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Biomedical subjects

R B Setlow

Publications and source records attributed to R B Setlow.

At least 73 records · Page 4Linked to original sources
PubMed1980

DNA repair after ultraviolet irradiation of ICR 2A frog cells. Pyrimidine dimers are long acting blocks to nascent DNA synthesis.

The ability of ICR 2A frog cells to repair DNA damage induced by ultraviolet irradiation was examined. These cells are capable of photoreactivation but are nearly totally deficient in excision repair. They have the ability to convert the small molecule weight DNA made after irradiation into large molecules but do not show an enhancement in this process when the UV dose is delivered in two separate exposures separated by a 3- or 24-h incubation. Total DNA synthesis is depressed and low molecular weight DNA continues to be synthesized during pulse-labeling as long as 48 h after irradiation. The effects of pyrimidine dimer removal through exposure of UV irradiated cells to photoreactivating light indicate that dimers act as the critical lesions blocking DNA synthesis.

Animals↗
PubMed1980

Postreplication repair in three murine melanomas, a mammary carcinoma, and a normal mouse lung fibroblast line.

Repair of ultraviolet light-induced damage to DNA was studied in three melanoma lines, a mammary carcinoma line, EMT6, and a normal lung fibroblast line, MLF, all from the mouse. The melanomas were B16CL4, a gamma-ray-resistant clonal line derived from B16; S91H-, an auxotrophic line derived from Cloudman S91; and HP, a freshly isolated line from s.c. grown Harding-Passey melanoma. The melanomas and MFL were found to perform minimal excision repair and photoreactivation. Postreplication repair, on the other hand, was an active process in all five of the lines. All three melanomas exhibited postreplication repair rates that were about twice that of MLF. The freshly isolated HP line evolved during subcultivation, and its postreplication repair rate dropped after 3 months to a rate comparable to EMT6, which was 1.5 times that of MLF. The results suggest that postreplication repair is an important process in melanomas and may be related to radiation response.

Animals↗
PubMed1980

Modulation by caffeine of enhanced postreplication repair in mammalian cells treated with N-acetoxy-acetylaminofluorene.

As shown previously, newly synthesized DNA from Chinese hamster, excision proficient and excision deficient xeroderma pigmentosum (XP) cells treated with split doses of N-acetoxy-acetylaminofluorene (AAAF) or ultraviolet radiation (uv) is larger in size than DNA from cells treated with only the single dose. In this report we determined the effects of caffeine, an inhibitor of postreplication repair, upon enhancement of repair by a split dose treatment with AAAF. Caffeine was added to cells either immediately following the first or the second dose of AAAF and the size of newly synthesized DNA was determined by alkaline sucrose gradient sedimentation. Results showed that: (a) the DNA from V79 and XP cells incubated with caffeine between the first and second dose of AAAF was smaller in size than DNA from cells not incubated with caffeine; (b) caffeine exhibited a lesser effect when added after the second dose during the pulse-chase; and (c) caffeine has little effect upon daughter DNA of normal human cells treated with single or split doses of AAAF. These data indicate that caffeine interferes with the enhancement of postreplication repair in V79 and XP cells treated with AAAF.

2-Acetylaminofluorene↗
PubMed1979

UV-endonuclease from calf thymus with specificity toward pyrimidine dimers in DNA.

We describe the partial purification of an endonuclease from calf thymus that nicks phage PM2 DNA irradiated with UV doses producing only a few pyrimidine dimers per molecule. It has much less activity on DNA that has been subjected to enzymatic photoreactivation after UV irradiation. The calf thymus endonuclease is different from other mammalian UV-endonucleases so far described in that it seems to be dimer specific. The enzyme is stimulated by Mg2+ and is inactive in the presence of EDTA. It binds to UV-irradiated DNA-Sepharose from which it is released by low concentrations of KCl. Gel filtration data indicate that the endonuclease may belong to a high molecular weight protein or protein complex. The enzyme is very labile and freezing increases its lability.

Animals↗
PubMed1979

Repair of ultraviolet light damage to the DNA of cultured human epidermal keratinocytes and fibroblasts.

Pure cultures of dermal fibroblasts and epidermal keratinocytes have been obtained from a single biopsy of newborn foreskin. The cells were labeled, exposed to several doses of UV light, and allowed to repair in the dark for 16 hr. The number of pyrimidine dimers before and after repair was assessed by measuring the numbers of sites in the DNA sensitive to a specific UV endonuclease. At all doses used, the extent of repair was similar in the cultured keratinocytes and cultured fibroblasts.

Cells, Cultured↗
PubMed1979

Migration of intraperitoneally injected thyroid cells in the Amazon molly, Poecilia formosa.

We have previously reported the development of an extensive invasive growth of the thyroid gland of the gynogenetic teleost, Poecilia formosa (the Amazon molly), following i.p. injection of UV- or gamma-irradiated thyroid cells. This result was surprising by comparison with mammalian work, in which the thyroid is rarely the site for tumor metastases, but the anatomy of the circulation of fish is different from mammals, and in fish the gills and thyroid gland would be among the first tissues in which injected cells might be arrested. Techniques using a fluorescent dye, 125I membrane label, or [3H]thymidine label were used to follow the distribution of i.p. injected cells in the Amazon molly. Fish sampled as soon as 30 min after injection had some labeled cells dispersed in the connective tissue around the ventral aorta and in the bases of the gills, and by 1 to 4 hr large numbers of cells had moved into the thyroid region. A few cells still persisted there 200 hr later. Experiments on the distribution of heat-killed cells indicated that the initial distribution of the cells was largely governed by mechanical factors. Injected cells would appear to be disseminated in fish by mechanisms similar to those in mammals.

Animals↗
PubMed1979

DNA repair in xeroderma pigmentosum cells treated with combinations of ultraviolet radiation and N-acetoxy-2-acetylaminofluorene.

We used three techniques to examine excision repair in human cells treated with ultraviolet radiation, N-acetoxy-2-acetylaminofluorene, and a combination of the two. The three techniques gave similar results. Two types of human cells were used: (a) excision repair proficient (normal human fibroblasts and xeroderma pigmentosum variants); and (b) excision repair deficient (xeroderma pigmentosum C, D, and E). Saturation doses were determined and used for combined treatments with both agents. We observed two patterns of repair: (a) in repair-proficient cells total repair was additive; and (b) in repair-deficient cells total repair was much less than additive (usually less than that repair was much less than additive (usually less than that observed for separate treatments) and N-acetoxy-2-acetylaminofluorene inhibited excision of pyrimidine dimers. We conclude that, in the first group of cells, pathways for repair of ultraviolet radiation- and N-acetoxy-2-acetylaminofluorene-induced lesions are not identical and, in the second group of cells, there is an inhibitory effect exerted by major or minor products of each agent on the repair enzyme(s) of the other.

Acetoxyacetylaminofluorene↗
PubMed1978

Excision repair in ataxia telangiectasia, Fanconi's anemia, Cockayne syndrome, and Bloom's syndrome after treatment with ultraviolet radiation and N-acetoxy-2-acetylaminofluorene.

Excision repair of damage due to ultraviolet radiation, N-acetoxy-2-acetyl-aminofluorene and a combination of both agents was studied in normal human fibroblasts and various cells from cancer prone patients (ataxia telangiectasia, Fanconi's anemia, Cockayne syndrome and Bloom's syndrome). Three methods giving similar results were used: unscheduled DNA synthesis by radioautography, photolysis of bromodeoxyuridine incorporated into parental DNA during repari, and loss of sites sensitive to an ultraviolet endonuclease. All cell lines were proficient in repair of ultraviolet and acetoxy acetylaminofluorene damage and at saturation doses of both agents repair was additive. We interpret these data as indicating that the rate limiting step in excision repair of ultraviolet and acetoxy acetylaminofluorene is different and that there are different enzyme(s) working on incision of both types of damages.

Ataxia Telangiectasia↗
PubMed1978

Repair deficient human disorders and cancer.

The analysis of the repair of damage to DNA in mammalian cells leads not only to a knowledge of which environmental agents are deleterious to living creatures, but also to an understanding of which reaction products in DNA are potentially carcinogenic and which tissues are the more sensitive.

Abnormalities, Multiple↗
PubMed1978

Modification of UV-induced mutation frequencies in Chinese hamster cells by dose fractionation, cycloheximide and caffeine treatments.

Chinese hamster (V79) cells were irradiated with a fractionated regime of ultraviolet light (UV1 + UV2). The fractionation of a UV dose always increased the colony-forming ability but reduced (or it did not change) the mutation frequencies. Treatment with cycloheximide between the two UV irradiations resulted in two types of effects, depending on the protocols used. Long exposures to cycloheximide (i.e., greater than 6 h) for the entire period between UV1 and UV2 or partial treatment of cycloheximide (i.e., 3 h) long before UV2 always resulted in reduced colony-forming ability and enhanced or unchanged mutation frequencies. Exposure to cycloheximide for the entire period in the short fractionated regime (i.e., 4 h) between UV1 and UV2 or partial treatment of cycloheximide just prior to UV2 tended to give the opposite effects. Caffeine treatment before UV2, with or without UV1, significantly increased the mutation frequencies. These results suggest that an error-free postreplication repair system exists in Chinese hamster cells which is inhibitable by particular cycloheximide or caffeine treatments.

Caffeine↗
PubMed1978

Enhancement of postreplication repair in ultraviolet-light-irradiated Chinese hamster cells by irradiation in G2 or S-phase.

Postreplication repair in synchronous Chinese hamster cells was determined after split doses of ultraviolet (UV) radiation. Repair was enhanced by irradiation of cells in G2 or S-phase with a small dose of UV radiation at least 1.5 h before a three-fold larger dose of UV. There was significantly greater enhancement when the first dose was given in G2 than when it was given in the S-phase 0.5-1.5 h before the test dose. These data indicate that enhancement of postreplication repair does not require active DNA replication and qualitatively is independent of when in the cell cycle the cells are irradiated.

Animals↗