Ionizing radiation activates the ATM kinase throughout the cell cycle

The ATM protein kinase is a critical intermediate in a number of cellular responses to ionizing irradiation (IR) and possibly other stresses. ATM dysfunction results in abnormal checkpoint responses in multiple phases of the cell cycle, including G1, S and G2. Though downstream targets of the ATM kinase are still being elucidated, it has been demonstrated that ATM acts upstream of p53 in a signal transduction pathway initiated by IR and can phosphorylate p53 at serine 15. The cell cycle stage-specificity of ATM activation and p53Ser15 phosphorylation was investigated in normal lymphoblastoid cell line (GM536). Ionizing radiation was found to enhance the kinase activity of ATM in all phases of the cell cycle. This enhanced activity was apparent immediately after treatment of cells with IR, but was not accompanied by a change in the abundance of the ATM protein. Since IR activates the ATM kinase in all phases of the cell cycle, DNA replication-dependent strand breaks are not required for this activation. Further, since p53 protein is not directly required for IR-induced S and G2-phase checkpoints, the ATM kinase likely has different functional targets in different phases of the cell cycle. These observations indicate that the ATM kinase is necessary primarily for the immediate response to DNA damage incurred in all phases of the cell cycle.     

Telomere stability correlates with longevity of human beings exposed to ionizing radiations

Normal somatic cells have a finite number of divisions, a limited capacity to proliferate. Human telomeres contain TTAGGG repeats which 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. There is no information available about telomere status in individuals who live long and have been exposed to ionizing radiations (IR). To determine the telomere stability, we examined telomeres at metaphase, G2-type chromosome aberrations after IR treatment and karyotypic analysis of 15 individuals. Three individuals were above the age of 80 years and 1 among the 3 was estimated to have received more than 10 Gy of occupational exposure about 30 years back. The other 12 were cancer patients that had received more than 50 Gy of gamma-radiation for therapeutic purposes. No telomere instability or defective G2 chromosome repair was found in 3 individuals above the age of 80 years. Whereas, 3 out of 7 prostate and 1 out of 5 breast cancer patients showed higher G2-type chromosome damage as well as a high frequency of telomeric association (also known as chromosome end associations) along with frequent loss of telomeres. Present studies demonstrate that telomere stability along with normal G2 chromosome repair correlates with the longevity of human beings, whereas defective G2 chromosome repair and telomere instability correlate with the radiotherapy related late toxicity.     

Two functional copies of the DGCR6 gene are present on human chromosome 22q11 due to a duplication of an ancestral locus

The DGCR6 (DiGeorge critical region) gene encodes a putative protein with sequence similarity to gonadal (gdl), a Drosophila melanogaster gene of unknown function. We mapped the DGCR6 gene to chromosome 22q11 within a low copy repeat, termed sc11.1a, and identified a second copy of the gene, DGCR6L, within the duplicate locus, termed sc11.1b. Both sc11.1 repeats are deleted in most persons with velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS), and they map immediately adjacent and internal to the low copy repeats, termed LCR22, that mediate the deletions associated with VCFS/DGS. We sequenced genomic clones from both loci and determined that the putative initiator methionine is located further upstream than originally described, but in a position similar to the mouse and chicken orthologs. DGCR6L encodes a highly homologous, functional copy of DGCR6, with some base changes rendering amino acid differences. Expression studies of the two genes indicate that both genes are widely expressed in fetal and adult tissues. Evolutionary studies using FISH mapping in several different species of ape combined with sequence analysis of DGCR6 in a number of different primate species indicate that the duplication is at least 12 million years old and may date back to before the divergence of Catarrhines from Platyrrhines, 35 mya. These data suggest that there has been selective evolutionary pressure toward the functional maintenance of both paralogs. Interestingly, a full-length HERV-K provirus integrated into the sc11.1a locus after the divergence of chimpanzees and humans.     

Spectral karyotyping identifies recurrent complex rearrangements of chromosomes 8, 17, and 20 in osteosarcomas

Conventional cytogenetic studies have shown that osteosarcomas (OSs) are often highly aneuploid, with a large number of both structural and numerical chromosomal alterations. To investigate the complexity of OS karyotypes in detail, we applied spectral karyotyping (SKY) to a series of 14 primary OS tumors and four established OS cell lines. A total of 531 rearrangements were identified by SKY, of which 300 breakpoints could be assigned to a specific chromosome band. There was an average of 38.5 breakpoints identified by SKY per primary tumor. Chromosome 20 was involved in a disproportionately high number of structural rearrangements, with 38 different aberrations being detected. Chromosomal rearrangements between chromosomes 20 and 8 were evident in four tumors. FISH analysis using a 20q13 subtelomeric probe identified frequent involvement of 20q in complex structural rearrangements of OS cell lines. Characterization of the structural aberrations of chromosomes 8 and 17 by use of SKY demonstrated frequent duplication or partial gains of chromosome bands 8q23-24 and 17p11-13. Other chromosomes frequently involved in structural alteration were chromosomes 1 (47 rearrangements) and 6 (38 rearrangements). Centromeric rearrangements often involving chromosomes 1, 6, 13, 14, 17, and 20 were present. Four of the 14 primary OS tumors were characterized by nonclonal changes that included both structural and numerical alterations. In summary, OS tumors have a very high frequency of structural and numerical alterations, compounded by gross changes in ploidy. This intrinsic karyotype instability leads to a diversity of rearrangements and the acquisition of composite chromosomal rearrangements, with the highest frequency of alteration leading to gain of 8q23-24 and 17p11-13 and rearrangement of 20q. These findings suggest that specific sequences mapping to these chromosomal regions will likely have a role in the development and progression of OS.     

