Polycyclic aromatic hydrocarbon carcinogens increase ubiquitination of p21 protein after the stabilization of p53 and the expression of p21

Polycyclic aromatic hydrocarbon carcinogens (PAHs) and their metabolites have been found to result in a rapid accumulation of p53 gene product in human and mouse cells. However, the induced p53 protein was reported to be transcriptionally inactive. In the present study, the induction of p53 target gene expression after the treatment with either benzo(a)pyrene (B[a]P) or 1-nitropyrene (1-NP) was investigated. A marked induction of messenger RNA (mRNA) expressions of Mdm2, Bax, and p21 was detected in wild-type p53-expressing cells after the treatment with either B[a]P or 1-NP, whereas no significant change in mRNA expression of these genes was observed in p53-negative and mutant cells. 1-NP activated the p21 promoter in a p53-dependent manner. Binding activity of p53 to a p53 consensus sequence increased after the treatment in wild-type p53-expressing cells. Nevertheless, the induced mRNA levels of the p21 did not result in a proportional p21 protein increase, indicating the possibility of post-transcriptional regulation of the protein. With the addition of MG-132, a proteasome inhibitor, to B[a]P or 1-NP treatments, both p21 and p53 protein levels were increased; however, the increase in p21 protein levels was significantly larger than the increase in p53 protein levels. PAHs treatment increased the level of ubiquitinated p21. These results suggest that the p21 product is degraded by the ubiquitin-proteasome system. We conclude that PAHs-induced p53 protein is transcriptionally active.

Leukotrienes and tyrosine phosphorylation mediate stretching-induced actin cytoskeletal remodeling in endothelial cells

We studied actin cytoskeletal remodeling and the role of leukotrienes and tyrosine phosphorylation in the response of endothelial cells to different types of cyclic mechanical stretching. Human aortic endothelial cells were grown on deformable silicone membranes subjected to either cyclic one-directional (strip) stretching (10%, 0.5 Hz), or biaxial stretching. After 1 min of either type of stretching, actin cytoskeletons of the stretched cells were already disrupted. After stretching for 10 and 30 min, the percentage of the stretched cells that had disrupted actin cytoskeletons were significantly increased, compared with control cells without stretching. Also, at these two time points, biaxial stretching consistently produced higher frequencies of actin cytoskeleton disruption. At 3 h, strip stretching caused the formation of stress fiber bundles, which were oriented nearly perpendicular to the stretching direction. With biaxial stretching, however, actin cytoskeletons in many stretched cells were remodeled into three-dimensional actin structures protruding outside the substrate plane, within which cyclic stretching was applied. In both stretching conditions, actin filaments were formed in the direction without substrate deformation. Moreover, substantially inhibiting either leukotriene production with nordihydroguaiaretic acid or tyrosine phosphorylation with tyrphostin A25 did not block the actin cytoskeletal remodeling. However, inhibiting both leukotriene production and tyrosine phosphorylation completely blocked the actin cytoskeletal remodeling. Thus, the study showed that the remodeling of actin cytoskeletons of the stretched endothelial cells include rapid disruption first and then re-formation. The resulting pattern of the actin cytoskeleton after remodeling depends on the type of cyclic stretching applied, but under either type of cyclic stretching, the actin filaments are formed in the direction without substrate deformation. Finally, leukotrienes and tyrosine phosphorylation are necessary for actin cytoskeletal remodeling of the endothelial cells in response to mechanical stretching.

The environmental pollutant pyrene induces the production of IL-4

BACKGROUND

Epidemiologic studies and experiments with mouse models suggest that polyaromatic hydrocarbons contained in, among others, diesel exhaust particles can promote the development of allergy.

OBJECTIVE

Because IL-4 organizes allergic responses in vivo, we have investigated whether pyrene, a major compound of diesel exhaust particles, can affect the production of IL-4.

METHODS

IL-4 production by primary human T cells was assessed by ELISA and messenger RNA transcription was detected by Northern blotting. Activation of the IL-4 promoter was tested in reporter gene assays with transiently transfected cell lines.

RESULTS

Pyrene induced transcription of IL-4 messenger RNA and expression of IL-4 protein in primary human T cells. Pyrene, but not related polyaromatic hydrocarbons, enhanced basal transcription of the human and mouse IL-4 promoter.

