Quante Michael, Heeg Steffen, von Werder Alexander, Goessel Gitta, Fulda Christine, Doebele Michaela, Nakagawa Hiroshi, Beijersbergen Roderick, Blum Hubert E, Opitz Oliver G
Department of Medicine and Institute of Molecular Medicine and Cell Research, University of Freiburg, Freiburg, Germany.
Carcinogenesis. 2005 Nov;26(11):1879-89. doi: 10.1093/carcin/bgi153. Epub 2005 Jun 15.
Telomerase activity is observed in approximately 90% of human cancer including esophageal squamous cell cancer. Normal somatic cells do not display telomerase activity on a regular basis. The major mechanism to regulate telomerase activity in human cells is the transcriptional control of the catalytic subunit, the human reverse transcriptase gene hTERT. However, the manner in which telomerase activity is regulated during malignant transformation and whether this regulation is influenced by single genetic alterations important in this process are not well understood. In this study we investigated the transcriptional regulation and activity of human telomerase in a cellular model representing important known genetic alterations observed in esophageal cancer. We characterized the respective cells with regard to their telomere biology and telomerase expression, transcriptional regulation using promoter--as well as electrophoretic mobility shift assay--analyses and their promoter methylation status. We could demonstrate that telomerase expression and subsequent activity are differentially regulated in the progression from normal esophageal epithelial cells to genetically defined esophageal cells harboring a specific genetic alteration frequently found in esophageal cancer and compared those changes with esophageal cancer cells. Whereas primary esophageal cells are mainly regulated by Sp1, in cells harboring a genetic alteration as cyclin D1 overexpression other transcription factors like E2F and c-myc as well as promoter methylation influence hTERT transcription. This model demonstrates that the transcriptional regulation of telomerase is influenced by a given genetic alteration important in esophageal cancer, and therefore provides new insight in telomerase regulation during carcinogenesis.
在包括食管鳞状细胞癌在内的约90%的人类癌症中可观察到端粒酶活性。正常体细胞通常不显示端粒酶活性。人类细胞中端粒酶活性的主要调节机制是对催化亚基——人类逆转录酶基因hTERT的转录控制。然而，在恶性转化过程中端粒酶活性的调节方式以及这种调节是否受该过程中重要的单一基因改变的影响尚不清楚。在本研究中，我们在一个代表食管癌中观察到的重要已知基因改变的细胞模型中研究了人类端粒酶的转录调节和活性。我们从端粒生物学、端粒酶表达、使用启动子分析以及电泳迁移率变动分析的转录调节及其启动子甲基化状态等方面对相应细胞进行了表征。我们能够证明，从正常食管上皮细胞进展到具有食管癌中常见的特定基因改变的基因定义的食管细胞过程中，端粒酶表达及随后的活性受到不同调节，并将这些变化与食管癌细胞进行了比较。原发性食管细胞主要受Sp1调节，而在具有细胞周期蛋白D1过表达等基因改变的细胞中，其他转录因子如E2F和c-myc以及启动子甲基化会影响hTERT转录。该模型表明，端粒酶的转录调节受食管癌中一种重要的特定基因改变影响，因此为癌变过程中端粒酶调节提供了新的见解。
