Telomeres and chromosomal instability

Telomeres are distinctive structures, composed of a repetitive DNA sequence and associated proteins, which enable cells to distinguish chromosome ends from DNA double-strand breaks. Telomere alterations, caused by replication-mediated shortening, direct damage or defective telomere-associated proteins, usually generate chromosomal instability, which is observed in senescence and during the immortalization process. In cancer cells, this chromosome instability could be extended by their ability to 'repair' chromosomes and terminate in break-fusion-bridge cycles. Dysfunctional telomeres can be healed by activation of telomerase or by the 'alternative mechanism' of telomere lengthening. Activation of such telomere maintenance mechanisms may help to preserve the integrity of chromosomes even if they play a role in chromosomal instability. This review focuses on molecular processes involved in telomere maintenance and chromosomal instability associated with dysfunctional telomeres in mammalian cells.

Rapid method for mean telomere length measurement directly from cell lysates

Telomere length is involved in cell survival, tumorigenesis, and early aging. We present here an innovative method to determine the mean telomere length without any DNA purification. Our strategy is to measure both the DNA concentration and the number of telomeric units (TTAGGG) directly from cell lysate produced by the combined action of NaOH (pH>13) and sonication directly on cell pellet. Telomere units are quantified using an enzyme hybridization assay on 96-well microtiter plates grafted with a captor sequence. A biotin-coupled-tracer oligonucleotide hybridizes with telomere fragments and the enzymatic reaction is performed with a streptavidin-acetylcholinesterase conjugate, using the colorimetric method of Ellman. OD measure is directly proportional to the number of telomere units in cell lysate. This scalable technique allows the determination of mean telomere length simultaneously in many samples. This assay will be highly efficient to screen new drugs involved in chemotherapy targeting telomerase or directly telomeres.

High levels of chromosome aberrations correlate with impaired in vitro radiation-induced apoptosis and DNA repair in human B-chronic lymphocytic leukaemia cells

PURPOSE

To investigate the relationship between the susceptibility of B-chronic lymphoid leukaemia (B-CLL) cells to DNA damage-induced apoptosis, the kinetics of DNA strand-break rejoining, and chromosome damage after exposure to ionizing irradiation.

MATERIALS AND METHODS

Lymphocytes from B-CLL patients were gamma-irradiated in vitro with 0.2-5 Gy and stimulated by Staphylococcus aureus cowan I (SAC I) for estimation of chromosomal damage. Induction of apoptosis after irradiation was studied in 50 patients by two methods: morphological characterization of apoptotic cells after fluorescent staining (Hoechst), and specific quantification of mono- and oligonucleosomes in cytoplasmic cell fractions (ELISA assay). Morphological chromosome damage was scored in the first cell generation after irradiation (13 patients). In parallel, the kinetics of DNA single-strand break rejoining were investigated by the alkaline comet assay (12 patients).

RESULTS

Ionizing irradiation did not induce apoptosis in lymphocytes from a subset of B-CLL patients. The results suggest that B-CLL cells resistant to radiation-induced apoptosis could repair DNA strand-breaks more rapidly and showed a higher level of chromosome aberrations than radiation-sensitive B-CLL cells.

CONCLUSION

Each of three biological effects observed (apoptosis, kinetics of DNA single-strand-break repair, chromosomal damage) might be explained by different modifications occurring in irradiated B-CLL cells. Their convergence strongly suggests that resistance to apoptotic death initiation by DNA damage may be impeded by a rapid engaging of the DNA repair mechanisms. The higher level of chromosome aberrations observed in these cells suggests that the type of DNA repair system involved may generate inaccurate repair.

