Telomeric association: another characteristic of cancer chromosomes?

High frequency of telomeric associations and chromatid exchanges and breaks in human ovarian carcinoma

Cytogenetic analysis of an unselected series of twenty human serous adenocarcinomas and undifferentiated carcinomas of the ovary revealed the presence of telomeric associations (tas) and unstable chromosomal aberrations, including chromatid-type exchanges (cte) and breaks (ctb) in high proportion of tumors studied. Tas and cte & ctb were present in 75% and 55% of tumors, respectively. Involvement of different chromosome telomeres in tas seemed to be random. This is the first report describing telomeric associations in ovarian cancer. Our findings suggest that the frequency of extensive spontaneous chromosome breakage in ovarian carcinoma may be higher than that reported in the literature.

Differential radiation effects in smokers--culture time dependence of the yield of gamma ray-induced chromosome damage in first division metaphases

PURPOSE

Telomeric associations (TA) and unstable chromosomal aberration (CA) transmission through M1-M4 metphases (first to fourth division) in gamma-ray irradiated G0 lymphocytes in 2 smokers were examined, since TA in conventionally stained chromosomes were reported earlier as a sensitive cytogenetic marker in mutagen-exposed populations. The purpose of the present study is an extension of our earlier studies on unstable CA transmission through successive mitotic divisions.

MATERIALS AND METHODS

The bromodeoxyuridine (BrdU) incorporation and fluorescence plus giemsa (FPG) method for M1-M5 metaphase analysis was carried out at 50, 72, 96 h to analyse TA and CA in conventionally and FPG stained chromosomes after irradiation of human blood samples with 3 Gy of gamma-rays. In situ hybridization (ISH) with enzymatic/fluorescence detection was used to analyse radiation-induced aneuploidy and TA. Analysis was carried out on sister chromatid exchanges (SCE) in M2 cells at 72 h and micronuclei (MN) at 24, 50, 72, 96 h.

RESULTS

TA, corroborated by the absence of acentric fragments, were not detected in conventional/FPG stained/ISH chromosomes. Chromosome 21 aneuploidy was observed. Significant differences in mean frequencies of dicentrics/micronuclei (MN)/SCE with high frequency cells (HFC) were found in smokers after irradiation compared to non-smokers. Higher radiation induced CA in M1 cells were found with extended culture time. Induction of giant cells with mirror dicentrics, tricentrics and rings were found.

CONCLUSION

TA in conventional or FPG stained metaphase chromosomes is not a sensitive cytogenetic marker for mutagen exposed population screening. Higher radiation induced CA frequencies in M1 cells with extended culture time were indicative of a delay in cell cycle progression of aberrant cells or different lymphocyte subset populations. Bridge-breakage-fusion (BBF) events due to dicentrics may be instrumental in the perpetuation of chromosomal instability. Differential effects were noted in radiation-induced dicentric, SCE and MN frequencies in smokers compared to non-smokers. Heavy smoking could be a confounding variable in chromosome-based biodosimetry and biomonitoring studies. Giant cells may denote a switch to amitotic modes of cell survival, providing additional mechanisms of genotoxic resistance.

Inactivation of 14-3-3sigma influences telomere behavior and ionizing radiation-induced chromosomal instability

Telomeres are complexes of repetitive DNA sequences and proteins constituting the ends of linear eukaryotic chromosomes. While these structures are thought to be associated with the nuclear matrix, they appear to be released from this matrix at the time when the cells exit from G(2) and enter M phase. Checkpoints maintain the order and fidelity of the eukaryotic cell cycle, and defects in checkpoints contribute to genetic instability and cancer. The 14-3-3sigma gene has been reported to be a checkpoint control gene, since it promotes G(2) arrest following DNA damage. Here we demonstrate that inactivation of this gene influences genome integrity and cell survival. Analyses of chromosomes at metaphase showed frequent losses of telomeric repeat sequences, enhanced frequencies of chromosome end-to-end associations, and terminal nonreciprocal translocations in 14-3-3sigma(-/-) cells. These phenotypes correlated with a reduction in the amount of G-strand overhangs at the telomeres and an altered nuclear matrix association of telomeres in these cells. Since the p53-mediated G(1) checkpoint is operative in these cells, the chromosomal aberrations observed occurred preferentially in G(2) after irradiation with gamma rays, corroborating the role of the 14-3-3sigma protein in G(2)/M progression. The results also indicate that even in untreated cycling cells, occasional chromosomal breaks or telomere-telomere fusions trigger a G(2) checkpoint arrest followed by repair of these aberrant chromosome structures before entering M phase. Since 14-3-3sigma(-/-) cells are defective in maintaining G(2) arrest, they enter M phase without repair of the aberrant chromosome structures and undergo cell death during mitosis. Thus, our studies provide evidence for the correlation among a dysfunctional G(2)/M checkpoint control, genomic instability, and loss of telomeres in mammalian cells.

High frequencies of telomeric associations, chromosome aberrations, and sister chromatid exchanges in ulcerative colitis

OBJECTIVE

Chromosome instability provides a predisposing background to malignancy, contributing to the crucial genetic changes in multistep carcinogenesis. The aim of this work was to analyze chromosome instability in patients with ulcerative colitis (UC) to achieve a better understanding of the increased risk for colorectal cancer.

METHODS

Peripheral blood lymphocyte cultures from 20 untreated UC patients and 24 controls were used to study chromosome instability by assessing telomeric associations (TAS), chromosome aberrations (CA), and sister chromatid exchanges (SCE).

RESULTS

Mean frequencies of TAS and CA were significantly increased in UC patients compared to controls (p < 0.001). Chromosomes 10, 11, 21, 16, and 19 were the most frequently involved in TAS. A total of 104 CA clustered in 66 breakpoints could be exactly localized. Seven nonrandom bands significantly affected in UC patients were found (p < 0.004), showing a significant correlation with the location of cancer breakpoints (p < 0.003), particularly with colorectal carcinoma rearrangements. SCE analysis showed higher levels in patients compared to controls (p < 0.006), but no differences were observed in cell cycle kinetics.

