title: mTORC1 upregulation via ERK-dependent gene expression change confers intrinsic resistance to MEK inhibitors in oncogenic KRas-mutant cancer cells.
abstract: Cancer cells harboring oncogenic BRaf mutants, but not oncogenic KRas mutants, are sensitive to MEK inhibitors (MEKi). The mechanism underlying the intrinsic resistance to MEKi in KRas-mutant cells is under intensive investigation. Here, we pursued this mechanism by live imaging of extracellular signal-regulated kinases (ERK) and mammalian target of rapamycin complex 1 (mTORC1) activities in oncogenic KRas or BRaf-mutant cancer cells. We established eight cancer cell lines expressing Förster resonance energy transfer (FRET) biosensors for ERK activity and S6K activity, which was used as a surrogate marker for mTORC1 activity. Under increasing concentrations of MEKi, ERK activity correlated linearly with the cell growth rate in BRaf-mutant cancer cells, but not KRas-mutant cancer cells. The administration of PI3K inhibitors resulted in a linear correlation between ERK activity and cell growth rate in KRas-mutant cancer cells. Intriguingly, mTORC1 activity was correlated linearly with the cell growth rate in both BRaf-mutant cancer cells and KRas-mutant cancer cells. These observations suggested that mTORC1 activity had a pivotal role in cell growth and that the mTORC1 activity was maintained primarily by the ERK pathway in BRaf-mutant cancer cells and by both the ERK and PI3K pathways in KRas-mutant cancer cells. FRET imaging revealed that MEKi inhibited mTORC1 activity with slow kinetics, implying transcriptional control of mTORC1 activity by ERK. In agreement with this observation, MEKi induced the expression of negative regulators of mTORC1, including TSC1, TSC2 and Deptor, which occurred more significantly in BRaf-mutant cells than in KRas-mutant cells. These findings suggested that the suppression of mTORC1 activity and induction of negative regulators of mTORC1 in cancer cells treated for at least 1 day could be used as surrogate markers for the MEKi sensitivity of cancer cells.
authors.affiliation: Laboratory of Bioimaging and Cell Signaling, Graduate School of Biostudies, Kyoto University, Kyoto, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Komatsu
authors.affiliation: Department of Pathology and Biology of Diseases, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Fujita
authors.affiliation: Laboratory of Bioimaging and Cell Signaling, Graduate School of Biostudies, Kyoto University, Kyoto, Japan.|Department of Pathology and Biology of Diseases, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Matsuda
authors.affiliation: Imaging Platform for Spatio-Temporal Information, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Aoki
mesh_terms: D045744:Cell Line, Tumor; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects* / Q000235:genetics; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes / Q000096:biosynthesis* / Q000235:genetics; D009154:Mutation; D009369:Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras); D058570:TOR Serine-Threonine Kinases / Q000096:biosynthesis* / Q000235:genetics; D019098:Telomerase / Q000235:genetics / Q000378:metabolism; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D048049:Extracellular Signal-Regulated MAP Kinases; D047908:Intracellular Signaling Peptides and Proteins; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D019869:Phosphatidylinositol 3-Kinases; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D048493:Proto-Oncogene Proteins B-raf; D016283:Proto-Oncogene Proteins p21(ras); D058570:TOR Serine-Threonine Kinases; D019098:Telomerase; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D018631:ras Proteins; C117307:KRAS protein, human; C000624653:TSC2 protein, human; C556139:DEPTOR protein, human; C482119:BRAF protein, human; C509186:TERT protein, human