Cell inactivation and double-strand breaks: the role of core ionizations, as probed by ultrasoft X rays

The large RBE (approximately 7) measured for the killing of Chinese hamster V79 cells by 340 eV ultrasoft X rays, which preferentially ionize the K shell of carbon atoms (Hervé du Penhoat et al., Radiat. Res. 151, 649-658, 1999), was used to investigate the location of sensitive sites for cell inactivation and the physical modes of action of radiation. The enhancement of the RBE above the carbon K-shell edge either may indicate a high intrinsic efficiency of carbon K-shell ionizations (due, for example, to a specific physical or chemical effect) or may be related to the preferential localization of these ionizations on the DNA. The second interpretation would indicate a strong local (within 3 nm) action of K-shell ionizations and consequently the importance of a direct mechanism for radiation lethality (without excluding an action in conjunction with an indirect component). To distinguish between these two hypotheses, the efficiencies of core ionizations in DNA atoms (phosphorus L-shell, carbon K-shell, and oxygen K-shell ionizations) to induce damages were investigated by measuring their capacities to produce DNA double-strand breaks (DSBs). The effect of photoionizations in isolated DNA was studied using pBS plasmids in a partially hydrated state. No enhancement of the efficiency of DSB induction by carbon K-shell ionizations compared to oxygen K-shell ionizations was found, supporting the hypothesis that it is the localization of these carbon K-shell events on DNA which gives to the 340 eV photons their high killing efficiency. In agreement with this interpretation, cell inactivation and DSB induction, which do not appear to be correlated when expressed in terms of yields per unit dose in the sample, exhibit a rather good correlation when expressed in terms of efficiencies per core event in the DNA. These results suggest that core ionizations in DNA, through core-hole relaxation in conjunction with localized effects of spatially correlated secondary and Auger electrons, may be the major critical events for cell inactivation, and that the resulting DSBs (or a constant fraction of these DSBs) may be a major class of unrepairable lesions.

Biological effects induced by K photo-ionisation in and near constituent atoms of DNA

In order to assess the lethal efficiency and other biological effects of inner shell ionisations of constituent atoms of DNA ('K' events), experiments were developed at the LURE synchrotron facility using ultrasoft X rays as a probe of K events. The lethal efficiency of ultrasoft X rays above the carbon K threshold was especially investigated using V79 cells and compared with their efficiency to induce double strand breaks in dry plasmid-DNA. A correlation between the K event efficiencies for these processes is shown. Beams at 340 eV were found to be twice as efficient at killing cells than were beams at 250 eV. In addition, a rough two-fold increase of the relative biological effectiveness for dicentric + ring induction has also been observed between 250 and 340 eV radiations.

Chromosomal DNA and p53 stability, ubiquitin system and apoptosis in B-CLL lymphocytes

The ubiquitin system regulates diverse biological processes such as DNA replication and repair, biogenesis of ribosome, peroxisome and nucleosome, cell cycle, stress response and signal transduction pathways. Thus, the reported role of the ubiquitin system in apoptotic death control as well the alteration of its control in carcinogenesis should come as no surprise. Indeed, we and other groups have reported that the ubiquitin system is involved in apoptotic cell death of normal human lymphocytes and that this control is altered in B lymphocytes derived from chronic lymphocytic leukemia patients (B-CLL), rendering these malignant cells hypersensitive to specific inhibition of protein degradation/processing through proteasomal function. This approach recently allowed us to demonstrate that the stability of the tumor suppressor and pro-apoptotic protein p53 is differentially regulated in B-CLL versus normal lymphocytes and that this difference might at least partly explain the impaired response of B-CLL lymphocytes to apoptotic death activation. These results strongly suggest an imbalance in p53 regulation in B-CLL cells that leads to a variable response to DNA damage and constitutively expressed chromosomal instability. The question we and others would like to address is whether this alteration, or more likely a subset of alterations of the ubiquitin-proteasome pathway, is specific to B-CLL malignancy or if it is a hallmark of cancer cells in general. In either case, a better understanding of the ubiquitin-dependent control of apoptosis should pave the way towards a methodological approach for in vitro development of discriminating treatments which may be of potential usefulness in clinical trials of B-CLL.

