Kiyono T, Foster S A, Koop J I, McDougall J K, Galloway D A, Klingelhutz A J
Cancer Biology Program, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA.
Nature. 1998 Nov 5;396(6706):84-8. doi: 10.1038/23962.
Normal human cells undergo a limited number of divisions in culture and enter a non-dividing state called replicative senescence. Senescence is accompanied by several changes, including an increase in inhibitors of cyclin-dependent kinases and telomere shortening. The mechanisms by which viral oncogenes reverse these processes are not fully understood, although a general requirement for oncoproteins such as human papillomavirus E6 and E7 has suggested that the p53 and Rb pathways are targeted. Expression of the catalytic component of telomerase, hTERT, alone significantly extends the lifespan of human fibroblasts. Here we show that telomerase activity is not sufficient for immortalization of human keratinocyte or mammary epithelial cells: we find that neither addition of hTERT nor induction of telomerase activity by E6, both of which are active in maintaining telomere length, results in immortalization. Inactivation of the Rb/p16 pathway by E7 or downregulation of p16 expression, in combination with telomerase activity, however, is able to immortalize epithelial cells efficiently. Elimination of p53 and of the DNA-damage-induced G1 checkpoint is not necessary for immortalization, neither is elimination of p19ARF.
正常人类细胞在培养中经历有限次数的分裂，然后进入一种称为复制性衰老的非分裂状态。衰老伴随着多种变化，包括细胞周期蛋白依赖性激酶抑制剂的增加和端粒缩短。尽管对人乳头瘤病毒E6和E7等癌蛋白的普遍需求表明p53和Rb途径是其作用靶点，但病毒癌基因逆转这些过程的机制尚未完全明了。单独表达端粒酶的催化成分hTERT可显著延长人成纤维细胞的寿命。在此我们表明，端粒酶活性不足以使人角质形成细胞或乳腺上皮细胞永生化：我们发现，添加hTERT或通过E6诱导端粒酶活性（二者均在维持端粒长度方面具有活性）均不会导致永生化。然而，通过E7使Rb/p16途径失活或下调p16表达，并结合端粒酶活性，能够有效地使上皮细胞永生化。消除p53和DNA损伤诱导的G1检查点对于永生化并非必要，消除p19ARF也不必要。
