Ataxia telangiectasia-mutated gene product inhibits DNA damage-induced apoptosis via ceramide synthase

DNA double-stranded breaks (dsb) activate surveillance systems that identify DNA damage and either initiate repair or signal cell death. Failure of cells to undergo appropriate death in response to DNA damage leads to misrepair, mutations, and neoplastic transformation. Pathways linking DNA dsb to reproductive or apoptotic death are virtually unknown. Here we report that metabolic incorporation of 125I-labeled 5-iodo-2'deoxyuridine, which produces DNA dsb, signaled de novo ceramide synthesis by post-translational activation of ceramide synthase (CS) and apoptosis. CS activation was obligatory, since fumonisin B1, a fungal pathogen that acts as a specific CS inhibitor, abrogated DNA damage-induced death. X-irradiation yielded similar results. Furthermore, inhibition of apoptosis using the peptide caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone did not affect CS activation, indicating this event is not a consequence of induction of apoptosis. ATM, the gene mutated in ataxia telangiectasia, is a member of the phosphatidylinositol 3-kinase family that constitutes the DNA damage surveillance/repair system. Epstein-Barr virus-immortalized B cell lines from six ataxia telangiectasia patients with different mutations exhibited radiation-induced CS activation, ceramide generation, and apoptosis, whereas three lines from normal patients failed to manifest these responses. Stable transfection of wild type ATM cDNA reversed these events, whereas antisense inactivation of ataxia telangiectasia-mutated gene product in normal B cells conferred the ataxia telangiectasia phenotype. We propose that one of the functions of ataxia telangiectasia-mutated gene product is to constrain activation of CS, thereby regulating DNA damage-induced apoptosis.

Phylogenetic reconstruction based on low copy DNA sequence data in an allopolyploid: the B genome of wheat

Study of bread wheat (Triticum aestivum) may help to resolve several questions related to polyploid evolution. One such question regards the possibility that the component genomes of polyploids may themselves be polyphyletic, resulting from hybridization and introgression among different polyploid species sharing a single genome. We used the B genome of wheat as a model system to test hypotheses that bear on the monophyly or polyphyly of the individual constituent genomes. By using aneuploid wheat stocks, combined with PCR-based cloning strategies, we cloned and sequenced two single-copy-DNA sequences from each of the seven chromosomes of the wheat B genome and the homologous sequences from representatives of the five diploid species in section Sitopsis previously suggested as sister groups to the B genome. Phylogenetic comparisons of sequence data suggested that the B genome of wheat underwent a genetic bottleneck and has diverged from the diploid B genome donor. The extent of genetic diversity among the Sitopsis diploids and the failure of any of the Sitopsis species to group with the wheat B genome indicated that these species have also diverged from the ancestral B genome donor. Our results support monophyly of the wheat B genome.

