title: p53 Deletion or Hotspot Mutations Enhance mTORC1 Activity by Altering Lysosomal Dynamics of TSC2 and Rheb.
abstract: The activity of mammalian target of rapamycin complex 1 (mTORC1) is frequently enhanced in carcinomas, an effect thought to contribute to the malignant phenotype. Here, it is demonstrated that either deletion or mutation of TP53 in colon or lung carcinoma cells substantially enhances mTORC1 kinase activity by an effect downstream of and independent of AMPK. Mechanistically, it was determined that loss or mutation of p53 decreased expression of TSC2 and Sestrin2 (SESN2). Complementation of p53 null cells with TSC2 or Sestrin2 reduced mTORC1 activity to levels found in p53 wild-type (wt) cells, whereas their genetic depletion enhanced mTORC1 activity in p53 wt cells. However, the primary causal event in enhanced mTORC1 activity upon loss of p53 appeared to be a diminished distribution of TSC2 to lysosomal membranes containing mTOR. Subsequently, there was increased Rheb in the lysosomal compartment, and a higher mTOR association with Raptor. Transfection of TSC2 into p53 null cells replaced TSC2 and diminished Rheb at the lysosome, recapitulating cells with wt p53. In contrast, transfection of Sestrin2 decreased mTOR in lysosomes, but the lower levels of Sestrin2 in p53 null cells did not change lysosomal mTOR. In summary, loss of the transcriptional activity of p53, either by deletion or by key mutations in the DNA-binding domain, diminishes expression of TSC2 and Sestrin2, thus, shifting membrane-bound TSC2 out of lysosomal membranes, increasing lysosomal Rheb and increasing the kinase activity of mTORC1.
  
  
  CONCLUSIONS
  This study establishes that loss of p53 function decreases lysosomal TSC2 and increases lysosomal Rheb resulting in hyperactive mTORC1, findings that are consistent with a more malignant phenotype.
authors.affiliation: Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Stuti
authors.initials: S
authors.lastname: Agarwal
authors.affiliation: Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Bell
authors.affiliation: Department of Microbiology and Immunology and Massey Cancer Center, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Shirley M
authors.initials: SM
authors.lastname: Taylor
authors.affiliation: Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia. richard.moran@vcuhealth.org.
authors.forename: Richard G
authors.initials: RG
authors.lastname: Moran
mesh_terms: D017353:Gene Deletion; D015972:Gene Expression Regulation, Neoplastic; D045325:HCT116 Cells; D006801:Humans; D008247:Lysosomes / Q000235:genetics / Q000378:metabolism*; D000076222:Mechanistic Target of Rapamycin Complex 1; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D000076205:Ras Homolog Enriched in Brain Protein; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D000077005:Tuberous Sclerosis Complex 2 Protein; D016159:Tumor Suppressor Protein p53 / Q000235:genetics*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D000084622:Sestrins
chemical_list: D000076222:Mechanistic Target of Rapamycin Complex 1; D020559:Monomeric GTP-Binding Proteins; D046912:Multiprotein Complexes; D009479:Neuropeptides; D009687:Nuclear Proteins; D000076205:Ras Homolog Enriched in Brain Protein; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C490211:RHEB protein, human; C465398:SESN2 protein, human; D000084622:Sestrins; C495901:TP53 protein, human; C000624653:TSC2 protein, human