Journal Article

mTORC1 upregulation via ERK-dependent gene expression change confers intrinsic resistance to MEK inhibitors in oncogenic KRas-mutant cancer cells

Aoki, K, Fujita, Y, Matsuda, M, Komatsu, N

2015

Overview

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.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 1-Phosphatidylinositol 3-kinase / 13/109 / 13/89 / 13/95 / 14/33 / 38/91 / 42/35 / 631/67/1059/2326 / 631/67/1059/602 / 631/80/86/2368 / 96/47 / Analysis / Apoptosis / Biosensors / Cancer / Cell Biology / Cell growth / Cell Line, Tumor / Cells / Drug resistance / Extracellular signal-regulated kinase / Extracellular Signal-Regulated MAP Kinases - antagonists & inhibitors / Extracellular Signal-Regulated MAP Kinases - genetics / Extracellular Signal-Regulated MAP Kinases - metabolism / Fluorescence resonance energy transfer / Gene expression / Gene Expression Regulation, Neoplastic - drug effects / Genetic regulation / Growth rate / Human Genetics / Humans / Influence / Internal Medicine / Intracellular Signaling Peptides and Proteins - genetics / Intracellular Signaling Peptides and Proteins - metabolism / K-Ras protein / Kinases / MAP Kinase Signaling System - drug effects / MAP Kinase Signaling System - genetics / Mechanistic Target of Rapamycin Complex 1 / Medicine / Medicine & Public Health / MEK inhibitors / Metabolic pathways / Multiprotein Complexes - biosynthesis / Multiprotein Complexes - genetics / Mutants / Mutation / Neoplasms - drug therapy / Neoplasms - genetics / Neoplasms - metabolism / Oncogenes / Oncology / original-article / Phosphatidylinositol 3-Kinases - genetics / Phosphatidylinositol 3-Kinases - metabolism / Phosphotransferases / Protein Kinase Inhibitors - pharmacology / Proto-Oncogene Proteins - genetics / Proto-Oncogene Proteins - metabolism / Proto-Oncogene Proteins B-raf - genetics / Proto-Oncogene Proteins B-raf - metabolism / Proto-Oncogene Proteins p21(ras) / Rapamycin / ras Proteins - genetics / ras Proteins - metabolism / Telomerase - genetics / Telomerase - metabolism / TOR protein / TOR Serine-Threonine Kinases - biosynthesis / TOR Serine-Threonine Kinases - genetics / Transcription / Tuberous Sclerosis Complex 1 / Tuberous Sclerosis Complex 2 / Tumor cell lines / Tumor Suppressor Proteins - genetics / Tumor Suppressor Proteins - metabolism / Up-Regulation - drug effects