Impaired TNFalpha-induced A20 expression in E1A/Ras-transformed cells.
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.
Huang
H-L
HL
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
Yeh
W-C
WC
Lai
M-Z
MZ
Mirtsos
C
C
Chau
H
H
Chou
C-H
CH
Benchimol
S
S
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
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