SUMO化修饰:一种多功能的蛋白质翻译后修饰方式

SUMO分子是一种结构上与泛素相似的分子,它参与蛋白质翻译后修饰。SUMO化循环与泛素化循环过程相似,但SUMO化修饰具有与泛素化修饰截然不同的功能。泛素化修饰的靶分子主要被蛋白酶体降解,而SUMO化修饰则介导靶分子定位和功能调节。新近发现SUMO化修饰参与调控线粒体分裂、DNA损伤修复及调节基因组稳定性、调控离子通道及生物节律。此外,SUMO化修饰功能的紊乱会导致某些疾病的发生。     

蛋白质SUMO化和泛素化修饰的关系

泛素化和SUMO化是蛋白质翻译后修饰的重要方式,广泛参与调节蛋白质功能和细胞生命活动各个环节.多聚泛素化降解蛋白质,而SUMO化主要调节蛋白质的相互作用和定位等.在不同情况下,SUMO化和泛素化既可协同调节蛋白质功能,也可相互拮抗. 最近研究发现,某些底物的SUMO化能够激活体内一类新发现的SUMO依赖的泛素连接酶,启动泛素-蛋白酶体途径降解底物, 导致蛋白质SUMO化和泛素化的关系进一步精细化和复杂化.     

端粒与年龄

端粒在细胞正常生理功能运转过程中起重要作用, 涉及到染色体末端复制、端粒酶作用机理、肿瘤及衰老等多方面问题, 端粒的缺失将造成多种病理状况, 直接影响到细胞的生存, 随着人们对端粒酶研究的日益深入，端粒与染色体不稳定性的关系及机理的探索已引起普遍关注。     

SUMO化修饰在病毒感染中的作用研究进展

Small ubiquitin-related modifier（SUMO）是一类重要的类泛素蛋白,其修饰过程与泛素类似,但功能不尽相同,SUMO通过对底物蛋白的修饰来调节蛋白间的相互作用、定位及稳定性等功能。近年来,包括一些病毒蛋白在内的大量底物蛋白陆续被发现,SUMO化作为一种重要的蛋白质翻译后修饰,在病毒对宿主细胞的感染中既可发挥促进病毒感染的作用,也可发挥抑病毒感染的作用。     

不同疱疹病毒相关蛋白与SUMO修饰系统的相互作用

小泛素化相关修饰物(small ubiquitin-related modifier,SUMO)修饰是一种与泛素化修饰具有相似酶促反应过程的翻译后修饰.近年来,研究者相继发现许多病毒蛋白能发生SUMO修饰,特别是疱疹病毒相关蛋白.研究表明,SUMO修饰能影响一些病毒蛋白的转录调控活性.此外,一些定位于核内功能性结构PODs(PML oncogenic domains)的病毒蛋白还能影响SUMO-1对PODs主要成分PML及Sp100的修饰并导致PODs解聚.因此了解SUMO修饰如何改变病毒与细胞相互作用的生物学特件对研究病毒的复制增殖机制具有重要的意义.本文就疱疹病毒相关蛋白与SUMO修饰系统相互作用的分子机制及功能影响进行综述.     

端粒与细胞分裂

端粒与细胞分裂的最新研究进展表明 ,端粒长度本身不能作为决定细胞分裂能力的指标。本文介绍了Blackburn提出的关于端粒功能的全新模型 ,在这一模型中以端粒的戴帽状态作为确定端粒是否具有功能的指标 ,端粒长度和端粒酶活性等因素对端粒功能的影响则通过其对端粒戴帽状态的影响来评价。这一模型可以很好地解释有关端粒与细胞分裂之间的关系 ,即无论端粒长短如何 ,只要处于戴帽状态细胞均可继续分裂 ,反之细胞则退出周期发生衰老和死亡     

替代性端粒延长机制与端粒

端粒的维持除了可以通过端粒酶的作用外,还可以通过其他途径.这种不依赖端粒酶的延长途径被称为替代性端粒延长机制.替代性端粒延长机制与端粒酶途径之间存在着抑制效应.二者延长端粒的效果不一样,以致其后续效应对肿瘤演变产生不同的影响.对替代性端粒延长机制的理解有助于阐明肿瘤的发生,并对肿瘤的预防和治疗提出新的建议.     

端粒耗损与心血管疾病

心血管疾病一直被认为是与年龄相关的退行性疾病,端粒随年龄增长而变短,是细胞老化的标志.最近,越来越多的研究表明端粒长度缩短与心血管疾病发生发展有关.该文仅就端粒耗损与心血管疾病相关性的研究进展作一综述,旨在为今后心血管疾病的预防和治疗提供新的思路.

