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PubMed1995

Telomere dynamics and telomerase activation in tumor progression: prospects for prognosis and therapy.

Eukaryotic telomeres provide a reservoir of redundancy to compensate for incomplete replication of chromosome ends. In multicellular eukaryotes, they are eroded by a varying number of base pairs at every cell division. When telomere repeats are critically shortened, DNA damage response pathways involving p53 (and in some cell types retinoblastoma protein) are invoked, leading to "M1 senescence" in normal cells; cancer cells, which frequently lack normal p53 and RB functions, often develop chromosomal instability leading to telomeric associations, ring chromosomes, and breakage-fusion-bridge cycles. These consequences of telomere erosion exert selection pressure for activation of the ribonucleoprotein enzyme telomerase, which adds new telomeric repeats at chromosome ends, and in vertebrates normally is active only in the germ line and the early embryo. Somatic cells that reactivate telomerase in vitro or in vivo become immortal. Telomerase activity has been found in many advanced and metastatic human cancers, suggesting that telomerase-dependent M2 immortalization may contribute to metastatic potential. When mammalian telomerases are isolated and their genes cloned and sequenced, the localization of telomerase expression in tumors may provide prognostic indicators of metastatic potential. The abrogation of telomerase function by pharmacological inhibition, genetic disruption, or repression of gene expression is a potential avenue of antimetastatic therapy.

Base Sequence↗
PubMedDate not supplied

[Genetic and somatic effects of ionizing radiation in humans and animals (comparative aspect)].

Genetic effects of ionizing radiation in the progeny of exposed parents could be conventionally subdivided on three main types. 1. Severe developmental disorders (fetus death, stillbirth, early postnatal mortality, malformation, hereditary disease, sterility). These effects are known to be caused by so called "gross" mutations (genomic, chromosomal, those of essential genes) with dominant harmful effects. Although found in rodents, insects, fishes they have not been found in humans. The proposal is made that the higher reproductive potency of a species the higher its tolerance for defective organisms. Due to strong selection against severe defects at the earliest stage of pregnancy, this genetic effect of radiation is likely to be difficult to detect in people. 2. Increased cancer risk manifested as elevated incidence of spontaneous tumors and increased sensitivity to carcinogenic agents. 3. Decreased fitness (non-carcinogenic negative health effects). These two last types of radiation genetic effects are presumably due to instability and functional inferiority of cell genome in the progeny of irradiated parents. The genetic background of these effects is suggested to be the load of induced minor mutations in regulatory genes (mini-, microsatelite loci) or/and epigenomic rearrangements of DNA in parental germ cells transmitted to progeny. These radiation genetic effects are much more obvious in animals as compared to humans. Apparently, they are difficult to find in humans because of their essential dependence on promotive (life style) factors, which are impossible to control in the offspring of irradiated people. A comparison of somatic (in irradiated organisms) and genetic (in the progeny of irradiated parents) effects of radiation provide evidence on the phenomenological as well as pathogenic similarity.

Animals↗
PubMed2003

DNA damage as a new emerging risk factor in atherosclerosis.

Atherosclerosis is the leading cause of illness and death in Western societies. It is now clear that the disease is a result of a chronic fibroproliferative-inflammatory response of the arterial intima leading to the formation of atherosclerotic plaque. There is, however, strong experimental evidence for a "mutation theory of atherosclerosis," underlining the similarity between atherosclerotic and carcinogenic processes. This review provides an overview of the studies that support the role of genetic alterations in the disease. The demonstration of microsatellite instability and loss of heterozygosity in smooth muscle cells of human plaques suggests that genomic destabilization may play a pivotal role in atherosclerotic mechanisms. Furthermore, the use of accepted biomarkers of carcinogenic exposure-such as DNA adducts and cytogenetic end points-recently has provided evidence consistent with the view that somatic cell alterations are critical in atherogenic process. It follows that the study of DNA damage may provide new insights into the pathogenesis of atherosclerosis and lead to the development of novel therapeutic approaches.

