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Biomedical subjects

Peter Robins

Publications and source records attributed to Peter Robins.

10 recordsLinked to original sources
PubMed2006

Mutations in the gene encoding the 3'-5' DNA exonuclease TREX1 cause Aicardi-Goutières syndrome at the AGS1 locus.

Aicardi-Goutières syndrome (AGS) presents as a severe neurological brain disease and is a genetic mimic of the sequelae of transplacentally acquired viral infection. Evidence exists for a perturbation of innate immunity as a primary pathogenic event in the disease phenotype. Here, we show that TREX1, encoding the major mammalian 3' --> 5' DNA exonuclease, is the AGS1 gene, and AGS-causing mutations result in abrogation of TREX1 enzyme activity. Similar loss of function in the Trex1(-/-) mouse leads to an inflammatory phenotype. Our findings suggest an unanticipated role for TREX1 in processing or clearing anomalous DNA structures, failure of which results in the triggering of an abnormal innate immune response.

Animals↗
PubMed2006

Direct removal of alkylation damage from DNA by AlkB and related DNA dioxygenases.

The cytotoxic alkylation lesions 1-methyladenine (1-alkyladenine) and 3-methylcytosine are removed efficiently from DNA by direct damage reversal, catalyzed by the Escherichia coli AlkB protein and its human homologs ABH2 and ABH3. The enzymes act by oxidative demethylation, employing Fe(II) and alpha-ketoglutarate as cofactors, and release the methyl moiety as formaldehyde. The isolation of these enzymes from overproducing cells is described, as well as the preparation of radioactively labeled substrates and procedures for enzyme assays. Functionality in vivo is examined by complementation of the low survival of alkylated single-stranded DNA bacteriophage in an E. coli alkB mutant.

Alkylation↗
PubMed2005

C --> T mutagenesis and gamma-radiation sensitivity due to deficiency in the Smug1 and Ung DNA glycosylases.

The most common genetic change in aerobic organisms is a C:G to T:A mutation. C --> T transitions can arise through spontaneous hydrolytic deamination of cytosine to give a miscoding uracil residue. This is also a frequent DNA lesion induced by oxidative damage, through exposure to agents such as ionizing radiation, or from endogenous sources that are implicated in the aetiology of degenerative diseases, ageing and cancer. The Ung and Smug1 enzymes excise uracil from DNA to effect repair in mammalian cells, and gene-targeted Ung(-/-) mice exhibit a moderate increase in genome-wide spontaneous mutagenesis. Here, we report that stable siRNA-mediated silencing of Smug1 in mouse embryo fibroblasts also generates a mutator phenotype. However, an additive 10-fold increase in spontaneous C:G to T:A transitions in cells deficient in both Smug1 and Ung demonstrates that these enzymes have distinct and nonredundant roles in suppressing C --> T mutability at non-CpG sites. Such cells are also hypersensitive to ionizing radiation, and reveal a role of Smug1 in the repair of lesions generated by oxidation of cytosine.

Animals↗
PubMed2005

F-18 FDG uptake associated with Elastofibroma dorsi.

A patient with a history of colon carcinoma and computed tomography (CT) evidence suggestive of a liver metastasis underwent an F-18 FDG PET scan. The PET scan confirmed a metastasis in the left lobe of the liver. The study also demonstrated bilateral symmetric uptake involving the inferior subscapular regions. Correlation with the previous CT showed this to correspond to bilateral elastofibroma dorsi, which had been prospectively reported on the CT. Elastofibroma dorsi is a rare benign mass consisting of fibroelastic tissue and fat. It has been previously described on PET, CT, ultrasound, and magnetic resonance imaging (MRI). On CT, the masses are of soft tissue density, similar to adjacent musculature, and may contain linear areas of low density secondary to fat. On MRI, elastofibroma dorsi has been shown to have variable enhancement, which may reflect increased vascularity of the lesion. In this case, the masses demonstrated low-grade diffuse F-18 FDG uptake.

Back↗
PubMed2004

Demethylation of 3-methylthymine in DNA by bacterial and human DNA dioxygenases.

Rare DNA lesions that are chemically stable and refractory to repair may add disproportionately to the accumulation of mutations in long lived cells. 3-Methylthymine is a minor lesion that is induced by DNA-methylating agents and for which no repair process has been described previously. Here we demonstrate that this lesion can be directly demethylated in vitro by bacterial and human DNA dioxygenases. The Escherichia coli AlkB and human ABH3 proteins repaired 3-methylthymine in both single-stranded and double-stranded polydeoxynucleotides, whereas the human ABH2 protein preferred a duplex substrate. Thus, the known substrates of these enzymes now include 3-methylthymine in DNA, as well as 1-methyladenine and 3-methylcytosine, which all have structurally similar sites of alkylation. Repair of 3-methylthymine by AlkB and ABH3 was optimal at pH 6, but inefficient. At physiological pH, 3-methylthymine, which is a minor methylated lesion, was more slowly repaired than the major lesion generated in single-stranded DNA, 3-methylcytosine. Our data suggest that 3-methylthymine residues in DNA will be repaired inefficiently in vivo and therefore may occur at a low steady-state level, but the residues should not gradually accumulate to high levels in long lived cells.

Adenine↗
PubMed2004

Gene-targeted mice lacking the Trex1 (DNase III) 3'-->5' DNA exonuclease develop inflammatory myocarditis.

TREX1, originally designated DNase III, was isolated as a major nuclear DNA-specific 3'-->5' exonuclease that is widely distributed in both proliferating and nonproliferating mammalian tissues. The cognate cDNA shows homology to the editing subunit of the Escherichia coli replicative DNA polymerase III holoenzyme and encodes an exonuclease which was able to serve a DNA-editing function in vitro, promoting rejoining of a 3' mismatched residue in a reconstituted DNA base excision repair system. Here we report the generation of gene-targeted Trex1(-/-) mice. The null mice are viable and do not show the increase in spontaneous mutation frequency or cancer incidence that would be predicted if Trex1 served an obligatory role of editing mismatched 3' termini generated during DNA repair or DNA replication in vivo. Unexpectedly, Trex1(-/-) mice exhibit a dramatically reduced survival and develop inflammatory myocarditis leading to progressive, often dilated, cardiomyopathy and circulatory failure.

Animals↗
PubMed2003

A comparison of conventional film, CR hard copy and PACS soft copy images of the chest: analyses of ROC curves and inter-observer agreement.

STUDY OBJECTIVE: The aim of this study was to determine whether the accuracy of diagnosis of a spectrum of chest pathology was affected by the imaging technique used, and to compare conventional film/screen, hard copy computed (phosphor plate) radiography (CR) and soft copy CR (PACS) images. MATERIALS AND METHODS: For each of 44 patients who had a CT examination of the thorax, PA and lateral chest radiographs were produced using conventional film, hard copy CR and soft copy PACS images. Five radiologists independently scored all images for the presence of abnormalities. The data were analysed in two stages using the result of the CT scan as the reference standard diagnosis: firstly, to investigate differences in abnormality scores between image modalities and observers using ROC analysis; secondly, to investigate the agreement of the diagnoses with the reference standard by the analysis of kappa scores. RESULTS: The ROC analyses and comparison of kappa scores showed no differences between image modalities (P=0.72, P=0.87), but highly significant differences between observers (P<0.001, P=0.003). CONCLUSION: The detection of chest lesions did not vary between conventional film, CR hard copy and PACS soft copy images. For all three image types, there were statistically significant differences between observers.

Analysis of Variance↗