title: c-Jun N-terminal kinase (JNK1) upregulates XIAP-associated factor 1 (XAF1) through interferon regulatory factor 1 (IRF-1) in gastrointestinal cancer.
abstract: OBJECTIVE
  X-linked inhibitor of apoptosis protein-associated factor 1 (XAF1) is a tumor suppressor that can sensitize cancer cell to apoptosis. Intrinsic expression of XAF1 in cancer cell is low. Our purpose is to determine the effect of c-Jun N-terminal kinase 1 (JNK1) on XAF1 expression and the putative mechanism.
  
  
  METHODS
  XAF1 expression in gastrointestinal (GI) cancer cell line AGS and SW1116 was detected by reverse transcription-polymerase chain reaction (PCR), real-time PCR and immunoblotting. The role of JNK1 was assessed by ectopic overexpression with wild-type (JNK1-WT) and dominant-negative (JNK1-DN) JNK1 constructs. The effects of JNK1 activator, interferon (IFN)-alpha, tumor necrosis factor (TNF)-alpha and phorbol-12-myristate-13-acetate (PMA), or JNK1 inhibitor, SP600125, were evaluated. An XAF1 promoter reporter pLUC107 with WT or mutated interferon regulatory factor 1-binding element (IRF-E) was used to assess JNK1-induced transcription by dual luciferase assay.
  
  
  RESULTS
  Ectopic overexpression of JNK1-WT or treatment with IFN-alpha, TNF-alpha and PMA induced whereas SP600125 suppressed intrinsic and induced XAF1 expression. Induction of XAF1 required de novo protein synthesis. Moreover, JNK1 stimulated whereas SP600125 suppressed XAF1 promoter activity. JNK1 stimulated interferon regulatory factor 1 (IRF-1) expression, whereas both IRF-1 small-interfering RNA and site mutation of IRF-E within XAF1 promoter abrogated the effect of JNK1.
  
  
  CONCLUSIONS
  JNK1 stimulated and mediated the effects of IFN and TNF-alpha on XAF1 expression through transcriptional regulation by induction of IRF-1. The linkage of JNK1, IRF-1 and XAF1 in the same signal pathway may unravel a novel mechanism in regulation of apoptosis and differentiation of GI cancers.
authors.affiliation: Department of Digestive Medicine, Nanfang Hospital, Southern Medical University, Guangzhou, China. jidewang@gmail.com
authors.forename: Jide
authors.initials: J
authors.lastname: Wang
authors.forename: Wenjing
authors.initials: W
authors.lastname: Zhang
authors.forename: Yusheng
authors.initials: Y
authors.lastname: Zhang
authors.forename: Ye
authors.initials: Y
authors.lastname: Chen
authors.forename: Bing
authors.initials: B
authors.lastname: Zou
authors.forename: Bo
authors.initials: B
authors.lastname: Jiang
authors.forename: Roberta
authors.initials: R
authors.lastname: Pang
authors.forename: Qing
authors.initials: Q
authors.lastname: Gu
authors.forename: Liang
authors.initials: L
authors.lastname: Qiao
authors.forename: Huiyao
authors.initials: H
authors.lastname: Lan
authors.forename: Hsiang-Fu
authors.initials: HF
authors.lastname: Kung
authors.forename: Benjamin C Y
authors.initials: BC
authors.lastname: Wong
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000873:Anthracenes / Q000494:pharmacology; D051017:Apoptosis Regulatory Proteins; D045744:Cell Line, Tumor; D005770:Gastrointestinal Neoplasms / Q000378:metabolism*; D006801:Humans; D050856:Interferon Regulatory Factor-1 / Q000378:metabolism*; D016898:Interferon-alpha / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D048055:Mitogen-Activated Protein Kinase 8 / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D010703:Phorbol Esters / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D015533:Transcriptional Activation; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000873:Anthracenes; D051017:Apoptosis Regulatory Proteins; C494257:IRF1 protein, human; D050856:Interferon Regulatory Factor-1; D016898:Interferon-alpha; D047908:Intracellular Signaling Peptides and Proteins; D009363:Neoplasm Proteins; D010703:Phorbol Esters; D014409:Tumor Necrosis Factor-alpha; C417551:XAF1 protein, human; C432165:pyrazolanthrone; C032974:12-O-retinoylphorbol-13-acetate; D048055:Mitogen-Activated Protein Kinase 8