Arteriosclerosis↗
PubMed2001

Genetics of nonmelanoma skin cancer.

Cancer is in essence a genetic disease characterized by genomic instability. Unlike classic genetic syndromes in which a single inherited mutation is often sufficient to determine the perturbed phenotype, most cancers, especially solid tumors, develop after an accumulation of multiple genetic lesions. Inherited mutations that predispose individuals to cancer formation are termed germline, while acquired mutations that contribute to tumor development are designated somatic. Bona fide hereditary cancers account for only a small proportion of all documented cancers. Most tumors result from mutations caused by inherent infidelities in DNA replication, carcinogens, or defects in the DNA reparative apparatus. When mutations occur in critical growth regulatory genes, variations in cellular proliferation and survival contribute to the selection of dominant tumor population(s). Furthermore, these mutations may alter the antigenic properties of the cancerous cell and encourage escape from the host response. Thus, cancer is evolution at the microscopic level.

Carcinoma, Adenoid Cystic↗
PubMed1978

Analysis of banding patterns and mosaic configurations in a case of ring chromosome 15.

Cytogenetic studies on lymphocytes from a 14-year-old mentally retarded girl with somatic anomalies suggestive of a chromosomal abnormality revealed a ring chromosome 15. The long arm of the defective chromosome is broken at band q24 or q25. The silver staining technique for nucleolus organizer regions showed that the ring had lost the achromatic stalk and the satellite. The chromosomal mosaicism resulting from the structural instability of the ring chromosome was analyzed and compared with 6 cases reported in the literature. It is proposed that the clinical manifestations in the different patients with ring chromosome 15 result from both the deficiency in the long arm and the mosaic configurations.

Adolescent↗
PubMed2005

Single cell amplification methods for the study of cancer and cellular ageing.

Accumulation of somatic mutations takes place in ageing organisms and during malignant cell transformation and is accompanied by changes in cellular phenotype and function. The genomic damage that underlies the ageing phenotype is thought to occur stochastically. In cancer some changes causing cellular deregulation will be selected by clonal expansion but due to increased genetic instability it is still unknown which aberrations initiated sporadic cancer development. Thus, in ageing and cancer research detection of stochastically arising mutational events within a genome of 3x10(9) base pair requires global screening techniques and the analysis on a single cell level in contrast to pooled DNA or pooled RNA. We therefore focus on the development of techniques that enable the genome wide study of single cells. We successfully applied global amplification methods to study DNA and mRNA of single cancer cells that disseminated to the bone marrow of carcinoma patients early in disease progression. Our results emphasize the importance to study age-related diseases such as cancer on the level of single cells.

Animals↗
PubMed2003

The emerging phenotype of the testicular carcinoma in situ germ cell.

This review summarises the existing knowledge on the phenotype of the carcinoma in situ (CIS) cell. CIS is a common pre-invasive precursor of testicular germ cell tumours of adolescents and young adults. These tumours display a variety of histological forms. Classical seminoma proliferates along the germ cell lineage, whereas embryonal carcinoma retains embryonic features and readily differentiates into teratomas that resemble various somatic cell lineages. A thorough review of the gene expression in CIS cells in comparison to normal testicular germ cells and overt tumours supports the view that CIS is a common precursor for both tumour types. Impaired cell differentiation resulting in a partial retention of the embryonic features, associated with an increasing genomic instability may be responsible for a remarkable phenotypic heterogeneity of CIS cells. Depending on the degree of differentiation and pluripotency, CIS cells found in adult patients seem to be predestined for further malignant progression into one or the other of the two main types of overt tumours. A new concept of phenotypic continuity of differentiation of germ cells along germinal lineage with a gradual loss of embryonic features based on the analysis of gene expression in all types of germ cells during their ontogeny is presented in this review. The data point out that despite the phenotypic continuum of gene expression, there are two periods of rapid changes of gene expression: first at the transition from primordial germ cells to pre-spermatogonia, and later during the pubertal switch from the mitotic to meiotic cell division. The persistent expression of embryonic traits in CIS cells, and the high expression of the cell cycle regulators that are typical of mitotic germ cells support our long-standing hypothesis that CIS cells originate from primordial germ cells or gonocytes and not from germ cells in the adult testis.

