中心体异常扩增和染色体不稳定性

中心体作为主要微管组织中心在细胞周期事件中起着重要的作用。异常中心体可产生纺锤体异常,使染色体错误分离,引起染色体不稳定性和非整倍体的形成。中心体异常同染色体不稳定性一样是肿瘤细胞的一个普遍特征,并且可出现在肿瘤发生的早期阶段。中心体异常在肿瘤的发生发展演化过程中可能具有重要作用。现综述中心体的结构、功能、复制和调控,阐述肿瘤中中心体异常的表现和导致中心体扩增的可能机制及中心体扩增与染色体不稳定之间的相关性。     

中心体扩增与肿瘤

中心体是动物细胞中非常重要的非膜结构细胞器,它除了作为微管组织中心在有丝分裂过程中具有指导两极纺锤体组装的功能外,还参与了细胞内的许多生命活动过程。中心体扩增通常导致异倍体的形成、以及染色体和细胞骨架的不稳定性。因而与肿瘤的发生、发展有着直接的关系。中心体扩增在肿瘤的诊、治中具有广阔的研究与应用前景。中心体扩增的参数可以作为肿瘤诊断以及预后的指标;中心体可望成为肿瘤治疗的靶位点。     

中心体异常扩增的研究进展及其与肿瘤发生之间的关系

中心体是肿瘤细胞中重要的研究对象。起初研究人员就假设中心体的异常及随之而来的有丝分裂紊乱,是导致肿瘤发生的重要原因之一。中心体既有基本的复制机器,也有完善的扩增制动机制。在多数肿瘤细胞中都可以观察到中心体异常扩增的现象。因此,中心体异常扩增也成为肿瘤细胞的"标志"之一。总结了中心体相关研究的最新进展,并重点讨论了中心体与肿瘤发生之间的关系,为进一步了解中心体发挥功能的机制提供参考。     

体细胞核移植与中心体遗传

体细胞克隆虽然在多种哺乳动物中成功获得后代, 但仍存在一系列的问题需要解决。克隆胚胎的发育能力由核移植后几小时内的细胞和分子过程决定, 包括染色体分离和纺锤体的重新组装。中心体的正常组成和分布能保证染色体分离的准确性及新生和出生后克隆动物发育过程中的基因组稳定性。文章在分析哺乳动物体细胞克隆存在的问题和简介中心体结构功能的基础上, 综述了中心体在配子和受精卵发育过程中的遗传机制, 同时阐述了体细胞克隆胚胎中心体及其相关蛋白的研究现状。     

DNA甲基化异常与肿瘤耐药

肿瘤耐药是导致肿瘤化疗失败的主要原因, 其产生机制复杂多样, 是多种因素共同作用的结果。近年来, 表观遗传改变在肿瘤耐药中的作用日益受到关注。DNA甲基化是一种重要的表观遗传修饰, 在调节基因表达和维持基因组稳定性中扮演着重要角色。原发性或获得性耐药的肿瘤细胞大多伴随DNA异常甲基化, 越来越多的证据显示, DNA甲基化异常是肿瘤细胞耐药表型产生的重要机制。文章就DNA甲基化异常与肿瘤细胞耐药的关系及相关作用机制进行了综述。     

脑胶质瘤中心体的异常扩增及其与疾病分期的相关性

目的:探讨脑胶质瘤中心体扩增情况及其与疾病分期的相关性。方法:对40例胶质瘤标本和10例正常脑组织标本进行HE染色的检测;免疫组织化学检测Ki67和γ-微管蛋白的表达;使用免疫荧光染色技术检测中心体扩增情况。结果:不同标本中,HE染色呈现不同的细胞形态特征;Ki67在正常脑组织中没有表达,但在Ⅰ/Ⅱ、Ⅲ和Ⅳ级胶质瘤中的阳性表达率分别为65%、80%和100%,各组间差异具有统计学意义(P<0.01),说明Ki67的表达与胶质瘤级别相关。γ-微管蛋白在正常脑组织和Ⅰ/Ⅱ、Ⅲ、Ⅳ级胶质瘤中的表达率分别为30%、50%、80%和100%,各组间差异具有统计学意义(P<0.01),说明胶质瘤级别升高,中心体扩增率增加;免疫荧光检测显示,中心体扩增率和脑胶质瘤的级别呈正相关。结论:中心体扩增是脑胶质瘤的恶性程度的特征之一,并且与胶质瘤发病阶段有关,提示中心体扩增和脑胶质瘤的发展具有密切的相关性。     

细胞骨架与中心体的分离过程

中心体作为细胞微管组织中心,对于细胞的生理活动具有重要的调控作用.在G2期末和有丝分裂期开始阶段,复制之后的中心体需要向细胞核两端运动,到达形成双极纺锤体的位置.这一过程受到微管和微丝两个骨架系统的调控.在相关动力蛋白的驱动下,两种骨架相互配合,共同完成中心体的分离过程,从而保证细胞顺利进入有丝分裂期.本文分析和比较了两种骨架蛋门对下中心体分离过程中所发挥的作用.     

