title: Impaired TNFalpha-induced A20 expression in E1A/Ras-transformed cells.
abstract: BACKGROUND
  Tumour necrosis factor (TNF) is capable of activating the cell death pathway, and has been implicated in killing transformed cells. However, TNF also activates survival signals, including NF-kappaB activation and the subsequent expression of anti-apoptotic genes, leading to protection against TNF toxicity.
  
  
  METHODS
  In this study, we show that, although untransformed mouse embryonic fibroblasts (MEFs) were resistant to TNF killing, E1A/Ras-transformed MEFs were susceptible to extensive apoptosis induced by TNF. The key factors for determining TNF sensitivity were explored by comparing wild-type and E1A/Ras-transformed MEFs.
  
  
  RESULTS
  TNF signalling to NF-kappaB and to its target genes such as IkappaBalpha seemed to be mostly intact in E1A/Ras-transformed cells. Instead, the induction of A20 was completely abolished in E1A/Ras-transformed MEFs, although A20 is known to be NF-kappaB dependent. Reintroduction of A20 into E1A/Ras-transformed MEFs rescued these cells from TNF-induced death and reduced the formation of the FADD/caspase-8 complex. This impaired A20 induction in E1A/Ras MEFs was not because of the stabilisation of p53 or a defective TNF-induced p38 and Jun N-terminal kinase (JNK) signalling. Consistently, we found a reduced A20 promoter activity but normal NF-kappaB activity in TNF-treated E1A/Ras MEFs. However, Bcl-3 seemed to have a role in the transactivation of the A20 promoter in E1A/Ras cells.
  
  
  CONCLUSIONS
  Our results suggest that specific inhibition of certain survival factors, such as A20, may determine the sensitivity to TNF-induced apoptosis in transformed cells such as E1A/Ras MEFs.
authors.affiliation: The Campbell Family Institute of Breast Cancer Research, Ontario Cancer Institute, University Health Network and Department of Medical Biophysics, University of Toronto, 620 University Avenue, Toronto, Ontario, Canada. hhuang@mail.cjcu.edu.tw
authors.forename: H-L
authors.initials: HL
authors.lastname: Huang
authors.forename: W-C
authors.initials: WC
authors.lastname: Yeh
authors.forename: M-Z
authors.initials: MZ
authors.lastname: Lai
authors.forename: C
authors.initials: C
authors.lastname: Mirtsos
authors.forename: H
authors.initials: H
authors.lastname: Chau
authors.forename: C-H
authors.initials: CH
authors.lastname: Chou
authors.forename: S
authors.initials: S
authors.lastname: Benchimol
mesh_terms: D017500:Adenovirus E1A Proteins / Q000235:genetics*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D000081242:B-Cell Lymphoma 3 Protein; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000032:analysis; D053181:Caspase 8 / Q000378:metabolism; D002461:Cell Line, Transformed; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000502:physiology*; D005786:Gene Expression Regulation; D011905:Genes, ras; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology*; D048031:JNK Mitogen-Activated Protein Kinases / Q000502:physiology; D051379:Mice; D016328:NF-kappa B / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000502:physiology
chemical_list: D017500:Adenovirus E1A Proteins; D000081242:B-Cell Lymphoma 3 Protein; C000631344:BCL3 protein, human; C000631345:Bcl3 protein, mouse; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D047908:Intracellular Signaling Peptides and Proteins; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D016159:Tumor Suppressor Protein p53; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3; C505526:Casp8 protein, mouse; D053181:Caspase 8; D003546:Cysteine Endopeptidases; C513261:Tnfaip3 protein, mouse