PubMed Health⌕ Search

Biomedical subjects

D B Yarosh

Publications and source records attributed to D B Yarosh.

At least 55 records · Page 3Linked to original sources
PubMed1989

Encapsulation of the UV-DNA repair enzyme T4 endonuclease V in liposomes and delivery to human cells.

T4 endonuclease V, a pyrimidine-dimer-specific DNA repair enzyme, was encapsulated in liposomes under mild conditions. The encapsulated enzyme was active, and when applied to ultraviolet (UV)-irradiated human cells in culture, the liposomes increased incision of UV-irradiated cellular DNA, enhanced DNA repair replication, and enhanced survival of UV-irradiated cells. This method is a first step in a new approach for topical application of DNA repair enzymes to human skin to prevent skin cancer.

Cell Line, Transformed↗
PubMed1988

Polyclonal antibodies against O6-methylguanine-DNA methyltransferase in adapted bacteria.

The similarity of the adaptive response and the methyltransferase component in bacterial strains from different phylogenic groups was investigated. An adaptive response with induction of transferase activity was found for the first time in the soil bacteria P. aeruginosa and X. maltophilia. Polyclonal antibodies against the E. coli ada protein were used to investigate the structural similarity of the transferases from several bacterial strains with adaptive responses and inducible transferase activity. These antibodies cross-reacted with transferase from M. luteus and P. aeruginosa but not with proteins from other related bacteria, and not with human transferase. The phylogenic relationships of bacteria with adaptive responses suggest that the response likely was present in the common ancestor of eubacteria. The restricted antibody cross-reactivity may reflect the dual role of the E. coli ada protein not only in DNA repair but in positive gene regulation.

Bacillus subtilis↗
PubMed1987

The role of O6-methylguanine in human cell killing, sister chromatid exchange induction and mutagenesis: a review.

O6-methylguanine (O6mG) produced in DNA by such SN1 methylating agents as N-methyl-N-nitrosourea and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) has been suggested by some to be the lesion that leads to certain biological endpoints in mammalian cells: cell killing, sister chromatid exchange (SCE) production, mutagenesis and cellular transformation. Other evidence is interpreted as inconsistent with this point of view. The finding of Karran & Williams (1985) that O6mG delivered to cells in culture resulted in the depletion of the activity of the protein responsible for repair of O6mG in DNA (O6mG-DNA methyltransferase, O6MT) provided a tool for the assessment of the role of O6mG in producing biological endpoints. In this paper we review much of the literature on human cells pertinent to this question. In addition we present our survival data obtained using the depletion technique of Karran & Williams as well as data supporting a model invoking a mismatch and excision response to O6mG proposed by Sklar & Strauss (1980). Although data linking O6mG to causation are inconclusive, it is premature to conclude that O6mG is not a lesion lethal to certain cultured cells.

Adenoviridae↗
PubMed1986

Transfection of DNA from a chloroethylnitrosourea-resistant tumor cell line (MER+) to a sensitive tumor cell line (MER-) results in a tumor cell line resistant to MNNG and CNU that has increased O-6-methylguanine-DNA methyltransferase levels and reduced levels of DNA interstrand crosslinking.

A subclone of a human glioma tumor cell strain which was deficient at O-6-alkylguanine repair was transfected with DNA from an O-6-alkylguanine DNA alkyltransferase-positive human colon tumor cell line (HT29). The transfected subclone, which was selected by its resistance to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), acquired increased resistance to chloroethylnitrosourea (CNU), contained O-6-methylguanine-DNA methyltransferase activity, and failed to accumulate interstrand crosslinks in its DNA upon treatment with CNU. The subclone morphologically resembled its CNU-sensitive parental glioma cell strain. The close correlation between the increased cellular resistance, increased O-6-alkylguanine repair activity and the absence of crosslinking suggests that the formation of DNA crosslinks is one important mechanism of cytotoxicity produced by CNU, and that repair of DNA lesions by O-6-alkylguanine DNA alkyltransferase may partially prevent CNU-induced cytotoxicity.