Disposition of L-732,531, a potent immunosuppressant, in rats and baboons

L-732,531 is a semi-synthetic analog of the macrolide tacrolimus (Prograf(R)). Like tacrolimus, L-732,531 is a potent immunosuppressant. In this study, its absorption, distribution, metabolism, and excretion were studied in rats and baboons. In rats, its blood and plasma levels were similar, whereas in baboons, its blood levels were, on average, twice as high as those in plasma. This was consistent with the in vitro blood-to-plasma ratio of L-732, 531, which in these two species, as well as in humans, was much lower than that of tacrolimus and showed a minimal concentration dependence. After iv administration to rats, the blood and plasma clearance of L-732,531 decreased from approximately 60 ml/min/kg at 0.2 mg/kg to 30 ml/min/kg when dosed at 1 and 3 mg/kg. After oral administration, plasma area under the concentration vs. time curve (AUC) and maximal plasma concentration (Cmax) increased more than proportionally to the dose. At 1, 5, and 15 mg/kg, plasma AUC was 29, 466, and 2832 ng.hr/ml, respectively, and Cmax was 10, 129, and 304 ng/ml, respectively. Bioavailability, although compromised by nonlinear kinetics, was estimated to be between 8% and 18%. In baboons, the clearance of L-732,531 was lower than that in rats, especially when calculated from blood concentrations (12 ml/min/kg at 0.2 mg/kg and 8 ml/min/kg at 1 mg/kg). After oral dosing, baboon plasma AUC and Cmax were much lower than those in rats, but as in rats, they increased more than proportionally with increasing doses. The bioavailability of L-732,531 in baboons was estimated at 3%, 9%, and 24% when animals were dosed at 5, 15, and 26 mg/kg po, respectively. After oral administration of [3H]L-732,531 at 5 mg/kg, approximately 32% of the radioactivity was recovered in bile and urine of rats, compared with 9% in baboons. High-performance liquid chromatography profiles of rat and baboon plasma, bile, urine, and feces indicated that L-732,531 was metabolized extensively to a complex mixture of products. Some intact parent drug was observed in feces of orally dosed animals, indicating incomplete absorption. In vitro, L-732,531 was metabolized more extensively by baboon liver microsomes than rat or human microsomes. Its metabolism in human liver microsomes was shown to be catalyzed primarily by cytochrome P450 3A isozymes.

Absence of ATM truncations in patients with severe acute radiation reactions

PURPOSE

Severe acute toxicity limits the effective use of radiotherapy in patients who are radiosensitive, and it is not usually possible to identify these radiohypersensitive (R-H) individuals before treatment commences. Five such R-H patients were detected over a 3-year period. We undertook this study to determine whether the severe acute radiohypersensitivity of these five individuals showed any correlation with cellular and molecular parameters known to be abnormal in radiosensitivity-related syndromes such as ataxia-telangiectasia (A-T).

METHODS AND MATERIALS

Lymphoblastoid cells were isolated from fresh blood from the 5 R-H individuals who had previously demonstrated clinical R-H at least 9 months prior to sampling. Lymphoblastoid cell lines (LCLs) were established to determine the extent of postradiation chromosomal aberrations, cell cycle delay, cell proliferation, and tumor suppressor p53 protein stabilization. The polymerase chain reaction (PCR) and protein truncation (PTT) assays were used to test for the possibility of mutations in the gene mutated in A-T, termed ATM.

RESULTS

LCLs derived from R-H subjects retained a significantly higher degree of radiation-induced chromosomal aberrations when compared to normal control LCLs. p53 stabilization by ionizing radiation appeared normal in all but one R-H subject. There was no evidence of A-T gene truncation mutations in any of the R-H subjects tested.

CONCLUSIONS

All R-H subjects in this study had their cellular radiosensitivity confirmed by the chromosomal aberration assay. Delayed p53 stabilization at 4 hours postirradiation in one R-H subject suggested that different etiologies may apply in the radiohypersensitivity investigated in this study.

Testing for mutations of the ataxia telangiectasia gene in radiosensitive breast cancer patients

BACKGROUND AND PURPOSE

To determine if clinical radiosensitivity in breast cancer patients is related to mutations of the ataxia telangiectasia gene (ATM).

MATERIALS AND METHODS

Fifteen patients who had developed a severe late reaction to a standard radiotherapy schedule were examined for evidence of increased in vitro radiosensitivity using the MTT assay. Mutation analysis was performed using a protein truncation assay.

RESULTS

No mutations were detected in the 15 patients despite evidence of increased in vitro radiosensitivity.

CONCLUSIONS

Testing for the ATM gene is unlikely to be useful for predicting clinical response to radiotherapy in breast cancer patients.

