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

• Published in: The Journal of biological chemistry Vol. 287; no. 13; pp. 10289 - 10300
• Main Authors: Kawabata, Takumi, Tanimura, Susumu, Asai, Kohei, Kawasaki, Ryohei, Matsumaru, Yumi, Kohno, Michiaki
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 23.03.2012; American Society for Biochemistry and Molecular Biology
• Subjects: Apoptosis; Apoptosis - drug effects; Apoptosis - genetics; Apoptosis Regulatory Proteins - genetics; Apoptosis Regulatory Proteins - metabolism; Bcl-2 Family Proteins; Bcl-2-Like Protein 11; Bim; Calcium-Binding Proteins - genetics; Calcium-Binding Proteins - metabolism; Cancer Therapy; Cell Cycle Checkpoints - drug effects; Cell Cycle Checkpoints - genetics; Cell Cycle Proteins - genetics; Cell Cycle Proteins - metabolism; Cell Line, Tumor; Down-Regulation - drug effects; Down-Regulation - genetics; Enzyme Inhibitors - pharmacology; ERK; ERK Pathway; Extracellular Signal-Regulated MAP Kinases - antagonists & inhibitors; Extracellular Signal-Regulated MAP Kinases - genetics; Extracellular Signal-Regulated MAP Kinases - metabolism; Gene Expression Regulation, Neoplastic - drug effects; Gene Expression Regulation, Neoplastic - genetics; Gene Knockdown Techniques; Humans; Mad2 Proteins; MAP Kinase Signaling System - drug effects; MAP Kinase Signaling System - genetics; Mcl-1; MEK Inhibitor; Membrane Proteins - genetics; Membrane Proteins - metabolism; Microtubular Inhibitor; Microtubules; Molecular Bases of Disease; Myeloid Cell Leukemia Sequence 1 Protein; Neoplasms - genetics; Neoplasms - metabolism; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - metabolism; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2 - genetics; Proto-Oncogene Proteins c-bcl-2 - metabolism; Repressor Proteins - genetics; Repressor Proteins - metabolism; RNA, Small Interfering - genetics; RNA, Small Interfering - pharmacology; Up-Regulation - drug effects; Up-Regulation - genetics; ERK Pathway; Cancer Therapy; Mcl-1; MEK Inhibitor; Microtubules; Bim; Microtubular Inhibitor; Apoptosis; Bcl-2 Family Proteins; ERK
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.319426

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. MEK inhibitors enhance apoptosis induction by microtubule inhibitors. MEK and microtubule inhibitors together induced up-regulation of Bim and down-regulation of Mcl-1 in association with prolongation of mitosis. The drug combination tips the balance between pro- and anti-apoptotic signaling toward induction of cell death. The combination of MEK inhibitors with agents that down-regulate or inactivate anti-apoptotic proteins is a promising anticancer strategy.