title: PRAS40 regulates mTORC1 kinase activity by functioning as a direct inhibitor of substrate binding.
abstract: Mammalian target of rapamycin (mTOR) functions in two distinct signaling complexes, mTORC1 and mTORC2. In response to insulin and nutrients, mTORC1, consisting of mTOR, raptor (regulatory-associated protein of mTOR), and mLST8, is activated and phosphorylates eukaryotic initiation factor 4E-binding protein (4EBP) and p70 S6 kinase to promote protein synthesis and cell size. Previously we found that activation of mTOR kinase in response to insulin was associated with increased 4EBP1 binding to raptor. Here we identify prolinerich Akt substrate 40 (PRAS40) as a binding partner for mTORC1. A putative TOR signaling motif, FVMDE, is identified in PRAS40 and shown to be required for interaction with raptor. Insulin stimulation markedly decreases the level of PRAS40 bound by mTORC1. Recombinant PRAS40 inhibits mTORC1 kinase activity in vivo and in vitro, and this inhibition depends on PRAS40 association with raptor. Furthermore, decreasing PRAS40 expression by short hairpin RNA enhances 4E-BP1 binding to raptor, and recombinant PRAS40 competes with 4E-BP1 binding to raptor. We, therefore, propose that PRAS40 regulates mTORC1 kinase activity by functioning as a direct inhibitor of substrate binding.
authors.affiliation: Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908, USA. lw6j@virginia.edu
authors.forename: Lifu
authors.initials: L
authors.lastname: Wang
authors.forename: Thurl E
authors.initials: TE
authors.lastname: Harris
authors.forename: Richard A
authors.initials: RA
authors.lastname: Roth
authors.forename: John C
authors.initials: JC
authors.lastname: Lawrence
mesh_terms: D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000378:metabolism; D020816:Amino Acid Motifs; D000818:Animals; D016466:CHO Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D018797:Cell Cycle Proteins; D006224:Cricetinae; D003412:Cricetulus; D039642:Eukaryotic Initiation Factors; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000378:metabolism; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D046912:Multiprotein Complexes; D041681:NIH 3T3 Cells; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D000076223:Regulatory-Associated Protein of mTOR; D015398:Signal Transduction / Q000502:physiology; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D000076242:mTOR Associated Protein, LST8 Homolog
chemical_list: C484523:AKT1S1 protein, human; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; C499527:Eif4ebp1 protein, mouse; D039642:Eukaryotic Initiation Factors; D047908:Intracellular Signaling Peptides and Proteins; C555285:MLST8 protein, human; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D021122:Protein Subunits; D011506:Proteins; C463659:RPTOR protein, human; D011994:Recombinant Proteins; D000076223:Regulatory-Associated Protein of mTOR; D014157:Transcription Factors; D000076242:mTOR Associated Protein, LST8 Homolog; C508191:proline-rich Akt substrate, 40 kDa protein, mouse; D011494:Protein Kinases; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases