端粒酶与食管癌、胃癌相关性的研究

端粒是染色体DNA端部的特化部分，由高度重复的短序列DNA一蛋白质组成的特殊结构，能维持染色体的稳定和完整．端粒酶是由RNA与蛋白质亚基组成的核糖核蛋白酶，能以自身RNA为模板，合成端粒序列，是一种非常特殊的逆转录酶．端粒的长度和端粒酶的活性与细胞永生化，细胞衰老和癌变密切相关，在肿瘤发生发展中，端粒酶成为一种重要的肿瘤生物学标志物，有望作为诊断和治疗肿瘤的新靶点．本对端粒酶的结构与功能，端粒酶与食管癌、胃癌相关性的研究新进展及端粒酶活性的检测方法做一简要综述．     

端粒与端粒酶的研究进展综述

端粒是存在于真核细胞的染色体末端的特殊结构,其作用是维持染色体末端的遗传稳定性,它的存在避免了染色体被酶降解。端粒酶负责延长端粒的长度,是一种逆转录酶。端粒酶在肿瘤细胞中具有高活性。端粒与端粒酶的存在在细胞的永生化中扮演着重要的角色,是细胞衰老与癌变的重要决定因素。本文综述了端粒与端粒酶目前的研究进展,并对其日后的发展提出展望。     

是否可以通过延长端粒的长度来减缓衰老?

<正>A:端粒是染色体末端的特殊结构,由许多重复序列和相关蛋白组成,它具有维持染色体结构完整性和稳定性的作用。细胞每进行一次有丝分裂,就有一段端粒序列丢失。而端粒酶能够合成端粒,维持其序列稳定性。1990年,科学家首次将端粒与人类细胞衰老联系在一起,发现成纤维细胞中端粒缩短到一定程度,细胞会停止分裂,变成衰老状态。2010年,科学家以端粒酶缺陷的转基因小鼠为研究对象,通过重新激活端粒酶,成功逆转了衰老过程。这一研究     

端粒和端粒酶的发现——2009年度诺贝尔生理学或医学奖成果介绍

2009年度诺贝尔生理学或医学奖在瑞典卡罗林斯卡医学院揭晓,美国加利福尼亚旧金山大学的Elizabeth H. Blackburn、美国巴尔的摩约翰&#183;霍普金斯医学院的Carol W. Greider和美国哈佛医学院的Jack W. Szostak获得该奖,以表彰他们发现了端粒和端粒酶保护染色体的机制。端粒是染色体末端由DNA重复序列组成的一种特殊结构,具有维持染色体结构稳定性的功能,会随染色体复制与细胞分裂而缩短。端粒酶作用于端粒,依靠自身RNA模板合成端粒DNA,维持端粒的长度与结构完整。端粒和端粒酶的发现解释了生物学中长期未解决的染色体末端复制问题,推动了生物学和生物医学相关领域的发展,为研究衰老、与衰老相关的疾病和肿瘤发生发展的分子机制提供了新的思路。     

染色体的保护者——端粒与端粒酶

端粒是位于染色体末端、能保护染色体不被降解的特殊结构。端粒酶则是能合成端粒DNA的酶,使得端粒的长度和结构得以稳定。端粒和端粒酶的发现推动了科学家对人类衰老和肿瘤发生机制的研究,有助于相关疾病的预防和治疗。文章对端粒和端粒酶的发现过程、其主要结构和功能、以及与相关疾病的预防和治疗作了简要介绍。     

端粒酶与肿瘤研究的新进展

端粒酶是维持染色体长度及功能稳定的重要物质．研究表明,端粒、端粒酶与细胞寿命直接相关．通过对端粒酶的活性及在表达程度的研究进—步发现其与肿瘤的发生和转移具有十分密切的关系．人们正在研究将端粒酶的表达水平作为肿瘤诊断和愈后的指标,并可能将端粒酶抑制列为肿瘤治疗的新方法．     

端粒、端粒酶和肿瘤、细胞衰老

端粒和端粒酶是现代生物学研究的热点,端粒的缺失与细胞的衰老,端粒酶的活性与细胞的老化及癌化均有密切的关系.文章综述了端粒和端粒酶的结构和功能及其与细胞衰老及肿瘤的关系,并在此基础之上展望了端粒酶在抗衰老、抑制肿瘤等方面的应用.     