Cell Line↗
PubMed1986

Inactivation of O6-methylguanine-DNA methyltransferase and sensitization of human tumor cells to killing by chloroethylnitrosourea by O6-methylguanine as a free base.

Human fibroblasts and tumor cells with constitutive levels of the DNA repair protein O6-methylguanine-DNA methyltransferase were incubated with mM concentrations of the free base O6-methylguanine for up to 24 h. This treatment depleted the cells of their transferase activity, and sensitized the cells to killing by the antineoplastic drug 1-[2-chloroethyl]-1-nitrosourea. Cells constitutively lacking the methyltransferase were not sensitized to cell killing. Cell free extracts incubated with O6-methylguanine also lost methyltransferase activity. Other alkylpurines, such as O6-methylguanosine, S6-methylthioguanine, O6-ethylguanine, and 3-methyladenine, did not have this effect on extracts of human tumor cells, while O6-methylguanosine and O6-methylguanine inactivated purified methyltransferase from Escherichia coli. The data suggest that the free base O6-methylguanine is probably a substrate for the methyltransferase. Calculation of the second order rate constants for free base versus O6-methylguanine in DNA, and experiments in which the free base was mixed with DNA containing O6-methylguanine before reaction with methyltransferase, indicated that the base in DNA is about 4 X 10(7) better as a substrate than is the free base. These results demonstrate that DNA repair capacity of tumor cells can be diminished without DNA damage, and suggest a method for increasing the efficiency of chemotherapy.

Cell Survival↗
PubMed1985

Quantitation of DNA repair capacities of human tumor cells by estimation of transfer of DNA adducts to repair proteins.

The repair of O6-methylguanine produced in DNA by alkylating agents is accomplished by a unique lesion reversal mechanism which recognizes the methyl group and transfers it to itself in a suicide reaction. Much of what we know about the importance of O6-methylguanine-DNA methyltransferase repair in human cells comes from the study of Mer- tumor cell strains which are deficient in transferase activity. The human transferase has a preference for repair of methyl groups, but will also act on other substrates. Assays for transferase activity detect either the loss of O6-methylguanine from DNA or the appearance of methylated protein. A new assay detects the recovery of a restriction site in a synthetic polymer following demethylation. Inhibition of transferase activity can be produced in cells by several methods.

Cell Line↗
PubMed1985

Human tumor cell strains both unable to repair O6-methylguanine and hypersensitive to killing by human alpha and beta interferons.

Human brain tumor cell strains were previously found by others to be sensitive to growth inhibition by human interferon-beta (HuIFN-beta). We noticed that the sensitive strains were some that we had found deficient in the repair of O6-methylguanine (O6MeG), a characteristic of 20% of the human tumor cell strains we have studied. We confirmed this sensitivity to HuIFN-beta, and have further shown that human brain tumor cells which repair O6MeG are resistant to the growth inhibitory effects of HuIFN-beta. In addition, treatment with HuIFN-alpha or HuIFN-beta resulted in more killing (reproductive inactivation) of six human tumor cell strains deficient in repairing O6-methylguanine in DNA than did such treatment of six strains of cells proficient in such repair. Further, we found two human lines, altered to become O6MeG repair deficient after establishment of the primary tumor cell culture, that were resistant to interferon. IFN treatment produced no DNA damage detectable by either chemical or biological assays. It is suggested that the genes responsible for resistance to IFN treatment and to agents that produce O6MeG are often coordinately shut down.

Brain Neoplasms↗
PubMed1985

Human O6-alkylguanine-DNA alkyltransferase fails to repair O4-methylthymine and methyl phosphotriesters in DNA as efficiently as does the alkyltransferase from Escherichia coli.