CONCLUSION

Our results suggest that pyrene may promote allergic diseases by inducing the production of IL-4.

Inhibitors of the carrier-mediated influx of auxin in suspension-cultured tobacco cells

Active auxin transport in plant cells is catalyzed by two carriers working in opposite directions at the plasma membrane, the influx and efflux carriers. A role for the efflux carrier in polar auxin transport (PAT) in plants has been shown from studies using phytotropins. Phytotropins have been invaluable in demonstrating that PAT is essential to ensure polarized and coordinated growth and to provide plants with the capacity to respond to environmental stimuli. However, the function of the influx carrier at the whole-plant level is unknown. Our work aims to identify new auxin-transport inhibitors which could be employed to investigate its function. Thirty-five aryl and aryloxyalkylcarboxylic acids were assayed for their ability to perturb the accumulation of 2,4-dichlorophenoxyacetic acid (2,4-D) and naphthalene-1-acetic acid (1-NAA) in suspension-cultured tobacco (Nicotiana tabacum L.) cells. As 2,4-D and 1-NAA are preferentially transported by the influx and efflux carriers, respectively, accumulation experiments utilizing synthetic auxins provide independant information on the activities of both carriers. The majority (60%) of compounds half-inhibited the carrier-mediated influx of [14C]2,4-D at concentrations of less than 10 microM. Most failed to interfere with [3H]NAA efflux, at least in the short term. Even though they increasingly perturbed auxin efflux when given a prolonged treatment, several compounds were much better at discriminating between influx and efflux carrier activities than naphthalene-2-acetic acid which is commonly employed to investigate influx-carrier properties. Structure-activity relationships and factors influencing ligand specificity with regard to auxin carriers are discussed.

Fluorophores at the N terminus of nascent chloramphenicol acetyltransferase peptides affect translation and movement through the ribosome

Structurally different fluorescent probes were covalently attached to methionyl-tRNA(f) and tested for their incorporation into nascent peptides and full-length protein using an Escherichia coli cell-free coupled transcription/translation system. Bovine rhodanese and bacterial chloramphenicol acetyltransferase (CAT) were synthesized using derivatives of cascade yellow, eosin, pyrene, or coumarin attached to [(35)S]Met-tRNA(f). All of the probes tested were incorporated into polypeptides, although less efficiently when compared with formyl-methionine. Eosin, the largest of the fluorophores used with estimated dimensions of 20 x 11 A, caused the largest reduction in product formed. The rate of initiation was reduced with the fluorophore-Met-tRNA(f) compared with fMet-tRNA(f) with pyrene having the least and eosin the biggest effect. Analysis of the nascent polypeptides showed that the modifications at the N terminus affected the rate at which nascent CAT peptides were elongated causing accumulation of peptides of about 4 kDa, possibly by steric hindrance inside the tunnel within the 50 S ribosomal subunit. Fluorescence measurements indicate that the probe at the N terminus of nascent pyrene-CAT peptides is in a relatively hydrophilic environment. This finding is in agreement with recent data showing cross-linking of the N terminus of nascent peptides to nucleotides of the 23 S ribosomal RNA.

Metabolism-based polycyclic aromatic acetylene inhibition of CYP1B1 in 10T1/2 cells potentiates aryl hydrocarbon receptor activity

We have used polycyclic aromatic hydrocarbon (PAH) alkyne metabolism-based inhibitors to test whether CYP1B1 metabolism is linked to aryl hydrocarbon receptor (AhR) activation in mouse embryo fibroblasts (MEF). 1-ethynylpyrene (1EP) selectively inactivated CYP1B1 dimethylbenzanthracene (DMBA) metabolism in C3H10T1/2 MEFs; whereas 1-(1-propynyl)pyrene (1PP) preferentially inhibited CYP1A1 activity in Hepa-1c1c7 mouse hepatoma cells (Hepa). In each cell type >90% inhibition of DMBA metabolism after 1 h treatment with each inhibitor (0.1 microM) was progressively reversed and then increased to levels seen with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induction (fourfold stimulation). It was found that 0.1 microM 1EP and 1PP maximally induce CYP1B1 and CYP1A1 mRNA levels in10T1/2 and Hepa cells, respectively, after 6 h. 1-Ethylpyrene (EtP), which lacks the activatable acetylene moiety, was far less effective as an inhibitor and as an inducer. AhR activation is essential for 1EP induction as evidenced by the use of AhR antagonists and AhR-deficient MEFs and absence of induction following inhibition of DMBA metabolism with carbon monoxide (CO). Inhibition of CYP1B1 was linked to enhanced AhR activation even at early stages prior to significant ligand depletion. 1EP and EtP were similarly effective in stimulating AhR nuclear translocation, though 5-10 times slower compared with TCDD, and produced no significant down-regulation of the AhR. TCDD activated AhR/Arnt complex formation with an oligonucleotide xenobiotic response element far more extensively than 1EP or EtP, even at concentrations of 1EP that increased CYP1B1 mRNA to similar levels. CO did not influence these responses to EtP, event hough CO treatment potentiated EtP induction of CYP1B1 mRNA. These differences suggest a fundamental difference between PAH/AhR and TCDD/AhR complexes where CYP1B1 metabolic activity regulates the potency, rather than the formation of the AhR/Arnt complex.