Radiosensitive melanoma cell line with mutation of the gene for ataxia telangiectasia

The human melanoma cell lines MM96L, A2058 and HT144 were examined for sensitivity to ionizing radiation and UVB radiation. HT144 demonstrated a significant increase in sensitivity to ionizing and UVB radiation compared with the MM96L and A2058 cells. Sensitivity to both agents was associated with susceptibility to apoptosis. Using a protein truncation assay, a mutation for the gene for ataxia telangiectasia (ATM) was identified in HT144 cells. This was confirmed to be a homozygous mutation by subsequent sequencing of the abnormal region. Protein truncation assay of the other two cell lines showed no abnormality. The results suggest that somatic mutation of the A-T gene may be important in determining tumour radiosensitivity.

Approaches to determine the specific role of the delta isoform of protein kinase C

Two dimensional gel electrophoresis of proteins from HL-60 human leukaemia cells treated with bistratene A, a specific activator of protein kinase C (PKC) delta, was performed in conjunction with sequencing in order to identify components of the signal transduction pathway of this isoform of PKC. Stathmin (oncoprotein 18) was identified in this way and the phosphorylation of this protein after treatment with bistratene A, was confirmed by Western blotting of 2D gels. Since stathmin has phosphorylation sites for mitogen activated protein (MAP) kinases, cyclin dependent kinases and calcium/calmodulin dependent protein kinases, it is assumed that one of these enzymes, acting downstream from PKC delta, is responsible for the phosphorylation. Another approach to determining the role of PKC delta involves the identification of interacting proteins using the yeast two hybrid screen. The sequence of nine out of ten independently isolated clones from a two hybrid screen showed perfect homology to human ribosomal protein L8. This protein has previously been shown to exist in complexes with ribosomal RNA, aminoacyl-tRNA and elongation factor-1 alpha, a known substrate of PKC delta, suggesting a role for PKC delta in protein synthesis regulation.

Cellular localisation of the ataxia-telangiectasia (ATM) gene product and discrimination between mutated and normal forms

The recently cloned gene (ATM) mutated in the human genetic disorder ataxia-telangiectasia (A-T) is involved in DNA damage response at different cell cycle checkpoints and also appears to have a wider role in signal transduction. Antibodies prepared against peptides from the predicted protein sequence detected a approximately 350 kDa protein corresponding to the open reading frame, which was absent in 13/23 A-T homozygotes. Subcellular fractionation, immunoelectronmicroscopy and immunofluorescence showed that the ATM protein is present in the nucleus and cytoplasmic vesicles. This distribution did not change after irradiation. We also provide evidence that ATM protein binds to p53 and this association is defective in A-T cells compatible with the defective p53 response in these cells. These results provide further support for a role for the ATM protein as a sensor of DNA damage and in a more general role in cell signalling, compatible with the broader phenotype of the syndrome.

Specific cleavage of the large subunit of replication factor C in apoptosis is mediated by CPP32-like protease

Recent evidence suggests that the growing family of cysteine proteases related to the interleukin-1beta-converting enzyme (ICE) is of central importance in mediating apoptosis. Proteolytic cleavage of a small group of cellular substrates by these enzymes in association with the onset of apoptosis has been reported. In the present study, we searched a protein data base for potential death substrates possessing the CPP32 cleavage site, DEVD, and identified several candidates including RFC140, the large subunit of replication factor C, which we subsequently demonstrated to be specifically cleaved in a variety of cell types undergoing apoptosis in response to different cytotoxic agents, whereas no degradation is observed in a cell line resistant to etoposide-induced apoptosis. The abrogation of RFC140 cleavage in apoptotic extracts by Ac-DEVD-CHO, a potent inhibitor of CPP32, together with the finding that a CPP32 consensus cleavage sequence, DEVD, exists in RFC140, suggests that CPP32 or a close relative is responsible for RFC140 degradation in apoptosis.

