Biomedical subjects

S F Barrett

Publications and source records attributed to S F Barrett.

9 recordsLinked to original sources

PubMed1991

Evidence for defective repair of cyclobutane pyrimidine dimers with normal repair of other DNA photoproducts in a transcriptionally active gene transfected into Cockayne syndrome cells.

Cockayne syndrome (CS) and xeroderma pigmentosum (XP), autosomal recessive diseases with clinical and cellular hypersensitivity to UV radiation, differ in ability to repair UV DNA photoproducts in their overall genome: normal repair in CS, defective repair in XP. In order to characterize a DNA repair defect in an active gene in CS, we measured the capacity of cells from patients with CS and XP to reactivate 2 major types of UV-induced DNA damage, photoreactivatable (i.e., cyclobutane pyrimidine dimers) and non-photoreactivatable (primarily pyrimidine-(6-4)pyrimidone photoproducts), in the actively transcribing chloramphenicol acetyltransferase (cat) gene of the plasmid expression vector pRSV-cat. Epstein-Barr virus-transformed lymphoblast lines from 4 normal persons and from 3 patients with CS and from two with XP were transiently transfected with the plasmid, and the cat activity in cell extracts was determined. When the cells were transfected with UV-irradiated plasmid, expression was abnormally decreased in both the CS and XP cells. When the cyclobutane pyrimidine dimers in the UV-irradiated plasmid were removed by photoreactivation prior to transfection, cat expression in the CS, but not in the XP, lines reached normal levels. These data imply that both the XP and CS cells are unable to repair normally the cyclobutane pyrimidine dimer photoproducts which block transcription of cat. However, the CS, but not XP, cells can repair normally the other UV-induced photoproducts which block transcription. The ability of CS, but not XP, cells to repair these non-dimer photoproducts indicates that the active gene repair mechanism treats the cyclobutane pyrimidine dimer differently from the non-dimer photoproducts.

Cell Line↗

PubMed1991

Neurological disease in xeroderma pigmentosum. Documentation of a late onset type of the juvenile onset form.

Xeroderma pigmentosum (XP) is an autosomal recessive, neurocutaneous disorder characterized by sunlight-induced skin cancers and defective DNA repair. Many XP children develop a primary neuronal degeneration. We describe 2 unusual XP patients who had a delayed onset of XP neurological disease. Somatic cell genetic studies indicated that they have the same defective DNA repair gene and are both in XP complementation group A. These 2 patients, together with a group A patient previously reported from London, establish as a distinct clinical entity the late onset type of the juvenile onset form of XP neurological disease. The functional capacity of these patients' cultured fibroblast strains to survive after treatment with ultraviolet radiation indicates that their DNA repair defect is less severe than that of typical group A patients who have a more severe neurodegeneration with an earlier symptomatic onset. The premature death of nerve cells in XP patients (which is presumably due to their inherited defects in DNA repair mechanisms) suggests that normal repair of damaged DNA in neurons is required to maintain integrity of the human nervous system.

Adolescent↗

PubMed1991

Induction by ionizing radiation of the gadd45 gene in cultured human cells: lack of mediation by protein kinase C.

The effect of ionizing radiation on the expression of two DNA-damage-inducible genes, designated gadd45 and gadd153, was examined in cultured human cells. These genes have previously been shown to be strongly and coordinately induced by UV radiation and alkylating agents in human and hamster cells. We found that the gadd45 but not the gadd153 gene is strongly induced by X rays in human cells. The level of gadd45 mRNA increased rapidly after X rays at doses as low as 2 Gy. After 20 Gy of X rays, gadd45 induction, as measured by increased amounts of mRNA, was similar to that produced by the most effective dose of the alkylating agent methyl methanesulfonate. No induction was seen after treatment of either human or hamster cells with 12-O-tetradecanoylphorbol-13-acetate, a known activator of protein kinase C (PKC). Therefore, gadd45 represents the only known mammalian X-ray-responsive gene whose induction is not mediated by PKC. However, induction was blocked by the protein kinase inhibitor H7, indicating that induction is mediated by some other kinase(s). Sequence analysis of human and hamster cDNA clones demonstrated that this gene has been highly conserved and encodes a novel 165-amino-acid polypeptide which is 96% identical in the two species. This gene was localized to the short arm of human chromosome 1 between p12 and p34. When induction in lymphoblast lines from four normal individuals was compared with that in lines from four patients with ataxia telangiectasia, induction by X rays of gadd45 mRNA was less in the cell lines from this cancer-prone radiosensitive disorder. Our results provide evidence for the existence of an X-ray stress response in human cells which is independent of PKC and which is abnormal in taxia telangiectasia.

Amino Acid Sequence↗

PubMed1978

Xeroderma pigmentosum neurological abnormalities correlate with colony-forming ability after ultraviolet radiation.

Xeroderma pigmentosum is an autosomal recessive disease in which DNA repair processes are defective. All xeroderma pigmentosum patients develop premature aging of sun-exposed skin, and some develop neurological abnormalities due to premature death of nerve cells. Sensitivity to ultraviolet radiation of 24 xeroderma pigmentosum fibroblast strains was studied in vitro by measuring each strain's ability to divide and form colonies after irradiation. The most sensitive strains were derived from patients who had an early onset of neurological abnormalities; less sensitive strains were from patients with a later onset; and the most resistant strains were from patients without neurological abnormalities. The UV sensitivities of strains from each member of a sibling pair with xeroderma pigmentosum were identical, indicating that UV sensitivity of xeroderma pigmentosum strains is determined by the patient's inherited DNA repair defect. The results suggest that effective DNA repair is required to maintain the functional integrity of the human nervous system by preventing premature death of neurons.

Adolescent↗

PubMed1978

Cockayne's syndrome fibroblasts have increased sensitivity to ultraviolet light but normal rates of unscheduled DNA synthesis.

Cockayne's syndrome is a form of cachectic dwarfism characterized by acute sun sensitivity and numerous other abnormalities of many organ systems. We studied fibroblasts from 9 Cockayne's syndrome patients to determine if their fibroblasts had abnormal post-ultraviolet light colony-forming ability or abnormal ultraviolet light-induced unscheduled DNA synthesis. The fibroblast strains from all the patients had markedly decreased post-ultraviolet light colony-forming ability in comparison with fibroblasts from control donors. Since this increased ultraviolet light sensitivity is propagable in vitro, it may be a manifestation of, or be closely associated with, the inherited genetic defect of this autosomal recessive disease. However, the patients' fibroblasts had normal rates of ultraviolet light-induced unscheduled DNA synthesis. Thus, unlike the UV sensitivity of DNA excision repair-deficient xeroderma pigmentosum strains, the UV sensitivity of Cockayne's syndrome strains is not related to abnormal DNA excision repair, at least to the extent that this repair process is reflected by rates of ultraviolet light-induced unscheduled DNA synthesis.

Cell Division↗

PubMed1976

Colony-forming ability of ultraviolet-irradiated xeroderma pigmentosum fibroblasts from different DNA repair complementation groups.

Patients with xeroderma pigmentosum develop severe sunlight-induced damage, including malignant neoplasms, on sun-exposed skin. Some patients also have neurological abnormalities. Xeroderma pigmentosum cells are known to have impaired ability to repair ultraviolet light- or chemical mutagen-induced damage to their DNA, and cell-fusion studies have shown five complementation groups among the DNA excision repair-deficient strains. All xeroderma pigmentosum fibroblast strains we tested had lower colony-forming abilities after ultraviolet irradiation than normal strains. Furthermore, we have found that strains from different complementation groups can have different post-ultraviolet colony-forming abilities and that strains from patients with neurological abnormalities are the most sensitive to ultraviolet light. These results suggest that extremely ineffective repair of damaged DNA in central nervous system neurons may be the cause of the neurological abnormalities.

DNA↗

PubMed1976

Relation of D.N.A. repair processes to pathological ageing of the nervous system in xeroderma pigmentosum.

The severity of neurological abnormalities in patients with xeroderma pigmentosum has been found to be related to their ability to repair ultraviolet (U.V.)-damaged D.N.A. Patients with the most severe neurological abnormalities have the least effective D.N.A. repair is shown by the decreased colony-forming ability of their U.V.-irradiated fibroblasts. These results suggest that the lack of adequate D.N.A. repair is causally related to the clinical manifestations of a human heredodegenerative nervous system disease.

Aging↗

PubMed1975

Five complementation groups in xeroderma pigmentosum.

A collaborative study was undertaken to determine the relationship between the three DNA repair complementation groups in xeroderma pigmentosum found at Erasmus University, Rotterdam, and the four groups found at the National Institutes of Health, Bethesda. The results of this study reveal that there are five currently known complementation groups in xeroderma pigmentosum.

Cell Fusion↗

PubMed1975

Genetic heterogeneity in xeroderma pigmentosum: complementation groups and their relationship to DNA repair rates.

Fibroblast strains from 12 patients with xeroderma pigmentosum had lower than normal rates of DNA repair, as determined by autoradiographic studies of ultraviolet-induced unscheduled nuclear DNA synthesis. The nuclei in binuclear cells, obtained by fusing fibroblasts from certain pairs of these strains, had a greater rate of DNA repair than the nuclei of either strain's unfused mononuclear cells. These results indicate that complementary corrections of the strains' repair defects had occurred in the fused cells. Four complementation groups were found, indicating that at least four mutations caused decreased DNA repair among these 12 strains. The unfused mononuclear cells of each group had a characteristic rate of repair that differed from the rates of the other groups.

Autoradiography↗