Plasmid-mediated expression of the UmuDC mutagenesis proteins in an Escherichia coli strain engineered for human cytochrome P450 1A2-catalyzed activation of aromatic amines

The mutagenic actions of many chemicals depend on the activities of bacterial "mutagenesis proteins", which allow replicative bypass of DNA lesions. Genes encoding these proteins occur on bacterial chromosomes and plasmids, often in the form of an operon (such as umuDC or mucAB) encoding two proteins. Many bacterial strains used in mutagenicity testing carry mutagenesis protein genes borne on plasmids, such as pKM101. Our objective was to introduce mutagenesis protein function into Escherichia coli strain DJ4309. This strain expresses recombinant human cytochrome P450 1A2 and NADPH-P450 reductase and carries out the metabolic conversion of aromatic and heterocyclic amines into DNA-reactive mutagens. We discovered that many mutagenesis-protein plasmids severely inhibit the response of strain DJ4309 to 2-amino-3,4-dimethylimid-azo[4,5-f]quinoline (MeIQ), a typical heterocyclic amine mutagen. Among many plasmids examined, one, pGY8294, a pSC101 derivative carrying the umuDC operon, did not inhibit MeIQ mutagenesis. Strain DJ4309 pGY8294 expresses active mutagenesis proteins, as shown by its response to mutagens such as 1-nitropyrene and 4-nitroquinoline 1-oxide (4-NQO), and is as sensitive as the parent strain DJ4309 to P450-dependent mutagens, such as MeIQ and 1-aminopyrene.

Synthesis of (E)-9-(1-pyrenyl)-4-hydroxynon-2-enal, a fluorescent probe of the (E)-4-hydroxynon-2-enal with retained biological properties

(E)-9-(1-pyrenyl)-4-hydroxynon-2-enal (FHNE), a fluorescent probe of (E)-4-hydroxynon-2-enal (HNE) is synthesised in seven steps and in 35% overall yield, starting from commercially available 1-pyrencarboxyaldehyde. When incubated with cultured HeLa cells this fluorescent probe penetrates cells and particularly concentrates in the region surrounding the nucleus. As the parent compound, HNE it is able to induce the activation of heat shock factor (HSF) and is able to induce the binding of HSF to heat shock element (HSE).

Pectins and xyloglucans exhibit antimutagenic activities against nitroaromatic compounds

Because a high daily consumption of polysaccharides-containing food is assessed to decrease the risk of cancer of the gastrointestinal system, different types of carbohydrates were investigated for their antimutagenic activity against different standard mutagens. Within the screening pronounced antimutagenic effects were found for xyloglucan and different pectins and pectin-like rhamnogalacturonans against 1-nitropyrene induced mutagenicity. Inhibition rates were dose-dependent and varied between 20 and 50%. Concerning the mode of action a direct interaction of the polymers with the cells is claimed, protecting the organisms from the mutagenic attack.

