title: MEK1/2 inhibitors potentiate UCN-01 lethality in human multiple myeloma cells through a Bim-dependent mechanism.
abstract: The role of Bim in synergistic interactions between UCN-01 and MEK1/2 inhibitors in human multiple myeloma cells was investigated. Exposure of U266 or RPMI8226 cells to UCN-01 resulted in ERK1/2 activation-associated Bim(EL) phosphorylation/down-regulation, events abrogated by MEK1/2 inhibitors. Enforced activation of ERK1/2 by transfection with constitutively active MEK1 diminished the capacity of PD98059 but not PD184352 to block UCN-01-mediated Bim(EL) phosphorylation and to potentiate apoptosis. Cotreatment with MEK1/2 inhibitors increased the association of Bim(EL) with both Bcl-2 and Bcl-x(L) in UCN-01-treated cells, leading to Bax/Bak conformational change and Bax mitochondrial translocation. Down-regulation of Bim(EL) by shRNA substantially diminished UCN-01/MEK inhibitor-mediated Bax/Bak activation and apoptosis. Furthermore, transfection of cells with S65A Bim, a mutant resistant to UCN-01-mediated phosphorylation, significantly sensitized cells to UCN-01 lethality. Conversely, ectopic expression of either Bcl-2 or Bcl-x(L) did not alter UCN-01/MEK1/2 inhibitor-mediated modifications in Bim(EL) phosphorylation but largely prevented cell death. Finally, IL-6 or IGF-1 failed to prevent MEK1/2 inhibitors from blocking UCN-01-induced Bim(EL) phosphorylation/degradation or cell death. Collectively, these findings argue that UCN-01-mediated ERK1/2 activation leads to Bim(EL) phosphorylation/inactivation, resulting in cytoprotection, and that interference with these events by MEK1/2 inhibitors plays a critical role in synergistic induction of apoptosis by these agents.
authors.affiliation: Departments of Medicine, Virginia Commonwealth University/Massey Cancer Center, Richmond, VA 23298, USA.
authors.forename: Xin-Yan
authors.initials: XY
authors.lastname: Pei
authors.forename: Yun
authors.initials: Y
authors.lastname: Dai
authors.forename: Sarah
authors.initials: S
authors.lastname: Tenorio
authors.forename: Jianghua
authors.initials: J
authors.lastname: Lu
authors.forename: Hisashi
authors.initials: H
authors.lastname: Harada
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D001549:Benzamides / Q000494:pharmacology; D015153:Blotting, Western; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D047468:Immunoprecipitation; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D011487:Protein Conformation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D019311:Staurosporine / Q000031:analogs & derivatives* / Q000494:pharmacology; D013347:Subcellular Fractions; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: C120227:2-(2-chloro-4-iodophenylamino)-N-cyclopropylmethoxy-3,4-difluorobenzamide; D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C494772:BAK1 protein, human; C494826:BAX protein, human; C494811:BCL2L1 protein, human; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D001549:Benzamides; D004791:Enzyme Inhibitors; C508600:IL6 protein, human; D015850:Interleukin-6; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D007334:Insulin-Like Growth Factor I; C054852:7-hydroxystaurosporine; C482128:MAP2K2 protein, human; D011493:Protein Kinase C; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D019311:Staurosporine