title: Adaptation to mTOR kinase inhibitors by amplification of eIF4E to maintain cap-dependent translation.
abstract: The mechanistic target of rapamycin (mTOR) protein kinase coordinates responses to nutrients and growth factors and is an anti-cancer drug target. To anticipate how cells will respond and adapt to chronic mTOR complex (mTORC)1 and mTORC2 inhibition, we have generated SW620 colon cancer cells with acquired resistance to the ATP-competitive mTOR kinase inhibitor AZD8055 (SW620:8055R). AZD8055 inhibited mTORC1 and mTORC2 signalling and caused a switch from cap-dependent to internal ribosome entry site (IRES)-dependent translation in parental SW620 cells. In contrast, SW620:8055R cells exhibited a loss of S6K signalling, an increase in expression of the eukaryotic translation initiation factor eIF4E and increased cap-dependent mRNA translation. As a result, the expression of CCND1 and MCL1, proteins encoded by eIF4E-sensitive and cap-dependent transcripts, was refractory to AZD8055 in SW620:8055R cells. RNAi-mediated knockdown of eIF4E reversed acquired resistance to AZD8055 in SW620:8055R cells; furthermore, increased expression of eIF4E was sufficient to reduce sensitivity to AZD8055 in a heterologous cell system. Finally, although the combination of MEK1/2 inhibitors with mTOR inhibitors is an attractive rational drug combination, SW620:8055R cells were actually cross-resistant to the MEK1/2 inhibitor selumetinib (AZD6244). These results exemplify the convergence of ERK1/2 and mTOR signalling at eIF4E, and the key role of eIF4E downstream of mTOR in maintaining cell proliferation. They also have important implications for therapeutic strategies based around mTOR and the MEK1/2-ERK1/2 pathway.
authors.affiliation: Signalling Programme, The Babraham Institute, Babraham Research Campus, Cambridge CB22 3AT, UK.
authors.forename: Claire L
authors.initials: CL
authors.lastname: Cope
authors.forename: Rebecca
authors.initials: R
authors.lastname: Gilley
authors.forename: Kathryn
authors.initials: K
authors.lastname: Balmanno
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Sale
authors.forename: Karen D
authors.initials: KD
authors.lastname: Howarth
authors.forename: Mark
authors.initials: M
authors.lastname: Hampson
authors.forename: Paul D
authors.initials: PD
authors.lastname: Smith
authors.forename: Sylvie M
authors.initials: SM
authors.lastname: Guichard
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Cook
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001562:Benzimidazoles / Q000494:pharmacology; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D039561:Eukaryotic Initiation Factor-4E / Q000235:genetics* / Q000378:metabolism; D059585:G1 Phase Cell Cycle Checkpoints; D005784:Gene Amplification; D006801:Humans; D009025:Morpholines / Q000494:pharmacology*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*
chemical_list: C517975:AZD 6244; D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; D001562:Benzimidazoles; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D039561:Eukaryotic Initiation Factor-4E; D009025:Morpholines; D010750:Phosphoproteins; D012333:RNA, Messenger; C546624:(5-(2,4-bis((3S)-3-methylmorpholin-4-yl)pyrido(2,3-d)pyrimidin-7-yl)-2-methoxyphenyl)methanol; C546842:MTOR protein, human; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases
keywords: 4EBP1; Cell proliferation; Drug resistance; Gene amplification; eIF4E; mTOR