Antimutagenic effects of natural phenolic compounds in beans

Polyphenols in fruits, vegetables (e.g., flavonols like quercetin) and tea (e.g., catechins such as epigallocatechin gallate) are good antioxidants with antimutagenic and anticarcinogenic properties. In the present study, the Salmonella typhimurium tester strain YG1024 was used in the plate-incorporation test to examine the antimutagenic effect of phenolic compounds, extracted from common beans (Phaseolus vulgaris), on 1-NP and B[a]P mutagenicity. Dose-response curves for 1-NP and B[a]P were obtained; the number of net revertants/plate at the peak mutagenic dosage were 880 for 1-NP and 490 for B[a]P. For the antimutagenicity studies doses of 0.1 microg/plate and 2 microg/plate for 1-NP and B[a]P, respectively, were chosen. We obtained a dose-response curve of ellagic acid (EA) against B[a]P and 1-NP mutagenicity. To test the bean extract, a dose of 300 microg/plate of EA was chosen as the antimutagenic control. The EA and bean extracts were not toxic to the bacteria at the concentrations tested. The inhibitory effects of the bean extracts and EA against B[a]P mutagenicity were dose-dependent. The percentages of inhibition produced against B[a]P (2 microg/plate) using 300 microg/plate of EA and for the extracts 500 microg equivalent catechin/plate were 82%, 83%, 81% and 83% for EA, water extract, water/methanol extract and methanol extract, respectively. However, for 1-NP mutagenicity, only the methanolic extract from beans showed an inhibitory effect. These results suggest that common beans, as other legumes, can function as health-promoting foods.

Adjuvant activities of pyrene, anthracene, fluoranthene and benzo(a)pyrene in production of anti-IgE antibody to Japanese cedar pollen allergen in mice

We have previously demonstrated that pyrene in diesel-exhaust particles (DEP) has an adjuvant activity on immunoglobulin E (IgE) antibody production in mice immunized with Japanese cedar pollen allergen (JCPA) or ovalbumin (OA) intraperitoneally. The present study is concerned with the adjuvant activity in IgE antibody production against JCPA of pyrene or DEP inoculated intranasally in mice. We show that anthracene, fluoranthene and benzo(a)pyrene in DEP have the ability to enhance anti-JCPA IgE antibody production in mice by intranasal immunization. Mice were grouped, immunized with 10 micrograms of JCPA plus 400 micrograms of pyrene, 10 micrograms of JCPA plus 100 micrograms of DEP, 10 micrograms of JCPA plus 2 mg of aluminum hydroxide and 10 micrograms of JCPA alone intranasally 7 times at 2 week intervals. Mice were also grouped, and immunized with JCPA (10 micrograms) plus 40 micrograms of anthracene, JCPA (10 micrograms) plus 400 micrograms of fluoranthene, JCPA (10 micrograms) plus 40 micrograms of benzo(a)pyrene, and JCPA (10 micrograms) plus 400 micrograms of pyrene and JCPA (10 micrograms) alone. We found that the IgE antibody responses to JCPA in mice immunized with JCPA plus pyrene, JCPA plus DEP or JCPA plus the three chemical organic compounds mentioned above were significantly enhanced compared with those immunized with JCPA alone. In addition, when the intraperitoneal macrophages obtained from the normal mice (unimmunized mice) were incubated with pyrene, anthracene, fluoranthene or benzo(a)pyrene in vitro, an enhanced chemiluminescence (CI) response and interleukin-1 alpha (IL-1 alpha) production of the macrophages was observed in each instance. These results suggest that in the production of IgE antibody to JCPA the adjuvancy of polycyclic aromatic hydrocarbons (PAHs) in DEP may be important in an attack of Japanese cedar pollinosis.

Isolation of a Chinese hamster fibroblast variant defective in dihydroxyacetonephosphate acyltransferase activity and plasmalogen biosynthesis: use of a novel two-step selection protocol