Abstract：

Cardiovascular disease (CVD)has been considered as an age-related degenerative diseases. Telomere shortens with age, that is a sign of cell senescence. Currently, more and more researches show that the shortening of telomere length is correlated with the occurrence and progress of cardiovascular diseases. This article reviewed the studies on the relationship of telomere loss and cardiovascular diseases in order to provide new ideas for the prevention and treatment of cardiovascular diseases.     

Human XPF controls TRF2 and telomere length maintenance through distinctive mechanisms

XPF-ERCC1, a structure-specific endonuclease, is involved in nucleotide excision repair, crosslink repair and homologous recombination. XPF-ERCC1 is also found to interact with TRF2, a duplex telomeric DNA binding protein. We have previously shown that XPF-ERCC1 is required for TRF2-promoted telomere shortening. However, whether XPF-ERCC1 by itself has a role in telomere length maintenance has not been determined. Here we report that overexpression of XPF induces telomere shortening in XPF-proficient cells whereas XPF complementation suppresses telomere lengthening in XPF-deficient cells. These results suggest that XPF-ERCC1 can function as a negative mediator of telomere length maintenance. In addition, we find that introduction of wild type XPF into XPF-deficient cells leads to over 40% reduction in TRF2 association with telomeric DNA, indicating that XPF-ERCC1 negatively regulates TRF2 binding to telomeric DNA. Furthermore, we show that XPF carrying mutations in the conserved nuclease domain fails to control TRF2 association with telomeric DNA but it is competent for modulating telomere length maintenance. These results imply that XPF-ERCC1 controls TRF2 and telomere length maintenance through two distinctive mechanisms, with the former requiring its nuclease activity. Our results further imply that TRF2 association with telomeres may be deregulated in cells derived from XPF patients.     

Effect of long-term hormone therapy on telomere length in postmenopausal women

Telomeres undergo attrition with each cell division, and telomere length is associated with age-related diseases and mortality in the elderly. Estrogen can influence the attrition of telomeres by diverse mechanisms. This is a retrospective case control study that investigated the influence of long-term hormone therapy (HT) on telomere length in postmenopausal women. We recruited 130 postmenopausal women from 55 to 69 years of age for this study, and divided them into two groups. The first group included 65 women who had been on estrogen and progesterone therapy for more than five years (HT group). The other group was composed of 65 women matched in age to the HT group who had never had HT (non- HT group). The relative ratios of telomere length of study subjects to a reference DNA from a healthy young female were measured using quantitative PCR. Plasma levels of lipid profiles, total antioxidant status (TAS), C-reactive proteins (CRP), fasting glucose levels, and estradiol levels were measured. Age at menopause, vitamin use, and exercise, alcohol, and cigarette smoking histories were also assessed in a questionnaire. Mean duration (+/- SD) of HT was 8.4 +/- 2.3 years. Prevalence of vitamin use and regular exercise were higher in the HT group than in the non-HT group (p < 0.01). Relative telomere length ratios in the HT group were significantly greater than those in the non-HT group (p < 0.01). HT was significantly correlated with the relative telomere length ratio in multivariate analysis when potential confounding variables were controlled for (p < 0.05). In conclusion, telomere lengths were longer in postmenopausal women who had a history of long-term HT than in postmenopausal women without HT. Long-term HT in postmenopausal women may alleviate telomere attrition.     

SUMO化修饰对高糖诱导的大鼠肾系膜细胞IKKγ/NF-κB信号的影响

 目的：探讨小泛素相关修饰物（SUMO）化修饰对高糖诱导的肾系膜细胞IκB激酶γ(IKKγ)/NF-κB信号的影响。方法：体外培养大鼠肾小球系膜细胞,设正常对照组、高糖干预组和渗透压对照组：用免疫印迹和RT-PCR法检测各组细胞SUMO1、SUMO2/3、IKKγ和NF-κB p65的表达;用免疫共沉淀检测SUMO与IKKγ蛋白间的相互作用。结果：高糖呈浓度和时间依赖性上调系膜细胞SUMO和NF-κB p65表达（均P<0.01）。各组细胞IKKγ 的蛋白与mRNA表达差异无统计学意义（均P<0.05）;高糖组SUMO与IKKγ蛋白间的相互作用减弱（均P<0.01）。结论:高糖影响IKKγ 的SUMO化修饰,可能参与了高糖诱导的肾系膜细胞NF-κB信号激活的调控。     

Post-translational modifications of TRF1 and TRF2 and their roles in telomere maintenance

Telomeres, heterochromatic structures, found at the ends of linear eukaryotic chromosomes, function to protect natural chromosome ends from nucleolytic attack. Human telomeric DNA is bound by a telomere-specific six-subunit protein complex, termed shelterin/telosome. The shelterin subunits TRF1 and TRF2 bind in a sequence-specific manner to double-stranded telomeric DNA, providing a vital platform for recruitment of additional shelterin proteins as well as non-shelterin factors crucial for the maintenance of telomere length and structure. Both TRF1 and TRF2 are engaged in multiple roles at telomeres including telomere protection, telomere replication, sister telomere resolution and telomere length maintenance. Regulation of TRF1 and TRF2 in these various processes is controlled by post-translational modifications, at times in a cell-cycle-dependent manner, affecting key functions such as DNA binding, dimerization, localization, degradation and interactions with other proteins. Here we review the post-translational modifications of TRF1 and TRF2 and discuss the mechanisms by which these modifications contribute to the function of these two proteins.     

