title: Up-regulation of pro-apoptotic protein Bim and down-regulation of anti-apoptotic protein Mcl-1 cooperatively mediate enhanced tumor cell death induced by the combination of ERK kinase (MEK) inhibitor and microtubule inhibitor.
abstract: Blockade of the ERK signaling pathway by ERK kinase (MEK) inhibitors selectively enhances the induction of apoptosis by microtubule inhibitors in tumor cells in which this pathway is constitutively activated. We examined the mechanism by which such drug combinations induce enhanced cell death by applying time-lapse microscopy to track the fate of individual cells. MEK inhibitors did not affect the first mitosis after drug exposure, but most cells remained arrested in interphase without entering a second mitosis. Low concentrations of microtubule inhibitors induced prolonged mitotic arrest followed by exit of cells from mitosis without division, with most cells remaining viable. However, the combination of a MEK inhibitor and a microtubule inhibitor induced massive cell death during prolonged mitosis. Impairment of spindle assembly checkpoint function by RNAi-mediated depletion of Mad2 or BubR1 markedly suppressed such prolonged mitotic arrest and cell death. The cell death was accompanied by up-regulation of the pro-apoptotic protein Bim (to which MEK inhibitors contributed) and by down-regulation of the anti-apoptotic protein Mcl-1 (to which microtubule and MEK inhibitors contributed synergistically). Whereas RNAi-mediated knockdown of Bim suppressed cell death, stabilization of Mcl-1 by RNAi-mediated depletion of Mule slowed its onset. Depletion of Mcl-1 sensitized tumor cells to MEK inhibitor-induced cell death, an effect that was antagonized by knockdown of Bim. The combination of MEK and microtubule inhibitors thus targets Bim and Mcl-1 in a cooperative manner to induce massive cell death in tumor cells with aberrant ERK pathway activation.
authors.affiliation: Laboratory of Cell Regulation, Department of Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8521.
authors.forename: Takumi
authors.initials: T
authors.lastname: Kawabata
authors.affiliation: Laboratory of Cell Regulation, Department of Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8521,; Nagasaki University Research Center for Genomic Instability and Carcinogenesis (NRGIC), Nagasaki 852-8523, and.
authors.forename: Susumu
authors.initials: S
authors.lastname: Tanimura
authors.affiliation: Laboratory of Cell Regulation, Department of Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8521.
authors.forename: Kohei
authors.initials: K
authors.lastname: Asai
authors.affiliation: Laboratory of Cell Regulation, Department of Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8521.
authors.forename: Ryohei
authors.initials: R
authors.lastname: Kawasaki
authors.affiliation: Laboratory of Cell Regulation, Department of Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8521.
authors.forename: Yumi
authors.initials: Y
authors.lastname: Matsumaru
authors.affiliation: Laboratory of Cell Regulation, Department of Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8521,; Department of Genetic Biochemistry, Kyoto University Graduate School of Pharmaceutical Sciences, Kyoto 606-8501, Japan. Electronic address: kohnom@nagasaki-u.ac.jp.
authors.forename: Michiaki
authors.initials: M
authors.lastname: Kohno
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D059447:Cell Cycle Checkpoints / Q000187:drug effects / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects* / Q000235:genetics; D055785:Gene Knockdown Techniques; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects* / Q000235:genetics; D064246:Mad2 Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D008565:Membrane Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D012097:Repressor Proteins; C584277:BUB1 protein, human; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases; D048049:Extracellular Signal-Regulated MAP Kinases