF-I resistance and thus potentially in lesions associated with tuberous sclerosis.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing
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Animals
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Cell Culture Techniques
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Cells, Cultured
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Humans
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Insulin Receptor Substrate Proteins
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Mice
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Monomeric GTP-Binding Proteins / metabolism
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Neuropeptides / metabolism
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Phosphoproteins / deficiency
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Phosphoproteins / metabolism*
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Phosphoserine / metabolism*
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Protein Kinases / metabolism*
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Proteins / metabolism*
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Ras Homolog Enriched in Brain Protein
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Regulatory-Associated Protein of mTOR
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Ribosomal Protein S6 Kinases / metabolism*
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Subcellular Fractions
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TOR Serine-Threonine Kinases
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Tuberous Sclerosis / pathology*
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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 / deficiency
Substances
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Adaptor Proteins, Signal Transducing
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IRS1 protein, human
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Insulin Receptor Substrate Proteins
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Irs1 protein, mouse
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Neuropeptides
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Phosphoproteins
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Proteins
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RHEB protein, human
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RPTOR protein, human
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Ras Homolog Enriched in Brain Protein
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Regulatory-Associated Protein of mTOR
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TSC1 protein, human
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TSC2 protein, human
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Tsc1 protein, mouse
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Tsc2 protein, mouse
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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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Phosphoserine
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Protein Kinases
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MTOR protein, human
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mTOR protein, mouse
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Ribosomal Protein S6 Kinases
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TOR Serine-Threonine Kinases
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Monomeric GTP-Binding Proteins