We have developed a two-step selection protocol to generate a population of Chinese hamster ovary (CHO) cell variants that are plasmalogen-deficient, but contain intact, functional peroxisomes (plasmalogen-/peroxisome+). This involved sequential exposures of a mutagenized cell population to photodynamic damage by using two different pyrene-labelled sensors, 9-(1'-pyrene)nonanol and 12-(1'-pyrene)dodecanoic acid. By this procedure we generated several isolates, all except one of which displayed a severe decrease in plasmalogen biosynthesis. Further characterization of one of the plasmalogen-deficient isolates, NRel-4, showed that it contained intact, functional peroxisomes. Whole-cell homogenates from NRel-4 displayed severely decreased dihydroxyacetone phosphate acyltransferase, which catalyses the first step in plasmalogen biosynthesis. NRel-4 and another, recently described, plasmalogen-deficient cell line, NZel-1 [Nagan, Hajra, Das, Moser, Moser, Lazarow, Purdue and Zoeller (1997) Proc. Natl. Acad. Sci. U.S. A. 94, 4475-4480] were hypersensitive to singlet oxygen, supporting the notion of plasmalogens as radical oxygen scavengers. Wild-type-like resistance could be conferred on NRel-4 upon restoration of plasmalogen content by supplementation with a bypass compound, sn-1-hexadecylglycerol. NRel-4 and other plasmalogen-/peroxisome+ strains will allow us to examine further the role of ether lipids in cellular functions without complications associated with peroxisome deficiency, and might serve as an animal cell model for certain forms of the human genetic disorder rhizomelic chondrodysplasia punctata.

Monitoring of occupational exposure to polycyclic aromatic hydrocarbons in a carbon-electrode manufacturing plant

An investigation is presented of occupational exposure to polycyclic aromatic hydrocarbons (PAH) in a carbon-electrode manufacturing plant, as assessed by three monitoring methods, viz. environmental monitoring of the external dose by analysis of personal air samples, biological monitoring of the internal dose by analysis of urinary 1-hydroxypyrene (1-OHpyrene), and biological effect monitoring by dosimetry of PAH-DNA adducts in blood lymphocytes. On the basis of job conditions, workers at the plant were divided into three groups with presumed low, intermediate and high exposure to air-borne PAH, respectively. All air samples showed levels of total PAH below the current MAC-value in the Netherlands, which is 200 micrograms/m3, whereas the benzo[a]pyrene level was occasionally higher than the recommended concentration of 2 micrograms/m3. The values of 1-OHpyrene in urine from the intermediate and high exposure groups were significantly higher than those of the low exposure group, namely 3.6- and 8.2-fold, respectively. Clear external and internal exposure was thus demonstrated for workers of the high and intermediate exposure groups, but this did not result in a measurable effect at the DNA level in blood lymphocytes. Tobacco smoking, on the other hand, caused a significant increase of the levels of PAH-DNA adducts but did not affect 1-OHpyrene values. These data suggest that smoking is a more important risk factor for adverse health effects, i.e. cancer, than occupational exposure to PAH in this plant.

Mutagenic activation of aromatic amines by molluscs as a biomarker of marine pollution

Mutagenic activation of arylamines by mollusc S9 fractions was evaluated as a biomarker for marine pollution. Two bivalve species were used as bioindicators, the common mussel (Mytilus edulis) and the striped venus (Chameleo gallina). A strain of Salmonella typhimurium overproducing O-acetyltransferase was used as indicator of mutagenicity. Mussels from an area of the North Atlantic Spanish zone that was exposed to an accidental crude oil spill were compared to bivalves from a reference area. C. gallina samples were from low polluted and highly polluted areas of the South Atlantic Spanish littoral. The promutagen 2-aminoanthracene (2-AA) was activated to mutagenic derivative(s) by S9 fractions from both C. gallina and M. edulis. Animals from contaminated sites showed higher arylamine activation capabilities than reference animals. This was further correlated with the mutagenic activities of corresponding cyclopentone-dichloromethane animal extracts. 2-AA activation by mollusc S9 was potentiated by alpha-naphthoflavone (ANF), known to inhibit PAH-inducible CYP1A cytochromes from vertebrates, but inhibited by methimazole (MZ), a substrate of the flavin monooxygenase (FMO) system. 2-AA-activating enzymes were mainly cytosolic; this localization clearly suggests that such activity could be attributed to soluble enzymes, different from the CYP1A or FMO systems. In conclusion, mutagenic activation of arylamines by mollusc S9, using as indicator a strain of Salmonella typhimurium that overproduces O-acetyltransferase, could be a reliable biomarker for marine pollution.