Adolescent↗
PubMed2000

Telomere length maintenance in aging and carcinogenesis.

Normal somatic cells have a finite number of divisions, a limited capacity to proliferate. Human telomeres, the long DNA TTAGGG repeats at the ends of chromosomes, are considered a molecular clock marker. The gradual and progressive telomere shortening at each replicative cycle is associated, through the activation of pRB and p53 pathways and genomic instability, to the replicative senescence, a non-dividing state and widespread cell death. Activation of telomere maintenance [telomerase; or alternative lengthening of telomeres mechanisms (ALT), or other adaptive responses] can revert this program. Although not completely known, several mechanisms and modulating agents may be able to up and down-regulate telomere length and its maintenance. Chemopreventive therapies for the up-regulation of telomerase activity, able to prolong the life of cell cultures in a phenotypically youthful state, could have important applications in research and medicine. On the contrary the therapeutic down-regulation of telomerase activity may be used in cancer therapy. Telomerase expression per se is not oncogenic, but telomere shortening and maintenance seem to be crucial events in tumor formation. Thus a particular focus has been pointed out relatively to the immortalization of normal or potential pre-cancerous cells. With the extension of life span the probability to get in contact with carcinogens increases, genetic instability, oncogene activation and/or onco-suppressor gene inactivation (i.e. p53, pRB, ras): the cancer transformation can be then induced in predisposed cells, depending on their genetic context, by the activation of telomere maintenance. Pharmacological intervention may be able to modulate the rate of living, by increasing life span of few specific target cells, or decreasing it in proliferating . Because of the unknown state of the enormous cell number of the human organism, is it safe to extend the human life span by therapeutic agents?

Aging↗
PubMed2002

The microtubule-destabilizing kinesin XKCM1 regulates microtubule dynamic instability in cells.

The dynamic activities of cellular microtubules (MTs) are tightly regulated by a balance between MT-stabilizing and -destabilizing proteins. Studies in Xenopus egg extracts have shown that the major MT destabilizer during interphase and mitosis is the kinesin-related protein XKCM1, which depolymerizes MT ends in an ATP-dependent manner. Herein, we examine the effects of both overexpression and inhibition of XKCM1 on the regulation of MT dynamics in vertebrate somatic cells. We found that XKCM1 is a MT-destabilizing enzyme in PtK2 cells and that XKCM1 modulates cellular MT dynamics. Our results indicate that perturbation of XKCM1 levels alters the catastrophe frequency and the rescue frequency of cellular MTs. In addition, we found that overexpression of XKCM1 or inhibition of KCM1 during mitosis leads to the formation of aberrant spindles and a mitotic delay. The predominant spindle defects from excess XKCM1 included monoastral and monopolar spindles, as well as small prometaphase-like spindles with improper chromosomal attachments. Inhibition of KCM1 during mitosis led to prometaphase spindles with excessively long MTs and spindles with partially separated poles and a radial MT array. These results show that KCM1 plays a critical role in regulating both interphase and mitotic MT dynamics in mammalian cells.

Animals↗
PubMed2003

In vitro aging of rat lung cells. Downregulation of telomerase activity and continuous decrease of telomere length are not incompatible with malignant transformation.

Most normal mammalian somatic cells cultivated in vitro enter replicative senescence after a finite number of divisions, as a consequence of the progressive shortening of telomeres during proliferation that reflects one aspect of organism/cellular aging. The situation appears more complex in rodent cells due to physiological telomerase expression in most somatic normal tissues, great telomere length, and the difficulties of finding suitable in vitro culture conditions. To study in vitro aging of rat lung epithelial cells, we have developed primary culture conditions adapted to rat fresh lung explants and have studied for 1 year (50 passages) the changes in cellular proliferation and mortality, genetic instability, telomerase activity, telomere length, and tumorigenic potential. We have observed an absence of senescence and/or crisis, a transient genetic instability, the persistence of a differentiated Clara cell phenotype, a steady decrease in telomerase activity followed by a low residual activity together with a continuous decrease in telomere length, a constant rate of proliferation, and the acquisition of tumorigenic potential. The bypass of the growth arrest and the acquisition of long-term growth properties could be explained by the loss of p16(INK4a) expression, the ARF/p53 pathway not being altered. In conclusion, these results clearly indicate that, in rat lung epithelial cells, in vitro transformation and acquisition of tumorigenic properties can occur even if the telomere length is still decreasing and telomerase activity remains downregulated.

Animals↗
PubMed2002

BRCA2 and pancreatic cancer.

Many factors, including a family history of cancer, have been implicated in the development of pancreatic cancer. Among these factors, germline BRCA2 mutations have been clearly associated with the development of this disease, while mutations in BRCA1 appear to have a limited role. Patients with pancreatic cancer and germline BRCA2 mutations tend to be Ashkenazi Jewish, have a younger than average age of onset, and in many cases, lack family history for breast, ovarian, or pancreatic cancers. In addition, somatic mutations of BRCA2 appear to be rare in tumors of the pancreas. The mechanism by which mutant BRCA2 contributes to development of pancreatic cancers is not well understood. However, it appears that inactivation of several independent functions of BRCA2 including regulation of gene transcription, chromatin remodeling, cell growth, DNA damage repair, and chromosomal instability may provide a pathophysiological basis for the association of BRCA2 mutations and pancreatic cancer.

BRCA2 Protein↗
PubMed1989

The Japan Society of Human Genetics award lecture. Cytogenetic aspects of cancer-predisposing genes.

Some human monogenic syndromes are characterized by a high cancer propensity, and provide a pathway to the understanding of genetic origin of human cancers. In this review, cytogenetic insights into the Fanconi's anemia (FA) and retinoblastoma (RB) genes have been presented as the model for recessively and dominantly transmitted cancer-predisposing genes, respectively. Some recessively transmitted genes are unequivocally associated with abnormalities in DNA metabolisms and homozygosity increases the genome instability, and some dominantly inherited genes are categorized into loss-of-function mutation of tumor suppressing genes. While the identified syndromes themselves are uncommon and constitute a minor fraction in population, the heterozygote expression of recessive genes is our major concern of genetic predisposition to cancer, and mutation of tumor suppressing genes, identified as somatic mutation, plays a crucial role in the development of a variety of common cancers. Moreover, their possible non-Mendelian inheritance of mutational susceptibility leads us to an even more rewarding area of cancer genetics.

Eye Neoplasms↗
PubMed2001

Demethylation, reactivation, and destabilization of human fragile X full-mutation alleles in mouse embryocarcinoma cells.

The major causes of fragile X syndrome are mutational expansion of the CGG repeat in the FMR1 gene, hypermethylation, and transcriptional silencing. Most fragile X embryos develop somatic mosaicism of disease-causing "full" expansions of different lengths. Homogeneity of the mosaic patterns among multiple tissues in the same individual indicates that these previously unstable expansions acquire mitotic stability early in fetal life. Since mitotic stability is found strictly associated with hypermethylation in adult tissues, current theory has fixed the time of instability to developmental stages when fully expanded CGG repeats exist in an unmethylated state. We used murine embryocarcinoma (EC) cells (PC13) as a model system of pluripotent embryonic cells. Hypermethylated and unmethylated full expansions on human fragile X chromosomes were transferred from murine A9 hybrids into EC cells, by means of microcell fusion. As demonstrated in the present study for the first time, even full expansion alleles that were fully methylated and stable in the donors' fibroblasts and in A9 became demethylated, reactivated, and destabilized in undifferentiated EC hybrids. When destabilized expansions were reintroduced from EC cells into A9, instability was reversed to stability. Our results strongly support the idea that fully expanded alleles are initially unstable and unmethylated in the human embryo and gain stability upon genetic or epigenetic change of the embryonic cells.

Alleles↗
PubMedDate not supplied

A tiger mouse and relatives. Variants caused by an activated transposable element?

In a laboratory-bred population of wild Peruvian house mice, one male had an excessive rate of non-pairing of the X and Y chromosomes. After crossing him with laboratory stock mice, a mouse of very unusual phenotype appeared from a yellow (AyA) mother. He was yellow with black dorsal stripes; hence Tiger. He was mated to many females, and inbred F2 and F3 generations were raised. There were no more tiger phenotypes, but his F1 contained an excess of black-and-tans over yellows, showing him to be a gonosomic mosaic Ayat/atat; the homozygous cell line probably arose from the heterozygous one. The mitotic karyotype was normal. Some of Tiger's mates were of known allozyme types and their progeny were scored. The allozyme segregations were normal, except at the Es-3 locus (esterase-3), for which Tiger was typed as homozygous. Several unusual events among Tiger's close relatives included a mutation to an unstable pattern mutant, three probable translocations, and several cases of somatic defect. All unusual mice derived from Tiger's yellow mother, whose genome was one-quarter Peruvian. Yellow is associated with an ecotropic murine leukemia virus. The Peru genome is characterized by a high occurrence of mutation and aberrant karyotypes. It is suggested that something from the Peru genome in Tiger's mother caused instability of the DNA sequence associated with yellow, with related disturbance at different locations thereafter. The nature of this instability, and of the Peru genome, is discussed.

Animals↗
PubMed2007

The lethality of Ku86 (XRCC5) loss-of-function mutations in human cells is independent of p53 (TP53).

Ku86 is one of the two regulatory subunits of the DNA-PK (DNA-dependent protein kinase) complex that is required for DNA double-strand break repair in mammalian cells. In a previous study, by means of somatic gene targeting, we generated human cell lines deficient in Ku86 (XRCC5). Heterozygous human Ku86 cells exhibited a wide array of haploinsufficient phenotypes, including sensitivity to ionizing radiation, defects in DNA-PK and DNA end-binding activities, elevated levels of p53 (TP53) and gamma-H2AX foci, and a defect in cell proliferation with an increase in the frequency of aneuploid cells. Here we demonstrate that the overexpression of a human Ku86 cDNA complemented the deficiencies of these cells to wild-type levels. In contrast, Ku86 overexpression only partially rescued the telomere defects characteristic of Ku86 heterozygous cells and did not rescue their genetic instability. Additionally, in stark contrast to every other species described to date, we had shown earlier that homozygous human Ku86(-/-) cells are inviable, because they undergo 8 to 10 rounds of cell division before succumbing to apoptosis. The tumor suppressor protein p53 regulates the DNA damage response in mammalian cells and triggers apoptosis in the face of excessive DNA damage. Correspondingly, ablation of p53 expression has repeatedly been shown to significantly ameliorate the pathological effects of loss-of-function mutations for a large number of DNA repair genes. Surprisingly, however, even in a p53-null genetic background, the absence of Ku86 proved lethal. Thus the gene encoding Ku86 (XRCC5) is an essential gene in human somatic cells, and its absence cannot be suppressed by the loss of p53 function. These results suggest that Ku86 performs an essential role in telomere maintenance in human cells.

Cell Proliferation↗
PubMed2001

A full-length and potentially active LINE element is integrated polymorphically within the IGL locus in a genomically unstable region of chromosome 22.

