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PubMed1991

Antimutagenic activities of naturally occurring polyamines in Chinese hamster ovary cells in vitro.

Spermine and spermidine, ubiquitous polyamines present in bacteria and animal cells, are also involved in cell growth. Since they interact with the double helix, they can stabilize the DNA molecule. Recent evidence of the antimutagenic and anticarcinogenic capacity of spermine has focused attention on the mechanism(s) by which such agents can protect cells from induced damages. In the present paper we show the ability of spermine and spermidine to decrease the level of sister chromatid exchanges induced in Chinese hamster ovary cells cultivated in vitro, by treating them with Psoralen + UVA irradiation (able to induce mainly monoadducts and DNA cross-links). Two different mechanisms of polyamine action can be invoked to explain the preservative activity of this class of agents.

Animals↗
PubMed1979

Mutagenicity of cross-links and monoadducts of furocoumarins (psoralen and angelicin) induced by 360-nm radiation in excision-repair-defective and radiation-insensitive strains of Saccharomyces cerevisiae.

The furocoumarin psoralen can form both monoadducts and cross-links with DNA when combined with 360-nm radiation, whereas the analog angelicin can form monoadducts only. Psoralen plus 360-nm radiation causes mutation induction with a slope of 2 (log-log plot) for a radiation-insensitive strain, whereas angelicin action with 360-nm radiation displays a slope of unity. For a radiation-sensitive mutant defective in the excision-repair pathway, the actions of both angelicin and psoralen plus 360-nm radiation exhibit one-target kinetics, but at higher exposures psoralen plus 360-nm radiation assumes a slope of 2. The excision-repair-defective strain is considerably more sensitive to the furocoumarins plus 360-nm radiation than is the radiation-insensitive strain, both for killing and mutation induction. The simplest explanation for the data is that both cross-links and monoadducts, formed by furocoumarins with DNA when exposed to 360-nm radiation, are capable of inducing mutations, and that monoadducts are repaired 20 times more efficiently than cross-links by the excision-repair pathway.

DNA Repair↗
PubMed1995

Melanoma and use of sunscreens: an Eortc case-control study in Germany, Belgium and France. The EORTC Melanoma Cooperative Group.

Use of sunscreens is widely advocated as a preventive measure against sun-induced skin cancers. However, to date, no epidemiologic study has reported a decreased melanoma risk associated with sunscreen use. We have conducted a case-control study aimed at evaluating the influence of sunscreen use on the occurrence of cutaneous malignant melanoma. In 1991 and 1992, 418 melanoma cases and 438 healthy controls were interviewed in Germany, France and Belgium. The questionnaire used differentiated between regular sunscreens, psoralen sunscreen (prepared with 5-methoxypsoralen, a tanning activator and photocarcinogen), and self-tanning cosmetics (which produce a tan without ultraviolet radiation). After adjusting for age, sex, hair colour and holiday weeks spent each year in sunny resorts, the melanoma risk was of 1.50 (95% Cl:1.09-2.06) for regular sunscreens, and of 2.28 (95% Cl: 1.28-4.04) for psoralen sunscreens. No melanoma risk was associated with use of self-tanning cosmetics. Among subjects with a poor ability to tan, psoralen sunscreen users displayed a melanoma risk of 4.45 (95% Cl: 1.25-15.8) when compared with regular sunscreen users. There was a significant negative interaction between regular sunscreen use and sunburns experienced in adulthood. Use of sunscreens, especially psoralen sunscreen, was associated with higher density of pigmented lesions of the skin. Although we cannot exclude the presence of an unknown confounding factor, our results support the hypothesis that sunscreens do not protect against melanoma, probably because of their ability to delay or avoid sunburn episodes, which may allow prolonged exposure to unfiltered ultraviolet radiation. Serious doubts are raised regarding the safety of sunscreens containing psoralens.

Adult↗
PubMed1993

Disruption of the nucleosomes at the replication fork.

The fate of parental nucleosomes during chromatin replication was studied in vitro using in vitro assembled chromatin containing the whole SV40 genome as well as salt-treated and native SV40 minichromosomes. In vitro assembled minichromosomes were able to replicate efficiently in vitro, when the DNA was preincubated with T-antigen, a cytosolic S100 extract and three deoxynucleoside triphosphates prior to chromatin assembly, indicating that the origin has to be free of nucleosomes for replication initiation. The chromatin structure of the newly synthesized daughter strands in replicating molecules was analysed by psoralen cross-linking of the DNA and by micrococcal nuclease digestion. A 5- and 10-fold excess of protein-free competitor DNA present during minichromosome replication traps the segregating histones. In opposition to published data this suggests that the parental histones remain only loosely or not attached to the DNA in the region of the replication fork. Replication in the putative absence of free histones shows that a subnucleosomal particle is randomly assembled on the daughter strands. The data are compatible with the formation of a H3/H4 tetramer complex under these conditions, supporting the notion that under physiological conditions nucleosome core assembly on the newly synthesized daughter strands occurs by the binding of H2A/H2B dimers to a H3/H4 tetramer complex.

Animals↗
PubMed1994

Assembly of phage phi 29 genome with viral protein p6 into a compact complex.

The formation of a multimeric nucleoprotein complex by the phage phi 29 dsDNA binding protein p6 at the phi 29 DNA replication origins, leads to activation of viral DNA replication. In the present study, we have analysed protein p6-DNA complexes formed in vitro along the 19.3 kb phi 29 genome by electron microscopy and micrococcal nuclease digestion, and estimated binding parameters. Under conditions that greatly favour protein-DNA interaction, the saturated phi 29 DNA-protein p6 complex appears as a rigid, rod-like, homogeneous structure. Complex formation was analysed also by a psoralen crosslinking procedure that did not disrupt complexes. The whole phi 29 genome appears, under saturating conditions, as an irregularly spaced array of complexes approximately 200-300 bp long; however, the size of these complexes varies from approximately 2 kb to 130 bp. The minimal size of the complexes, confirmed by micrococcal nuclease digestion, probably reflects a structural requirement for stability. The values obtained for the affinity constant (K(eff) approximately 10(5) M-1) and the cooperativity parameter (omega approximately 100) indicate that the complex is highly dynamic. These results, together with the high abundance of protein p6 in infected cells, lead us to propose that protein p6-DNA complexes could have, at least at some stages, during infection, a structural role in the organization of the phi 29 genome into a nucleoid-type, compact nucleoprotein complex.

Bacillus Phages↗
PubMed1979

Specific cellular defects in patients with Fanconi anemia.

Measurements of plating efficiency, accumulation of metaphases and generation times have shown that fibroblast from patients with Fanconi anemia (FA) have decreased probability of completing a further division after successful mitosis. Thus FA cells show decreased growth rates and increased generation times. We have also measured the survival of FA fibroblasts and lymphoblasts after treatment with a variety of mutagens. All FA cells show an increased sensitivity to drugs such as MMC and psoralen plus long wave length UV which cause DNA interstrand crosslinks. FA strains show varying degrees of sensitivity to these drugs and the extent of this sensitivity seems to be characteristic of each patient. FA cells are equal to controls in their sensitivity to other alkylating agents such as ethyl methane sulfonate, N-methyl-N1-nitro-N-nitrosoguanidine and actinomycin D. Both the decreased growth and increased drug sensitivity may result from defect in DNA replication or repair.

Adolescent↗
PubMed2001

Reversed-phase high-performance liquid chromatography (RP-HPLC) determination of lipophilicity of furocoumarins: relationship with DNA interaction.

The partition coefficient (P) of 82 furocoumarins and analogs (psoralens, angelicins, allopsoralens, 8-azapsoralens, angular furoquinolin-2-ones, sulfur and selenium isosters of psoralen and angelicin) has been determined by reversed-phase HPLC. The chromatographic behavior correlates well with the in vitro affinity of the compounds toward DNA.

Chromatography, High Pressure Liquid↗
PubMed1977

Preparation and skin-photosensitizing activity of substituted psoralens.

8-Monosubstituted and 5,8-disubstituted psoralen derivatives were prepared, and their skin-photosensitizing activity was evaluated. The results were correlated in terms of molecular configuration, and 8-allyloxypsoralen can be considered was a new agent of potent photodynamic activity.

Adjuvants, Pharmaceutic↗
PubMed2004

Mutation frequencies in murine keratinocytes as a function of carcinogenic status.

A link between genetic abnormalities and carcinogenesis is well established. It follows that a correlation exists between mutation frequency and malignant progression. We have determined the spontaneous and DNA damage-induced mutation frequencies for a series of cell lines derived from SENCAR mouse keratinocytes at various stages of malignant progression. Nontumorigenic mouse keratinocytes (3PC), papillomas (MT1/2), squamous-cell carcinomas (CH72), and spindle-cell carcinomas (CH72T4) were transfected with damaged or undamaged shuttle vectors containing a supF mutation reporter gene. The plasmid mutation frequencies were determined by blue/white screening. The spontaneous plasmid mutation frequency of the squamous-cell carcinoma line was slightly higher than the mutation frequencies of the other cell lines tested. The DNA damage induced by triplex-directed psoralen crosslinks increased the mutation frequencies sixfold to eighteenfold in all cell lines tested, with no significant differences among the cell lines. Sequence analyses revealed that the spindle-cell carcinoma line had a different spontaneous mutation spectrum from the other cell lines. DNA damage-induced mutations were predominantly point mutations at the triplex-duplex junction in all of the cell lines tested, as expected. These data suggested that a strong mutator phenotype was not required for progression to an advanced malignant phenotype in our model system.

Animals↗
PubMed2001

Characterization of the mutational specificity of DNA cross-linking mutagens by the Lac+ reversion assay with Escherichia coli.

The mutational specificities of DNA cross-linking compounds such as cisplatin, transplatin, carboplatin, mitomycin C, psoralen, and 8-methoxypsoralen were investigated in lacZ reversion assay systems of Escherichia coli. Tester strains were constructed by introducing the six kinds of F' plasmids (lacI-, lacZ461, and proAB+), each of which carries a different base-substitution mutation within the lacZ gene. Each of the six possible base-substitution mutations was assayed by Lac+ reversion. Cisplatin induced G.C-->A.T transitions and G.C-->T.A transversions, with the former predominating. Transplatin induced A.T-->G.C transitions in addition to G.C-->A.T transitions and G.C-->T.A. Carboplatin weakly induced G.C-->A.T transitions. On the other hand, mitomycin C induced only G.C-->T.A transversions, while psoralen and 8-methoxypsoralen reactivated with near-UV irradiation induced A.T-->G.C transitions preferentially. The Lac(+) reversion system was very convenient for rapidly determining mutational spectra.

Antineoplastic Agents↗
PubMed1994

Quantitation of interferon gamma mRNA levels in psoralen/UVA-treated HUT-78 cells by competitive PCR.

We have developed a method to accurately quantitate IFN gamma mRNA in HUT-78 cells before and after PUVA treatment by the competitive RT/PCR technique, which could be utilized to accurately quantitate any mRNA species of interest. Total RNA was isolated from HUT-78 cells before and after PUVA treatment. A synthetic IFN gamma mRNA was made to contain a 54 bp deletion in the middle of IFN gamma cDNA gene and used as an internal standard. 0.5 microgram of target RNA was co-reverse transcribed and co-amplified with increasing concentrations of synthetic IFN gamma RNA using the same primers. The products of the synthetic RNA were separated from that of the target RNA by gel electrophoresis. This allowed determination of the amount of target IFN gamma mRNA to be quantitated by extrapolating against a standard curve. PUVA treatment of HUT-78 cells resulted in an increase in IFN gamma mRNA level from 32 to 80 pg/microgram of total RNA, suggesting that PUVA induces transcription of T-helper 1 cytokines as part of its mechanism of action.

Base Sequence↗
PubMedDate not supplied

Psoralen and UVA light: an in vitro investigation of multiple immunological mechanisms underlying the immunosuppression induction in allograft rejection.

Photopheresis (ECP) is a novel immunomodulatory therapy effectively used to treat several T-cell-mediated diseases and to reverse allograft rejection after organ transplantation. It consists of infusion of UVA-irradiated autologous leukocytes collected by apheresis and extracorporeally incubated with 8-methoxypsoralen (8-MOP). In this study we explored the potential immunological events for therapeutic efficacy of photopheresis in preventing allograft rejection by evaluating in vitro the combined effects of 8-MOP and UVA (PUVA) on multiple immunological parameters, such as induction of apoptosis, production of soluble mediators, and expression of cell antigens. Peripheral blood mononuclear cells (PBMCs) obtained from healthy subjects were treated with 8-MOP and UVA at the same doses as those clinically used in ECP. We demonstrate that PUVA treatment induced leukocyte hyporesponsiveness and a decrease in expression of co-stimulatory and adhesion molecules as well as of cytokine levels. Additionally, PUVA treatment induced apoptosis in both mononuclear cells (possibly through the Fas/FasL system and/or the CD38 pathway) and purified monocytes. In conclusion, our work focuses attention on the initial phase of immune response and identifies some new targets of therapy (e.g., costimulatory molecules) able to trigger final effects underlying therapeutic efficacy of photopheresis.

Adolescent↗
PubMed1998

Abnormal DNA damage-inducible protein in cells from Sjögren's syndrome patients.

Antinuclear antibodies are commonly found in patients with Sjögren's syndrome. It has been suggested that the development of antinuclear antibodies depends on the activation of the spliceosome and other transcription-related subcellular particles, some of which have recently been shown also to function in DNA-modifying processes, such as DNA repair and V(D)J recombination. These observations add weight to a previously proposed model for the aetiology of Sjögren's syndrome. This includes the abnormal processing of the T-cell receptor and immunoglobulin genes. To test this hypothesis further, the present study on DNA-modifying proteins in Sjögren's syndrome was initiated. Gel-shift experiments using protein extracted from UV-treated Sjögren cells provided evidence of high molecular weight DNA-binding protein in six out of 12 Sjögren patients studied (but not among seven healthy controls). Some Sjögren sera displayed antibodies to protein extracts from cells treated with psoralen plus UVA radiation. These results indicate an abnormal DNA damage-inducible response in Sjögren's syndrome. It may therefore be concluded that alterations in nuclear protein may play a role in the aetiology of Sjögren's syndrome.

Antibodies, Antinuclear↗
PubMed1996

The stability of nucleosomes at the replication fork.

Purified simian virus (SV40) minichromosomes were photoreacted with psoralen under various conditions that moderately destabilize nucleosomes. This assay allows indirect distinction between stable nucleosomes, partially unravelled nucleosomes and nucleosomes containing (or lacking) histone H1. In replicating molecules the passage of the replication machinery destabilizes the nucleosomal organization of the chromatin fiber over a distance of 650 to 1100 bp. In front of the fork, an average of two nucleosomes are destabilized presumably by the dissociation of histone H1 and the advancing replication machinery. On daughter strands, the first nucleosome is detected at a distance of about 260 nucleotides from the elongation point. This nucleosome is interpreted to contain no histone H1, while no stepwise association of (H3-H4)2 tetramers with H2A/H2B dimers on nascent DNA can be detected in vivo. The second nucleosome after the replication fork appears to contain histone H1. The prolonged nuclease sensitivity of newly replicated chromatin described in the literature therefore may not be due to a slow reassociation of histone H1.

Animals↗
PubMed1999

Asymmetric recognition of psoralen interstrand crosslinks by the nucleotide excision repair and the error-prone repair pathways.

Psoralen is an asymmetric photoreactive intercalator with a furane and a pyrone side. When intercalated at 5'-TpA-3' sites and upon UVA irradiation, the psoralen can react with the thymine residues on both strands, introducing an interstrand crosslink. Using psoralen-coupled triple-helix-forming oligonucleotides, psoralen interstrand crosslinks can be site-specifically introduced in the coding sequence of URA3, a yeast auxotrophic marker carried on plasmid vectors. In addition, crosslinks introduced via a triple-helix-forming oligonuleotide are oriented with the furane side of the psoralen associated with a specific strand of the target sequence. Here, the transformation efficiency, the mutation frequency and the mutational spectra of site-specifically placed and oriented crosslinks were examined in yeast cells. We found that the nature of the targeted mutations depended on the crosslink orientation: bypass of the pyrone-adducted thymine yielded T-->A or T-->C substitutions and A insertions, while bypass of the furane-adducted thymine yielded T-->G substitutions and G insertions. Thus, the structure of the damage strongly influences the choice of the nucleotide incorporated during translesion synthesis. In addition, the observed pattern of mutagenesis suggests a coupling to transcription, similar to the one observed in mammalian cells. Finally, the substitutions affected only the coding strand when the pyrone link of the psoralen crosslink was on this strand, whereas they affected both strands when the pyrone link was on the transcribed strand, suggesting that the incision preference of psoralen crosslinks, which has been observed with purified uvrABC proteins in bacteria, is conserved in live eucaryotic cells.

Base Sequence↗
PubMed2001

Selective recognition of pyrimidine motif triplexes by a protein encoded by the bacterial transposon Tn7.

The bacterial transposon Tn7 is distinguished among mobile genetic elements by its targeting abilities. Recently, we reported that Tn7 is able to selectively insert adjacent to triple-helical DNA. The binding of TnsC, a Tn7-encoded protein, to the triplex DNA target leads to the specific transposition of Tn7 adjacent to both inter- and intramolecular pyrimidine motif triplexes. Here, we further probe how Tn7 targets triplex DNA. We report that TnsC discriminates between different types of triplexes, showing binding preference for pyrimidine but not for purine motif intermolecular triplex DNA. The binding preferences of TnsC and the Tn7 insertion profiles were obtained using psoralenated, triplex- forming oligonucleotides annealed to plasmid DNAs. Although the presence of psoralen is not required for targeting nor is it alone able to attract TnsC, we show that the location of psoralen within the pyrimidine motif triplex does alter the position of Tn7 insertion relative to the triplex. Comparison between the triplex-targeting pathway and the highly site-specific targeting pathway mediated by the binding of the Tn7-encoded protein, TnsD, to the unique site attTn7, suggests that similar structural features within each target DNA are recognized by TnsC, leading to site-specific transposition. This work demonstrates that a prokaryotic protein involved in the targeting and regulation of Tn7 translocation, TnsC, can selectively recognize pyrimidine motif triplexes.

Animals↗
PubMed2001

The crystal structures of psoralen cross-linked DNAs: drug-dependent formation of Holliday junctions.

The single-crystal structures are presented for two DNA sequences with the thymine bases covalently cross-linked across the complementary strands by 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT). The HMT-adduct of d(CCGCTAGCGG) forms a psoralen-induced Holliday junction, showing for the first time the effect of this important class of chemotheraputics on the structure of the recombination intermediate. In contrast, HMT-d(CCGGTACCGG) forms a sequence-dependent junction. In both structures, the DNA duplex is highly distorted at the thymine base linked to the six-member pyrone ring of the drug. The psoralen cross-link defines the intramolecular interactions of the drug-induced junction, while the sequence-dependent structure is nearly identical to the native Holliday junction of d(CCGGTACCGG) alone. The two structures contrast the effects of drug- and sequence-dependent interactions on the structure of a Holliday junction, suggesting a role for psoralen in the mechanism to initiate repair of psoralen-lesions in mammalian DNA.

Animals↗
PubMed1999

Psoralen cross-linking as probe of torsional tension and topological domain size in vivo.

DNA within a cell is organized with unrestrained torsional tension, and each molecule is divided into multiple individual topological domains. Psoralen photobinding can be used as an assay for supercoiling and topological domain size in living cells. Psoralen photobinds to DNA at a rate nearly linearly proportional to superhelical density. Comparison of the rate of photobinding to supercoiled and relaxed DNA in cells provides a measure of superhelical density. For this, in vivo superhelical tension is relaxed by the introduction of nicks by either ionizing radiation or photolysis of bromodeoxyuridine in the DNA. Since nicks are introduced in a random fashion, the distribution of nicks is described by a Poisson distribution. Thus, after nicking, the fraction of topological domains containing no nicks is described by the zero term of the Poisson distribution. From measurement of the number of nicks introduced in the DNA and the fraction of torsional tension remaining, an average topological domain size can be estimated. Using this logic, procedures were designed and described for measuring supercoiling and domain size at specific sites in eukaryotic genomes.

Amanitins↗