Activation of ARF by oncogenic stress in mouse fibroblasts is independent of E2F1 and E2F2.
The ARF tumour suppressor protein (p14(ARF) in human and p19(ARF) in mouse) is a major mediator of the activation of p53 in response to oncogenic stress. Little is known about the signalling pathways connecting oncogenic stimuli to the activation of ARF. Regulation of ARF occurs primarily at the transcriptional level and several modulators of ARF transcription have been identified. Notably, ectopic expression of E2F1 upregulates ARF transcriptionally, and both E2F1 and ARF have been implicated in apoptosis and cell-cycle arrest. We have used primary mouse fibroblasts deficient for E2F1, E2F2, or both to determine the possible role of these E2F proteins as upstream regulators of ARF in response to oncogenic stimuli and other stresses. In particular, we have studied the effects of oncogenic Ras and the viral oncoprotein E1A on ARF levels, neoplastic transformation, and sensitization to apoptosis. We have also examined the behaviour of the E2F-deficient MEFs with respect to immortalization and sensitivity to DNA damage. None of the ARF-mediated responses that we have analysed is significantly affected in E2F1(-/-), E2F2(-/-) or E2F1/2(-/-) MEFs, and ARF is upregulated normally in all cases. Taken together, our results indicate that the activation of ARF in response to oncogenic stress can occur by E2F1- and E2F2-independent mechanisms. This challenges previous suggestions implicating E2F factors as key mediators in the activation of ARF by oncogenic stress.
Palmero
Ignacio
I
Department of Immunology and Oncology, National Centre of Biotechnology, CSIC, Campus de Cantoblanco, Madrid E-28049, Spain.
Murga
Matilde
M
Zubiaga
Ana
A
Serrano
Manuel
M
D017500:Adenovirus E1A Proteins / Q000502:physiology*; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D018797:Cell Cycle Proteins; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D002472:Cell Transformation, Viral / Q000235:genetics; D002478:Cells, Cultured / Q000166:cytology / Q000378:metabolism; D016922:Cellular Senescence; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004249:DNA Damage; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050703:E2F2 Transcription Factor; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism / Q000528:radiation effects; D005720:Gamma Rays; D011905:Genes, ras; D005822:Genetic Vectors / Q000235:genetics; D005838:Genotype; D051379:Mice; D018345:Mice, Knockout; D008938:Mitosis; D015689:Oncogene Protein p21(ras) / Q000502:physiology*; D014157:Transcription Factors / Q000172:deficiency / Q000502:physiology*; D025803:Tumor Suppressor Protein p14ARF / Q000378:metabolism*
D017500:Adenovirus E1A Proteins; C417743:Cdkn2a protein, mouse; D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050703:E2F2 Transcription Factor; C493754:E2f1 protein, mouse; D014157:Transcription Factors; D025803:Tumor Suppressor Protein p14ARF; D015689:Oncogene Protein p21(ras)