Malignant thymoma in a patient with HIV positivity: a case report with a review of the differential cytologic diagnoses

A 33-yr-old African-American male with known human immunodeficiency virus (HIV) positivity underwent CT guided fine-needle aspiration biopsy of an anterior mediastinal mass. The aspirate was composed of a dimorphic population of cells that included small mature lymphoid cells and scattered cohesive groups of large epithelial cells in equal numbers. The neoplasm stained strongly for low weight molecular cytokeratin, epithelial membrane antigen (EMA), leukocyte common antigen (LCA), and Leu-7 which was consistent with a diagnosis of thymoma. Subsequent biopsies determined the neoplasm to be a malignant (invasive) thymoma. This case emphasizes the efficacy of FNA biopsy for the evaluation of anterior mediastinal masses in HIV infected individuals. Additionally, the differential cytologic diagnoses for HIV infected individuals for this anatomic site are discussed.

The physical and adhesive properties of dental cements used for atraumatic restorative treatment

Atraumatic restorative treatment (ART), a recently reported field dentistry technique, involves removal of carious debris using only hand instruments and placement of a glass-ionomer cement (GIC) restoration. While small ART-GIC restorations are effective short-term replacements for lost tooth form, many larger ART-GIC restorations are defective after two years. Presently, resin-modified GICs (R-M GIC) are available which require no special activation equipment and handle easily in field settings. This study measured the compressive, tensile, and shear bond strengths to enamel and dentin of a conventional ART-GIC (Fuji IX) and two R-M GICs (Fuji Plus and Advance) at a powder-to-liquid ratio of 3.6:1. The compressive strengths of the GICs tested were significantly different. Fuji IX had the highest compressive strength, and Advance had the lowest strength (p < 0.05). The tensile strength of the R-M GICs was greater than that of the ART-GIC. Fuji Plus showed the highest shear bond strength to enamel and dentin and was significantly different from both Fuji IX and Advance. A clinical protocol is presented followed by case reports where the ART technique was used for management of acute caries in a modern dental setting.

Bistratene A causes phosphorylation of talin and redistribution of actin microfilaments in fibroblasts: possible role for PKC-delta

Bistratene A is a marine toxin which induces phosphorylation of cellular proteins. Our current evidence indicates that this occurs through activation of protein kinase C-delta. In fibroblasts bistratene A causes rounding up of the cells and a rapid disappearance of vinculin staining and actin stress fibers as detected by fluorescence immunohistochemistry. Phosphorylation of the focal adhesion protein, talin, is increased after bistratene A treatment and this is inhibited by calphostin C, a specific inhibitor of PKC. No changes in the phosphorylation status of vinculin, tubulin, or vimentin were observed in the presence of the toxin. Treatment with bistratene A caused a redistribution of PKC-delta from cytosolic and membrane compartments to the nuclear fraction. There was no effect on the subcellular distribution of any other PKC isoform. These results demonstrate that phosphorylation of talin is implicated in the disruption of actin microfilaments in fibroblasts by bistratene A and that this is most likely mediated by PKC-delta.

Partners in powersharing--the role of midwives in information technology

The contribution which midwives can make to the successful implementation of information systems is described. Issues such as Change Management, Quality, Benefits Realisation, and Public Relations are discussed. Damage limitation in the information age is outlined.

Heteronuclear ribonucleoproteins C1 and C2, components of the spliceosome, are specific targets of interleukin 1beta-converting enzyme-like proteases in apoptosis

Apoptosis induced by a variety of agents results in the proteolytic cleavage of a number of cellular substrates by enzymes related to interleukin 1beta-converting enzyme (ICE). A small number of substrates for these enzymes have been identified to date, including enzymes involved in DNA repair processes: poly(ADP-ribose) polymerase and DNA-dependent protein kinase. We describe here for the first time the specific cleavage of the heteronuclear ribonucleoproteins (hnRNPs) C1 and C2 in apoptotic cells induced to undergo apoptosis by a variety of stimuli, including ionizing radiation, etoposide, and ceramide. No cleavage was observed in cells that are resistant to apoptosis induced by ionizing radiation. Protease inhibitor data implicate the involvement of an ICE-like protease in the cleavage of hnRNP C. Using recombinant ICE-like proteases and purified hnRNP C proteins in vitro, we show that the C proteins are cleaved by Mch3alpha and CPP32 and, to a lesser extent, by Mch2alpha, but not by ICE, Nedd2, Tx, or the cytotoxic T-cell protease granzyme B. The results described here demonstrate that the hnRNP C proteins, abundant nuclear proteins thought to be involved in RNA splicing, belong to a critical set of protein substrates that are cleaved by ICE-like proteases during apoptosis.

Rapamycin resistance in ataxia-telangiectasia

The gene mutated in the human genetic disorder ataxia-telangiectasia (A-T) has been described recently (Savitsky et al., 1995a) and the complete coding sequence of this gene, ATM, has been reported (Savitsky et al., 1995b). The derived amino acid sequence demonstrates significant homologies to several proteins containing a phosphatidylinositol 3-kinase (PI3-kinase) domain, including the yeast TOR proteins and the human protein FRAP. Since the TOR and FRAP proteins are targets for the immunosuppressive drug rapamycin, we have investigated the effects of this compound on A-T cells. We report here that 3 A-T cell lines are more resistant than control cells to rapamycin's growth inhibiting effects but were more sensitive to the PI3-kinase inhibitor wortmannin. As expected rapamycin (1 nM) inhibited the rate of exit of control cells from G1 phase but failed to perturb the progression of A-T cells. This difference in cell cycle progress after rapamycin treatment is reflected in ribosomal S6 protein kinase (p70S6k) by both a downward mobility shift on SDS-PAGE and inhibition of activity. Furthermore, the G1 phase cyclin-dependent kinase, cyclin E-cdk2, was rapidly inhibited in control cells post-treatment, whereas in A-T cells it took considerably longer to observe inhibition. There was no evidence that a GST-FKBP12 fusion protein specifically precipitated the ATM protein in the presence of rapamycin in either cell type. These results demonstrate that the ATM protein is not a direct target for rapamycin but its functional loss renders cells more resistant to this compound.

Ataxia-telangiectasia: mutations in ATM cDNA detected by protein-truncation screening

We have examined the distal half of the ataxia-telangiectasia (A-T) gene transcript for truncation mutations in 48 A-T affecteds. We found 21 mutations; 4 of the mutations were seen in more than one individual. Genotyping of the individuals sharing mutations, by using nearby microsatellite markers, established that three of the four groups shared common haplotypes, indicating that these were probably founder effects, not public mutations. The one public mutation was found in two American families, one of Ashkenazi Jewish background and the other not. Most truncations deleted the PI3-kinase domain, although some exceptions to this were found in patients with typical A-T phenotypes. All patients not previously known to be consanguineous were found to be compound heterozygotes when mutations could be identified--that is, normal and abnormal protein segments were seen on SDS-PAGE gels. All 48 patients gave RT-PCR products, indicating the presence of relatively stable mRNAs despite their mutations. These results suggest that few public mutations or hot spots can be expected in the A-T gene and that epidemiological studies of A-T carrier status and associated health risks will have to be designed around populations with frequent founder-effect mutations, despite the obvious limitations of this approach.

A genetic register for von Hippel-Lindau disease

A genetic register for von Hippel-Lindau disease was set up in the north west of England in 1990. Population statistics, clinical features, age at onset, and survival of 83 people affected with von Hippel-Lindau (VHL) disease were studied. In addition, the effectiveness of the screening programme used and the occurrence of central nervous system haemangioblastomas in the general population were examined. The diagnostic point prevalence of heterozygotes in the North Western Region was 1 center dot 18/100 000 (1/85 000) people, with an estimated birth incidence of 2 center dot 20/100 000 (1/45 500) live births. The mutation rate was estimated directly to be 1 center dot 4 x 10(-6)/gene/generation (1/714 200). The mean age at onset of first symptoms was 26 center dot 25 years, with cerebellar haemangioblastoma being the most common presenting manifestation (34 center dot 9% of cases). The mean age at diagnosis of VHL disease was 30 center dot 87 years. Overall, 50 patients (60 center dot 2%) developed a cerebellar haemangioblastoma, 34 (41 center dot 0%) a retinal angioma, 21 (25 center dot 3%) a renal cell carcinoma, 12 (14 center dot 5%) a spinal haemangioblastoma, and 12 (14 center dot 5%) a phaeochromocytoma. Mean age at diagnosis of renal cell carcinoma (38 center dot 9 years) was significantly higher than that for cerebellar haemangioblastoma (30 center dot 0 years) and retinal angioma (21.1 years). Mean age at death was 40 center dot 9 years with cerebellar haemangioblastoma being the most common cause (47 center dot 7% of deaths). A total of 65 VHL manifestations were diagnosed asymptomatically following appropriate clinical and radiological screening tests, and failure to detect manifestations of VHL disease in spite of appropriate screening occurred on only two occasions. The use of DNA linkage analysis and direct mutation testing reduced the personal risk of carrying the VHL gene to below 1% in 14 people. In addition to the 83 clinically affected subjects, three obligate carriers who were considered to be lesion free in spite of extensive screening tests were identified. Fourteen percent of all CNS haemangioblastomas on the regionally based Cancer Registry were found to occur as part of VHL disease, but investigations for VHL in apparently sporadic disease appeared to be limited.

Variability in wheat based on low-copy DNA sequence comparisons

The chromosomes of the B genome of hexaploid wheat (AABBDD) do not pair completely with those of any of the diploid species with genomes similar to B. Various biochemical and molecular analyses have suggested that each of the five diploid species in section Sitopsis of Triticum are ancestral to B. These observations have led to the hypothesis that the B genome may be polyphyletic, descending from more than one diploid ancestor. This hypothesis may account for differences between the wheat B genome and the diploids and also for variability that currently exists among different wheat accessions. In this study, we cloned and compared nucleotide sequences for three low-copy DNA fragments from the B and D genomes of several wheat accessions and from diploid relatives of the B and D genomes. Our results suggested that the amount of DNA sequence variability in wheat is low, although somewhat more variability existed in the B genome than in the D genome. The B genome of wheat was significantly diverged from all the Sitopsis diploid species, and Triticum speltoides was closer to B than to other members of this section. The D genome of wheat was very similar to that of its progenitor, Triticum tauschii. No evidence for a polyphyletic origin of the B genome was found. A more parsimonious hypothesis is that the wheat B genome diverged from its diploid ancestor after the original hybridization event occurred.

MR staging of acute dural sinus thrombosis: correlation with venous pressure measurements and implications for treatment and prognosis

PURPOSE

To correlate parenchymal brain changes, venous sinus pressure measurements, and outcome in 29 patients with acute dural sinus thrombosis.

METHODS

A retrospective review of 29 patients with angiographically proved acute dural sinus thrombosis was made from January 1989 to December 1993. MR examinations were performed on either a 0.5- or 1.5-T superconductive scanner in multiple planes. Direct dural sinus venography, cerebral angiography, and MR venography were performed. Venous sinus pressure measurements were obtained in 11 of 29 patients.

RESULTS

We identified five distinct stages of brain parenchymal changes; each stage correlated with increasing intradural sinus pressure. The pressures measured in this study ranged from 20 to 50 mm Hg. Brain parenchymal changes were reversible up to stage III if thrombolytic treatment was performed. Beyond stage III, there were some residual changes, even after thrombolysis. All stage V patients died.

CONCLUSION

Acute dural sinus thrombosis leads to distinct stages of parenchymal changes, the severity of which depends on the degree of venous congestion, which, in turn, is closely related to intradural sinus pressure. As intradural sinus pressure increases, progression from mild parenchymal change to severe cerebral edema and/or hematoma may occur if thrombolysis is delayed.