The repair of alkylated poly(dT) annealed to poly(dA) and alkylated DNA was studied using human cells in culture, extracts of human liver and Escherichia coli, and partially purified O6-alkylguanine-DNA alkyltransferase from human liver. The human alkyltransferase behaved as if the transferring and accepting functions of the repair process resided on the same molecule. Extracts of E. coli efficiently repaired O6-methylguanine, O4-methylthymine and methyl phosphotriesters in DNA. In contrast, cultured human cells and extracts from human liver repaired O6-methylguanine but did not repair O4-methylthymine or methyl phosphotriesters in DNA nearly as efficiently as did the E. coli extracts.

Alkylation↗
PubMed1984

Relationship of methyl purines produced by MNNG in adenovirus 5 DNA to viral inactivation in repair-deficient (Mer-) human tumor cell strains.

Adenovirus 5 treated with MNNG (N-methyl-N'-nitro-N-nitrosoguanidine) has greater plaque-forming ability in cell strains having the Mer+ phenotype than in strains having the Mer- phenotype. MNNG-treated Mer- strains repair the N3-methyladenine (N3MeA) but not the O6-methylguanine (O6MeG) produced in their DNA, while MNNG-treated Mer+ strains repair both of these adducts. The fate of N7-methylguanine (another DNA adduct produced by MNNG) is similar in Mer+ and Mer- strains. We show in this paper that 2.3 +/- 0.4 O6MeG and 1.4 N3MeA per adenovirus genome correlate with one lethal hit when the survival assay is done using Mer- strains as viral hosts. We suggest that O6MeG is the lesion lethal to the virus.

Adenoviruses, Human↗
PubMed1984

O6-Methylguanine-DNA methyltransferase in human cells.

O6-Methylguanine-DNA methyltransferase activity was measured in extracts of human tumor cells and was partially purified from human placenta. Repair of O6-methylguanine in DNA inactivated the methyltransferase, and treatment of cells with MNNG, which produces this alkylated base in DNA, depleted the cells of active methyltransferase. RNA and protein synthesis were required for restoration of methyltransferase activity, which transiently exceeded the original levels by 50% 48 h after treatment. One species of methyltransferase of Mr = 22 kd was present in human tumor cells and human placenta.

Astrocytoma↗
PubMed1984

Comparison of repair of O6-methylguanine produced by N-methyl-N'-nitro-N-nitrosoguanidine in mouse and human cells.

The repair of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-produced O6-methylguanine (O6-MeG) in DNA and its correlation with MNNG-produced cell-killing and sister chromatid exchange (SCE) induction were compared in mouse and reference human tumor cell strains. As a result, mouse cell strains were divided into three groups: (i) cells proficient in O6-MeG-repair and insensitive to MNNG similar to human Mer+ Rem+ strains; (ii) cells deficient in O6-MeG-removal and sensitive to MNNG similar to human Mer-Rem- strains; (iii) cells deficient in O6-MeG-removal but insensitive to MNNG similar to some SV40-transformed human strains. Attempts at correlating lack of capacity for O6-MeG-removal, MNNG-sensitivity and high SCE induction showed that O6-MeG in DNA may be a lesion common to cell-killing and SCE induction only in mouse cells of groups i and ii. Levels of O6-MeG-DNA methyltransferase activity in mouse cells were measured and the enzyme had the same molecular weight as that in human cells.

Animals↗
PubMed1984

Hybrids between human tumor cell strains differing in repair of MNNG-produced DNA damage.

Human tumor cell strains with differing responses to MNNG damage in their DNA were treated with precipitates of the plasmids pSV2gpt or pSV2neo . Transfected clones were selected on the basis of the drug resistance which each plasmid confers. Cells with different drug resistances were fused and hybrids were selected in medium requiring the expression of both markers. Hybrids produced by fusion of two different strains hypersensitive to MNNG-produced cytotoxicity and which lack the DNA repair enzyme O6-methylguanine-DNA methyltransferase ( O6MT ) failed to show complementation, suggesting that these strains share a common genetic defect. Hybrids from fusions of each of three strains containing O6MT activity with the same strain lacking O6MT activity were of surprising character. In one case the hybrid had resistance to MNNG-produced cell killing and O6MT activity similar to the parent strain possessing O6MT activity. In a second case, the hybrid had greater resistance to MNNG produced cytotoxicity than either parent strain although the level of O6MT activity was not higher. In a third case, the hybrid had little or no O6MT and as great hypersensitivity to MNNG-produced cytotoxicity as the parent strain lacking O6MT activity. We conclude that the survival of human tumor cell strains after MNNG-produced DNA damage is controlled by several genes. Even individual repair enzymes, like O6MT , are likely to be regulated by the interaction of these genes.

Animals↗
PubMed1983

Repair of O6-methylguanine in DNA by demethylation is lacking in Mer- human tumor cell strains.

The ability of extracts of human tumor cells to demethylate O6-methylguanine (O6-MeG) in DNA was assayed using the synthetic DNA polymer poly(dC,dG,m6dG). Cell strains proficient in repair of O6-MeG in vivo (Mer+ phenotype) contained a methyltransferase activity while repair deficient cells (Mer- phenotype) had little or no activity. Mixing extracts of different Mer- strains did not result in the appearance of the activity. Extracts of Mer- cells did not inhibit the activity in extracts of Mer+ cells. Both Mer+ and Mer- strains contained methylnitrosourea-damage-specific endonuclease activity. The data suggest that the Mer- strains are deficient in methyltransferase and that this is the fundamental reason for their hypersensitivity to the cytotoxic effects of DNA alkylation. The activity was partially purified from a Mer+ colon carcinoma cell strain. Its kinetics parallel the repair of O6-MeG in DNA in vivo and suggest that the activity is inactivated during repair of DNA.

DNA Repair↗
PubMed1981

Excision repair and patch size in UV-irradiated bacteriophage T4.

We determined the average size of excision repair patches in repair of UV lesions in bacteriophage T4 by measuring the photolysis of bromodeoxyuridine incorporated during repair. The average patch was small, approximately four nucleotides long. In control experiments with the denV1 excision-deficient mutant, we encountered an artifact, a protein(s) which remained bound to phenol-extracted DNA and prevented nicking by the UV-specific endonucleases of Micrococcus luteus and bacteriophage T4.

Carrier Proteins↗
PubMed1981

Permeabilization of ultraviolet-irradiated Chinese hamster cells with polyethylene glycol and introduction of ultraviolet endonuclease from Micrococcus luteus.

Chinese hamster V-79 cells were made permeable by treatment with polyethylene glycol and then incubated with a Micrococcus luteus extract containing ultraviolet-specific endonuclease activity. This treatment introduced nicks in irradiated, but not in unirradiated, deoxyribonucleic acid. The nicks remained open for at least 3 h; there was no loss of endonuclease-sensitive sites, and no excision of dimers as measured by chromatography was detected. In addition, there was no increase in ultraviolet resistance in treated cells. This suggests that the absence of a significant amount of excision repair in rodent cells is due to the lack of both incision and excision capacity.

Animals↗
PubMed1978

UV-induced mutation in bacteriophage T4.

Two late gene am mutants of bacteriophage T4 that can be induced to revert by UV were crossed to a temperature-sensitive ligase mutant. In the double mutants, UV-induced reversion was eliminated at a semirestrictive temperature. When the single am mutants were irradiated and then allowed a single passage in a permissive host, the UV-induced reversion frequency was increased by 15- to 25-fold. This increased mutagenesis was also abolished by the presence of the ligase allele. When the UV-irradiated single am mutants multiply infected a permissive host, allowing multiplicity reactivation to occur, the induced reversion frequency was reduced similarly to the reduction in lethality. The mutagenesis that remained was again abolished by the presence of the ligase allele. It is concluded that UV induces mutations in phage T4 through the action of a pathway that includes polynucleotide ligase. The increase in mutation frequency after growth in a permissive host implies that mutagenesis can occur at more than one stage of the infection rather than only in an early stage before expression of the mutant genome. The process of multiplicity reactivation appears to be error-free since it overcomes lethal lesions without inducing new mutations.

Coliphages↗