The role of Alu repeat clusters as mediators of recurrent chromosomal aberrations in tumors

There is increasing evidence for the involvement of repetitive DNA sequences as facilitators of some of the recurrent chromosomal rearrangements observed in human tumors. The high densities of repetitive DNA, such as Alu elements, at some chromosomal translocation breakpoint regions has led to the suggestion that these sequences could provide hot spots for homologous recombination, and could mediate the translocation process and elevate the likelihood of other types of chromosomal rearrangements taking place. The Alu core sequence itself has been suggested to promote DNA strand exchange and genomic rearrangement, and it has striking sequence similarity to chi (which has been shown to stimulate recBCD-mediated recombination in Escherichia coli). Alu repeats have been shown to be involved in the generation of many constitutional gene mutations in meiotic cells, attributed to unequal homologous recombination and consequent deletions and/or duplication events. It has recently been demonstrated that similar deletion events can take place in neoplasia because several types of leukemia-associated chromosomal rearrangements frequently have submicroscopic deletions immediately adjacent to the translocation breakpoint regions. Significantly, these types of deletions appear to be more likely to take place when the regions subject to rearrangement contain a high density of Alu repeats. With the completion of the Human Genome Project, it will soon be possible to create more comprehensive maps of the distribution and densities of repetitive sequences, such as Alu, throughout the genome. Such maps will offer unique insights into the relative distribution of cancer translocation breakpoints and the localization of clusters of repetitive DNA.     

Double interatrial septum with persistent interatrial chamber: A rare but clinically significant anomaly

Double interatrial septum is an extremely rare congenital anomaly which forms a distinguished midline interatrial chamber between the two atria. The objective of this case report is to highlight this unusual anomaly and to discuss the potential complications of this condition. We report the case of a 6-year-old asymptomatic child who underwent cardiac evaluation for a soft systolic murmur eventually being diagnosed with double interatrial septum.     

Diagnosis of intraventricular cysticercosis by magnetic resonance imaging: improved detection with three-dimensional spoiled gradient recalled echo sequences

Neurocysticercosis (NCC) is caused when the cysticercus larvae of Taenia solium infect the central nervous system. The larvae usually land in the parenchymal tissue, but quite rarely can lodge in the ventricles and cisterns of the brain. Unlike parenchymal NCC, it is not easy to demonstrate the cysticercus cysts within the cerebrospinal fluid spaces. Computed tomography and even conventional MR sequences can fail to detect such cysts. However, obtaining three-dimensional spoiled gradient recalled echo imaging sequences can help in improving the detection of intraventricular NCC, as is borne out by a case described in the present report. The use of such special MR sequences is therefore strongly advocated in suspected cases of intraventricular NCC.     

Urodynamic effects of intravesical administration of the new small/intermediate conductance calcium activated potassium channel activator NS309 in freely moving, conscious rats

PURPOSE: We investigated the effects of the new K+ channel activator NS309, which acts on small and intermediate conductance Ca2+ activated K+ channels, on detrusor activity in normal rats. MATERIALS AND METHODS: NS309 was given intravesically at different concentrations to conscious female Sprague-Dawley rats undergoing continuous cystometry. The effects of the drug on oxyhemoglobin induced detrusor overactivity were also tested. RESULTS: Intravesical NS309 (100, 300 and 1,000 ng ml(-1)) increased bladder capacity, micturition volume and intercontraction intervals in a concentration dependent way. NS309 (1,000 ng ml(-1)) given intravesically for 1 hour before instillation of intravesical oxyhemoglobin (250 microM) decreased or completely prevented the detrusor overactivity induced by oxyhemoglobin. CONCLUSIONS: Opening small and intermediate conductance Ca2+ activated K+ channels with NS309 given intravesically increased bladder capacity, micturition volume and intercontraction intervals in a concentration dependent way and prevented oxyhemoglobin induced detrusor overactivity. Results suggest that these channels can be interesting targets for drugs aiming to control micturition.     

A chromosomal region 7p11.2 transcript map: its development and application to the study of EGFR amplicons in glioblastoma

Cumulative information available about the organization of amplified chromosomal regions in human tumors suggests that the amplification repeat units, or amplicons, can be of a simple or complex nature. For the former, amplified regions generally retain their native chromosomal configuration and involve a single amplification target sequence. For complex amplicons, amplified DNAs usually undergo substantial reorganization relative to the normal chromosomal regions from which they evolve, and the regions subject to amplification may contain multiple target sequences. Previous efforts to characterize the 7p11.2 epidermal growth factor receptor ) amplicon in glioblastoma have relied primarily on the use of markers positioned by linkage analysis and/or radiation hybrid mapping, both of which are known to have the potential for being inaccurate when attempting to order loci over relatively short (<1 Mb) chromosomal regions. Due to the limited resolution of genetic maps that have been established through the use of these approaches, we have constructed a 2-Mb bacterial and P1-derived artificial chromosome (BAC-PAC) contig for the EGFR region and have applied markers positioned on its associated physical map to the analysis of 7p11.2 amplifications in a series of glioblastomas. Our data indicate that EGFR is the sole amplification target within the mapped region, although there are several additional 7p11.2 genes that can be coamplified and overexpressed with EGFR. Furthermore, these results are consistent with EGFR amplicons retaining the same organization as the native chromosome 7p11.2 region from which they are derived.