Montalto M C, Ray F A
Department of Microbiology, Immunology and Molecular Genetics, Albany Medical College, NY 12208, USA.
Carcinogenesis. 1996 Dec;17(12):2631-4. doi: 10.1093/carcin/17.12.2631.
The ribonucleoprotein enzyme telomerase is active in most immortal cell lines, most tumors and all tumor-derived cell lines. The enzyme is important because it prevents continual shortening of telomeres and therefore plays a significant role in chromosome maintenance. In man, telomerase is not active in most somal cells with finite lifespans. Using the SV40 T antigen we immortalized and transformed to fully tumorigenic a human fibroblast cell strain. We wished to determine when telomerase was activated during this progression to tumorigenicity. Using the PCR-based TRAP assay we found that eight of eight immortal cell lines that were either not tumorigenic or rarely formed tumors were telomerase positive at the time of inoculation. Additionally, 10 of 11 newly immortal cell lines contained telomerase activity within the first 25-33 population doublings after crisis. None of the precrisis cells from which these immortal cells were derived were positive for telomerase activity. Thus we found that telomerase activation is not the final in vivo step in the transformation of these cells and the window of activation is usually near the escape from crisis or M2. These results strengthen the hypothesis that telomerase activation may allow the rare cell to escape from crisis in those immortal cell populations dependent on telomerase for telomere maintenance.
核糖核蛋白酶端粒酶在大多数永生化细胞系、大多数肿瘤及所有肿瘤衍生细胞系中均有活性。该酶之所以重要，是因为它能防止端粒持续缩短，因此在染色体维持中发挥着重要作用。在人类中，端粒酶在大多数寿命有限的体细胞中无活性。我们利用猿猴病毒40大T抗原将一株人成纤维细胞系永生化并转化为具有完全致瘤性的细胞系。我们希望确定在这种向致瘤性发展的过程中端粒酶何时被激活。利用基于聚合酶链反应（PCR）的端粒重复序列扩增法（TRAP）检测，我们发现8株不具有致瘤性或很少形成肿瘤的永生化细胞系在接种时端粒酶均呈阳性。此外，11株新的永生化细胞系中有10株在危机后最初的25 - 33次群体倍增内含有端粒酶活性。这些永生化细胞所源自的危机前细胞均无端粒酶活性阳性。因此我们发现端粒酶激活并非这些细胞转化过程中的最终体内步骤，且激活窗口通常接近从危机或M2期逃脱之时。这些结果强化了这样一种假说，即端粒酶激活可能使那些依赖端粒酶维持端粒的永生化细胞群体中的稀有细胞从危机中逃脱。
