Localization of Human Cadherin Genes to Chromosome Regions Exhibiting Cancer-Related Loss of Heterozygosity

This report presents the chromosomal localization of cadherin genes. Cadherins are cellular adhesion molecules. Since disturbance of intracellular adhesion is important for invasion and metastasis of tumor cells, cadherins are considered prime candidates for tumor suppressor genes. A variety of solid tumors show loss of heterozygosity of the long arm of chromosome 16, which is indicative of the potential location of tumor suppressor genes. Refined and new localizations of six cadherin genes (CDH3, 5, 8, 11, 13, and 15) to the long arm of chromosome 16 are shown. CDH15 was localized to 16q24.3, in a region that exhibits loss of heterozygosity in a number of sporadic breast cancer tumors. Previous localization of CDH13 (H-cadherin) to 16q24 suggested this gene as a tumor suppressor candidate in the 16q24.3 loss of heterozygosity region; however, refined mapping presented in this report localizes CDH13 proximal to this region. A human EST homologous to the chicken cadherin-7 was partially sequenced and found to represent a new human cadherin. This cadherin mapped to chromosome 18q22–q23, a region that exhibits loss of heterozygosity in head and neck squamous cell carcinomas. CDH16 was localized to 8q22.1, a region exhibiting loss of heterozygosity in adult acute myeloid leukemia.     

DNA错配修复与肺癌

肺癌是目前世界上最常见的恶性肿瘤之一,虽然近年来对其研究较多,但其发生发展的确切机制仍不清楚。DNA错配修复作为一种重要的复制后修复系统,在确保DNA复制保真性、控制基因突变和维持基因组稳定等方面具有重要作用。近年研究表明,DNA错配修复系统与肺癌的发生、治疗及预后判断有着密切关系。本文主要对DNA错配修复系统在肺癌中的研究进展作一简要综述。     

Dichotomy in Hedgehog Signaling between Human Healthy Vessel and Atherosclerotic Plaques

The major cause for plaque instability in atherosclerotic disease is neoangiogenic revascularization, but the factors controlling this process remain only partly understood. Hedgehog (HH) is a morphogen with important functions in revascularization, but its function in human healthy vessel biology as well as in atherosclerotic plaques has not been well investigated. Hence, we determined the status of HH pathway activity both in healthy vessels and atherosclerotic plaques. A series of 10 healthy organ donor-derived human vessels, 17 coronary atherosclerotic plaques and 24 atherosclerotic carotid plaques were investigated for HH pathway activity. We show that a healthy vessel is characterized by a high level of HH pathway activity but that atherosclerotic plaques are devoid of HH signaling despite the presence of HH ligand in these pathological structures. Thus, a dichotomy between healthy vessels and atherosclerotic plaques with respect to the activation status of the HH pathway exists, and it is tempting to suggest that downregulation of HH signaling contributes to long-term plaque stability.     

Leukotriene B4 Levels in Human Atherosclerotic Plaques and Abdominal Aortic Aneurysms

Background

Leukotriene B4 (LTB4) has been associated with the initiation and progression of atherosclerosis and abdominal aortic aneurysm (AAA) formation. However, associations of LTB4 levels with tissue characteristics and adverse clinical outcome of advanced atherosclerosis and AAA are scarcely studied. We hypothesized that LTB4 levels are associated with a vulnerable plaque phenotype and adverse clinical outcome. Furthermore, that LTB4 levels are associated with inflammatory AAA and adverse clinical outcome.

Methods

Atherosclerotic plaques and AAA specimens were selected from two independent databases for LTB4 measurements. Plaques were isolated during carotid endarterectomy from asymptomatic (n = 58) or symptomatic (n = 317) patients, classified prior to surgery. LTB4 levels were measured without prior lipid extraction and levels were corrected for protein content. LTB4 levels were related to plaque phenotype, baseline patient characteristics and clinical outcome within three years following surgery. Seven non-diseased mammary artery specimens served as controls. AAA specimens were isolated during open repair, classified as elective (n = 189), symptomatic (n = 29) or ruptured (n = 23). LTB4 levels were measured similar to the plaque measurements and were related to tissue characteristics, baseline patient characteristics and clinical outcome. Twenty-six non-diseased aortic specimens served as controls.

Results

LTB4 levels corrected for protein content were not significantly associated with histological characteristics specific for vulnerable plaques or inflammatory AAA as well as clinical presentation. Moreover, it could not predict secondary manifestations independently investigated in both databases. However, LTB4 levels were significantly lower in controls compared to plaque (p = 0.025) or AAA (p = 0.017).

Conclusions

LTB4 levels were not associated with a vulnerable plaque phenotype or inflammatory AAA or clinical presentation. This study does not provide supportive evidence for a role of LTB4 in atherosclerotic plaque destabilization or AAA expansion. However, these data should be interpreted with care, since LTB4 measurements were performed without prior lipid extractions.     

骨髓干细胞动员对动脉粥样硬化破裂斑块的稳定与修复作用

目的研究自体骨髓干细胞动员对兔动脉粥样硬化（AS）破裂斑块的稳定与修复作用。方法用液氮冻伤术创建兔AS破裂斑块模型,动员组注射重组人粒细胞刺激因子（rhG-CSF）动员自体骨髓干细胞,对照组注射等量生理盐水,连续5 d。动员第5天抽血分离获取单个核细胞,BrdU标记后经静脉注入动物体内;分别于动员后3d和4周末抽血,ELISA法检测兔血清MMP-9、hsC-RP及PAI-1水平;动员后4周处死兔,HE染色和Masson三色染色观察斑块病理形态,免疫组化染色观察BrdU在斑块区表达情况。结果动员5 d后,动员组兔外周血有核细胞计数及单核细胞比例明显增高;动员后4周,动员组新生内皮细胞及胶原纤维明显增多,在斑块区发现有BrdU标记的阳性细胞,动员组血清MMP-9、hsC-RP及PAI-1水平明显降低。结论应用rhG-CSF动员自体骨髓干细胞能通过促进血管内皮细胞和胶原纤维再生,降低炎症因子及凝血纤溶因子而稳定与修复AS破裂斑块。     

Evolutionary Consequences of DNA Mismatch Inhibited Repair Opportunity

Double strand breaks (DSBs) are often repaired via homologous recombination. Recombinational repair processes are expected to be influenced by nucleotide heterozygosity through mismatch detection systems. Unrepaired DSBs have severe biological consequences and are often lethal. We show that natural selection due to inhibition of recombinational repair associated with polymorphisms could influence their molecular evolution. The main conclusions from this analysis are that, for increasing population size, mismatch detection leads to a limit on average heterozygosity of otherwise selectively neutral polymorphism, an excess of rare variants, and a slowing down of the rate of neutral molecular evolution. The first two results suggest that mismatch detection may account for the surprisingly narrow range of observed average heterozygosities, given the great variation in population size between species.     

DNA错配修复系统研究进展

DNA错配修复(mismatch repair, MMR)系统广泛存在于生物体中.从原核生物大肠杆菌到真核生物及人类,MMR系统有不同的组成成分和修复机制.人体内MMR基因缺陷会造成基因组的不稳定并诱发遗传性非息肉型直肠癌以及其他自发性肿瘤.大肠杆菌MMR系统中的MutS蛋白可特异识别错配或未配对碱基,目前已经发展了多种基于MutS蛋白的基因突变/多态性检测技术.     

新发现的人类错配DNA修复蛋白0hMLH3

近年来的研究认为 ,防止人类ＤＮＡ复制错误的因素涉及 5个错配修复 (ＭＭＲ)蛋白 ,即ｈＭＳＨ2、ｈＭＳＨ3、ｈＭＳＨ6、ｈＭＬＨ1和ｈＰＭＳ2。最新研究报告发现了ＭＭＲ家族的第 6种成员 ,ｈＭＬＨ3,也与错配修复过程有关[1] 。　　错配修复是将ＤＮＡ复制时产生的错误修复 ,是维持正确的遗传信息的重要机制。错配修复机制的异常是遗传倾向性癌症产生的原因之一。人的错配修复过程与大肠杆菌类似。都有几种蛋白质的复合物的参与。即有错配结合活性的ＭｕｔＳ同源二聚体和蛋白质相互作用的ＭｕｔＬ同源二聚体 ,这两种同源二聚体又结合形成…     

DNA错配修复、染色体不稳定和肿瘤的关系

DNA错配修复系统可以识别并纠正DNA复制过程中出现的错误.保证基因组的稳定性和完整性.错配修复系统缺陷可能导致遗传物质发生突变,引发恶性肿瘤.肿瘤患者经常表现出染色体不稳定,具体表现为微卫星不稳定性和杂合性缺失.本文就DNA错配修复、染色体不稳定和肿瘤之间的联系予以综述.     

DNA错配修复与癌症的发生及治疗

DNA错配修复是细胞复制后的一种修复机制,具有维持DNA复制保真度,控制基因变异的作用。DNA错配修复缺陷使整个基因组不稳定,最终会导致肿瘤和癌症的发生。DNA错配修复系统不仅通过矫正在DNA重组和复制过程中产生的碱基错配而保持基因组的稳定,而且通过诱导DNA损伤细胞的凋亡而消除由突变细胞生长形成的癌变。错配修复缺陷细胞的抗药性也引起了癌症化疗研究方面的关注。大多数情况下,错配修复健全型细胞对肿瘤化疗药物敏感,而错配修复缺陷细胞却有较高的抗性。DNA错配修复系统通过修复和诱导细胞凋亡维护基因组稳定的功能,显示了错配修复途径在癌症生物学和分子医学中的重要性。     

Stochastic Processes and Component Plasticity Governing DNA Mismatch Repair

DNA mismatch repair (MMR) is a DNA excision–resynthesis process that principally enhances replication fidelity. Highly conserved MutS (MSH) and MutL (MLH/PMS) homologs initiate MMR and in higher eukaryotes act as DNA damage sensors that can trigger apoptosis. MSH proteins recognize mismatched nucleotides, whereas the MLH/PMS proteins mediate multiple interactions associated with downstream MMR events including strand discrimination and strand-specific excision that are initiated at a significant distance from the mismatch. Remarkably, the biophysical functions of the MLH/PMS proteins have been elusive for decades. Here we consider recent observations that have helped to define the mechanics of MLH/PMS proteins and their role in choreographing MMR. We highlight the stochastic nature of DNA interactions that have been visualized by single-molecule analysis and the plasticity of protein complexes that employ thermal diffusion to complete the progressions of MMR.     

A Novel Role for DNA Mismatch Repair and the Autophagic Processing of Chemotherapy Drugs in Human Tumor Cells

DNA Mismatch repair (MMR) maintains genome integrity by correcting DNA replication errors and blocking homologous recombination between divergent DNA sequences. The MMR system also activates both checkpoint and apoptotic responses following certain types of DNA damage. In a recent study, we describe a novel role for MMR in mediating an autophagic response to 6-thioguanine (6-TG), a DNA modifying chemical. Our results show that MMR proteins (MLH1 or MSH2) are required for signaling to the autophagic pathway after exposure to 6-TG. Using PFT-α, a p53 inhibitor, and shRNA-mediated silencing of p53 expression, we also show that p53 plays an essential role in the autophagic pathway downstream of the MMR system. This study suggests a novel function of MMR in mediating autophagy following chemical (6-TG) DNA mismatch damage through p53 activation. Here, we present the model and the clinical implications of the role of MMR in autophagy.

Addendum to:

DNA Mismatch Repair Initiates 6-Thioguanine-Induced Autophagy through p53 Activation in Human Tumor Cells

X. Zeng, T. Yan, J.E. Schupp, Y. Seo and T.J. Kinsella

Clin Cancer Res 2007; 13:1315-21     

Increased Platelet Reactivity Is Associated with Circulating Platelet-Monocyte Complexes and Macrophages in Human Atherosclerotic Plaques

Objective

Platelet reactivity, platelet binding to monocytes and monocyte infiltration play a detrimental role in atherosclerotic plaque progression. We investigated whether platelet reactivity was associated with levels of circulating platelet-monocyte complexes (PMCs) and macrophages in human atherosclerotic carotid plaques.

Methods

Platelet reactivity was determined by measuring platelet P-selectin expression after platelet stimulation with increasing concentrations of adenosine diphosphate (ADP), in two independent cohorts: the Circulating Cells cohort (n = 244) and the Athero-Express cohort (n = 91). Levels of PMCs were assessed by flow cytometry in blood samples of patients who were scheduled for percutaneous coronary intervention (Circulating Cells cohort). Monocyte infiltration was semi-quantitatively determined by histological examination of atherosclerotic carotid plaques collected during carotid endarterectomy (Athero-Express cohort).

Results

We found increased platelet reactivity in patients with high PMCs as compared to patients with low PMCs (median (interquartile range): 4153 (1585–11267) area under the curve (AUC) vs. 9633 (3580–21565) AUC, P<0.001). Also, we observed increased platelet reactivity in patients with high macrophage levels in atherosclerotic plaques as compared to patients with low macrophage levels in atherosclerotic plaques (mean±SD; 8969±3485 AUC vs. 7020±3442 AUC, P = 0.02). All associations remained significant after adjustment for age, sex and use of drugs against platelet activation.

Conclusion

Platelet reactivity towards ADP is associated with levels of PMCs and macrophages in human atherosclerotic carotid plaques.     

Mismatch Repair Balances Leading and Lagging Strand DNA Replication Fidelity

The two DNA strands of the nuclear genome are replicated asymmetrically using three DNA polymerases, α, δ, and ε. Current evidence suggests that DNA polymerase ε (Pol ε) is the primary leading strand replicase, whereas Pols α and δ primarily perform lagging strand replication. The fact that these polymerases differ in fidelity and error specificity is interesting in light of the fact that the stability of the nuclear genome depends in part on the ability of mismatch repair (MMR) to correct different mismatches generated in different contexts during replication. Here we provide the first comparison, to our knowledge, of the efficiency of MMR of leading and lagging strand replication errors. We first use the strand-biased ribonucleotide incorporation propensity of a Pol ε mutator variant to confirm that Pol ε is the primary leading strand replicase in Saccharomyces cerevisiae. We then use polymerase-specific error signatures to show that MMR efficiency in vivo strongly depends on the polymerase, the mismatch composition, and the location of the mismatch. An extreme case of variation by location is a T-T mismatch that is refractory to MMR. This mismatch is flanked by an AT-rich triplet repeat sequence that, when interrupted, restores MMR to >95% efficiency. Thus this natural DNA sequence suppresses MMR, placing a nearby base pair at high risk of mutation due to leading strand replication infidelity. We find that, overall, MMR most efficiently corrects the most potentially deleterious errors (indels) and then the most common substitution mismatches. In combination with earlier studies, the results suggest that significant differences exist in the generation and repair of Pol α, δ, and ε replication errors, but in a generally complementary manner that results in high-fidelity replication of both DNA strands of the yeast nuclear genome.     

Isolation and Characterization of Point Mutations in Mismatch Repair Genes That Destabilize Microsatellites in Yeast

The stability of simple repetitive DNA sequences (microsatellites) is a sensitive indicator of the ability of a cell to repair DNA mismatches. In a genetic screen for yeast mutants with elevated microsatellite instability, we identified strains containing point mutations in the yeast mismatch repair genes, MSH2, MSH3, MLH1, and PMS1. Some of these mutations conferred phenotypes significantly different from those of null mutations in these genes. One semidominant MSH2 mutation was identified. Finally we showed that strains heterozygous for null mutations of mismatch repair genes in diploid strains in yeast confer subtle defects in the repair of small DNA loops.     

Mismatch Repair Status and the Response of Human Cells to Cisplatin

The emergence of resistance to cisplatin is a serious drawback of cancer therapy. To help elucidate the molecular basis of this resistance, we examined matched ovarian cancer cell lines that differ in their DNA mismatch repair (MMR) status and the response to cisplatin. Checkpoint activation by cisplatin was identical in both lines. However, sensitive cells delayed S-phase transition, arrested at G2/M and died by apoptosis. The G2/M block was characterized by selective disappearance of homologous recombination (HR) proteins, which likely resulted in incomplete repair of the cisplatin adducts. In contrast, resistant cells transiently arrested at G2/M, maintained constant levels of HR proteins and ultimately resumed cell cycle progression. The net contribution of MMR to the cisplatin response was examined using matched semi-isogenic (HCT116±chr3) or strictly isogenic (293T-Lα-/+) cell lines. Delayed transition through S-phase in response to cisplatin was also observed in the MMR-proficient HCT116+chr3 cells. Unlike in the ovarian cell lines, however, both HCT116+chr3 and HCT116 permanently arrested at G2/M with an intact complement of HR proteins and died by apoptosis. A similar G2/M arrest was observed in the strictly isogenic 293T-Lα-/+ cells. This confirmed that although MMR undoubtedly contributes towards the cytotoxicity of cisplatin, it is only one of several pathways that modulate the cellular response to this drug. However, our data highlighted the importance of HR to cisplatin cytotoxicity and suggested that HR status might represent a novel prognostic marker and possibly also a therapeutic target, the inhibition of which would substantially sensitize cells to cisplatin chemotherapy.     

DNA Repair in Human Leukaemic Lymphocytes

CHRONIC lymphocytic leukaemia (CLL) is a common human leukaemia¹ in older people. Its gradual progressive clinical course is frequently associated with lymphocyte dysfunction². In this disease lymphocyte counts are elevated and lymph nodes and organs are infiltrated with small abnormal lymphocytes which have scanty blue cytoplasm and round or clefted nuclei with clumped chromatin.