title: Inhibition of c-Jun-N-terminal-kinase sensitizes tumor cells to CD95-induced apoptosis and induces G2/M cell cycle arrest.
abstract: Loss of susceptibility to apoptosis signals is a crucial step in carcinogenesis. Therefore, sensitization of tumor cells to apoptosis is a promising therapeutic strategy. c-Jun-N-terminal-kinases (JNK) have been implicated in stress-induced apoptosis, but may also contribute to survival signaling. Here we show that CD95-induced apoptosis is augmented by the JNK inhibitor SP600125 and small interfering RNA directed against JNK1/2. SP600125 potently inhibited methyl methane sulfonate-induced phosphorylation of c-Jun, but had minimal effect on apoptosis alone. In contrast, it strongly enhanced CD95-mediated apoptosis in six of eight tumor cell lines and led to a G2/M phase arrest in all cell lines. SP600125 enhanced cleavage of caspase 3 and caspase 8, the most upstream caspase in the CD95 pathway. JNK inhibition up-regulates p53 and its target genes p21Cip1/Waf1 and CD95. However, although HCT116 p53-/- cells and p21+/+ cells were less sensitive to CD95 stimulation than their p53+/+ and p21-/- counterparts, p53 and p21 were not involved in the JNK-mediated effect. JunD, which was described to be protective in tumor necrosis factor-induced apoptosis, was not regulated by JNK inhibition on the protein level. When transcription was blocked by actinomycin D, JNK inhibition still enhanced apoptosis to a comparable extent. We conclude that JNK inhibition has antitumor activity by inducing growth arrest and enhancing CD95-mediated apoptosis by a transcription-independent mechanism.
authors.affiliation: Department of Internal Medicine II, University Hospital Grosshadern, Ludwig-Maximilians-University, Munich, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Kuntzen
authors.forename: Nilüfer
authors.initials: N
authors.lastname: Sonuc
authors.forename: Enrico N
authors.initials: EN
authors.lastname: De Toni
authors.forename: Christine
authors.initials: C
authors.lastname: Opelz
authors.forename: Simon R
authors.initials: SR
authors.lastname: Mucha
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Gerbes
authors.forename: Sören T
authors.initials: ST
authors.lastname: Eichhorst
mesh_terms: D000873:Anthracenes / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004789:Enzyme Activation / Q000187:drug effects; D016195:G2 Phase / Q000187:drug effects / Q000502:physiology; D006801:Humans; D019169:Jurkat Cells; D008113:Liver Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D048055:Mitogen-Activated Protein Kinase 8 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D048056:Mitogen-Activated Protein Kinase 9 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D016755:Proto-Oncogene Proteins c-jun / Q000502:physiology; D034741:RNA, Small Interfering / Q000235:genetics; D014158:Transcription, Genetic; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000502:physiology; D019014:fas Receptor / Q000235:genetics / Q000502:physiology*
chemical_list: D000873:Anthracenes; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016755:Proto-Oncogene Proteins c-jun; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D019014:fas Receptor; C432165:pyrazolanthrone; D048056:Mitogen-Activated Protein Kinase 9; D048055:Mitogen-Activated Protein Kinase 8; C505407:CASP3 protein, human; C505530:CASP8 protein, human; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases