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Biomedical subjects

J D Regan

Publications and source records attributed to J D Regan.

At least 91 records · Page 5Linked to original sources
PubMed1973

Recovery of the ability to synthesize DNA in segments of normal size at long times after ultraviolet irradiation of human cells.

DNA synthesized in human cells within the first hour after ultraviolet (UV) irradiation is made in segments of lower molecular weight than in nonirradiated cells. The size of these segments approximates the average distance between pyrimidine dimers in the parental DNA. This suggests that the dimers interrupt normal DNA synthesis and result in gaps in the newly synthesized DNA. However, DNA synthesized in human cells at long times after irradiation is made in segments equal or nearly equal to those synthesized by nonirradiated cells. The recovery of the ability to synthesize DNA in segments of normal size occurs in normal human cells, where the dimers are excised, and also in cells of the human mutants xeroderma pigmentosum (XP), where the dimers remain in the DNA. This observation implies that the pyrimidine dimer may not be the lesion that causes DNA to be synthesized in smaller than normal segments.

Cell Line↗
PubMed1972

DNA chain elongation and joining in normal human and xeroderma pigmentosum cells after ultraviolet irradiation.

DNA synthesized in human cells after ultraviolet (UV) irradiation is made in segments of lower molecular weight than in unirradiated cells. Within several hours after irradiation these smaller units are both elongated and joined together. This repair process has been observed in normal human fibroblasts, HeLa cells, and fibroblasts derived from three types of xeroderma pigmentosum patients-uncomplicated with respect to neurological problems, complicated (de Sanctis-Cacchione syndrome), and one with the clinical symptoms of xeroderma pigmentosum but with normal repair replication. The ability of human cells to elongate and to join DNA strands despite the presence of pyrimidine dimers enables them to divide without excising the dimers present in their DNA. It may be this mechanism which enables xeroderma pigmentosum cells to tolerate small doses of UV radiation.

Carbon Isotopes↗
PubMed1971

Xeroderma pigmentosum: a rapid sensitive method for prenatal diagnosis.

When normal human cells, capable of repairing ultraviolet-induced lesions in their DNA, are incubated in the thymidine analog 5-bromodeoxyuridine after ultraviolet irradiation, the analog is incorporated into the repaired regions. When such repaired cells are subsequently irradiated with 313-nanometer radiation and placed in alkali, breaks appear in the DNA at sites of incorporation of 5bromodeoxyuridine, inducing a dramatic downward shift in the sedimentation constant of the DNA. Cells from patients with the disease xeroderma pigmentosum, which causes sensitivity to ultraviolet, are incapable or only minimally capable of repair; such cells incorporate little 5-bromodeoxyuridine into their DNA under these conditions and, upon 313-nanometer irradiation and sedimentation in alkali, exhibit only minor shifts in DNA sedimentation constants. When fibroblasts developed from biopsies of normal skin and of skin from patients with xeroderma pigmentosum, as well as cells cultured from midtrimester amniotic fluid, were assayed in this fashion unequivocal differences between normal and xeroderma pigmentosum cells were shown. Xeroderma pigmentosum heterozygotes are clearly distinguishable from homozygous mutants, and results are available 12 hours after irradiation.

Amniocentesis↗
PubMed1971

Normal and defective repair of damaged DNA in human cells: a sensitive assay utilizing the photolysis of bromodeoxyuridine.

A new technique has been developed for studying the extent of repair of UV-radiation damage to DNA in human cells. It is easy to use, has excellent sensitivity, and provides rapid quantitative estimates of repair. UV-irradiated cells whose DNA has been previously labeled with a radioisotope are grown after irradiation in non-radioactive bromodeoxyuridine, which is incorporated at the breaks induced by repair enzymes. After a period of growth in the thymidine analog the cells are exposed to a large flux of 313 nm radiation and then lysed on top of an alkaline sucrose gradient. Bromodeoxyuridine-containing sections of the DNA are thus selectively photolysed. Sedimentation in the alkaline gradient reveals the average molecular weight of disrupted segments and gives a measure of the number of breaks induced by repair enzymes over the whole period allowed for repair. The large change in average molecular weight observed upon exposure of normal repairing cells to 313 nm radiation is not observed in the repair-deficient cells from patients with xeroderma pigmentosum. The quantitative aspects of this assay for repair and its sensitivity should make it applicable to the study of repair induced by agents other than UV radiation.

Animals↗
PubMed1969

Serine requirement in leukemic and normal blood cells.

In a serine-deficient medium, cells from humangt chronic granulocytic leukemia and normal human bone marrow exhibited a marked inhibition of incorporation of-radioactive precursors of DNA, RNA, and protein into an acid insoluble cell fraction. Normal diploid human fibroblasts did not exhibit inhibition without serine. Chronic granulocytic leukemia and normal marrow cells were essentially unable to synthesize C(14)-serine from C(14)-glucose, while human diploid fibroblasts were highly capable of this synthesis.

Alanine↗
PubMed1969

Evidence that xeroderma pigmentosum cells do not perform the first step in the repair of ultraviolet damage to their DNA.

Xeroderma pigmentosum (XP) is a recessively transmitted disorder of man characterized by increased sensitivity to ultraviolet light. Homozygous, affected individuals, upon exposure to sunlight, sustain severe damage to the skin; this damage is characteristically followed by multiple basal and squamous cell carcinomas and not uncommonly by other malignant neoplasia. A tissue culture cell line was derived from the skin of a man with XP. Our measurements of ultraviolet-induced pyrimidine dimers in cellular DNA show that normal diploid human skin fibroblasts excise up to 70 per cent of the dimers in 24 hours, but that fibroblasts derived from the individual with XP excise less than 20 per cent in 48 hours. Alkaline gradient sedimentation experiments show that during the 24 hours after irradiation of normal cells a large number of single-strand breaks appear and then disappear. Such changes are not observed in XP cells. XP cells apparently fail to start the excision process because they lack the required function of an ultraviolet-specific endonuclease. These findings, plus earlier ones of Cleaver on the lack of repair replication in XP cells, raise the possibility that unexcised pyrimidine dimers can be implicated in the oncogenicity of ultraviolet radiation.

Adult↗
PubMed1968

Evidence for excision of ultraviolet-induced pyrimidine dimers from the DNA of human cells in vitro.

Within 12-24 hr after human cells were irradiated with ultraviolet light, approximately 50% of the ultraviolet-induced pyrimidine dimers were lost from the DNA. Pyrimidine dimers were found in the TCA-soluble fraction of ultraviolet-irradiated cells at 24 hr. Excess thymidine, caffeine, or hydroxyurea had no effect on the loss of pyrimidine dimers from the DNA of ultraviolet-irradiated cells.

Amnion↗