Simian virus 40 large T antigen J domain and Rb-binding motif are sufficient to block apoptosis induced by growth factor withdrawal in a neural stem cell line.
Serum-free mouse embryo (SFME) cells are a neural stem cell line that is dependent upon epidermal growth factor (EGF) for survival. Removal of EGF results in the G1 arrest and apoptosis of SFME cells. We have shown that the expression of simian virus 40 large T antigen in SFME cells blocks apoptosis and allows cell survival and division in the absence of EGF. Therefore the presence of T antigen abrogates the EGF requirement. The steady-state levels of p53, p21, and mdm-2 do not increase as SFME cells undergo apoptosis upon EGF withdrawal. Furthermore, the amino-terminal 136 amino acids (N136) of T antigen are sufficient to block death and to promote proliferation in the absence of EGF, while the carboxy-terminal fragment (C251-708), which contains the p53 binding site, is unable to block death. Taken together, these data suggest that SFME cells deprived of EGF undergo p53-independent apoptosis. Mutations that disrupt either the J domain or Rb family binding abolish the ability of T antigen to block SFME cell apoptosis and to promote cell growth. We conclude that T antigen must act on one or more members of the Rb family to inhibit SFME cell apoptosis.
Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
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Slinskey
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Barnes
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Pipas
D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism*; D017209:Apoptosis; D001665:Binding Sites; D002455:Cell Division; D002460:Cell Line; D002470:Cell Survival; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D009474:Neurons / Q000166:cytology* / Q000378:metabolism; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2; D016160:Retinoblastoma Protein / Q000378:metabolism; D013539:Simian virus 40 / Q000378:metabolism*; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D000952:Antigens, Polyomavirus Transforming; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D004815:Epidermal Growth Factor; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2