端粒酶核酶抑制肿瘤细胞生长的研究

已证明有84.7%的人类恶性肿瘤组织细胞中端粒酶表达异常增高.端粒酶的作用是合成染色体末端端粒重复序列维持染色体稳定及细胞永生化的关键因素.因此,端粒酶在肿瘤发生发展中起重要作用,是目前最广泛的肿瘤标志物.核酶是一种具有内切酶活性的RNA分子,只要满足一定的空间结构就能定点切割RNA底物.切割端粒酶的核酶(简称为端粒酶核酶)主要针对端粒酶的两个亚单位hTR和hTERT抑制两基因的表达,降低端粒酶的活性,抑制肿瘤细胞的生长.     

溴化乙锭-TRAP法检测端粒酶活性(英文)

端粒酶是一种核蛋白,在真核生物体内,通过将端粒重复顺序转移到染色体末端而维持染色体的稳定．端粒酶活性存在于生殖细胞和永生癌细胞,但在正常细胞中却极低乃至无法检测．我们使用ＥＢ染色简化了端粒酶活性检测的传统的ＴＲＡＰ（Ｔｅｌｏｍ ｅｒｉｃ Ｒｅｐｅａｔ Ａｍ ｐｌｉｆｉｃａｔｉｏｎ Ｐｒｏｔｏｃｏｌ）法．结果表明,对粗抽提物而言,ＥＢ染色具有足够的可信度和灵敏度,同时又经济省时,便于推广使用     

The human CST complex is a terminator of telomerase activity

The lengths of human telomeres, which protect chromosome ends from degradation and end fusions, are crucial determinants of cell lifespan. During embryogenesis and in cancer, the telomerase enzyme counteracts telomeric DNA shortening. As shown in cancer cells, human telomerase binds the shelterin component TPP1 at telomeres during the S phase of the cell cycle, and adds ~60 nucleotides in a single round of extension, after which telomerase is turned off by unknown mechanisms. Here we show that the human CST (CTC1, STN1 and TEN1) complex, previously implicated in telomere protection and DNA metabolism, inhibits telomerase activity through primer sequestration and physical interaction with the protection of telomeres 1 (POT1)–TPP1 telomerase processivity factor. CST competes with POT1–TPP1 for telomeric DNA, and CST–telomeric-DNA binding increases during late S/G2 phase only on telomerase action, coinciding with telomerase shut-off. Depletion of CST allows excessive telomerase activity, promoting telomere elongation. We propose that through binding of the telomerase-extended telomere, CST limits telomerase action at individual telomeres to approximately one binding and extension event per cell cycle. Our findings define the sequence of events that occur to first enable and then terminate telomerase-mediated telomere elongation.     

Defects in mismatch repair promote telomerase-independent proliferation

Mismatch repair has a central role in maintaining genomic stability by repairing DNA replication errors and inhibiting recombination between non-identical (homeologous) sequences. Defects in mismatch repair have been linked to certain human cancers, including hereditary non-polyposis colorectal cancer (HNPCC) and sporadic tumours. A crucial requirement for tumour cell proliferation is the maintenance of telomere length, and most tumours achieve this by reactivating telomerase. In both yeast and human cells, however, telomerase-independent telomere maintenance can occur as a result of recombination-dependent exchanges between often imperfectly matched telomeric sequences. Here we show that loss of mismatch-repair function promotes cellular proliferation in the absence of telomerase. Defects in mismatch repair, including mutations that correspond to the same amino-acid changes recovered from HNPCC tumours, enhance telomerase-independent survival in both Saccharomyces cerevisiae and a related budding yeast with a degree of telomere sequence homology that is similar to human telomeres. These results indicate that enhanced telomeric recombination in human cells with mismatch-repair defects may contribute to cell immortalization and hence tumorigenesis.     

端粒酶活性检测研究进展

端粒酶是细胞内常见的一种逆转录酶,其功能在于维持细胞内染色体末端端粒的长度。端粒酶活性的异常升高通常与肿瘤细胞的产生以及生长相关。端粒酶的活性已经成为了癌症诊疗领域中非常重要的生物标志物。因此,对于端粒酶活性准确且高效的定量分析检测方案是当今分析科学,临床医学等相关学科领域研究的重点之一。随着分析测试技术的发展,提出了一系列具有超高性能的端粒酶活性检测方案。总结了近5年来端粒酶活性检测方案的发展全貌并且预估了端粒酶活性检测的未来发展方向。     

TPP1 is a homologue of ciliate TEBP-beta and interacts with POT1 to recruit telomerase

Telomere dysfunction may result in chromosomal abnormalities, DNA damage responses, and even cancer. Early studies in lower organisms have helped to establish the crucial role of telomerase and telomeric proteins in maintaining telomere length and protecting telomere ends. In Oxytricha nova, telomere G-overhangs are protected by the TEBP-alpha/beta heterodimer. Human telomeres contain duplex telomeric repeats with 3' single-stranded G-overhangs, and may fold into a t-loop structure that helps to shield them from being recognized as DNA breaks. Additionally, the TEBP-alpha homologue, POT1, which binds telomeric single-stranded DNA (ssDNA), associates with multiple telomeric proteins (for example, TPP1, TIN2, TRF1, TRF2 and RAP1) to form the six-protein telosome/shelterin and other subcomplexes. These telomeric protein complexes in turn interact with diverse pathways to form the telomere interactome for telomere maintenance. However, the mechanisms by which the POT1-containing telosome communicates with telomerase to regulate telomeres remain to be elucidated. Here we demonstrate that TPP1 is a putative mammalian homologue of TEBP-beta and contains a predicted amino-terminal oligonucleotide/oligosaccharide binding (OB) fold. TPP1-POT1 association enhanced POT1 affinity for telomeric ssDNA. In addition, the TPP1 OB fold, as well as POT1-TPP1 binding, seemed critical for POT1-mediated telomere-length control and telomere-end protection in human cells. Disruption of POT1-TPP1 interaction by dominant negative TPP1 expression or RNA interference (RNAi) resulted in telomere-length alteration and DNA damage responses. Furthermore, we offer evidence that TPP1 associates with the telomerase in a TPP1-OB-fold-dependent manner, providing a physical link between telomerase and the telosome/shelterin complex. Our findings highlight the critical role of TPP1 in telomere maintenance, and support a yin-yang model in which TPP1 and POT1 function as a unit to protect human telomeres, by both positively and negatively regulating telomerase access to telomere DNA.     

Telomeres shorten during ageing of human fibroblasts

The terminus of a DNA helix has been called its Achilles' heel. Thus to prevent possible incomplete replication and instability of the termini of linear DNA, eukaryotic chromosomes end in characteristic repetitive DNA sequences within specialized structures called telomeres. In immortal cells, loss of telomeric DNA due to degradation or incomplete replication is apparently balanced by telomere elongation, which may involve de novo synthesis of additional repeats by novel DNA polymerase called telomerase. Such a polymerase has been recently detected in HeLa cells. It has been proposed that the finite doubling capacity of normal mammalian cells is due to a loss of telomeric DNA and eventual deletion of essential sequences. In yeast, the est1 mutation causes gradual loss of telomeric DNA and eventual cell death mimicking senescence in higher eukaryotic cells. Here, we show that the amount and length of telomeric DNA in human fibroblasts does in fact decrease as a function of serial passage during ageing in vitro and possibly in vivo. It is not known whether this loss of DNA has a causal role in senescence.     

POT1 as a terminal transducer of TRF1 telomere length control

Human telomere maintenance is essential for the protection of chromosome ends, and changes in telomere length have been implicated in ageing and cancer. Human telomere length is regulated by the TTAGGG-repeat-binding protein TRF1 and its interacting partners tankyrase 1, TIN2 and PINX1 (refs 5-9). As the TRF1 complex binds to the duplex DNA of the telomere, it is unclear how it can affect telomerase, which acts on the single-stranded 3' telomeric overhang. Here we show that the TRF1 complex interacts with a single-stranded telomeric DNA-binding protein--protection of telomeres 1 (POT1)--and that human POT1 controls telomerase-mediated telomere elongation. The presence of POT1 on telomeres was diminished when the amount of single-stranded DNA was reduced. Furthermore, POT1 binding was regulated by the TRF1 complex in response to telomere length. A mutant form of POT1 lacking the DNA-binding domain abrogated TRF1-mediated control of telomere length, and induced rapid and extensive telomere elongation. We propose that the interaction between the TRF1 complex and POT1 affects the loading of POT1 on the single-stranded telomeric DNA, thus transmitting information about telomere length to the telomere terminus, where telomerase is regulated.