Telomerase activation cooperates with inactivation of p16 in early head and neck tumorigenesis

Alteration of the p16/pRb pathway may cooperate with telomerase activation during cellular immortalization and tumour progression. We studied p16 expression status by immunohistochemistry and telomerase activity using the TRAP assay in 21 premalignant lesions of the head and neck epithelium as well as 27 squamous-cell carcinomas. We also examined expression of other components of the pathway (cyclin D1 and pRb) as well as presence of human papillomavirus genomes which can target these molecules. 4 of 9 mild dysplastic lesions (44%), 8 of 12 moderate/severe dysplastic lesions (67%), and 25 of 27 squamous-cell carcinomas (92%) demonstrated high telomerase activity (P = 0.009). There was a parallel increase with severity of lesions for the trend in proportions of cases demonstrating p16 inactivation or cyclin D1 overexpression (P = 0.02 and P = 0.01, respectively). For Ki67, a marker of cell proliferation, this trend was not significant (P = 0.08). Human papillomavirus infection was only found in 4 cases among the 48 samples tested (8.3%). In conclusion, progression of disease is accompanied by a parallel and continuous increase in telomerase activity and alterations in cell cycle regulators (p16, cyclin D1), as proposed by in vitro models.

The relationship between spontaneous telomere loss and chromosome instability in a human tumor cell line

Chromosome instability plays an important role in cancer by promoting the alterations in the genome required for tumor cell progression. The loss of telomeres that protect the ends of chromosomes and prevent chromosome fusion has been proposed as one mechanism for chromosome instability in cancer cells, however, there is little direct evidence to support this hypothesis. To investigate the relationship between spontaneous telomere loss and chromosome instability in human cancer cells, clones of the EJ-30 tumor cell line were isolated in which a herpes simplex virus thymidine kinase (HSV-tk) gene was integrated immediately adjacent to a telomere. Selection for HSV-tk-deficient cells with ganciclovir demonstrated a high rate of loss of the end these "marked" chromosomes (10-4 events/cell per generation). DNA sequence and cytogenetic analysis suggests that the loss of function of the HSV-tk gene most often involves telomere loss, sister chromatid fusion, and prolonged periods of chromosome instability. In some HSV-tk-deficient cells, telomeric repeat sequences were added on to the end of the truncated HSV-tk gene at a new location, whereas in others, no telomere was detected on the end of the marked chromosome. These results suggest that spontaneous telomere loss is a mechanism for chromosome instability in human cancer cells.

Assessment of DNA damage induced by high-LET ions in human lymphocytes using the comet assay

The alkaline single-cell gel electrophoresis assay (comet assay) was used to analyze DNA damage induced in human lymphocytes by irradiation with high linear energy transfer (LET) ions. Our aim was to measure DNA breaks and to demonstrate the heterogeneity of the damage levels in a lymphocyte population irradiated with ions of different energies and LETs. Four experiments with heavy ions (Ar, C and U), as well as gamma-ray exposure, were conducted to enable comparisons. We demonstrated that the comet assay is able to assess the variability in DNA damage induced at the single cell level. The amount of DNA damage and its heterogeneity increased with particle fluence and LET, but saturated at high LETs. However, when expressed in terms of the mean dose, gamma-rays were more efficient than most of the ions used. The comet assay also allowed the detection of highly damaged cells (HDC), which were previously described as cells in late apoptotic stages. The rapid emergence of HDC in this study suggests that they were generated following ion irradiation-induced creation of DNA break clusters induced by ion exposure. Another clue was that the proportion of HDC increased with LET and fluence. We hypothesized that the LET threshold observed and the higher efficiency of low-LET radiation might be linked to the impossibility of measuring small DNA fragments in HDC.

Biological dosimetry for astronauts: a real challenge

Manned space missions recently increased in number and duration, thus it became important to estimate the biological risks encountered by astronauts. They are exposed to cosmic and galactic rays, a complex mixture of different radiations. In addition to the measurements realized by physical dosimeters, it becomes essential to estimate real biologically effective doses and compare them to physical doses. Biological dosimetry of radiation exposures has been widely performed using cytogenetic analysis of chromosomes. This approach has been used for many years in order to estimate absorbed doses in accidental or chronic overexposures of humans. In addition to conventional techniques (Giemsa or FPG staining, R- or G-banding), faster and accurate means of analysis have been developed (fluorescence in situ hybridization [FISH] painting). As results accumulate, it appears that strong interindividual variability exists in the basal level of aberrations. Moreover, some aberrations such as translocations exhibit a high background level. Radiation exposures seem to induce variability between individual responses. Its extent strongly differs with the mode of exposure, the doses delivered, the kind of radiation, and the cytogenetic method used. This paper aims to review the factors that may influence the reliability of cytogenetic dosimetry. The emphasis is on the exposure to high linear energy transfer (LET) particles in space as recent studies demonstrated interindividual variations in doses estimated from aberration analysis after long-term space missions. In addition to the problem of dose estimates, the heterogeneity of cosmic radiation raises questions relating to the real numbers of damaged cells in an individual, and potential long-term risks. Actually, densely ionizing particles are extremely potent to induce late chromosomal instability, and again, interindividual variability exists in the expression of damage.

The influence of interstitial telomeric sequences on chromosome instability in human cells

Although most telomere repeat sequences are found at the ends of chromosomes, some telomeric repeat sequences are also found at intrachromosomal locations in mammalian cells. Several studies have found that these interstitial telomeric repeat sequences can promote chromosome instability in rodent cells, either spontaneously or following ionizing radiation. In the present study we describe the extensive cytogenetic analysis of three different human cell lines with plasmids containing telomeric repeat sequences integrated at interstitial sites. In two of these cell lines, Q18 and P8SX, instability has been detected in the chromosome containing the integrated plasmid, involving breakage/fusion/bridge cycles or amplification of the plasmid DNA, respectively. However, the data suggest that the instability observed is characteristic of the general instability in these cell lines and that the telomeric repeat sequences themselves are not responsible. Consistent with this interpretation, the chromosome containing an integrated plasmid with 500 bp of telomeric repeat sequences is highly stable in the third cell line, SNG28, which has a relatively stable genome. The stability of the chromosome containing the integrated plasmid sequences in SNG28 makes this an excellent cell line to study the effect of ionizing radiation on the stability of interstitial telomeric sequences in human cells.

Telomere instability in a human cancer cell line

Telomere maintenance is essential in immortal cancer cells to compensate for DNA lost from the ends of chromosomes, to prevent chromosome fusion, and to facilitate chromosome segregation. However, the high rate of fusion of chromosomes near telomeres, termed telomere association, in many cancer cell lines has led to the proposal that some cancer cells may not efficiently perform telomere maintenance. Deficient telomere maintenance could play an important role in cancer because telomere associations and nondisjunction have been demonstrated to be mechanisms for genomic instability. To investigate this possibility, we have analyzed the telomeres of the human squamous cell carcinoma cell line SQ-9G, which has telomere associations in approximately 75% of the cells in the population. The absence of detectable telomeric repeat sequences at the sites of these telomere associations suggests that they result from telomere loss. The analysis of telomere length by quantitative in situ hybridization demonstrated that, compared to the human squamous cell carcinoma cell line SCC-61 which has few telomere associations, SQ-9G has more extensive heterogeneity in telomere length and more telomeres without detectable telomeric repeat sequences. The dynamics of the changes in telomere length also demonstrated a higher rate of fluctuation in telomere length, both on individual telomeres and coordinately on all telomeres. These results demonstrate that telomere maintenance can play a role in the genomic instability seen in cancer cells.

Cytogenetic study of eight new cases of radiation-induced solid tumors

Radiation-induced tumors were selected according to the criteria defined by Cahan (1948) for sarcomas. Cell cultures and/or xenografts in nude mice were performed with biopsies obtained from second primary tumors. Karyotypes of eight tumors were established after R-banding. After comparison with literature data on 15 other cases, two distinct cytogenetic patterns could be distinguished. One was characterized by polyclonal karyotypes, of which a large proportion were simple and carriers of balanced translocations. Another one was characterized by monoclonal chromosome alterations observed in highly aneuploid and complex karyotypes, in which many deletions were observed. These two different patterns could be related to the modality of metaphase harvesting. Polyclonal karyotypes were preferentially observed after long-term cultures, and monoclonal karyotypes after short-term cultures or xenografts. The following scheme of radiation oncogenesis is proposed: a) induction of recessive gene mutations including that of tumor suppressor genes; b) accumulation of genomic alterations in the irradiated tissue with aging, including deletions or mutations of normal alleles from mutated tumor suppressor genes; and c) loss of tumor suppressor gene function and initiation of a multistage tumor development and progression. Polyclonal abnormalities are assumed to exist in noncancerous cells which acquired radiation-induced chromosome aberrations.

Telomere dynamics, end-to-end fusions and telomerase activation during the human fibroblast immortalization process

Loss of telomeric repeats during cell proliferation could play a role in senescence. It has been generally assumed that activation of telomerase prevents further telomere shortening and is essential for cell immortalization. In this study, we performed a detailed cytogenetic and molecular characterization of four SV40 transformed human fibroblastic cell lines by regularly monitoring the size distribution of terminal restriction fragments, telomerase activity and the associated chromosomal instability throughout immortalization. The mean TRF lengths progressively decreased in pre-crisis cells during the lifespan of the cultures. At crisis, telomeres reached a critical size, different among the cell lines, contributing to the peak of dicentric chromosomes, which resulted mostly from telomeric associations. We observed a direct correlation between short telomere length at crisis and chromosomal instability. In two immortal cell lines, although telomerase was detected, mean telomere length still continued to decrease whereas the number of dicentric chromosomes associated was stabilized. Thus telomerase could protect specifically telomeres which have reached a critical size against end-to-end dicentrics, while long telomeres continue to decrease, although at a slower rate as before crisis. This suggests a balance between elongation by telomerase and telomere shortening, towards a stabilized 'optimal' length.

Lethal effect of carbon K-shell photoionizations in Chinese hamster V79 cell nuclei: experimental method and theoretical analysis

To test a possible specific effect of carbon K-shell ionizations in DNA, survival curves for Chinese hamster V79 cells were measured for X irradiations at energies below and above the carbon K-shell ionization threshold. Specific values of the X-ray energies (250 and 340 eV) were chosen to ensure isoattenuation of the two kinds of radiation within the cell. An enhancement of lethality by a factor of about 2 was found for X rays at 340 eV compared to below the threshold at 250 eV. This may be attributed to the production of highly efficient carbon K-shell ionizations located on DNA. A model of X-ray lethality (Goodhead et al., Radiat. Prot. Dosim. 52, 217-223, 1994) was extended to allow for a possible lethal effect from clusters of reactive species induced by K-shell photoionizations (K-shell clusters). Within this model, the increase in lethality above the carbon K-shell threshold may be explained by a value of 2% for the lethal efficiency of K-shell clusters overlapping the DNA. An extrapolation to the lethal effect of more complex ion-induced K-shell ionizations indicates that K-shell ionization may be a major process in the biological effectiveness of heavy ions.

Molecular detection of telomerase-positive circulating epithelial cells in metastatic breast cancer patients

The detection of circulating tumor cells and micrometastases may have important therapeutic and prognostic implications. Telomerase is a hallmark of cancer and is absent from normal epithelial cells. The aim of this study was to use telomerase activity as a molecular marker for the detection of cancer cells in blood of patients with breast cancer. Blood samples were collected from 25 women with stage IV breast cancer and 9 healthy volunteers. Peripheral blood mononuclear cells were isolated by using Ficoll/Hypaque. Immunomagnetic beads coated with an epithelial-specific antibody (BerEP4) were used to harvest epithelial cells from peripheral blood mononuclear cells. Telomerase activity was detected in harvested epithelial cells (HECs) using two different telomerase-PCR-ELISA methods. HECs from blood samples of 21 of 25 (84%) patients with breast cancer were telomerase positive. Telomerase activity was undetectable in HECs from the nine healthy volunteers, demonstrating the specificity of the association between telomerase activity in HECs and stage IV breast cancer. Thus, determination of telomerase activity in HECs appears to be a sensitive, specific, and noninvasive approach for detecting circulating epithelial cancer cells in patients with metastatic breast cancer. This method could be of great value in monitoring the cancer cell proliferation during chemotherapy. This study should be now extended to patients with early-stage breast cancer to investigate the role of telomerase expression by HECs and to evaluate its prognostic value.

Telomere dynamics in a human cancer cell line

Telomere maintenance is thought to be essential for immortalization of human cancer cells to compensate for the loss of DNA from the ends of chromosomes and to prevent chromosome fusion. We have investigated telomere dynamics in the telomerase-positive squamous cell carcinoma cell line SCC-61 by marking the ends of chromosomes with integrated plasmid sequences so that changes in the length of individual telomeres could be monitored. Despite having very short telomeres, SCC-61 has a relatively stable genome and few telomere associations. The marked telomeres in different SCC-61 clones have similar mean lengths which show little change with increasing time in culture. Thus, each marked telomere is maintained at a specific length, which we term the equilibrium mean length (EML). The Gaussian distribution in the length of the marked telomeres demonstrates that telomeres continuously fluctuate in length. Consistent with this observation, the mean lengths of the marked telomere in subclones of these cell lines initially differ, but then gradually return to the EML of the original clone with increasing time in culture. The analysis of a clone with two marked telomeres demonstrated that changes in telomere length can occur on each marked telomere independently or coordinately on both telomeres. These results suggest that the short telomeres in many tumor cell lines do not result from an inability to properly maintain telomeres at a specific length.

The incidence of cytogenetically abnormal rogue cells in peripheral blood

PURPOSE

To compare the occurrence of cytogenetically abnormal rogue cells, characterized by a high frequency of chromosome-type aberrations, in people exposed to ionizing radiation and in non-exposed subjects.

MATERIALS AND METHODS

Data on rogue cells from a total of nine cytogenetic studies on radiation-exposed populations and controls were collected from three laboratories in the United Kingdom, France and Finland. The studies were conducted on first-division metaphases of peripheral blood lymphocytes. Solid Giemsa-stained, G- or R-banded and FISH chromosome-painted material was included.

RESULTS

Rogue cells were found both from controls and from exposed subjects. The highest incidence of these cells was observed in a control group of young trainees (1:400), whereas the lowest incidence of rogue cells (1:36 500) was demonstrated in a follow-up study of people accidentally exposed to high levels of ionizing radiation. Rogue cells were found to be distributed non-randomly among individuals; the highest individual frequency was 1 in 50 analysed metaphases.

CONCLUSIONS

The origin of rogue cells is still unclear. The incidence of rogue cells showed a large variability between studies and individuals. No correlation between long-term radiation exposure and the occurrence of rogue cells was demonstrated. Although the presence of rogue cells in astronauts after a 6 month space flight may be attributable to high-LET radiation, the frequencies were not remarkable when compared with those in the other studies in this review.

Increased radiation-induced chromosome breakage after progesterone addition at the G1/S-phase transition

Pregnant females appear to have an increased chromosomal sensitivity to gamma-irradiation. This hypersensitivity was found to parallel the increase of gestation hormone amounts [M. Ricoul, L. Sabatier, B. Dutrillaux, Increased chromosome radiosensitivity during pregnancy, Mutat. Res. 374(1997) 73-78]. An in vitro experiment was developed to study the effect of progesterone. We performed irradiations of whole blood from normal human donors and chromosome were analysed in first generation metaphases. By comparison to untreated controls, all cultures in which progesterone was added around the 24th h of culture exhibited an increased frequency of chromosome rearrangements, principally dicentrics and rings, which confirms the role of progesterone in the results of in vivo studies. BrdU incorporation studies suggested that progesterone was particularly efficient just before the entry into S-phase, which corresponds to the G1/S transition period. Cultures with an increased frequency of chromosome breakage had a slightly higher mitotic index than controls. It is suggested that progesterone may stimulate DNA repair in cells which reached the end of G1-phase with unrepaired breaks. This would allow the cells to enter the S-phase and survive, although some illegitimate repair leads to chromosome rearrangements, visible at the following metaphase.

Role of chromosome instability in long term effect of manned-space missions

Astronauts are exposed to heavy ions during space missions and heavy ion induced-chromosome damages have been observed in their lymphocytes. This raises the problem of the consequence of longer space flights. Recent studies show that some alterations can appear many cell generations after the initial radiation exposure as a delayed genomic instability. This delayed instability is characterized by the accumulation of cell alterations leading to cell transformation, delayed cell death and mutations. Chromosome instability was shown in vitro in different model systems (Sabatier et al., 1992; Marder and Morgan, 1993, Kadhim et al., 1994 and Holmberg et al., 1993, 1995). All types of radiation used induce a chromosome instability, however, heavy ions cause the most damage. The period of chromosome instability followed by the formation of clones with unbalanced karyotypes seems to be shared by cancer cells. The shortening of telomere sequences leading to the formation of telomere fusions is an important factor in the appearance of this chromosome instability.

Chromosomal aberrations induced in human lymphocytes by high-LET irradiation

High linear energy transfer (LET) particles are more efficient than sparsely ionizing radiations in inducing chromosomal aberrations, in particular complex rearrangements. We analysed R-banded chromosome rearrangements in human lymphocytes irradiated with several ions having a wide range of LET (31.3-1435 keV/micron). The frequency of chromosome breaks unrejoined or inferred from observed rearrangements, and of complex rearrangements induced by a single particle, increased with the LET up to about 100-150 keV/micron and seemed to level off for higher LET values. Additional study was focused on damage induced by oxygen ions of three different energies. Significant cell cycle delay, and multiple chromosome rearrangements and breaks were demonstrated using Giemsa and Fluorescence-plus-Giemsa stainings, coupled with chromosome painting. Damage increased with the fluence and the LET, but at the higher LET damage decreased for fluences > 10(7) particles/cm2. Cell death and G2 block might be involved in this phenomenon. Chromosome 1 painting exhibited a high frequency of breaks and complex rearrangements, which would not have been detected using a standard staining. Complex rearrangements were induced by as few as one particle per cell nucleus and may be considered as a biological fingerprint of high-LET irradiation.

Strong decrease in biotin content may correlate with metabolic alterations in colorectal adenocarcinoma

Short-chain fatty acids are an important source of energy for colonocytes. One of these is propionate, which is metabolized through carboxylation by propionyl-CoA carboxylase (PCC), an enzyme encoded by 2 genes, PCCA and PCCB. The co-factor of this reaction is biotin, a product of intestinal bacterial metabolism, as is propionate. Despite detailed knowledge about the metabolic effects and physiology of biotin, the relative amounts of this vitamin in normal colonic mucosae and in tumour tissue remains quite unknown. The biotin content in normal and cancerous cells from the distal digestive tract was examined on 10 pairs of tissue specimens of colorectal cancer and adjacent normal mucosae using reflectance in situ hybridization (RISH). Having observed a high biotin content in colon mucosae and a low content in colorectal-cancer cells, we then studied the transcription levels of PCCA and PCCB genes in 9 colorectal cancers and the corresponding mucosae. In all cases, the levels of mRNA were lower in colorectal cancers than in normal mucosae, the decrease being always more marked for PCCB than for PCCA. In normal mucosae and in adenocarcinoma cancer cells, PCCA and PCCB transcription levels were strongly related to the amount of biotin detected, but not to the number of chromosomes 13 (which carries PCCA) or 3 (which carries PCCB).

Dosimetric and cytogenetic studies of multiple radiation-induced meningiomas for a single patient

No criteria are currently available to determine the spontaneous or radiation-induced origin of a malignant tumor occurring in a previously irradiated area. This study presents the dosimetric and cytogenetic analysis of meningiomas diagnosed in irradiated brain areas from a single patient and a discussion of the karyotypes of spontaneous meningiomas and radiation-induced tumors published in the literature.