Development of retinoblastoma in the absence of telomerase activity
Development of retinoblastoma in the absence of telomerase activity
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DOI：
10.1093/jnci/88.16.1152
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发表时间：
1996-08-21
期刊：
影响因子：
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通讯作者：
Bacchetti, S
中科院分区：
文献类型：
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作者：
Gupta, J;Han, LP;Bacchetti, S
背景：端粒（真核染色体末端的基本功能结构）的长度和稳定性与细胞寿命的控制有关。大多数体细胞缺乏端粒酶，即合成端粒DNA的酶，它们的端粒会随着细胞分裂而缩短。另一方面，体外永生化的细胞表达端粒酶并维持其端粒。在多种癌症的大多数肿瘤中也检测到了端粒酶活性。这些观察结果表明，端粒维持是无限细胞增殖所必需的，并且端粒酶是体外和体内细胞永生的标志。目的：我们研究了在视网膜母细胞瘤的发展过程中端粒酶是否被激活。这是一种与胚胎组织中有限数量的突变相关的儿童眼癌，因此很可能在具有长端粒的细胞中发生。视网膜母细胞瘤易于转移，使得在恶性细胞广泛增殖之前筛查相对较小的肿瘤成为可能。方法：我们测量了 34 个视网膜母细胞瘤样本、四种视网膜母细胞瘤来源的细胞系和六种来自其他癌症的细胞系的端粒酶活性。只有三种来自其他癌症的细胞系表达视网膜母细胞瘤蛋白。通过聚合酶链式反应方案测定从肿瘤或细胞系制备的提取物中的端粒酶活性。在蛋白质量标准化后，在几种蛋白质浓度下对细胞提取物中的酶活性水平进行定量，并相对于阳性对照中的酶活性水平进行表达。端粒长度通过基因组DNA与端粒特异性探针的Southern印迹杂交来测量。通过两侧、两个样本学生 t 检验比较端粒酶阳性和端粒酶阴性肿瘤以及细胞系中端粒长度的平均值。结果：34 例视网膜母细胞瘤中有 17 例（50%）未检测到端粒酶活性。对源自其他癌症的细胞系的分析显示，酶活性的存在或水平与视网膜母细胞瘤蛋白的表达之间没有关联。端粒酶阴性肿瘤中的端粒明显长于端粒酶阳性肿瘤中的端粒 (P = .0008)。结论：我们的结果表明，当端粒仍然相对较长且缺乏端粒酶时，视网膜母细胞瘤就可能发生，然而，在 50% 的视网膜母细胞瘤和视网膜母细胞瘤衍生细胞系中观察到与短端粒相关的端粒酶活性。意义：对于源自长端粒细胞且与少量突变相关的肿瘤，端粒酶可能不是获得恶性表型的标志物。
Background: The length and stability of telomeres (essential functional structures at the end of eukaryotic chromosomes) have been implicated in the control of cell lifespan. Most somatic cells lack telomerase, the enzyme that synthesizes telomeric DNA, and their telomeres shorten with cell division. Cells immortalized in vitro, on the other hand, express telomerase and maintain their telomeres. Telomerase activity has also been detected in the large majority of tumors from a variety of cancers. These observations have suggested that telomere maintenance is required for unlimited cell proliferation and that telomerase is a marker for cell immortality in vitro and in vivo. Purpose: We investigated whether telomerase is activated during the development of retinoblastoma. This is a childhood eye cancer associated with a limited number of mutations in an embryonic tissue and thus likely to develop in cells that have long telomeres. The ease of defection of retinoblastoma makes it possible to screen relatively small tumors before extensive proliferation of the malignant cells. Methods: We measured telomerase activity in 34 samples of retinoblastoma, four retinoblastoma-derived cell lines, and six cell lines derived from other cancers. Only three of the cell lines from other cancers expressed the retinoblastoma protein. Telomerase activity was assayed by a polymerase chain reaction protocol in extracts prepared from tumors or cell lines. The level of enzyme activity in cell extracts was quantified at several protein concentrations and expressed relative to that in a positive control, after normalization for the amount of protein. Telomere length was measured by Southern blot hybridization of genomic DNA with a telomere-specific probe. Average values of telomere length in telomerase-positive and telomerase-negative tumors and in cell lines were compared by two-sided, two-sample Student's t test. Results: No telomerase activity was detected in 17 (50%) of 34 retinoblastomas. Assays of cell lines derived from other cancers revealed no association between the presence or the level of the enzyme activity and the expression of the retinoblastoma protein. Telomeres were significantly longer in telomerase-negative tumors than in telomerase-positive tumors (P = .0008). Conclusions: Our results indicate that retinoblastoma can develop when telomeres are still relatively long and in the absence of telomerase, Telomerase activity associated with short telomeres is, however, observed in 50% of the retinoblastomas and in retinoblastoma-derived cell lines. Implications: Telomerase may not be a marker for acquisition of the malignant phenotype in the case of tumors that are derived from cells with long telomeres and that are associated with a low number of mutations.