The mutational specificity of 1-nitroso-6-nitropyrene in the lacI gene of Escherichia coli strains deficient in nucleotide excision repair

We have examined the mutational specificity of 1-nitroso-6-nitropyrene (1,6-NONP), an activated metabolite of the carcinogen 1,6-dinitropyrene, in the lacI gene of Escherichia coli strains which are deficient in nucleotide excision repair (strain NR6113, delta uvrB; strain CM6114, delta uvrB, plasmid pKM101). Separate collections of lacI- mutations and dominant lacI-d mutations, which contain DNA sequence alterations in the region of the lacI gene that encodes the DNA binding domain of the lacI repressor, were made following 1,6-NONP treatment. The DNA sequence of 418 mutations was determined, of which 228 were lacI- mutations and 190 were lacI-d mutations. Ninety three percent of the induced point mutations occurred at G:C residues.0 -(G:C) frameshifts were the dominant mutational class in the lacI- collections of both NR6113 and CM6114, and in the lacI-d collection of NR6113. The frameshift mutations occurred preferentially in runs of guanine residues and their frequency increased markedly with the length of the reiterated sequence. In strain CM6114, which contained the plasmid pKM101, there was a marked stimulation in the frequency of G:C-->T:A transversions that was particularly apparent in the lacI-d collection. We discuss models which might account for the apparent differences in mutational specificity resulting from the presence of the UmuD/C and MucA/B proteins. The results suggest that major classes of mutation are recovered in both the lacI- and lacI-d collections. However, the proportions of the major classes of mutations within the two collections can differ significantly. Depending on the genetic background of the host strain, the relative ratios of base substitutions to frameshift mutations in the lacI-d target can differ by almost an order of magnitude as compared with the lacI- target. This is primarily a function of the relative mutational target size of the different classes of mutation.

Enzymatic recognition and biological effects of photodynamic damage induced in DNA by 1,6-dioxapyrene plus UVA

The specific recognition of DNA modifications by repair endonucleases was used to characterize DNA damage induced by 1,6-dioxapyrene (1,6-DP) in the presence of ultraviolet light at 365 nm (UVA) in the plasmid YEplac181. Under cell free conditions, 1,6-DP plus UVA generated lesions are recognized by the UvrABC endonuclease, the proteins Nth, Nfo and Fpg. The number of UvrABC sensitive sites was at least ten-fold higher than that of Fpg or Nth sensitive sites. Moreover, 1,6-DP plus UVA generated single-strand breaks which are the second most frequent lesions. To investigate the biological effect of DNA damage, YEplac181 DNA was treated with 1,6-DP plus UVA and transformed into Escherichia coli or Saccharomyces cerevisiae. In Escherichia coli, the transformation efficiency of 1,6-DP plus UVA treated DNA was greatly reduced in the uvrA mutant compared to that in the wild-type strain. However, the transforming efficiency was not affected in Fpg-deficient strains. In Saccharomyces cerevisiae, the transformation efficiency of 1,6-DP plus UVA treated YEplac181 was greatly reduced in the rad14::URA3 strain. The photobiological effect of 1,6-DP plus UVA was also analysed in haploid yeast strains of various repair capacities. The results show that the yeast strain defective in the nucleotide excision repair pathway (rad14::URA3) is hypersensitive to 1,6-DP plus UVA treatment as compared to the parental wild-type strain. It is confirmed that the lethal effect of 1,6-DP plus UVA on wild-type yeast is strongly oxygen dependent, whereas the survival of the rad14::URA3 mutant only exhibits a minor oxygen dependence. To conclude, our data show that the photodynamic DNA lesions induced by 1,6-DP plus UVA can be recognized and repaired in pro- and eukaryotic cells by the nucleotide excision repair pathway.

Relationship between adduct formation, rates of excision repair and the cytotoxic and mutagenic effects of structurally-related polycyclic aromatic carcinogens

The cytotoxic and mutagenic effect of 1-nitrosopyrene (1-NOP) and N-acetoxy-2-acetylaminofluorene (N-AcO-AAF) were compared with that of (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) as a function of the initial frequency of adducts formed in the DNA of repair-proficient diploid human fibroblasts and the fraction remaining at the time the cells replicate their DNA. The principal adducts of all three agents involve guanine. The initial level of BPDE-, 1-NOP-, or N-AcO-AAF-induced adducts per 10(6) nucleotides required to lower the survival of these cells to 37% of the control was 8, 25, and 50, respectively. The frequency of mutants per 10(6) clonable cells induced at those levels of initial adduct formation was 160, 80, and 40, respectively. We determined the rate of excision repair of these adducts from the overall genome, from the individual strands of the hypoxanthine phosphoribosyltransferase (HPRT) gene, and in the case of 1-NOP and BPDE, at the level of individual nucleotides in the nontranscribed strand of exon 3 of that gene, a region where mutations induced by those agents are particularly frequent. 1-NOP-induced adducts were excised from the overall genome and from the individual strands of HPRT at a rate 2-3 times faster than BPDE-induced adducts. The average rate of repair of 1-NOP-induced adducts in exon 3 was also 2-3 times faster than the average rate of repair of BPDE-induced adducts. However, at particular nucleotides 1-NOP-induced adducts were repaired much faster, or slower, or in some cases at a rate equal to that of BPDE-induced adducts. Excision repair of N-AcO-AAF-induced adducts (i.e., deacetylated aminofluorene residues) was significantly slower than that of BPDE- or 1-NOP-induced adducts, and was not strand-specific. In an in vitro assay, BPDE adducts were four times more effective in blocking transcription than were 1-NOP or N-AcO-AAF-induced adducts. We conclude that the cytotoxic and mutagenic effect of these carcinogens reflect a complex interplay of adduct conformation, ability of adducts to block replication and transcription, and variation in the rate of excision repair, even at the nucleotide level.

Aryl acetylenes as mechanism-based inhibitors of cytochrome P450-dependent monooxygenase enzymes

Aryl acetylenes have been investigated as inhibitors of cytochrome P450 (P450)-dependent alkoxyresorufin dealkylation dealkylation activities in liver microsomes prepared from rats exposed to beta-naphthoflavone, isosafrole, or phenobarbital. Many of the acetylenes investigated produce pseudo-first-order time-dependent and NADPH-dependent losses of the dealkylation activities characteristic of mechanism-based irreversible inactivation (suicide inhibition). Replacing the terminal hydrogen of aryl acetylenes with a methyl group to convert ethynes into propynes enhances the inhibition of P450 1A enzymes; in some instances, this modification converts a reversible inhibitor of P450s into a suicide inhibitor. In contrast, ethynes are more effective suicide inhibitors of P450 2B-dependent dealkylations than the corresponding propynes. Aryl acetylenes with an ethynyl group on the 2 position of naphthalene or on the 9 position of phenanthrene and arylalkyl acetylenes with alkyl chains containing 2, 3, or 4 methylene groups are selective inhibitors of P450 2B1/2B2 in liver microsomes from rats. Aryl acetylenes also act as suicide inhibitors of P450 1A2 in human liver microsomes, of purified P450 1A2 from rabbit or rat liver in reconstituted systems, and of purified recombinant human P450 1A2 and 1A1 in reconstituted systems. 4-(1-Propynyl)biphenyl (4PBi) inactivated P450 1A2-dependent ethoxyresourfin deethylation (EROD) activity in human liver microsomes in an NADPH-dependent process (k(inactivation), 0.23 min-1; KI, 2.3 microM). 4PBi also inactivated purified recombinant human P450 1A2 (k(inactivation), 0.24 min-1; KI, 4.3 microM). In agreement with previous reports [Yun, C.-H., Hammons, G. J., Jones, G., Martin, M. V., Hopkins, N. E., Alworth, W. L., and Guengerich, F. P. (1992) Biochemistry 31, 10556-10563], 2-ethynylnaphthalene (2EN) was not a suicide inhibitor of the P450 1A2 activity in human liver microsomes but did inactivate purified human P450 1A2. Neither 4PBi nor 2EN affected diagnostic activities of human microsomal P450 2E1, 2C9/10, 3A4, or 2C19. In the systems examined, the losses of P450-dependent activity produced by these aryl acetylenes were not accompanied by corresponding decreases in the measured P450 absorption spectra. Thus P450 inactivation by these aryl acetylenes does not involve labeling and destruction of the heme. Incubation of 4PBi with microsomal P450 1A1 or 1A2 from rat liver under conditions that lead to P450-dependent, enzyme inactivations generates a 2-biphenylylpropionic acid product. This suggests that the suicide inhibition of P450s by propynylaryl acetylenes proceeds via a methylaryl ketene formed by a 1,2-methyl rearrangement, analogous to the mechanism of suicide inhibition by ethynyl acetylenes that proceed via ketene intermediates formed by 1,2-hydrogen shifts [Ortiz de Montellano, P. R., and Kunze, K. L. (1981) Arch. Biochem. Biophys. 209, 710-712].

A novel stopped-flow method for measuring the affinity of actin for myosin head fragments using microgram quantities of protein

The dissociation constant for actin binding to myosin and its subfragments (S1 & HMM) is <<1 microM at physiological ionic strength. Many of the methods used to measure such affinities are unreliable for a Kd below 0.1 microM. We show here that the use of phalloidin to stablise F-actin and fluorescently labelled proteins allows the affinity of actin for myosin S1 to be measured in a simple transient kinetic assay. The method can be used for Kd's as low as 10 nM and we demonstrate that the Kd's can be estimated using only microgram quantities of material. Furthermore we suggest how this method may be adapted for ng quantities of protein. This will allow the affinity of actin for myosin fragments to be estimated for proteins which are difficult to obtain in large quantities i.e. from biopsy material or from proteins expressed in baculovirus.

Solution conformation of the N-(deoxyguanosin-8-yl)-1-aminopyrene ([AP]dG) adduct opposite dC in a DNA duplex

Combined NMR-molecular mechanics computational studies were undertaken on the C8-deoxyguanosine adduct formed by the carcinogen 1-nitropyrene embedded in the d(C5-[AP]G6-C7).d(G16-C17-G18) sequence context in a 11-mer duplex, with dC opposite the modified deoxyguanosine. The exchangeable and nonexchangeable protons of the aminopyrene moiety and the nucleic acid were assigned following analysis of two-dimensional NMR data sets in H2O and D2O solution. There was a general broadening of several proton resonances for the three nucleotide d(G16-C17-G18) segment positioned opposite the [AP]dG6 lesion site resulting in weaker NOEs involving these protons in the adduct duplex. The solution conformation of the [AP]dG.dC 11-mer duplex has been determined by incorporating intramolecular and intermolecular proton-proton distances defined by upper and lower bounds deduced from NOESY spectra as restraints in molecular mechanics computations in torsion angle space. The aminopyrene ring of [AP]dG6 is intercalated into the DNA helix between intact Watson-Crick dC5.dG18 and dC7.dG16 base pairs. The modified deoxyguanosine ring of [AP]dG6 is displaced into the major groove and stacks with the major groove edge of dC5 in the adduct duplex. Both carbon and proton chemical shift data for the sugar resonances of the modified deoxyguanosine residue are consistent with a syn glycosidic torsion angle for the [AP]dG6 residue. The dC17 base on the partner strand is displaced from the center of the helix toward the major groove as a consequence of the aminopyrene ring intercalation into the helix. This base-displaced intercalative structure of the [AP]dG.dC 11-mer duplex exhibits several unusually shifted proton resonances which can be accounted for by the ring current contributions of the deoxyguanosinyl and pyrenyl rings of the [AP]dG6 adduct. In summary, intercalation of the aminopyrene moiety is accompanied by displacement of both [AP]dG6 and the partner dC17 into the major groove in the [AP]dG.dC 11-mer duplex.

Non-hydrogen bonding 'terminator' nucleosides increase the 3'-end homogeneity of enzymatic RNA and DNA synthesis

We report the use of novel non-polar nucleoside analogues as terminators of enzymatic RNA and DNA synthesis. Standard 'runoff' RNA synthesis by T7 RNA polymerase gives RNA products which have ragged ends as a result of transcription which often extends beyond the end of the template DNA strand. Similarly, the Klenow fragment of Escherichia coli DNA polymerase I tends to run past the end of the template strand during DNA synthesis. We report here that certain non-hydrogen-bonding nucleoside analogues, when placed at the downstream 5'-end of a template DNA strand, cause the polymerases to stop more abruptly at the last coding nucleotide. This results in a considerably more homogeneous oligonucleotide being produced. Three novel nucleosides are tested as potential terminators: 4-methylindole beta-deoxynucleoside (M), 1-naphthyl alpha-deoxynucleoside (N) and 1-pyrenyl alpha-deoxynucleoside (P). Comparison is made to an abasic nucleoside (phi) and to unterminated synthesis. Of these, M is found to be the most efficient at terminating transcription, and both P and M are highly effective at terminating DNA synthesis. It is also found that the ability of a nucleoside to stall synthesis when it is internally placed in the template strand is not necessarily a good predictor of terminating ability at the end of a template. