title: Activation of AP-1 is required for bufalin-induced apoptosis in human leukemia U937 cells.
abstract: In a previous study, we demonstrated that bufalin caused apoptosis in human leukemia U937 cells by the anomalous activation of mitogen-activated protein kinase (MAPK) via a signaling pathway that included Ras, Raf-1 and MAPK kinase-1. We report here the effect of bufalin on c-Jun N-terminal protein kinase (JNK), a member of the MAPK family, and on the signaling pathway downstream of MAPKs in U937 cells. When U937 cells were treated with 10(-8) M bufalin, the activity of JNK1 was markedly elevated 3 h after the start of treatment and remained so for 9 h. This activation of JNK and the induction of apoptosis by bufalin were suppressed by expression of antisense mRNA for MAPK kinase-1. c-Jun was translocated from the cytoplasm to the nucleus after treatment of U937 cells with bufalin. The transcriptional activity of AP-1 was transiently enhanced by the treatment with bufalin and this activation was suppressed by the expression of antisense mRNA for MAPK kinase-1. Both curcumin (1,7-bis[4-hydroxy-3-methoxy-phenyl]-1,6-heptadiene-3,5-dione), an inhibitor of the biosynthesis of AP-1, and the expression of dominant negative c-Jun inhibited the activation of AP-1 and the induction of apoptosis by bufalin. Expression of a constitutively active mutant form of MAPK kinase-1 induced the activation of AP-1 and subsequent apoptosis in U937 cells. These results suggest that the activation of AP-1 via a MAPK cascade that includes JNK is required for the induction of apoptosis by bufalin in U937 cells.
authors.affiliation: Laboratory of Biological Chemistry, School of Pharmaceutical Sciences, Showa University, Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Watabe
authors.forename: K
authors.initials: K
authors.lastname: Ito
authors.forename: Y
authors.initials: Y
authors.lastname: Masuda
authors.forename: S
authors.initials: S
authors.lastname: Nakajo
authors.forename: K
authors.initials: K
authors.lastname: Nakaya
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002018:Bufanolides / Q000494:pharmacology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D003474:Curcumin / Q000494:pharmacology; D004789:Enzyme Activation; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D007938:Leukemia; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D002018:Bufanolides; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D018808:Transcription Factor AP-1; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D003474:Curcumin; C022777:bufalin