Apoptosis in human papillomavirus16 E7-, but not E6-immortalized human uroepithelial cells.
We compared the ability of E6-, versus E7-, immortalized human uroepithelial cells (HUC) to undergo apoptosis in response to gamma radiation. Two independent HPV16 E6-immortalized cell lines, alphaE6#1 and alphaE6#2, that showed low or undetectable p53 levels, failed to undergo apoptosis in response to 18 Gray (Gy) gamma radiation as determined by DNA fragmentation. In contrast, two independent HPV16 E7-immortalized cell lines, alphaE7#1 and alphaE7#2, both of which showed stabilized wildtype p53, underwent apoptosis in the same experiment. Interestingly, both alphaE7#1 and alphaE7#2 showed constitutively elevated BAX and lowered BCL-2 levels, compared to either alphaE6#1 or alphaE6#2. However, elevated BAX and reduced BCL-2 per se were insufficient to trigger apoptosis, as apoptosis occurred only after exposure to gamma radiation. These results support a model in which HPV16 E7-immortalized cells are primed to undergo apoptosis, given an appropriate trigger. This apoptotic response was not observed in alphaE6/E7#1 cells which, like alphaE6-HUCs, showed low p53 levels, nor in late passage alphaE7#1 with spontaneously mutated TP53. These results suggest that E7 immortalization primes HUC for apoptosis in response to gamma radiation, and that this enhanced apoptotic response is p53 dependent.
Puthenveettil
J A
JA
University of Wisconsin Medical School, Department of Human Oncology, Madison 53792, USA.
Frederickson
S M
SM
Reznikoff
C A
CA
D017209:Apoptosis / Q000502:physiology* / Q000528:radiation effects; D002453:Cell Cycle / Q000528:radiation effects; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004847:Epithelial Cells; D004848:Epithelium / Q000528:radiation effects / Q000821:virology; D006801:Humans; D009154:Mutation; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000494:pharmacology*; D027383:Papillomaviridae; D050725:Papillomavirus E7 Proteins; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D014551:Urinary Tract / Q000166:cytology* / Q000528:radiation effects / Q000821:virology*; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; C068651:E6 protein, Human papillomavirus type 16; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; C059731:oncogene protein E7, Human papillomavirus type 16