Leukemic cells of a patient diagnosed with chronic myeloid leukemia (CML) showed a complex BCR-ABL1 rearrangement hidden within a normal appearing karyotype. Previous molecular studies had established that the 3' BCR had recombined at a novel site within the variable region of the immunoglobulin lambda locus ( IGL). A segment of DNA mapping very close to the site of the IGL/3' BCR recombination recognized a previously undescribed insertion polymorphism. A combination of molecular hybridization studies and long-range polymerase chain reaction was used to isolate a 6-kb full-length long interspersed nuclear element (LINE or L1), here designated L1(IGL), which occupies 19% of alleles in the general population. Although unclonable, DNA sequence analysis by a primer walking approach established that L1(IGL) has features characteristic of an actively retrotransposing element. The L1(IGL) element has a 5' untranslated region, two open reading frames (ORF-1 and ORF-2), a 3' untranslated region and terminates in a poly-A tail. We compared the DNA sequence and the predicted amino acid sequence of L1(IGL) with a consensus sequence compiled from seven reported active L1 elements. This analysis indicated that L1(IGL) has high potential for involvement in as yet undetermined somatically and constitutionally acquired disease, not only through recombination mechanisms, but also through retrotransposition events. This full-length L1 element maps close within the IGLlocus to L1.2, one of only nine active L1 elements that have been reported so far. L1(IGL) and L1.2 map within a wider and well-recognized region of genomic instability on chromosome 22.

Base Sequence↗
PubMed1999

Climacteric symptoms and sleep quality.

OBJECTIVE: To evaluate the effect of climacteric vasomotor symptoms on sleep quality measured by self-report and polysomnography in postmenopausal women. METHODS: Seventy-one healthy postmenopausal women were recruited, of whom 63 completed the study. Each subject recorded climacteric symptoms and subjective sleep quality for 14 days. Sleep quality was evaluated objectively by all-night polysomnography using the static charge-sensitive bed. RESULTS: During polysomnography, a high frequency of climacteric vasomotor symptoms was not associated with changes in sleep latency, percentage of sleep stages, number of arousals, sleep efficiency, or total sleep time. However, a high frequency of climacteric vasomotor symptoms (range 0-8.9, r = .60, P < .001), somatic symptoms (range 0-5.0, r = .25-.44, P < .05), and mental symptoms (range 0-5.0, r = .41-.51, P < .001) was related to impaired subjective sleep quality. In stepwise regression analysis, 32% of the impairment in subjective sleep quality was explained by vasomotor symptoms (P < .001), 14% by palpitations (P < .001), and 4% by mood instability (P = .029). High body mass index predicted impaired objective sleep quality, such as prolonged latencies to stage-2 sleep (r = .27, P = .031) and slow-wave sleep (r = .51, P = .003) and decreased oxygen saturations (r = -.54, P < .001). Older women had decreased sleep efficiency (r = -.27, P = .030) and lower oxygen saturations (r = -.36, P = .004). Serum estradiol level had only a minor effect on objective sleep quality. CONCLUSION: Impaired subjective sleep quality associated with climacteric vasomotor symptoms did not manifest as abnormalities in polysomnographic sleep recordings. Body mass index and age appeared to have the strongest effect on objective sleep quality.

Aged↗
PubMed1994

Genetic instability of plant tissue cultures: breakdown of normal controls.

Plants regenerated from relatively undifferentiated callus cultures possess a vast array of genetic changes. Such variations can result in useful agricultural and horticultural products. For other purposes, however, variations in traits other than those of interest may be undesirable--for example, using cultured cells for genetic engineering. Any steps made toward understanding the basis of tissue culture-induced genetic variation should be helpful in developing a more stable and manipulatable somatic cell system. This review provides a glimpse at the specific kinds of genetic changes encountered among regenerated plants and their progeny. Included among these variations are cytosine methylation alterations of the genome. The repeat-induced point mutation (RIP) phenomenon, reported for filamentous fungi, is invoked to provide a framework to consider the origin of variation in plant tissue cultures.

5-Methylcytosine↗