title: Inhibition of mTORC1 induces loss of E-cadherin through AKT/GSK-3β signaling-mediated upregulation of E-cadherin repressor complexes in non-small cell lung cancer cells.
abstract: BACKGROUND
  mTOR, which can form mTOR Complex 1 (mTORC1) or mTOR Complex 2 (mTORC2) depending on its binding partners, is frequently deregulated in the pulmonary neoplastic conditions and interstitial lung diseases of the patients treated with rapalogs. In this study, we investigated the relationship between mTOR signaling and epithelial mesenchymal transition (EMT) by dissecting mTOR pathways.
  
  
  METHODS
  Components of mTOR signaling pathway were silenced by shRNA in a panel of non-small cell lung cancer cell lines and protein expression of epithelial and mesenchymal markers were evaluated by immunoblotting and immunocytochemistry. mRNA level of the E-cadherin repressor complexes were evaluated by qRT-PCR.
  
  
  RESULTS
  IGF-1 treatment decreased expression of the E-cadherin and rapamycin increased its expression, suggesting hyperactivation of mTOR signaling relates to the loss of E-cadherin. Genetic ablation of rapamycin-insensitive companion of mTOR (Rictor), a component of mTORC2, did not influence E-cadherin expression, whereas genetic ablation of regulatory-associated protein of mTOR (Raptor), a component of mTORC1, led to a decrease in E-cadherin expression at the mRNA level. Increased phosphorylation of AKT at Ser473 and GSK-3β at Ser9 were observed in the Raptor-silenced NSCLC cells. Of the E-cadherin repressor complexes tested, Snail, Zeb2, and Twist1 mRNAs were elevated in raptor-silenced A549 cells, and Zeb2 and Twist1 mRNAs were elevated in Raptor-silenced H2009 cells. These findings were recapitulated by treatment with the GSK-3β inhibitor, LiCl. Raptor knockdown A549 cells showed increased expression of N-cadherin and vimentin with mesenchymal phenotypic changes.
  
  
  CONCLUSIONS
  In conclusion, selective inhibition of mTORC1 leads to hyperactivation of the AKT/GSK-3β pathway, inducing E-cadherin repressor complexes and EMT. These findings imply the existence of a feedback inhibition loop of mTORC1 onto mTORC2 that plays a role in the homeostasis of E-cadherin expression and EMT, requiring caution in the clinical use of rapalog and selective mTORC1 inhibitors.
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Kim
authors.forename: Arum
authors.initials: A
authors.lastname: Kim
authors.forename: Se Kyu
authors.initials: SK
authors.lastname: Kim
authors.forename: Hyung Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Joon
authors.initials: J
authors.lastname: Chang
authors.forename: Chul Min
authors.initials: CM
authors.lastname: Ahn
authors.affiliation: Department of Internal Medicine, Yonsei University College of Medicine, 50-1, Yonsei-ro, Seodaemun-gu, Seoul 120-752, Republic of Korea. yschang@yuhs.ac.
authors.forename: Yoon Soo
authors.initials: YS
authors.lastname: Chang
mesh_terms: D015820:Cadherins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D058750:Epithelial-Mesenchymal Transition / Q000187:drug effects / Q000502:physiology; D020868:Gene Silencing / Q000502:physiology; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism*; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D012189:Retrospective Studies; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
chemical_list: D015820:Cadherins; D004791:Enzyme Inhibitors; D046912:Multiprotein Complexes; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D000076222:Mechanistic Target of Rapamycin Complex 1; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3