鼻咽癌患者和EB病毒IgA/VCA抗体阳性者染色体脆性部位研究

分析58例鼻咽癌患者和54例IgA/VCA抗体阳性者的染色体脆性部位,并与正常人对照,发现鼻咽癌患者染色体畸变率明显高于其他两组。从非随机的脆性部位断裂点分析中,提出脆性部位5P~(13)、5P~(14)和8P~(24)及其相应部位癌基因激活可能与鼻咽癌发生有关;非脆性部位断裂点1P~(11)、1 cen、2P~(23)和5P~(34)及相应部位癌基因激活也可能对肿瘤的发生起作用。而出现频率较高的脆性部位3P~(14)3P~(14)则与肿瘤的发生没有特异相关。     

鼻咽癌患者染色体断裂热点与SCE高发位点、脆性部位、原癌基因位点的相关研究

采用在染色体标本上同时显示ＳＣＥ及Ｇ带带型的方法，对鼻咽癌患者染色体断裂热点与ＳＣＥ高发位点、染色体脆性部位及原癌基因位点之间的相关性进行了分析。结果表明：患者的ＳＣＥ频率、染色体畸变率均显著的高于对照组（Ｐ＜０．０１），患者的染色体断裂点和ＳＣＥ位点都主要分布在染色体的Ａ、Ｂ、Ｃ、Ｄ组和浅带上，且两者所累及的染色体号存在着明显的相关（ｒ＝０．９５７６，Ｐ＜０．０１），患者的１５个断裂热点与ＳＣＥ高发位点的一致率为５３．３３％，与脆性部位的一致率为８０％，与原癌基因位点的一致率为４０％     

鼻咽癌高发家系遗传学、EB病毒血清学分析

目的:分析鼻咽癌高发家系遗传因素、EB病毒感染在其病因学中的意义。方法:家系资料采用系谱分析及问卷调查,家系成员行外周血染色体脆性位点分析,免疫酶联法检测EB病毒VCA/IgA、EA/IgA。结果:患者一级亲属鼻咽癌检出率高达19.60%。家系成员与对照组染色体总畸变率分别为5.81%和4.93%(P>0.05),3p14、1p32、1q32等脆性位点表达率较高。家系成员EBVVCA/IgA阳性率为23.56%,显著高于人群(P<0.001)。结论:在鼻咽癌高发家系中,由血缘关系决定的遗传易感性和EB病毒感染是鼻咽癌发病的重要因素。     

鼻咽癌患者染色体端粒联合与染色体畸变关系的研究

为了探讨鼻咽癌染色体端粒联合与染色体畸变的关系，采用Ｇ显带技术，对２５例鼻咽癌患者外周血的染色体端粒联合频率进行观察，同时与染色体畸变的关系进行了分析。结果表明：鼻咽癌患者染色体端粒联合频率（３５．０７％）及染色体畸变率（１２．３３％）均显著高于对照组（２０．２７％及２．４６％），２者有非常显著性差异（Ｐ＜０．０１）。端粒联合的位点与染色体畸变断裂点在染色体上的分布密切相关（γ＝０．８１４９，Ｐ＜０．０５），说明染色体端粒联合发生是染色体畸变形成的机理之一。     

鼻咽癌患者染色体断裂热点与SCE高发位点,脆性部位,原癌基因位…

采用在染色体标本上同是显示ＳＣＥ及Ｇ带带型的方法，对鼻咽癌患者染色体断裂热点与ＳＣＥ高发位点，染色体脆性部位及原癌基因位点之间的相关性进行了分析。结果表明：患者的ＳＣＥ频率，染色体畸变率均显著的高对照组，患者的染色断裂点和ＳＣＥ位点都主要分布在染色体的Ａ、Ｂ、Ｃ、Ｄ组浅带上，且两者所累及的染色体号存在着明显的相关，患者的１５个断裂热点与ＳＣＥ高发位点的一致率为５３．３３％，与脆性部位的一致率为８０     

双色荧光原位杂交检测放疗后鼻咽癌患者外周血淋巴细胞染色体畸变

目的 :评价辐射诱发的染色体畸变作为癌患风险评估指标的可行性。方法 :应用双色荧光原位杂交 (FISH)技术检测 10例放疗后及 6例放疗前鼻咽癌患者外周血淋巴细胞染色体畸变并与常规法比较。结果 :放疗后 1～ 10年 ,鼻咽癌患者淋巴细胞染色体易位率、双着丝粒体率仍显著高于放疗前对照组的相应数值 (P <0 .0 0 1)。患者的易位率约为双着丝粒体率的 3 .5倍 ,照后 3年以上患者染色体易位率与照后小于 3年患者的易位率之间差别无显著性 (P >0 .1) ,而照后 3年以上患者染色体双着丝粒体率显著低于照后小于 3年患者的双着丝粒体率 (P <0 .0 0 1)。 结论 :稳定性染色体畸变 (易位 )在照后相当长时间 (10年 )仍可保持较高百分率 ,有望成为癌患风险评估的生物标志。     

食管癌贲门癌患者淋巴细胞染色体对促癌剂PMA易感性的观察

近年来,染色体不稳定性与肿瘤发生、发展的关系是肿瘤遗传病因学研究的重要内容之一。国内已有部分作者对胃癌、食管癌、鼻咽癌患者自发和经某些致断剂诱发的染色体畸变、脆性位点进行了研究。佛波醇醛(phorbol-12-mytistate-13-acetate,PMA是一种经典的促癌因子(promoter),它对人淋巴细胞鼠上皮细胞又是有效的染色体断裂剂。为探讨促癌剂PMA诱发染色体畸变与肿癌易感性之间的关系,本文就食管、贲门癌患者淋巴细胞自发与PMA诱发染色体畸变率(CAR进行研究,其结果如下。     

鼻咽癌患者染色体畸变率与血清EBVCA—IgA抗体水平关系的研究

本研究采用特殊的细胞培养方法,观察32例鼻咽癌患者和22例健康对照外周血细胞染色体结构畸变;并同时测定血清EBVCA—IgA抗体。结果发现:1.鼻咽癌组染色体结构畸变率明显高于健康对照组,2.EBVCA—IgA抗体阳性患者染色体畸变率明显高于阴性组患者;3.染色体畸变率随EBVCA—IgA抗体滴度的升高而有增高趋势。文中简要讨论了EB病毒与遗传因素在鼻咽癌发生、发展中的可能作用。     

膀胱癌患者染色体畸变的研究

 本文对19例膀胱癌患者和16例正常人外周血淋巴细胞染色体畸变的研究，结果表明膀胱癌患者染色体总畸变率，断裂及裂隙、脆性位点的表达、四倍体都极显著高于正常人(＜0.01)；在国内首次报道肿瘤患者外周血淋巴细胞中着丝粒后期相，其发生率极显著高于正常人．     

氯乙烯中毒性肝病和乙型肝炎染色体畸变分析

本文对２１例氯乙烯中毒性肝病、９例乙型肝炎患者及１０例正常人外周血淋巴细胞染色体Ｇ显带分析表明：中毒性肝病组、乙肝组染色体数目畸变率和结构畸变率均明显高于对照组（Ｐ＜０．０１）．其中氯乙烯中毒性肝病组染色体结构畸变率还高于乙肝组（Ｐ＜０．０１）。对结构畸变中断裂点的分析表明，两种肝病的断裂点分布不同，同时还发现染色体上某些位点断裂频率较高，并初步探讨了这些位点和肿瘤发生之间的关系。     

Spontaneous unusual expression of frequency of chromosome aberrations and common fragile in human lymphocytes of colorectal cancer patients induced by Aphidicolin

Chromosomal fragile sites are distributed all over the human genome. Aphidicolin mediated expression frequency of common fragile sites and other chromosomal changes were evaluated in prometaphase/metaphase chromosomes obtained from peripheral blood lymphocytes of colorectal cancer patients. The present study reveals first time high incidence i.e. 6 % of aphidicolin induced chromosome breaks / gaps designated as "common fragile sites" in cell population of clinically diagnosed patients of colorectal cancer patients in Nepalese population. These chromosomal changes including structural and numerical were compare to clinically healthy normal individual of same sex / age groups, act as controls for statistical analysis. The frequency of chromosomal aberration in cancer patients were significantly higher (p<0.001) when compare to normal individuals. The increased genetics instability probably either due to nutritional factor i.e. lack of folic acid component in diet--an essential component required for DNA synthesis or unknown environmental factor for such genetic disorder. The present study indicates aphidicolin high frequency of induced chromosome aberrations and "common fragile sites" because of late replication of DNA in mitosis in colorectal cancer patients suggesting these sites could be used as suitable marker for determining genetic predisposition in cancer patients.     

Chromosome arm 8p and cancer: a fragile hypothesis

Chromosome arm 8p is one of the most frequently altered regions in human cancers. Several potential oncogenes and tumour suppressor genes have been identified but further investigations are needed to confirm which are bona fide oncogenic targets. In cancer cells, chromosome breaks may occur at fragile sites throughout the genome. Some fragile sites lie within genes that may have a role in cancer; the best example is FHIT at 3p14, which contains the fragile site FRA3B. We have found that chromosome breaks disrupt the NRG1 gene at 8p12 in breast and pancreatic cancers. We hypothesise that alteration of the NRG1 gene could occur through breakage at a non-common fragile site.     

喉癌及鼻腔鼻窦癌患者淋巴细胞染色体脆性部位的研究

用ＴＣ１９９培养基及原位显带的方法，对３７例喉癌、鼻腔鼻窦癌及２０例正常人染色体脆性部位进行分析。结果表明癌症患者脆性部位表达率显著高于正常人，且其表达的脆性部位与癌相关断裂点及癌基因位点密切相关。     

Common fragile sites

Common fragile sites are regions showing site-specific gaps and breaks on metaphase chromosomes after partial inhibition of DNA synthesis. Common fragile sites are normally stable in somatic cells. However, following treatment of cultured cells with replication inhibitors, fragile sites display gaps, breaks, rearrangements and other features of unstable DNA. Studies showing that fragile sites and associated genes are frequently deleted or rearranged in many cancer cells have clearly demonstrated their importance in genome instability in cancer. Until recently, little was known about the molecular nature and mechanisms involved in fragile site instability. From studies conducted in many laboratories, it is now known that fragile sites extend over large regions, are associated with genes, exhibit delayed replication, and contain regions of high DNA flexibility. Recent findings from our laboratory showing that the key cell cycle checkpoint genes are important for genome stability at fragile sties have shed new light on these mechanisms and on the significance of these sites in cancer and normal chromosome structure. Since their discovery over two decades ago, much has been learned regarding their significance in chromosome structure and instability in cancer, but a number of key questions remain, including why these sites are 'fragile' and the impact of this instability on associated genes in cancer cells. These and other questions have been addressed by participants of this meeting, which highlighted instability at common fragile sites. This brief review is intended to provide background on common fragile sites that has led up to many of the studies presented in the accompanying reports in this volume and not to summarize the findings presented therein. Some aspects of this review were taken from Glover et al. (T.W. Glover, M.F. Arlt, A.M. Casper, S.G. Durkin, Mechanisms of common fragile site instability, Hum. Molec. Genet. 14 (in press). [1]).     

Nonrandom distribution of mutagen-induced chromosome breaks in lymphocytes of patients with different malignancies

Data regarding specific chromosomal alterations in most solid neoplasms are scarce because the complex changes observed in tumor biopsies are often a challenge to interpret. The present investigation using chromosomal banding, was designed to analyze exact regions of spontaneous and mutagen-induced lymphocytic chromosomal breaks and investigate if they are unique for different cancers. Tissue from three groups of individuals were included in the study, viz., normal individuals, untreated head and neck cancer patients, and untreated melanoma patients. For every individual three samples were analyzed for spontaneous, bleomycin (radiomimetic)-induced and 4-nitroquinoline-N-oxide(4NQO) (ultraviolet rays mimetic)-induced chromosome damage. The results revealed that in melanoma patients, chromosomes 1, 6, and 9 showed a significantly higher number of breaks than other chromosomes. A clustering of breaks was observed at loci 1p32, 1q32, 6p21, 6q21 and 9q11. Among the head and neck cancer patients, a significantly larger number of breaks was found in chromosomes 3 and 7 with clustering of breaks mainly in regions 3p21, 3q21, 7q22 and 7q32. Thus, it was found that regardless of the mutagen used, specific chromosomes are more susceptible to breakage than others. Our results indicate that chromosomal fragility is specific for particular cancers and that challenging the cells with mutagens reveals it at a more pronounced rate. Mutagen-induced chromosome breaks appear to be nonrandom affecting different chromosomes in different cancers. Clustering of breaks that occur in specific regions of these chromosomes might provide definite clues for molecular analysis and further in-depth studies of cancer predisposed individuals.     

FRA1E common fragile site breaks map within a 370kilobase pair region and disrupt the dihydropyrimidine dehydrogenase gene (DPYD)

Common fragile sites represent components of normal chromosome structure that are particularly prone to breakage under replication stress. Although the cytogenetic locations of 88 common fragile sites are listed in the Genome database, the DNA at only 14 of them has been defined and characterized at the molecular level. Here, we identify the precise genomic position of the common fragile site FRA1E, mapped to the chromosomal band 1p21.2, and characterize the genetic complexity of the fragile DNA sequence. We show that FRA1E extends over 370kb within the dihydropyrimidine dehydrogenase (DPYD) gene, which genomically spans approximately 840kb. The 185kb region of the highest fragility, which accounts for 86% of all observed breaks at FRA1E, encompasses the central part of DPYD including exons 13-16. DPYD encodes dihydropyrimidine dehydrogenase (DPD), which is the first and rate-limiting enzyme in a three-step metabolic pathway involved in degradation of the pyrimidine bases uracil and thymine. Deficiency in human DPD is associated with autosomal recessive disease, thymine-uraciluria, and with severe 5-fluorouracil toxicity in cancer patients. To which extent the disruption of the DPYD gene by the fragile site break is only transient, followed by DNA repair to restore the original structure, or occasionally may result in genomic damage associated with human disease remains to be determined.     

Expression of fragile site 8q22 in peripheral blood lymphocytes taken from patients with acute leukemia M2 having t(8;21)(q22;q22)

The relation between the expression of common fragile sites and chromosomal breakpoints in neoplastic cells in the same patients has not been well studied. In the present study, the frequency and distribution of aphidicolin-induced breaks on chromosomes 8 and 21 in peripheral blood lymphocytes (PBL) taken from three patients with acute myeloid leukemia, French-American-British classification type M2, having chromosomal translocation t(8;21)(q22;q22) (M2t) were studied prior to any initial treatment. Seven patients with other types of acute leukemia without t(8;21) and 13 healthy people were also studied. In PBL from patients with M2t, the numbers of chromosomal breaks were 1, 7 and 3/216 metaphasees at bands 8q21, 8q22 and 8q24, respectively; the frequencies at 8q22 and 8q24 being significantly higher than those for patients with the other leukemias and for the healthy subjects (p less than 0.001 and p less than 0.01, respectively). These results suggest that the fragility on chromosome 8q21-24 is related to a predisposition to this particular type of leukemia.     

The fragile histidine triad/common chromosome fragile site 3B locus and repair-deficient cancers

In various studies of sporadic breast cancers, 40-70% were strongly positive for fragile histidine triad (Fhit) protein expression, whereas only 18% of BRCA2 mutant breast cancers demonstrated strong Fhit expression, suggesting that the BRCA2 repair function may be necessary to retain intact fragile common chromosome fragile site 3B(FRA3B)/FHITloci. In the current study, 22 breast tumors with deleterious BRCA1 mutations were analyzed for Fhit expression by immunohistochemistry in a case-control matched pair analysis. Loss of Fhit expression was significantly more frequent in the BRCA1 cancers compared with sporadic breast tumors (9% Fhit positive versus 68% Fhit positive), suggesting that the BRCA1 pathway is also important in protecting the FRA3B/FHIT locus from damage. To investigate the relationship between repair gene deficiencies and induction of chromosome fragile sites in vitro, we have analyzed the frequency of aphidicolin induction of chromosome gaps and breaks in PMS2-, BRCA1-, MSH2-, MLH1-, FHIT-, and TP53-deficient cell lines. Each of the repair-deficient cell lines showed elevated expression of chromosome gaps and breaks, consistent with the proposal that proteins involved in mismatch and double-strand break repair are important in maintaining the integrity of common fragile regions. Correspondingly, genes at common fragile sites may sustain elevated levels of DNA damage in cells with deficient DNA repair proteins such as those mutated in several familial cancer syndromes.     

Are fragile sites "hot-spots": a causative factor in tumor biology

Genomic integrity of the cancer cell is doubt-full because of fragility on chromosome. Fragile--sites are non-randomly distributed on human genome prone to form gaps or breaks at either pre/or metaphase chromosome arise when cells are exposed to a perturbation of DNA replication process. Cancer cells commonly show various form of "hot spots" including point mutation, chromosome copy number and translocation involving specific gene mutation but the genetic diversity of fragile sites are still not clear. The chromosomal fragile sites (rare & common fragile sites) make the cancer cells not only susceptible to genomic instability but also contribute the process of malignancy due to expansions of microsatellite CGG or AT rich minisatellite. Fragile sites have been implicated due to inter chromosomal amplification events by initiation breakage - fusion cycles. The mechanisms behind these changes give raise to new insight the cytogenetic manifestation of oncogenesis. Fragile sites loci are associated with activation of oncogenesis during cell--cycle analysis. However, these mutations at fragile sites loci might have play a causative or functional role in tumor biology. The topography organization and informatics complexity of the fragile sites remained unexplored due to lack of systematic approach towards molecular cloning of the fragile sites DNA sequences and specific models as not are under taken. The information regarding mode of inheritance of fragile sites are still lacking but the first degree relative specially young proband and maternal side having variable prevalence in different population could be uses as suitable marker for determining genetic predisposition to cancer. This comprehensive review of fragile sites in tumor biology probably helpful to explore to understand the molecular mechanism of carcinogenesis or tumorgenesis.