Effect of tissue fixatives on telomere length determination by quantitative PCR

Telomere length is a well established marker of cellular senescence and thus biological age. Quantitative PCR allows the determination even from very low amounts of tissue by using telomere specific and single copy gene primers. Comparing a directly processed tissue sample to a 4% formaldehyde fixed one showed a significantly reduced efficiency of PCR reactions (mainly in single copy gene experiments) in a storage time-dependent manner resulting in an artificial increase in reported relative telomere length. This effect was not seen when the tissue was stored in RNA later solution. In summary, telomere length determination from formaldehyde fixed material by quantitative PCR is not a reliable method. Unfortunately therefore, many easily accessible tissue samples from pathology laboratories are unsuitable for this technique.     

端粒与肿瘤细胞耐药关系的研究进展

端粒是人类染色体末端结构,在维持基因组稳定性中发挥重要作用.有丝分裂导致的端粒长度的进行性缩短是细胞衰老的标志,肿瘤细胞则克服了这种现象,保留了无限增殖的能力,故端粒成为临床治疗的靶点.肿瘤细胞对化疗药物的耐受现象是临床治疗的难题.如何克服肿瘤的耐药性一直是肿瘤治疗研究的重点.该文从端粒的基本组成结构人手,对端粒与肿瘤细胞获得性耐药的关系以及端粒如何介导肿瘤细胞耐药性的产生进行综述,旨在为克服肿瘤耐药性提供新的治疗思路.     

Reduced telomere length variation in healthy oldest old

Telomeres protect against DNA degradation at the ends of linear chromosomes. The number of telomere repeats is reduced over time in human aging. Using flow FISH we have assessed telomere length in 134 exceptionally healthy seniors aged 85 or older who have never been diagnosed with cancer, cardiovascular disease, major pulmonary disease, diabetes or Alzheimer disease (the ‘Super-seniors’) and 47 randomly-ascertained mid-life individuals aged 40-50 years. We compared their telomere lengths to a reference interval based on 400 individuals aged 1-100 years and show that Super-seniors do not have exceptionally long telomeres for their age. Consistent with the known trend of telomere shortening over time; however, they have shorter telomeres than the younger control group.Furthermore, we show that variability in telomere length was lower in the Super-seniors than in the mid-life controls or the reference data. Reduced telomere length variation was observed for lymphocytes, CD45RA-positive T-cells and memory T-cells. These results suggest that individuals, some types of their somatic cells, or both, may be selected for an optimal rather than extreme telomere length. Selection of individuals and/or cells that have an optimal telomere repeat length could contribute to disease resistance and promote healthy aging.     

原发性胃癌组织中的端粒及端粒酶表达

目的观察端粒（ＴＲＦ）及端粒酶在胃癌形成及发展中的作用。方法采用ＤＮＡ琼脂糖凝胶杂交技术及端粒重复扩增ＰＣＲ方法检测１７例早期胃癌、８９例进展期胃癌组织及邻近正常组织中的平均ＴＲＦ长度及端粒酶活性。结果早期、进展期胃癌的ＴＲＦ长度及端粒酶活性表达均显著短于或高于邻近胃组织（Ｐ＜０．０５～０．０１），且端粒酶活性的表达主要表现在ＴＲＦ缩短或延长的胃癌组织中，而ＴＲＦ缩短与胃癌的分化程度相一致。结论端粒及端粒酶的异常状态可能与胃癌的发生发展密切相关，端粒酶活性及端粒缩短可以作为胃癌的诊断标志     

No evidence of substantia nigra telomere shortening in Parkinson's disease

Telomeres are repetitive tracts of DNA which protect chromosomal integrity. Increased oxidative stress leads to shorter telomeres, which have been associated with several late-onset human diseases. Given independent evidence of oxidative stress and Parkinson's disease (PD), and conflicting reports of the role of telomere length in PD, we measured telomere length in both PD peripheral blood monocytes and in substantia nigra from affected individuals and controls. We confirmed previous findings of a paradoxically longer telomere length in blood from PD patients, but found no difference in telomere length in substantia nigra. Confounding factors provide a likely explanation for the findings in blood, and possibly the reduced frequency of cigarette smoking in PD patients. We conclude that telomere shortening is unlikely to be involved in the pathogenesis of PD.