Puthenveettil J A, Frederickson S M, Reznikoff C A
University of Wisconsin Medical School, Department of Human Oncology, Madison 53792, USA.
Oncogene. 1996 Sep 19;13(6):1123-31.
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.
我们比较了E6永生化与E7永生化的人尿道上皮细胞（HUC）对γ辐射诱导凋亡的反应能力。两个独立的HPV16 E6永生化细胞系，αE6#1和αE6#2，其p53水平较低或无法检测到，通过DNA片段化检测发现，它们在受到18格雷（Gy）γ辐射时未能发生凋亡。相比之下，两个独立的HPV16 E7永生化细胞系，αE7#1和αE7#2，二者均显示野生型p53稳定，在同一实验中发生了凋亡。有趣的是，与αE6#1或αE6#2相比，αE7#1和αE7#2的BAX水平均持续升高，BCL-2水平均降低。然而，单独的BAX升高和BCL-2降低不足以触发凋亡，因为凋亡仅在暴露于γ辐射后才发生。这些结果支持了一种模型，即HPV16 E7永生化细胞在有适当触发因素时易于发生凋亡。在αE6/E7#1细胞中未观察到这种凋亡反应，该细胞与αE6-HUCs一样，p53水平较低，在晚期传代的αE7#1细胞中也未观察到，其TP53发生了自发突变。这些结果表明，E7永生化使HUC对γ辐射诱导的凋亡产生反应，并且这种增强的凋亡反应依赖于p53。
