title: Switch in signaling control of mTORC1 activity after oncoprotein expression in thyroid cancer cell lines.
abstract: BACKGROUND
  Thyroid growth is regulated by TSH and requires mammalian target of rapamycin (mTOR). Thyroid cancers frequently exhibit mutations in MAPK and/or phosphoinositol-3-kinase-related kinase effectors.
  
  
  OBJECTIVE
  The objective of the study was to explore the contribution of RET/PTC, RAS, and BRAF to mTOR regulation and response to mTOR inhibitors.
  
  
  METHODS
  PCCL3 cells conditionally expressing RET/PTC3, HRAS(G12V), or BRAF(V600E) and human thyroid cancer cells harboring mutations of these genes were used to test pathways controlling mTOR and its requirement for growth.
  
  
  RESULTS
  TSH/cAMP-induced growth of PCCL3 cells requires mTOR, which is stimulated via protein kinase A in a MAPK kinase (MEK)- and AKT-independent manner. Expression of RET/PTC3, HRAS(G12V), or BRAF(V600E) in PCCL3 cells induces mTOR but does not entirely abrogate the cAMP-mediated control of its activity. Acute oncoprotein-induced mTOR activity is regulated by MEK and AKT, albeit to differing degrees. By contrast, mTOR was not activated by TSH/cAMP in human thyroid cancer cells. Tumor genotype did not predict the effects of rapamycin or the mTOR kinase inhibitor AZD8055 on growth, with the exception of a PTEN-null cell line. Selective blockade of MEK did not influence mTOR activity of BRAF or RAS mutant cells. Combined MEK and mTOR kinase inhibition was synergistic on growth of BRAF- and RAS-mutant thyroid cancer cells in vitro and in vivo.
  
  
  CONCLUSIONS
  Thyroid cancer cells lose TSH/cAMP dependency of mTOR signaling and cell growth. mTOR activity is not decreased by the MEK or AKT inhibitors in the RAS or BRAF human thyroid cancer cell lines. This may account for the augmented effects of combining the mTOR inhibitors with selective antagonists of these oncogenic drivers.
authors.affiliation: Human Oncology and Pathogenesis Program (R.M., K.-Y.C., T.-Y.K., J.M.D., F.V., S.K.V., J.A.K., J.A.F.) and Department of Medicine (J.A.K., J.A.F.), Memorial Sloan-Kettering Cancer Center, New York, New York 10065; and Division of Endocrinology (B.O.), University of Cincinnati College of Medicine, Cincinnati, Ohio 45267.
authors.forename: Roberta
authors.initials: R
authors.lastname: Malaguarnera
authors.forename: Kuen-Yuan
authors.initials: KY
authors.lastname: Chen
authors.forename: Tae-Yong
authors.initials: TY
authors.lastname: Kim
authors.forename: Jose M
authors.initials: JM
authors.lastname: Dominguez
authors.forename: Francesca
authors.initials: F
authors.lastname: Voza
authors.forename: Bin
authors.initials: B
authors.lastname: Ouyang
authors.forename: Sushil K
authors.initials: SK
authors.lastname: Vundavalli
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Knauf
authors.forename: James A
authors.initials: JA
authors.lastname: Fagin
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D001562:Benzimidazoles / Q000494:pharmacology; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000378:metabolism; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D000076222:Mechanistic Target of Rapamycin Complex 1; D008819:Mice, Nude; D009025:Morpholines / Q000494:pharmacology; D046912:Multiprotein Complexes / Q000378:metabolism*; D009368:Neoplasm Transplantation; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism; D051381:Rats; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000378:metabolism* / Q000473:pathology; D013972:Thyrotropin / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C517975:AZD 6244; D000903:Antibiotics, Antineoplastic; D001562:Benzimidazoles; C528429:Hras protein, rat; D009025:Morpholines; D046912:Multiprotein Complexes; D015513:Oncogene Proteins; D013972:Thyrotropin; C546624:(5-(2,4-bis((3S)-3-methylmorpholin-4-yl)pyrido(2,3-d)pyrimidin-7-yl)-2-methoxyphenyl)methanol; D000242:Cyclic AMP; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human; C495001:Ret protein, rat; C482119:BRAF protein, human; C482123:Braf protein, rat; D000076222:Mechanistic Target of Rapamycin Complex 1; D048493:Proto-Oncogene Proteins B-raf; D058570:TOR Serine-Threonine Kinases; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; D020123:Sirolimus