Control of hTERT in initiation and progression of aging

耐受酶催化亚单位hTERT在防止与细胞衰老相关的端粒磨损中的作用已被证实，最近的研究表明，hTERT主要通过转录机制来控制。最近的研究发现，hTERT的表达可能通过组蛋白乙酰化和/或hTERT启动子DNA甲基化的改变而在端粒酶阴性细胞中诱导，这一发现引起了相当大的兴奋。由于hTERT基因在胚胎发生期间被失活，并在大多数体细胞衰老细胞中保持转录沉默，这些发现不仅引起了那些关注衰老原因的人的强烈兴趣，也引起了肿瘤学家的强烈兴趣，因为hTERT在大多数人类癌症中都是激活的。我们的假设是，在胚胎细胞分化中，组蛋白去乙酰化和DNA甲基化共同作用于胚胎细胞分化，以沉默hTERT启动子，并且这一机制在老化的细胞中被减弱，导致随着年龄的增长hTERT激活和肿瘤的可能性更高。为了验证这一假设，我们设计了以下研究：1)用曲古抑素A和/或5-氮胞苷分别诱导组蛋白乙酰化和hTERT启动子的低甲基化，并评估这些细胞中的hTERT活性；2)用这些药物处理年轻和衰老的WI-38成纤维细胞，分析组蛋白去乙酰化和/或DNA甲基化在衰老细胞中维持hTERT基因沉默的能力；以及3)评估hTERT启动子在分化胚胎细胞和衰老成纤维细胞中的调节作用。本研究的总体目的是进一步阐明组蛋白乙酰化和DNA甲基化在衰老和癌症中控制端粒酶的机制。这些研究旨在加强在衰老和癌症等与年龄相关的疾病中对hTERT表达进行治疗控制的发展潜力。

A role of the toleromerase catalytic subunit, hTERT, in preventing telomeric attrition associated with cellular senescence has been established and recent studies have shown that hTERT is controlled primarily through transcriptional mechanisms. Considerable excitement has been generated by recent findings that hTERT expression may be induced in telomerase-negative cells through changes in histone acetylation and/or DNA methylation of the hTERT promoter. Since hTERT gene expression is inactivated during embryogenesis and remains transcriptionally silent in most somatic aging cells, these findings are of intense interest not only to those concerned with the causes of aging, but also to oncologists as hTERT is activated in most human cancers. Our hypothesis is that histone deacetylation and DNA methylation work in conjunction in embryonic cellular differentiation in embryonic cellular differentiation to silence the hTERT promoter and that this mechanism is attenuated in aging cells leading to a higher probability of hTERT activation and neoplasia with aging. To test this hypothesis, we have designed studies to 1) subject differentiating embryonic cells to trichostatin A and/or 5-azacytidine, which induce histone acetylation and hypomethylation of the hTERT promoter respectively, and assess hTERT activity in these cells, 2) treat young and senescent WI-38 fibroblasts with these agents to analyze the ability of histone deacetylation and/or DNA methylation to maintain hTERT gene silencing in aging cells, and 3) assess hTERT promoter regulation in differentiating embryonic cells and aging fibroblasts transfected with luciferase reporter constructs and subjected to histone acetylation and/or DNA hypomethylation. The overall purpose of this study is to further elucidate the mechanisms of histone acetylation and DNA methylation in the control of telomerase in aging and cancer. These studies are intended to strengthen the potential for development of therapeutic control of hTERT expression during aging and in age-associated diseases such as cancer.