中心体异常在咖啡因增强顺铂杀伤人肝癌细胞系中的作用

为了探讨咖啡因是否影响细胞周期检验点而增强顺铂杀伤肿瘤细胞及其作用机制 ,选取同步化于S期的肝癌细胞系SMMC 772 1,用顺铂和咖啡因进行不同方式的处理 ,包括顺铂处理、咖啡因处理以及先经顺铂 ,再用咖啡因处理 .利用相关方法对不同处理的细胞进行了分析 ,包括细胞形态 ,细胞生长速率 ,多核细胞的形成与死亡 ,中心体的异常等 .结果显示 ,顺铂与咖啡因联合处理的细胞出现明显的多核化现象 ,多核细胞占总细胞的百分比可以达到 30 %以上 ,高于用顺铂或用咖啡因处理的细胞 .同时观察到多核细胞生存能力较差 ,它们会通过细胞凋亡的形式死亡 .抗中心体人自身免疫血清的免疫荧光结果显示 ,中心体异常与多核细胞的形成直接相关 .在部分多核细胞的核周围有多个不同强度的荧光点 ,在另部分多核细胞中 ,在其中央有一个大的荧光点 ,被多个细胞核围绕 ,荧光较强 .根据结果推测 ,由多个不完整的中心体导致的多极分裂形成多核细胞 ,随后多个中心体聚集到中央形成大的中心体 ,负责间期微管的组装 .结果表明 ,受到顺铂损伤的细胞由于检验点的作用而使细胞周期阻断 ,咖啡因可消除周期的阻断 ,使细胞在中心体未完成正常复制状态下进入有丝分裂 ,产生大量多核细胞 ,这些多核细胞最终发生凋亡 .     

大鼠中心体蛋白家族基因的克隆及其在睾丸中的表达特征

centrin是进化上高度保守的中心体蛋白家族, 已从多种生物中克隆到其同源基因, 但基因文库中尚无大鼠centrin序列的报道. 采用RT-PCR从大鼠睾丸组织中克隆到centrin-1, -2和 -3 cDNA片段, 对其衍生的氨基酸序列进行同源性比较, 结果显示, 人、小鼠、大鼠中相应的centrin蛋白同源性很高. 采用半定量RT-PCR技术研究了它们在大鼠精子发生过程中的表达特征. 结果表明, centrin-1的表达具有睾丸组织和生精细胞特异性, 并呈现出发育阶段相关的规律, 它仅在减数分裂开始后转录, 其mRNA水平在圆形精子细胞中达到高峰. centrin-2和centrin-3在睾丸精原细胞中有高表达, 进入减数分裂后其mRNA水平迅速降低, 同时在一些体细胞中也有表达. 推测centrin-1可能在减数分裂或精子细胞变态分化过程中发挥作用, 而centrin-2, -3可能与有丝分裂有关.     

中心体蛋白centrin研究进展

Centrin是普遍存在于中心体上的蛋白成分 ,具有钙离子结合能力。Centrin家族包含多种同源蛋白 ,这些蛋白在结构上高度保守。研究表明centrin可能与细胞的分化 ,纤毛的生成定向和切断 ,精子尾部的生成 ,中心体复制及其结构维持有密切关系 ,同时也和细胞的癌变、生长及细胞周期调控有关 ,还有许多未知功能有待研究     

Centrosome positioning in interphase cells

The position of the centrosome is actively maintained at the cell center, but the mechanisms of the centering force remain largely unknown. It is known that centrosome positioning requires a radial array of cytoplasmic microtubules (MTs) that can exert pushing or pulling forces involving MT dynamics and the activity of cortical MT motors. It has also been suggested that actomyosin can play a direct or indirect role in this process. To examine the centering mechanisms, we introduced an imbalance of forces acting on the centrosome by local application of an inhibitor of MT assembly (nocodazole), and studied the resulting centrosome displacement. Using this approach in combination with microinjection of function-blocking probes, we found that a MT-dependent dynein pulling force plays a key role in the positioning of the centrosome at the cell center, and that other forces applied to the centrosomal MTs, including actomyosin contractility, can contribute to this process.     

Centrobin与BRCA2蛋白间相互作用及其细胞定位

为分析乳腺癌易感基因2（breast cancer susceptibility gene 2, BRCA2）蛋白与中心体BRCA2相互作用蛋白（centromal BRCA2 interacting protein, centrobin）间相互作用及其细胞定位的关系,探讨二者功能上的联系,本研究采用哺乳细胞双杂交实验检测体内结合并初步判定BRCA2分子上的结合区域;免疫共沉淀实验进一步验证其体内结合活性,GST-pulldown法检测其体外结合活性,免疫组织化学染色观测BRCA2蛋白的细胞定位及在有丝分裂各期centrobin的细胞定位.结果显示,BRCA2与centrobin间存在体内和体外结合,且BRCA2分子的结合区域主要位于2　393～2　952氨基酸残基处;外源表达BRCA2定位于中心体,在有丝分裂各时相centrobin均定位于中心体. BRCA2与centrobin在体内形成复合物,并存在直接物理结合作用,二者存在细胞空间定位的一致性.该结果为进一步研究BRCA2在中心体复制中的调控作用提供了线索.     

Centrosome function is critical during terminal erythroid differentiation

Red blood cells are produced by terminal erythroid differentiation, which involves the dramatic morphological transformation of erythroblasts into enucleated reticulocytes. Microtubules are important for enucleation, but it is not known if the centrosome, a key microtubule‐organizing center, is required as well. Mice lacking the conserved centrosome component, CDK5RAP2, are likely to have defective erythroid differentiation because they develop macrocytic anemia. Here, we show that fetal liver‐derived, CDK5RAP2‐deficient erythroid progenitors generate fewer and larger reticulocytes, hence recapitulating features of macrocytic anemia. In erythroblasts, but not in embryonic fibroblasts, loss of CDK5RAP2 or pharmacological depletion of centrosomes leads to highly aberrant spindle morphologies. Consistent with such cells exiting mitosis without chromosome segregation, tetraploidy is frequent in late‐stage erythroblasts, thereby giving rise to fewer but larger reticulocytes than normal. Our results define a critical role for CDK5RAP2 and centrosomes in spindle formation specifically during blood production. We propose that disruption of centrosome and spindle function could contribute to the emergence of macrocytic anemias, for instance, due to nutritional deficiency or exposure to chemotherapy.     

Centrosome function in normal and tumor cells

Centrosomes nucleate microtubules that form the mitotic spindle and regulate the equal division of chromosomes during cell division. In cancer, centrosomes are often found amplified to greater than two per cell, and these tumor cells frequently have aneuploid genomes. In this review, we will discuss the cellular factors that regulate the proper duplication of the centrosome and how these regulatory steps can lead to abnormal centrosome numbers and abnormal mitoses. In particular, we highlight the newly emerging role of the Breast Cancer 1 (BRCA1) ubiquitin ligase in this process.     

Parallels and Antagonisms of Embryogenesis and Carcinogenesis

The main similarities of embryonic and tumor cells, as well as the mechanisms preventing the malignant transformation of embryonic cells, are presented in this review. Special attention is paid to the role of specific polypeptide growth factors in reciprocally excluding processes: embryogenesis and carcinogenesis. Based on the presented analysis, new potential targets for antitumor drugs are considered.     

Centrosome Function: Sometimes Less Is More

Tight regulation of centrosome duplication is critical to ensure that centrosome number doubles once and only once per cell cycle. Superimposed onto this centrosome duplication cycle is a functional centrosome cycle in which they alternate between phases of quiescence and robust microtubule (MT) nucleation and MT-anchoring activities. In vertebrate cycling cells, interphase centrioles accumulate less pericentriolar material (PCM), reducing their MT nucleation capacity. In mitosis, centrosomes mature, accumulating more PCM to increase their nucleation and anchoring capacities to form robust MT asters. Interestingly, functional cycles of centrosomes can be altered to suit the cell's needs. Some interphase centrosomes function as a microtubule-organizing center by increasing their ability to anchor MTs to form centrosomal radial arrays. Other interphase centrosomes maintain their MT nucleation capacity but reduce/eliminate their MT-anchoring capacity. Recent work demonstrates that Drosophila cells take this to the extreme, whereby centrioles lose all detectable PCM during interphase, offering an explanation as to how centrosome-deficient flies develop to adulthood. Drosophila stem cells further modify the functional cycle by differentially regulating their two centrioles – a situation that seems important for stem cell asymmetric divisions, as misregulation of centrosome duplication in stem/progenitor cells can promote tumor formation. Here, we review recent findings that describe variations in the functional cycle of centrosomes.     

Centrosome behaviour and orientation of centrioles under the action of energy transfer inhibitors.

2,4-dinitrophenol, dinitrophenol together with deoxyglucose, sodium azide and ouabain didn't alter cytoplasmic microtubule (MT) network of cultured PK (pig kidney embryo) cells, meanwhile they induced an increase in the average number of pericentriolar satellites and percentage of centrioles with the primary cilium in these cells. Also all drugs studied increase number of MTs attached to and oriented towards the centrosome. Under the action of ouabain the total number of MTs around the centrosome doubled, meanwhile the number of long MTs emanating from the centrosome increased more than 15 times. Under the action of all drugs studied, except sodium azide, the number of maternal centrioles oriented perpendicularly to the substrate surface increased significantly from that in control cells.     

Aldehyde Dehydrogenases and Their Role in Carcinogenesis

Abstract

Aldehydes are highly reactive molecules that may have a variety of effects on biological systems. They can be generated from a virtually limitless number of endogenous and exogenous sources. Although some aldehyde-mediated effects such as vision are beneficial, many effects are deleterious, including cytotoxicity, mutagenicity, and carcinogenicity. A variety of enzymes have evolved to metabolize aldehydes to less reactive forms. Among the most effective pathways for aldehyde metabolism is their oxidation to carboxylic acids by aldehyde dehydrogenases (ALDHs).

ALDHs are a family of NADP-dependent enzymes with common structural and functional features that catalyze the oxidation of a broad spectrum of aliphatic and aromatic aldehydes. Based on primary sequence analysis, three major classes of mammalian ALDHs — 1, 2, and 3 — have been identified. Classes 1 and 3 contain both constitutively expressed and inducible cytosolic forms. Class 2 consists of constitutive mitochondrial enzymes. Each class appears to oxidize a variety of substrates that may be derived either from endogenous sources such as amino acid, biogenic amine, or lipid metabolism or from exogenous sources, including aldehydes derived from xenobiotic metabolism.

Changes in ALDH activity have been observed during experimental liver and urinary bladder carcinogenesis and in a number of human tumors, including some liver, colon, and mammary cancers. Changes in ALDH define at least one population of preneoplastic cells having a high probability of progressing to overt neoplasms. The most common change is the appearance of class 3 ALDH dehydrogenase activity in tumors arising in tissues that normally do not express this form. The changes in enzyme activity occur early in tumorigenesis and are the result of permanent changes in ALDH gene expression.

This review discusses several aspects of ALDH expression during carcinogenesis. A brief introduction examines the variety of sources of aldehydes. This is followed by a discussion of the mammalian ALDHs. Because the ALDHs are a relatively understudied family of enzymes, this section presents what is currently known about the general structural and functional properties of the enzymes and the interrelationships of the various forms.

The remainder of the review discusses various aspects of the ALDHs in relation to tumorigenesis. The expression of ALDH during experimental carcinogenesis and what is known about the molecular mechanisms underlying those changes are discussed. This is followed by an extended discussion of the potential roles for ALDH in tumorigenesis. The role of ALDH in the metabolism of cyclophosphamidelike chemotherapeutic agents is described. This work suggests that modulation of ALDH activity may be an important determinant of the effectiveness of certain chemotherapeutic agents. The evidence that changes in ALDH are part of an adaptive response of preneoplastic and neoplastic cells to altered cell physiology or stress is then considered. Roles in the metabolism of aldehydes generated from lipid peroxidation and as part of the Ah gene-mediated response to xenobiotic exposure are both discussed. The data are consistent with a role for certain ALDHs in lipid aldehyde metabolism. Biochemical and genetic data also imply that changes in ALDH may be linked, in part, to cellular adaptation to oxidative stress.

Finally, a model of inducible ALDH gene regulation is proposed. The model incorporates current information about ALDH gene expression with the regulation of other genes known to be part of the adaptive responses occurring in neoplastic cells. The model suggests that regulation of class 1 and 3 ALDH gene activity may be complex, involving the tissue-specific ability to respond to a variety of physiological cues. The model also suggests several avenues for future research that should provide a clearer understanding of the regulation of this important gene family in response to a variety of factors.