title: REDD1 enhances protein phosphatase 2A-mediated dephosphorylation of Akt to repress mTORC1 signaling.
abstract: The protein kinase mTOR (mechanistic target of rapamycin) in complex 1 (mTORC1) promotes cell growth and proliferation in response to anabolic stimuli, including growth factors and nutrients. Growth factors activate mTORC1 by stimulating the kinase Akt, which phosphorylates and inhibits the tuberous sclerosis complex [TSC; which is composed of TSC1, TSC2, and TBC1D7 (Tre2-Bub2-Cdc16 domain family member 7)], thereby stimulating the mTORC1 activator Rheb (Ras homolog enriched in brain). We identified the mechanism through which REDD1 (regulated in DNA damage and development 1) represses the mTORC1 signaling pathway. We found that REDD1 promoted the protein phosphatase 2A (PP2A)-dependent dephosphorylation of Akt on Thr(308) but not on Ser(473). Consistent with previous studies showing that phosphorylation of Akt on Thr(308), but not on Ser(473), is necessary for phosphorylation of TSC2, we observed a REDD1-dependent reduction in the phosphorylation of TSC2 and subsequently in the activation state of Rheb. REDD1 and PP2A coimmunoprecipitated with Akt from wild-type but not REDD1 knockout mouse embryonic fibroblasts, suggesting that REDD1 may act as a targeting protein for the catalytic subunit of PP2A. Furthermore, binding to both Akt and PP2A was essential for REDD1 to repress signaling to mTORC1. Overall, the results demonstrate that REDD1 acts not only as a repressor of mTORC1 but also as a constant modulator of the phosphorylation of Akt in response to growth factors and nutrients.
authors: Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, PA 17033, USA.
authors: Michael D
authors: MD
authors: Dennis
authors: Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, PA 17033, USA.
authors: Catherine S
authors: CS
authors: Coleman
authors: Division of Biostatistics and Bioinformatics, Penn State University College of Medicine, Hershey, PA 17033, USA.
authors: Arthur
authors: A
authors: Berg
authors: Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, PA 17033, USA.
authors: Leonard S
authors: LS
authors: Jefferson
authors: Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, PA 17033, USA. skimball@psu.edu.
authors: Scot R
authors: SR
authors: Kimball
mesh_terms: D000818:Animals; D005347:Fibroblasts; D057809:HEK293 Cells; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D018345:Mice, Knockout; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: C469991:DDIT4 protein, human; C469992:Ddit4 protein, mouse; D046912:Multiprotein Complexes; D014157:Transcription Factors; D000076222:Mechanistic Target of Rapamycin Complex 1; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D054648:Protein Phosphatase 2