CONCLUSIONS

Our results demonstrate the presence of an unstable genome in UC patients that could be related to the cancer development observed in this disease.

Mosaic telomeric (2;14) association in a child with motor delay

In a 6-year-old girl referred because of mild motor delay and hyperextensible joints, chromosome analysis disclosed a derivative chromosome consisting of end-to-end fusion of chromosomes 2 and 14. Two cell lines existed in which this telomere association was present, one with a 45,XX,tas(2;14)(q37;p11) karyotype and one with a 45,XX,tas(2;14) (q37;q32) karyotype. The cell line with the telomeric fusion of 2q and 14p was present in 90% of the cells; a telomeric fusion of 2q and 14q was seen in the remaining 10% of the cells. In both association complexes, only the centromere of chromosome 14 was active. Fluorescence in situ hybridization with telomere and subtelomere probes disclosed no deletion of chromosomal material. Microsatellite analysis showed that the patient had a normal biparental contribution of chromosomes 14.

Current Concepts in Biomarker Technology for Bladder Cancers

Background: Transitional cell carcinoma of the bladder (TCC) is the second most common malignancy of the urinary tract. More than 70% of treated tumors recur, and 30% of recurrent tumors progress. Currently, pathologic staging and grading are valuable prognostic factors for detecting and monitoring TCC. Urinalysis, cystoscopy, and cytology are either invasive or lack sensitivity and specificity. The availability of a noninvasive, reliable, and simple test would greatly improve the detection and monitoring of patients with TCC. Several biomarkers for bladder cancer have been proposed, but no single marker has emerged as the test of choice.

Approach: We undertook a comprehensive literature search using Medline to identify all publications from 1980 to 1999. Articles that discussed potential biomarkers for TCC were screened. Only compounds that demonstrated high sensitivity or specificity, significant correlation with TCC diagnosis and staging, and extensive investigation were included in this review.

Content: Potential biomarkers of disease progression and prognosis include nuclear matrix protein, fibrin/fibrinogen product, bladder tumor antigen, blood group-related antigens, tumor-associated antigens, proliferating antigens, oncogenes, growth factors, cell adhesion molecules, and cell cycle regulatory proteins. The properties of the biomarkers and the methods for detecting or quantifying them are presented. Their sensitivities and specificities for detecting and monitoring disease were 54–100% and 61–97%, respectively, compared with 20–40% and 90% for urinalysis and cytology.

Summary: Although urine cytology and cystoscopy are still the standard of practice, many candidate biomarkers for TCC are emerging and being adopted into clinical practice. Further research and better understanding of the biology of bladder cancer, improved diagnostic techniques, and standardized interpretation are essential steps to develop reliable biomarkers. It is possible that using the current biomarkers as an adjuvant modality will improve our ability to diagnose and monitor bladder cancer.

Histopathological and cytogenetic findings in benign, atypical and anaplastic human meningiomas: a study of 60 tumors

Meningiomas may display benign (Grade I), atypical (Grade II) and anaplastic (Grade III) histopathological findings. The cytogenetic studies strongly suggest that secondary changes (moreover loss of chromosome 22) appear to be associated with more atypical features and with greater clinical aggressivity. We studied 60 tumors from 52 patients. Histopathological features such as nuclear pleomorphism, nucleolar prominence, mitosis, necrosis, cellular density, PCNA labeling index, and karyotype have been evaluated. Nuclear pleomorphism and nucleolar prominence showed a progressive increase in Grades I-III. Multifocal micronecrosis was considered a criterion of malignancy. A significant correlation was observed between PCNA-LI, mitotic index and grades. Complex karyotypes increased progressively: benign (34% of cases), atypical (45% of cases) and anaplastic (70% of cases). The most common numerical alterations were losses of chromosomes 10, 14, 18 and 22. The chromosomes most often involved in structural anomalies were: 1, 4, 7, 14 and 22. Telomeric associations was present in four cases and double minutes in two cases. Prognostic criteria for these tumors have been analyzed on the basis of these data.

Telomeric DNA: marker for human prostate cancer development?

BACKGROUND

Telomeres that protect chromosomes at both ends are shortened with each somatic cell division through replication-dependent sequence loss at DNA termini. The chromosomes with shortened telomeres tend to become unstable, leading to cell death. Due largely to reactivation/upregulation of telomerase, a ribonucleoprotein that adds nucleotide sequences onto chromosome ends, cancer cells become immortal and neoplastically transformed.

METHODS

The purpose of the present study was to study three newly established human prostate cancer cell lines and three prostate-derived fibroblastic cell cultures at different passages for telomeric DNA signal intensity, telomeric restriction fragment length (TRFL), telomerase activity, and spontaneous apoptotic index.

RESULTS

Compared with the three fibroblastic cell cultures, the three new prostate cancer cell lines showed: 1) telomerase activity, 2) stronger telomeric signals, 3) relatively longer TRFLs, and 4) much lower apoptotic indices. On the other hand, three fibroblastic cell cultures showed: 1) no telomerase activity, 2) weaker telomeric signals, 3) shorter TRFLs (fibroblasts derived from surrounding tissue of prostate tumor showed intermediate TRFLs), and 4) comparatively higher apoptotic indices.

CONCLUSIONS

Based on these results, we conclude that telomeric DNA signal intensity, TRFL, and telomerase activity can be used to distinguish prostate cancer cells from adjacent fibroblasts.

Nonrandom pattern of telomeric associations in atypical lipomatous tumors with ring and giant marker chromosomes

Atypical lipomatous tumors (ALTs) are cytogenetically characterized by supernumerary ring and giant marker chromosomes. Another common finding in ALT is that the tumor cells are cytogenetically heterogeneous with a variety of mostly nonclonal numerical and structural chromosome aberrations, including telomeric associations. In a series of 48 cytogenetically investigated ALTs, all chromosomal aberrations, clonal as well as nonclonal, were registered. Clonal ring chromosomes were present in 47 cases and giant markers in 11 cases. In 7 cases, 12 clonal telomeric associations were found and 37 cases showed nonclonal associations involving 344 identified telomeres. The telomere associations were nonrandomly distributed, with the telomeres of 11p, 20p, 20q, 9q, 15p, 19q, and 22q being most frequently (8.7-4.1% of all associations) involved; only Xp and Xq were never affected. The pattern of telomeric associations in ALT was compared with literature data on 47 giant cell tumors (880 telomeres), previously reported to show a nonrandom distribution of associations, and 36 sporadic cases of a variety of other human neoplasms (583 telomeres). The analysis indicated that the telomeres of 11p, 19q, and 20q are preferentially involved in associations in several tumor types. Among other structural aberrations in the ALT series, 221 nonclonal and 52 clonal breakpoints were identified, as well as 342 nonclonal and 14 clonal numerical aberrations. The combined data suggest that telomeric associations may predispose to acquired chromosome aberrations in neoplasia.

Preclinical and clinical strategies for development of telomerase and telomere inhibitors

BACKGROUND

Telomerase is an important enzyme whose activity has been convincingly demonstrated in humans recently. It is required for maintenance of ends of chromosomes (telomeres) during cell division. Since its presence has been selectively demonstrated in dividing cells including tumor cells, it has generated considerable excitement as a potential anti-cancer strategy.

DESIGN

In this article, we review the current relevant biology of the enzyme, the challenges encountered in the preclinical phase of target development and the current efforts that focus on telomeres and telomerase as therapeutic targets. We also speculate on the potential toxicities and mechanisms of resistance that may be encountered during use of such therapies.

Telomeric association in women with breast and uterine cervix cancer

This study compares the frequency of telomeric associations in the peripheral blood of women suffering breast and cervix uterine cancer with a healthy control group. Two kinds of cultures were developed for each individual: with and without aphidicolin. In the normal cultures, the number of telomeric associations observed was 95.5 times higher in individuals affected by breast cancer and 41.3 times higher in those affected by cervix uterine cancer when compared to the control group (p < 0.001). In the cultures with aphidicolin, higher numbers of altered metaphases were observed in both groups as compared to the control groups (p < 0.001). Statistically significant differences (p < 0.001) could also be observed when comparing telomeric associations between the two types of cancer in both cultures. When we compared individuals affected by breast cancer in both types of cultures statistical differences were found (p < 0.05), and similar results were found in individuals affected by uterine cervix cancer (p < 0.001). The findings suggest that telomeric associations may be reflecting chromosome instability observed in cancer and that this instability behaves differently for various types of cancer.

Applications of telomerase in urologic oncology

Vertebrates have special structures at the ends of their chromosomes, known as telomeres, which are composed of 5- to 15-kb pairs of a guanine-rich hexameric repeat (TTAGGG)n. In normal somatic cells there is a progressive degradation of telomeres with aging. The cell can afford to lose only a finite number of these telomeres before significant sequences of the parent DNA are lost, resulting in chromosomal instability and cell death. However, germ-cell telomeres are maintained despite multiple rounds of replication. This suggests that they produce an enzyme that maintains their telomere length. This enzyme, a ribonucleoprotein, is called telomerase. In this review, we discuss the presence of telomerase activity in various human cancers and, in particular, in urologic tumors. We describe the potential clinical utility of detection of the presence of telomerase activity in cells from voided urine samples of patients with bladder cancer.

Neoplastic transformation of mouse C3H10T1/2 cells following exposure to neutrons does not involve mutation of ras gene as analyzed by SSCP and cycle sequencing

About 25% of human tumors contain a mutated member of the ras gene family. Neutron exposure is an occupational risk in several work places and while we know that cells exposed to neutrons can become transformed, the molecular basis of this process is not understood. To determine whether neutron-induced cellular transformation involves ras mutation, C3H10T1/2 cells were exposed to a single dose of 5.9 MeV neutrons. Type II and type III foci were isolated and established as cell lines. A total of 34 foci were selected and expanded for analysis of tumorigenicity, chromosomal aberrations and mutations in members of the ras gene family. The presence of mutations in genomic DNA in N-ras or K-ras of each focus was examined by either single-strand conformational polymorphism (SSCP) analysis or by asymmetric PCR coupled cell cycle sequence analysis. Although chromosomal aberrations were detected at metaphase, no alterations in either ras gene were detected. We conclude that in vitro neutron-induced transformation must occur through a mechanism other than ras mutation.

Cell senescence and a mechanism of clonal evolution leading to continuous cell proliferation, loss of heterozygosity, and tumor heterogeneity: studies on two immortal colon cancer cell lines

Extensive karyotypic analysis was performed on early and late passages of two continuous human cell lines, SW480 and SW620, that were derived from the same colon cancer patient. We cultivated these two cell lines in vitro for a period of 24 months and periodically examined their chromosome constitution. SW480 cells, from passage 138, were injected subcutaneously into 20 nude mice. The tumors that grew in nude mice were then cultivated in vitro for several passages to compare histopathologic findings and tumor growth patterns with clonal chromosomal profiles. Despite some karyotypic diversity, the two cell lines exhibited common marker chromosomes and followed similar patterns of evolution. During subsequent passages, acquisition of new chromosomal abnormalities gave rise to sidelines with a near-diploid genome that frequently underwent endoreduplication. Genomic instability seemed to play an important role in the emergence, growth, and subsequent elimination of the heterogenous sidelines by selection, clonal expansion, and cell death by senescence. Despite continuous growth, both the cell lines occasionally showed telomeric associations and random dicentric and multicentric formations. These lesions were considered evidence of cell senescence and were related to the disappearance of particular sidelines through evolution. Successful evolutionary steps were characterized by elimination of pre-existing marker chromosomes that were subsequently replaced in the karyotype by their cytologically intact homologous chromosomes possibly after selective endoreduplication. Frequent loss of heterozygosity for the chromosomes taking part in this process is postulated. We suggest that one of the mechanisms by which cancer cells bypass senescence may be related to their potential for continuous clonal diversification.

Cytogenetic findings in renal cell carcinoma

Cytogenetic characterization of 24 renal cell carcinomas (RCCs) was performed. The various RCC subtypes included 8 chromophobe RCCs, 12 nonpapillary RCCs, and 4 papillary RCCs. Loss of chromosomes 1, 2, 6, 10, and 17 were observed in 5 of 8 chromophobe RCCs. Five of the 12 nonpapillary RCCs showed abnormalities involving chromosome 3. These were deletion of the 3p13 region, loss of the whole chromosome 3, and unbalanced translocation resulting in a derivative. Of the 4 papillary RCCs, two showed trisomy 7 and 17 along with other abnormalities, one had trisomy for chromosomes 7, 12, and 13, along with loss of chromosome #5 and Y chromosomes, and another papillary RCC revealed trisomy 15 and trisomy 17. These results further show that specific cytogenetic abnormalities are associated with various subtypes of RCCs.

Accelerated telomere shortening in ataxia telangiectasia

Ataxia telangiectasia (AT) is characterized by neurological deterioration, immunodeficiency, spontaneous chromosomal instability, hypersensitivity to ionizing radiation, predisposition to cancer, particularly T cell leukaemia and lymphoma, and premature ageing. The most commonly observed defect affecting telomeres in humans is telomeric fusions, particularly in T lymphocytes in AT patients. Rarely, some tumour cells, like senescent cells, have dicentric chromosomes that may arise as a result of telomeric sequence loss. We show that the AT mutation in the homozygous state confers a predisposition to accelerated telomere shortening with increasing age in peripheral blood lymphocytes (PBLs), which may be linked to premature senescence. We also show that telomeric fusions are associated with large (> 90%) preleukaemic translocation clones in T cells. We propose that these fusions may result from a compound effect of accelerated telomere shortening, together with a growth advantage of cells in large clones which leads to further telomere loss. Fusions are not observed in leukaemic cells in these patients. There is no evidence that either accelerated telomere loss per se or telomeric fusions are important in tumourigenesis. Telomerase is present in both normal and AT lymphocytes and so neither telomere shortening nor telomeric fusions can be explained by the absence of telomerase.

Mammary epithelial hyperplasias: alterations related solely to proliferation?

The cytogenetic analysis of five mammary epithelial hyperplasias is reported. Only two cases had clonal chromosome alterations. Structural alterations involved chromosomes 1 and 5. Numerical alterations involved chromosomes X, 1, 6, 9, and 19. In four cases, the modal number was in the diploid range, and one case was tetraploid. The study of benign proliferations and their comparison with the chomosome alterations of their malignant counterparts could lead to a better understanding of the genes acting solely in cell proliferation and those that cause these cells to undergo malignant transformation and to become invasive.

Radiation-induced carcinogenesis: individual sensitivity and genomic instability

In spite of a well-known relationship between exposure to radiation and increased risk for cancer development, the biological mechanisms involved in radiation-induced carcinogenesis remain poorly documented. Various hypotheses are discussed in this paper. It appears that radiation cannot be directly responsible for the numerous genetic alterations of cancer cells. Most of them occur during tumor progression. Only one or a very limited number of them was induced by radiation many years before tumor growth. This long delay is a major difficulty for experimental research and raises many questions. Recently, it has been shown that a genomic instability occurs after many generations in cells descending from irradiated cells. This instability leads to multiple genetic alterations and, preferentially, affects some chromosome structures, particularly telomeres. This kind of telomeric instability - related to the shortening of telomeric DNA sequences - has also been observed in senescent cells as well as in non-senescent cells from patients predisposed to cancer, and this process may possibly also occur in the progeny of irradiated cells.

Chromosome rearrangements at telomeric level in hematologic disorders

Following retrospective screening of our karyotype data from 414 consecutive non-childhood, neoplastic, and preneoplastic hematologic diseases, we have isolated 11 cases with alterations involving one or two chromosome termini, including: a) nonclonal telomeric telomeric associations (tas), b) subclonal terminal rearrangements consisting of additional (add) material of unknown origin fused at the end of the chromosome, c) clonal telomere-centromere fusion (t telcen) with pseudodicentric structure. Most of these abnormalities were present in karyotypes with multiple alterations and associated to an evolutive stage of the disease (9 of 94 cases studied in progression, including three of 22 CML studied in blast crisis). The immunophenotype of the cell populations was lymphoid in eight cases, six of which were NHL, and myeloid, erythroid, and undifferentiated in the other three. More data on telomeric abnormalities may clarify whether there is ubiquitous genomic instability of neoplastic cells or an inborn cell lineage predisposition favoring rearrangements involving telomeres.

Structural instability of a transmissible end-to-end dicentric chromosome in a xeroderma pigmentosum fibroblast clone

Cytogenetic analysis was performed in a fibroblast clone (XP9UV25) selected for anchorage-independent growth from an XP strain of normal origin and characterized by the presence of clonal chromosome rearrangements. A dicentric chromosome involving the 5p and 16q telomeric regions was observed in XP9UV25 cells at the fifth passage from colony isolation and at successive passages. The specific anomaly was present with increasing frequency (from 22 to 60% of mitoses) during culture propagation, undergoing rearrangements that gave rise to: 1) (5;16) dicentrics with deletions or duplications of the intercentromeric region; 2) homodicentrics for chromosomes 5 or 16, either end-to-end associations or rearranged; and 3) derivative 5p+ and 16q+ monocentric chromosomes. The frequency of other anomalies involving other chromosomes was negligible. These findings represent the first demonstration that a telomeric association leads to a variety of balanced and unbalanced chromosome rearrangements. These rearrangements may result from asymmetric interchanges between sister chromatids, "bridge-breakage-fusion" events during cell division, breakage and reunion of isochromatids, and breakage followed by healing of the ends. The type of anomaly and the sequence of karyotypic changes we observed in the XP9UV25 clone and their mechanisms of origin may be the same as those occurring during transformation from diploidy to aneuploidy in neoplastic cells.

Telomere length variation in normal and malignant human tissues

Tissue and tumor specific length variation of telomere (TTAGGG)n repeats was studied in DNAs from various normal and malignant tissues. DNA was isolated from bone marrow and blood cells, malignant tissues, and established tumor cell lines. Nonisotopic Southern hybridization revealed a reduction of telomere repeat arrays in 14 of the 35 tumors analyzed. However, other cases (60%) showed no reduction, or even an increase, in telomeric length. Our finding of elongated telomere stretches in several tumors of different origin compared with normal tissue is in contrast to previous reports describing a general shortening of terminal repeat length in colorectal cancer and neuroblastoma. We tentatively conclude that there is no general tendency to telomere reduction in malignant tissues.

Chromosomal instability and alterations of telomeric repeats in irradiated human fibroblasts

In recent years, evidence has been presented suggesting that genomic instability can appear several generations after cellular exposure to radiations. Kadhim et al. (1992) have shown that irradiation by alpha-particles of Pu238 (LET = 120 keV/microns) induce a transmissible instability in mouse haematopoietic cells. Working with human dermis fibroblasts irradiated by heavy ions in a large range of LETs (386-13,600 keV/microns), we demonstrated that an instability could also be acquired by human cells and that particular chromosomes (13, 16, 1) were recurrently involved in telomeric associations (Sabatier et al. 1992). This instability resulted in specific chromosome imbalances and in a particular monosomy 13 (Martins et al. 1993). In this study, we wanted to determine whether telomeres are shortened with the appearance of the chromosomal instability. Our results show no drastic shortening of the mean length of telomeres by Southern blot. By in situ hybridization we are looking to see if chromosomes specifically involved in instability have alterations of the telomeres. We have observed large variations of the hybridization signal of individual telomeres with no telomeric sequences detectable at the junction of end to end associations.

Two human breast cancer cell lines showing decreasing telomeric repeat length during early in vitro passaging

Specific DNA repeats serve as a molecular protection shield at the telomeric ends of mammalian chromosomes. The absence of telomerase activity leads to a gradual decrease of telomeric repeat length in normal somatic cells. In contrast, immortalized cells from malignant tumors are usually thought to re-express telomerase to overcome a self-limited growth. Following this hypothesis, re-expression of telomerase is due to a rare mutational event. Herein we describe our results of telomeric length determination in two newly established breast cancer cell lines. During in vitro establishment from pleural effusions, both cell lines showed a marked decrease of the upper border range of telomeric repeat length distribution. The lower border remained within a constant range characteristic for each cell line. In no case was decrease of repeat length accompanied by an increased incidence of telomeric associations or fusions. The results show that a constant telomeric repeat length does not constitute a characteristic feature of immortalized cells. Furthermore, the kinetics of repeat length decrease and the constant range of the lower border reveal that the onset of telomerase activity is not necessarily due to a rare, i.e., mutational, event.

Increasing complexity of the karyotype in 50 human gliomas. Progressive evolution and de novo occurrence of cytogenetic alterations

We studied the karyotypes of eight differentiated gliomas, 19 anaplastic gliomas, and 23 glioblastomas (GBM). Normal stemlines were present in 70% of the differentiated and anaplastic gliomas; abnormalities were mostly characterized by loss of sex chromosomes. In GBM, on the contrary, only 13% of the stemlines were normal and three groups, 45,XO, near-diploid, and near tetraploid, could be identified. The most frequent alterations among GBM were: total or partial loss of chromosome 10 in nine cases, structural abnormalities of chromosome 9 in seven cases, and loss of the Y chromosome in stemline clones of seven cases. Less frequent abnormalities included chromosomes 7, 1, 3, and 19. Our data support the cytogenetic model of gliomas as multi-stage tumors. GBM, in particular, can originate from the evolution of astrocytomas but can also develop de novo. In both cases loss of genetic material on chromosome 10 seems to play a crucial role.

Activation of telomerase in a human tumor

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Restoration of telomeres in human papillomavirus-immortalized human anogenital epithelial cells

Loss of telomeres has been hypothesized to be important in cellular senescence and may play a role in carcinogenesis. In this study, we have measured telomere length in association with the immortalization and transformation of human cervical and foreskin epithelial cells by the human papillomavirus type 16 or 18 E6 and E7 open reading frames. By using a telomeric TTAGGG repeat probe, it was shown that the telomeres of precrisis normal and E6-, E7-, and E6/E7-expressing cells gradually shortened with passaging (30 to 100 bp per population doubling). Cells that expressed both E6 and E7 went through a crisis period and gave rise to immortalized lines. In contrast to precrisis cells, E6/E7-immortalized cells generally showed an increase in telomere length as they were passaged in culture, with some later passage lines having telomeres that were similar to or longer than the earliest-passage precrisis cells examined. No consistent association could be made between telomere length and tumorigenicity of cells in nude mice. However, of the three cell lines that grew in vivo, two had long telomeres, thus arguing against the hypothesis that cancer cells favor shortened telomeres. Our results indicate that arrest of telomere shortening may be important in human papillomavirus-associated immortalization and that restoration of telomere length may be advantageous to cells with regard to their ability to proliferate.

Restoration of telomeres in human papillomavirus-immortalized human anogenital epithelial cells

Loss of telomeres has been hypothesized to be important in cellular senescence and may play a role in carcinogenesis. In this study, we have measured telomere length in association with the immortalization and transformation of human cervical and foreskin epithelial cells by the human papillomavirus type 16 or 18 E6 and E7 open reading frames. By using a telomeric TTAGGG repeat probe, it was shown that the telomeres of precrisis normal and E6-, E7-, and E6/E7-expressing cells gradually shortened with passaging (30 to 100 bp per population doubling). Cells that expressed both E6 and E7 went through a crisis period and gave rise to immortalized lines. In contrast to precrisis cells, E6/E7-immortalized cells generally showed an increase in telomere length as they were passaged in culture, with some later passage lines having telomeres that were similar to or longer than the earliest-passage precrisis cells examined. No consistent association could be made between telomere length and tumorigenicity of cells in nude mice. However, of the three cell lines that grew in vivo, two had long telomeres, thus arguing against the hypothesis that cancer cells favor shortened telomeres. Our results indicate that arrest of telomere shortening may be important in human papillomavirus-associated immortalization and that restoration of telomere length may be advantageous to cells with regard to their ability to proliferate.

Telomeric fusions in a Wilms' tumor

The present report describes the karyotypic findings in cells from a Wilms' tumor. The most consistent cytogenetic abnormalities detected consisted of translocations involving break and fusion of chromosomal telomeres and telomeric associations frequently affecting the terminus of the short arms of chromosomes 14 and 17.

True telomeric translocation in a baby with the Prader-Willi phenotype

We report on a baby with a nonreciprocal de novo unbalanced translocation between chromosomes 12 and 15. Her karyotype was 45,XX, -12, -15, +der(12)t(12;15)(pter-->qter::q13-->qter). The paternal origin of the 15q11-13 region was shown by DNA marker studies and, consistent with this, the baby had the Prader-Willi (PWS) phenotype. The breakpoint on 12q was distal to D12S11 (lambda MS43) which maps to 12q24.3-qter. Fluorescent in situ hybridization using the oligonucleotides (TTAGGG)7 and (AATCCC)7 showed that the 12q telomere was still present within the translocated chromosome. Thus, the translocation was within or onto the end of the telomere of 12q. This unusual translocation is further evidence of an unexplained instability of the 15q11-13 region.

Correlation between cytogenetic and histopathological findings in 75 human meningiomas

The correlations between cytogenetic and histopathological findings were analyzed in 75 human meningiomas. The tumors were classified according to increasing degrees of anaplasia into three grades: Grade I, benign; Grade II, atypical; Grade III, anaplastic. In 45 tumors of Grade I (benign), we more often observed a normal karyotype or monosomy 22. In 23 tumors of Grade II (atypical), we observed karyotypes with structural and/or numerical abnormalities with the presence of telomeric associations in 8 of them. These last tumors were fibroblastic. In seven Grade III tumors (anaplastic), we also observed complex abnormalities, and in one case, we observed telomeric associations. Our observations show that complex chromosome abnormalities and telomeric associations are observed in tumors that histologically display a certain degree of anaplasia. It is possible that the result of histopathological and cytogenetic correlations might represent a prognostic factor in meningiomas.

Telomeric associations and loss of telomeric DNA repeats in renal tumors

In a series of cytogenetically analyzed renal tumors of different histological types (chromophobe carcinoma, clear-cell carcinoma, chromophilic carcinoma, and oncocytoma) and normal renal tissue, the length of the telomeric DNA repeats was assessed using a (TTAGGG)3 oligonucleotide probe. A strong correlation was noted between pronounced telomere shortening and the appearance of telomeric associations of chromosomes. These data suggest an etiologic role of the loss of telomeric DNA repeats in the formation of telomeric associations and a possible involvement of this mechanism in the pathogenesis of chromosome aberrations in human tumors.

Telomeric structure in cells with chromosome end associations

End-to-end associations of metaphase chromosomes have been observed in a variety of human tumors, ageing cells, and several chromosome instability syndromes. Since telomeres of tumor cells and ageing tissues are often reduced in length, it has been suggested that chromosome end associations may be due to loss of telomeric repeats. We report the molecular structure of telomeres of two human tumor cell lines with frequent end-to-end associations of metaphase chromosomes. These telomeres were shown to be severely reduced compared with most other human cells with functional telomeres. However, we also describe two cell lines with severely shortened telomeres that are not detectably compromised in their function. We suggest that telomeric length is not the only determinant of the fusigenic behavior of human telomeres in tumor cells.

Cytogenetic findings in a case of pediatric glioblastoma

We report a patient with glioblastoma multiforme (GBM) which showed stable and unstable telomeric associations involving the short arms of chromosomes 4 and 7. The karyotype was hyperdiploid, with chromosome numbers ranging from 84 to 87 in all cells, and showed a single stemline with variations in the number of marker chromosomes, teleomeric associations, and double minutes (dmin). The karyotype designation is 83-86,XX,-X,rea(X),-4,tas(4;7)(p16;?p22),der(6)t(6;?)(p21;?), -8, -9, der(9)t(9;?)(?p11;?), dup(9)(p12p23), -10 x 2, del(10)(p11), -11,del(11)(p11), -12, der(12)t(12;?) (p13;?),-13, -14 x 2,der(14)t(14;?) (p11;?), -16 x 2, -19, -21 x 2, -22 x 2, + 9-13mar, + dmin. Loss of the short arm of chromosome 10, structural aberrations of the short arm of chromosome 9, and dmin are consistent findings in GBM, whereas the high chromosome number is less common. Chromosome instability associated with the phenomenon of telomeric association/fusion has not been reported in GBM.

Jumping translocations originate clonal rearrangements in SV40-transformed human fibroblasts

A comparative study of chromosomal rearrangements occurring in 4 independent clones obtained from SV40-transformed cornea and skin human fibroblasts was performed. Rearrangements principally affect some constitutive heterochromatin and, to a lesser degree, telomeric regions. This results in multiple exchanges between a limited number of chromosome structures, i.e., in jumping translocations. Such rearrangements occur even at early passages and some of them give rise to clonal rearrangements that accumulate at late passages. This process is responsible for progressive modification of the karyotypes, principally characterized by deletion of a number of chromosome segments. Thus, clonal rearrangements are selected among many others not occurring at random. The selective pressure retaining clonal rearrangement seems to be similar for the 4 independent clones, since selection of the derivative chromosomes leads to the same imbalances, whatever the origin of the clone. This sequence of events recalls that of human solid tumors, since jumping rearrangements are generally observed in pre-malignant conditions or in low-grade malignancies, whereas clonal rearrangements leading to typical imbalances are detected in more advanced malignant tumors.

Telomeric associations evolving to ring chromosomes in a recurrent pleomorphic xanthoastrocytoma

Telomeric associations observed in a recurrent untreated pleomorphic xanthoastrocytoma were apparently the primary cytogenetic events that evolved by fusion and breakage events, resulting in subclones with ring chromosomes. The telomeric fusions between chromosomes 15pter and 20qter, and between an extra copy of the long arm of chromosome 1 and chromosome 22qter, evolved in a stepwise fashion to ring chromosomes 20 and 22. The findings in this tumor demonstrate that telomeric association is one mechanism that can initiate chromosome instability by generating subclones with unstable chromosome intermediates and result in ring chromosomes and subsequent chromosome loss.

Cytogenetic findings in liposarcoma correlate with histopathologic subtypes

The cytogenetic findings in 31 liposarcomas from 26 patients are reported. Four other tumors did not grow. Three histologic types are represented in this analysis. The well-differentiated liposarcomas were characterized by telomeric associations, large marker chromosomes and ring chromosomes, and in some cases, double minutes. The pleomorphic liposarcomas contained very high clonal chromosomal numbers with near-tetraploid modes and numerous variable, often unidentifiable, chromosomal abnormalities. The myxoid liposarcomas were characterized primarily by a t(12;16)(q13;p11) as the sole abnormality or additional changes. These results indicate that cytogenetic findings may provide a new criterion, not only for establishing the diagnosis of liposarcoma, but also for differentiating confusing histologic types of liposarcoma and these lesions from other types of sarcomas.

Telomere shortening associated with chromosome instability is arrested in immortal cells which express telomerase activity

Loss of telomeric DNA during cell proliferation may play a role in ageing and cancer. Since telomeres permit complete replication of eukaryotic chromosomes and protect their ends from recombination, we have measured telomere length, telomerase activity and chromosome rearrangements in human cells before and after transformation with SV40 or Ad5. In all mortal populations, telomeres shortened by approximately 65 bp/generation during the lifespan of the cultures. When transformed cells reached crisis, the length of the telomeric TTAGGG repeats was only approximately 1.5 kbp and many dicentric chromosomes were observed. In immortal cells, telomere length and frequency of dicentric chromosomes stabilized after crisis. Telomerase activity was not detectable in control or extended lifespan populations but was present in immortal populations. These results suggest that chromosomes with short (TTAGGG)n tracts are recombinogenic, critically shortened telomeres may be incompatible with cell proliferation and stabilization of telomere length by telomerase may be required for immortalization.

Cytogenetic comparison of two poorly differentiated human lung squamous cell carcinoma lines

This paper presents a cytogenetic analysis of two established but early-passage (passages 5 and 18) cell lines derived from histologically similar, poorly differentiated lymph node metastases of squamous cell carcinoma of the lung. The cell lines showed 3 shared marker chromosomes, del(1)(q11), del(2)(p11.1) and del(2)(q11.1). One of the lines (DLKP) had 8 additional markers including structural rearrangements such as translocations and isochromosomes. Five additional markers (including two deletions of chromosome 3) were found in DLRP. A notable feature of DLRP was the high incidence of telomeric association evident in the majority of metaphase plates. Over-representation of chromosome 7 was a characteristic feature of metaphases derived from DLKP, and identification of i(21q) in this cell line was an unusual finding. The results indicate significant cytogenetic heterogeneity between these early-passage cell lines derived from two apparently histologically similar tumors.

Chromosomal abnormalities in giant cell tumors of bone

Cytogenetic analysis of short-term cultures from ten giant cell tumors of bone revealed clonal and nonclonal chromosome abnormalities in three tumors and nonclonal changes only in seven. None of the clonal aberrations, inv(21)(p11q21) in one tumor, +5 in another, and t(15q22q), dic(4;22)(p16;p1?), double minutes, dicentrics, and ring chromosomes present in three separate clones in the third tumor, were identical to previously reported clonal changes in giant cell tumors. Telomeric associations were found in five tumors. The telomeres of chromosome arms 19q and 15p were particularly frequently involved.

Nonreciprocal and jumping translocations of 15q1----qter in Prader-Willi syndrome

We analyzed 33 cases of Prader-Willi syndrome (PWS) (including 2 personal observations) with translocations of 15q1----qter onto the terminals of different, apparently whole chromosomes. In all but one of the 23 informative cases the translocations was de novo. Thirty of the patients were unbalanced and 27 had a 45-chromosome constitution compatible with a 3:1 segregation. One balanced and 2 unbalanced translocations were jumping ones. The possible existence of actual non-reciprocal translocations in man is indicated by the following considerations about these and other PWS-associated rearrangements: 1) The observed excess of de novo translocations; 2) the relatively frequent familial occurrence of reciprocal 15q translocations; 3) the concurrence in 3 terminal translocation cases of an idic (15); 4) the visualization of jumping terminal translocations as simple transpositions rather than as successive reciprocal exchanges; 5) the predominance of true isodicentrics in PWS patients with extra inv dup(15) chromosomes; and 6) the rarity of extra derivatives resulting in 15q proximal tertiary trisomy. Additional findings in the present series were normal parental age in the de novo 45-chromosome cases, an apparently random distribution of telomeric breakpoints, and the occurrence of different breakpoints within the 15q1 region.

YAC cloning of telomeres

Human telomeres have been successfully cloned in Saccharomyces cerevisiae by complementing deficient yeast artificial chromosomes (YACs). This technique allows cloning of DNA sequences that can recognize particular chromosomal ends, and therefore facilitates the mapping of eukaryotic genomes. Although the biology of adopting foreign telomeres in yeast is not fully understood, the cloning system itself seems to be a useful tool for constructing telomeric DNA libraries from higher eukaryotes. Here we describe the techniques that are currently being used in cloning of telomeric DNA.

Telomeres shorten during ageing of human fibroblasts

The terminus of a DNA helix has been called its Achilles' heel. Thus to prevent possible incomplete replication and instability of the termini of linear DNA, eukaryotic chromosomes end in characteristic repetitive DNA sequences within specialized structures called telomeres. In immortal cells, loss of telomeric DNA due to degradation or incomplete replication is apparently balanced by telomere elongation, which may involve de novo synthesis of additional repeats by novel DNA polymerase called telomerase. Such a polymerase has been recently detected in HeLa cells. It has been proposed that the finite doubling capacity of normal mammalian cells is due to a loss of telomeric DNA and eventual deletion of essential sequences. In yeast, the est1 mutation causes gradual loss of telomeric DNA and eventual cell death mimicking senescence in higher eukaryotic cells. Here, we show that the amount and length of telomeric DNA in human fibroblasts does in fact decrease as a function of serial passage during ageing in vitro and possibly in vivo. It is not known whether this loss of DNA has a causal role in senescence.

Cytogenetic abnormalities in cancer: with special emphasis on tumor heterogeneity

There is a considerable amount of cytogenetic data available to support the statements that (1) cancer is a genetic disease; (2) most cancers are monoclonal in origin; (3) tumor cells are more genetically unstable than normal cells; (4) the genetic instability may be inherited, acquired, or both during the lifespan of the individual tumor; (5) tumor metastasis is a nonrandom, controlled process, and clonal in origin; (6) malignant tumors are genetically heterogeneous and contain multiple subpopulations that may differ in their biological properties; (7) some tumors might be difficult to treat successfully because of their resistant nature; and (8) tumor cells may acquire resistance because of gene amplification. For these reasons it is extremely important to study the biology of malignant tumor cells in order to determine their effective treatments and control this dreadful disease.

Benign metastasizing giant cell tumors of bone. A DNA flow cytometric study

Approximately 2% of histologically benign giant cell tumors (BGCT) of bone are complicated by lung metastases, which can progress despite their benign histologic appearance. Almost all BGCT studied by DNA flow cytometry (FCM) have been reported to be diploid. However, the very few cases with lung metastases previously analyzed were all aneuploid. To assess the usefulness of DNA FCM in predicting the metastatic potential of BGCT, seven metastasizing BGCT were studied by DNA FCM using paraffin-embedded tissue. Five were purely diploid, one was tetraploid, and one was aneuploid. The primary and the metastasis showed the same DNA distribution in all but the tetraploid case, in which the metastasis was purely diploid. A single patient, who was in the diploid group, had unresectable tumor in the lungs; she remains alive with stable disease at 30 months. The other six patients, who underwent complete resections of their lung metastases, are free of disease. These results suggest that DNA FCM is not a sensitive method for predicting the metastatic potential of BGCT since most metastasizing cases appear to be diploid.

Cytogenetic study on eleven cutaneous neoplasms and two pre-tumoral lesions from Xeroderma pigmentosum patients

Eleven independent tumors (5 basa-cell carcinomas, 5 squamous-cell carcinomas and 1 malignant melanoma), 2 pretumoral lesions and one common nevus, developing in the skin of 10 unrelated XP patients were cytogenetically analyzed. No specific chromosomal changes were observed. Two features were relevant, however: emergence of several independent clones and over-involvement of telomeric and centromeric regions in the formation of chromosomal rearrangements. Jumping translocations were observed in 2 squamous-cell carcinomas involving telomeric and centromeric regions.

Solid tumor cytogenetics. Progress since 1979

Some of the advances in the past decade in the field of solid tumor cytogenetics are described, with particular reference to nonrandom structural chromosome changes. Although it had been known for many years that meningiomas and salivary gland tumors were associated with changes involving particular chromosomes, it has only quite recently become clear, following the application of suitable culture techniques, that other benign tumors such as lipomas and leiomyomas may also be characterized by specific changes, particularly reciprocal translocations. Reciprocal translocations may also be found in malignant soft-tissue tumors such as liposarcomas (involving 12q as in lipomas) and Ewing's sarcoma. In contrast, the common forms of carcinoma present a more variable picture, although certain chromosomes may undergo nonrandom changes of various types, including translocations, which, however, are generally nonreciprocal. Some of these chromosomes may be quite specific (e.g., chromosome 10 in prostatic and #18 in colorectal cancer), while others appear to be common to many or all types of carcinoma, such as chromosomes 1, 3, 11, and 17, and a small metacentric that may be an i(5p). In carcinoma of the bladder, different chromosome changes may characterize subsets of the tumors. In carcinoma of the cervix, however, the commonly involved chromosomes, 1, 3, ?5, 11, and 17, appear in markers in any combination and are thus not mutually exclusive. Although further study of the chromosome changes in carcinomas is essential to an understanding of their relationship to the molecular changes that are associated with malignant transformation, it can be hypothesized that, while some of the changes result in the duplication of particular genes, e.g., on chromosome 1q, a more important role may be to bring about the loss of chromosomal segments containing tumor-suppressor genes. Evidence from molecular studies that has recently been accumulating for the loss of alleles on, for instance, 3p, 11p, and 17p, which could in part be due to gross chromosomal rearrangements, also strongly suggests the importance of genic loss in malignant transformation. In carcinomas, at least, the changes probably involve a number of genes, each change representing one of the several steps necessary for tumorigenesis.

Jumping end-to-end dicentrics in a case of squamous cell carcinoma from a patient with xeroderma pigmentosum

Cytogenetic studies of a skin squamous cell carcinoma from a xeroderma pigmentosum patient were performed at several passages. They show the existence of recurrent rearrangements: 53% were dicentrics, of which 67% were of the telomere-telomere type. The telomeric region of the long arm of chromosome 12 was the most involved (in 38% of dicentrics), followed by 22p. The origin of this type of jumping rearrangement and its possible role on cell proliferation are discussed.