Abrogation of p53-induced G1 arrest by the HPV 16 E7 protein does not inhibit p53-induced apoptosis.
Wild type (wt) p53 expressed from a temperature-sensitive construct (ts p53) can induce both G1 cell cycle arrest and apoptosis in the p53-negative J3D mouse T lymphoma line (Wang et al, 1995). The human papillomavirus (HPV) 16 E7 protein has been shown to prevent p53-induced G1 cell cycle arrest following DNA damage. We asked whether inhibition of p53-induced G1 arrest by overexpression of the HPV16 E7 protein in the ts p53-transfected J3D cells would interfere with p53-induced apoptosis. Whereas a majority of the ts p53-expressing J3D cells were arrested in the G1 phase 22 h after induction of wt p53 by temperature shift to 32 degrees C, the E7/ts p53-expressing cells showed only a minor increase in the number of cells in G1 at this time point. In addition, the E7/ts p53-expressing cells showed a much less dramatic reduction in number of cells in S phase than the ts p53-expressing cells. This demonstrates that E7 at least partially rescues the cells from p53-induced G1 arrest. In contrast, overexpression of HPV16 E7 did not have any effect on the kinetics nor the frequency of p53-triggered apoptotic death, as shown by FACS analysis, trypan blue exclusion, and DNA fragmentation analysis. These findings support the notion that p53-induced G1 arrest and p53-induced apoptosis are two separate independent pathways.
Wang
Y
Y
Microbiology and Tumor Biology Center, Karolinska Institute, Sweden.
Okan
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I
Pokrovskaja
K
K
Wiman
K G
KG
D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D001483:Base Sequence; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics; D016193:G1 Phase / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D016158:Genes, p53; D051379:Mice; D008969:Molecular Sequence Data; D009856:Oncogene Proteins, Viral / Q000096:biosynthesis* / Q000235:genetics*; D050725:Papillomavirus E7 Proteins; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2; D014162:Transfection; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein
C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; C059731:oncogene protein E7, Human papillomavirus type 16