Telomerase activation, cellular immortalization and cancer

The maintenance of specialized nucleoprotein structures termed telomeres is essential for chromosome stability. Without new synthesis of telomeres at chromosome ends the chromosomes shorten with progressive cell division, eventually triggering either replicative senescence or apoptosis when telomere length becomes critically short. The regulation of telomerase activity in human cells plays a significant role in the development of cancer. Telomerase is tightly repressed in the vast majority of normal human somatic cells but becomes activated during cellular immortalization and in cancers. While the mechanisms for telomerase activation in cancers have not been fully defined, they include telomerase catalytic subunit gene (hTERT) amplification and trans-activation of the hTERT promoter by the myc oncogene product. Ectopic expression of hTERT is sufficient to restore telomerase activity in cells that lack the enzyme and can immortalize many cell types. Understanding telomerase biology will eventually lead to several clinically relevant telomerase-based therapies. These applications include inhibiting or targeting telomerase as a novel antineoplastic strategy and using cells immortalized by telomerase for therapeutic applications.     

白血病患者端粒酶活性及相关基因的表达

目的 研究端粒酶活性和相关基因表达在白血病患者中的变化及其在白血病发病机制中的意义。方法 通过半定量端粒重复序列扩增（TRAP）－银染和RT－PCR方法检测了47例白血病患者骨髓细胞的端粒酶活性和相关基因hEST2、TP1、hTR mRNA表达水平。结果 42例白血病进展阶段标本的端粒酶活性和相关基因表达水平高于急性白血病完全缓解期、慢性粒细胞白血病（慢粒）慢性期、正常和贫血标本（P＜0．01）;14例急性白血病完全缓解期和（或）慢粒慢性期标本端粒酶活性和TP1、hTR基因表达水平高于正常和贫血标本（P＜0．05）;在部分正常和贫血标本中检测到相对低水平的端粒酶活性和相关基因表达,3例贫血标本经短期常规培养后检测到端粒酶活性和基因表达增高。结论 端粒酶活性和相关基因表达异常升高是造血细胞恶性转化的特异性标记之五,检测端粒酶活性和相关基因表达有助于白血病患者的疗效观察。正常骨髓的端粒酶活性与具有增殖分化能力的造血干细胞有关。hEST2可能是端粒酶的正调控结构基因,hTR基因表达与端粒酶的反馈调控机制有关。     

人端粒酶反转录酶小发夹RNA质粒表达载体的构建及鉴定

背景:端粒酶反转录酶是端粒酶的活性亚基,已成为肿瘤研究的热点。RNA干扰技术作为一种基因沉默方法,具有高效、特异等优点,现已广泛应用于肿瘤、病毒等研究领域。目的:构建针对人端粒酶反转录酶的小发夹RNA质粒表达载体,并观察其对乳腺癌T47D细胞人端粒酶反转录酶基因的表达和端粒酶活性的影响。方法:以Genbank中人端粒酶反转录酶基因的mRNA序列为基础,设计人端粒酶反转录酶基因的小干扰RNA序列,将其连接到具有G418抗性的质粒pBAsi-hU6-Neo(BamHⅠ/HindⅢ)中,应用基因测序加以验证,扩增提取质粒,以脂质体转染表达小发夹RNA的质粒到乳腺癌T47D细胞,抗生素G418筛选出转染成功的各组细胞。结果与结论:实验所构建的人端粒酶反转录酶的小发夹RNA质粒表达载体,经测序验证无误。将pBAsi-hU6-Neo重组质粒转染入T47D细胞,经G418筛选获得了转染成功的细胞。经RT-PCR和Western blot检测,转染后的人端粒酶反转录酶基因在mRNA和蛋白水平的表达均明显降低(P<0.01),经TRAP-ELISA法检测实验组细胞端粒酶活性出现显著下降(P<0.01)。结果证实,实验成功构建人端粒酶反转录酶的小发夹RNA质粒表达载体,实验所设计的小干扰RNA能有效抑制肿瘤细胞人端粒酶反转录酶基因的表达,进而降低细胞的端粒酶活性。     

RNA干扰人端粒酶hTR基因对HeLa细胞增殖的影响

目的:探讨RNA干扰抑制人端粒酶RNA组分human telomerase RNA component,hTR)的表达时宫颈癌细胞(HeLa细胞)增殖的影响.方法:hTR基因的RNA干扰表达重组体用脂质体介导方法稳定转染HeLa细胞.RTPCR法检测hTR的mRNA表达水平,TRAP-PCR法检测端粒酶活性,MTT法检测细胞增殖.结果:RT-PCR结果表明,稳定转染RNA干扰表达重组体的细胞株,其hTR基因的mRNA抑制率较无转染对照组下降了(59.7±3.3)%,较转染空载体组下降了(56.3±4.4)%;实验组细胞端粒酶活性下降,生长速度明显减慢.结论:利用RNA干扰技术抑制hTR基因在HeLa细胞的表达能抑制该细胞端粒酶活性和增殖活性.     

Telomere/telomerase interplay in virus‐driven and virus‐independent lymphomagenesis: pathogenic and clinical implications

Telomerase is a ribonucleoprotein complex critically involved in extending and maintaining telomeres. Unlike the majority of somatic cells, in which hTERT and telomerase activity are generally silent, normal lymphocytes show transient physiological hTERT expression and telomerase activity according to their differentiation/activation status. During lymphomagenesis, induction of persistent telomerase expression and activity may occur before or after telomere shortening, as a consequence of the different mechanisms through which transforming factors/agents may activate telomerase. Available data indicate that the timing of telomerase activation may allow the distinction of two different lymphomagenetic models: (i) an early activation of telomerase via exogenous regulators of hTERT, along with an increased lymphocyte growth and a subsequent selection of cells with increased transforming potential may characterize several virus‐related lymphoid malignancies; (ii) a progressive shortening of telomeres, leading to genetic instability which favors a subsequent activation of telomerase via endogenous regulators may occur in most virus‐unrelated lymphoid tumors. These models may have clinically relevant implications, particularly for the tailoring of therapeutic strategies targeting telomerase. © 2010 Wiley Periodicals, Inc. Med Res Rev     

端粒、端粒酶及hTERT／hTERC基因的研究进展

端粒是真核细胞染色体的末端DNA序列,在维持染色体稳定性中起重要作用。染色体的不完全复制使得端粒随着细胞的分裂而逐渐缩短,快速分裂细胞通过端粒酶合成端粒,以弥补端粒的消耗。端粒酶相关基因突变可导致端粒酶活性的降低和端粒缩短,过短的端粒不再保护基因组稳定性,将引起细胞的老化、凋亡或恶变。端粒酶基因的扩增出现在一些肿瘤细胞中,是癌细胞增殖的重要原因,其扩增的机制及其对端粒酶活性的调节作用尚不完全清楚。近期研究表明,端粒酶基因扩增是基因组不稳定的结果,扩增的hTERT／hTERC基因对端粒酶激活和癌变进展有促进作用。     

体外合成特异siRNA及其对Hela细胞端粒酶基因表达抑制的研究

目的 针对端粒酶蛋白催化亚单位(hTERT)基因不同片断合成2条siRNA,比较其对Hela细胞端粒酶基因表达干扰作用的强弱,从而选择出更好的干扰靶位点.方法 用T7RNA聚合酶在体外转录合成siRNA,将合成的2段siRNA转染Hela细胞,对其干扰作用进行分析、鉴定.结果 用2段合成的特异siRNA转染Hela细胞...     

端粒酶活性及其hTERT基因在增生性组织中的表达

目的:探讨端粒酶在增生性组织中的表达状况。方法:采用Kim的TRAP法和RT-PCR技术检测增生性肉芽组织、子宫内膜组织以及部分生长旺盛的癌旁组织的端粒酶活性及其催化亚基hTERT基因的表达。结果:以Hela细胞对照作为阳性对照,3类组织可部分检测到低水平的端粒酶活性及hTERT基因的表达。结论:端粒酶在生长旺盛的增生性组织中呈低水平表达,与细胞的生长状态有关。     

端粒酶hTERT促进肿瘤细胞侵袭与转移及其机制研究

目的观察hTERT基因修饰对人骨肉瘤细胞系U-2OS生物学行为的影响。方法采用脂质体法将克隆有人全长cDNAhTERT的真核荧光质粒(pIRES2-EGFP-hTERT)转染端粒酶阴性的人骨肉瘤U-2OS细胞,经G418筛选,免疫组化和Westorn Blot鉴定后,检测其端粒酶活性的改变、生长周期以及生物力学的变化。结果成功转染人真核荧光表达载体的U-2OS细胞能有效抵抗G418,并可有效表达hTERT蛋白,细胞内端粒酶活性明显增强,G1期细胞比例下降,S期细胞比例升高,并且还明显增强了对细胞外基质的粘附力。进一步采用Transwell小孔迁移实验检测发现,hTERT/U2OS侵袭能力明显增强。结论转染hTERT基因后,U-2OS细胞内可同时通过端粒酶途径延长端粒。hTERT基因修饰可促进细胞周期进程,促使细胞从G1期→S期。通过替代途径延长端粒的肿瘤细胞在hTERT基因修饰后,增殖能力及侵袭能力明显增强。     

Treatment of bladder cancer cells in vitro and in vivo with 2-5A antisense telomerase RNA

Bladder cancer is the most common malignant tumor of the urinary tract. Novel treatment approaches are essential because of the failure of current treatment options to cure a high percentage of patients. Telomerase, a ribonucleoprotein, is detected in almost all bladder cancer, but not in normal bladder tissues. Therefore, telomerase is expected to be a very promising candidate for targeted therapy of bladder cancer. In this study, we synthesized a 19-mer antisense oligonucleotide against the RNA component of human telomerase (hTR) linked to a 2-5A molecule (2-5A-anti-hTR) and investigated its antitumor effect against bladder cancer cells. The 2-5A antisense strategy relies on the recruitment and activation of RNase L at the site of targeted RNA sequence. Here we demonstrate that treatment with 2-5A-anti-hTR reduced the viability of seven bladder cancer cell lines (UM-UC-2, UM-UC-3, UM-UC-6, UM-UC-9, UM-UC-14, RT4 and T24) expressing telomerase activity to 21-55% within 4 days. The cytotoxicity was mainly due to induction of caspase-dependent apoptosis. In contrast, normal fibroblast WI38 cells lacking telomerase activity were resistant to the treatment. Furthermore, treatment of subcutaneous UM-UC-2 tumors in nude mice with 2-5A-anti-hTR significantly suppressed the tumor growth through induction of apoptosis (P < 0.001). These findings may offer a strong support to the feasibility of the 2-5A-anti-hTR treatment for human bladder cancer.     

高三尖杉酯碱诱导HL-60细胞人端粒酶逆转录酶mRNA的变化

为了探讨高三尖衫酯碱(homohardngtonine，HHT)抑制HL-60细胞端粒酶活性的机制及意义，采用半定量RT-PCR和PCR-ELISA法检测HHT作用后的HL-60细胞人端粒酶逆转录酶(hTERT)mRNA表达和端粒酶活性的变化，用TUNEL法检测HL-60细胞的凋亡率。结果发现：与空白对照相比，0．005-0．03μg/ml,HHT作用HL-60细胞12小时，hTERTmRNA表达无明显变化，随HHT浓度增加至0．04-0．05μg/ml，hTERTmRNA表达明显下降至检测不出。与0小时相比，0．02μg/ml HHT作用6-18小时后，HL-60细胞hTERT mRNA表达无明显变化，24小时后hTERT mRNA表达明显减少，至30小时未能检出hTERT mRNA表达。HL-60细胞端粒酶活性的抑制与hTERT mRNA的表达下降趋势基本一致。随HL60细胞hTERT mRNA的表达下降和端粒酶活性的抑制，其凋亡率明显增加。结论：HHT能抑制HL-60细胞hTERT mRNA的转录，其与细胞凋亡的关系值得进一步研究。     

Telomerase inhibition by retinoids precedes cytodifferentiation of leukemia cells and may contribute to terminal differentiation

Human promyelocytic leukemia HL60 cells display high telomerase activity, a phenotype related to their immortal status. All-trans retinoic acid (ATRA) is a clinically effective cytodifferentiating agent. To understand the mechanism underlying ATRA-induced cytodifferentiation, we did a kinetic analysis of the role of ATRA in inhibiting telomerase in HL60 cells. Our studies indicate that telomerase inhibition by ATRA occurred relatively early after treatment of HL60 cells due to a rapid decrease in hTERT gene expression. More importantly, however, we found through monitoring the expression of CD11b, a marker for granulocytic differentiation of HL60 cells, that down-regulation of telomerase preceded the differentiation of HL60 cells. These observations suggest that the hTERT gene may be a primary target of ATRA regulation of cellular differentiation and the antileukemia activity of ATRA may be mediated by its ability to induce the differentiation of the promyelocytic leukemia cells through down-regulation of the hTERT gene.