Genetic and pharmacologic inhibition of mTORC1 promotes EMT by a TGF-β-independent mechanism.
Epithelial-to-mesenchymal transition (EMT) is a transdifferentiation process that converts epithelial cells into highly motile mesenchymal cells. This physiologic process occurs largely during embryonic development but is aberrantly reactivated in different pathologic situations, including fibrosis and cancer. We conducted a siRNA screening targeted to the human kinome with the aim of discovering new EMT effectors. With this approach, we have identified mTOR complex 1 (mTORC1), a nutrient sensor that controls protein and lipid synthesis, as a key regulator of epithelial integrity. Using a combination of RNAi and pharmacologic approaches, we report here that inhibition of either mTOR or RPTOR triggers EMT in mammary epithelial cells. This EMT was characterized by the induction of the mesenchymal markers such as fibronectin, vimentin, and PAI-1, together with the repression of epithelial markers such as E-cadherin and ZO-3. In addition, mTORC1 blockade enhanced in vivo migratory properties of mammary cells and induced EMT independent of the TGF-β pathway. Finally, among the transcription factors known to activate EMT, both ZEB1 and ZEB2 were upregulated following mTOR repression. Their increased expression correlated with a marked reduction in miR-200b and miR-200c mRNA levels, two microRNAs known to downregulate ZEB1 and ZEB2 expression. Taken together, our findings unravel a novel function for mTORC1 in maintaining the epithelial phenotype and further indicate that this effect is mediated through the opposite regulation of ZEB1/ZEB2 and miR-200b and miR-200c. Furthermore, these results suggest a plausible etiologic explanation for the progressive pulmonary fibrosis, a frequent adverse condition associated with the therapeutic use of mTOR inhibitors.
Authors' Affiliations: Université Lyon 1, ISPB; CNRS UMR5286, INSERM U1052, Centre de Recherche en Cancérologie de Lyon, Centre Léon Bérard; CIRI INSERM U1111, CNRS UMR5308, ENS Lyon, Lyon; INSERM, U823, Université Joseph Fourier-Grenoble 1, Institut Albert Bonniot; In Ovo, Grenoble, France; and Inositide Laboratory-Signaling Program, Babraham Institute-Babraham Research Campus, Babraham, Cambridge, United Kingdom.
Ivan
I
Mikaelian
Mouhannad
M
Malek
Rudy
R
Gadet
Jean
J
Viallet
Amandine
A
Garcia
Anaïs
A
Girard-Gagnepain
Cédric
C
Hesling
Germain
G
Gillet
Philippe
P
Gonzalo
Ruth
R
Rimokh
Marc
M
Billaud
D000818:Animals; D002465:Cell Movement / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D002642:Chick Embryo; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D058750:Epithelial-Mesenchymal Transition / Q000235:genetics / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D018398:Homeodomain Proteins / Q000378:metabolism; D006801:Humans; D061986:MCF-7 Cells; D000076222:Mechanistic Target of Rapamycin Complex 1; D035683:MicroRNAs / Q000378:metabolism; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D009361:Neoplasm Invasiveness; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D012097:Repressor Proteins / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000502:physiology; D000074165:Zinc Finger E-box Binding Homeobox 2; D000071799:Zinc Finger E-box-Binding Homeobox 1
D018398:Homeodomain Proteins; C533896:MIRN200 microRNA, human; D035683:MicroRNAs; D046912:Multiprotein Complexes; D047428:Protein Kinase Inhibitors; D012097:Repressor Proteins; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; C486307:ZEB1 protein, human; C492363:ZEB2 protein, human; D000074165:Zinc Finger E-box Binding Homeobox 2; D000071799:Zinc Finger E-box-Binding Homeobox 1; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases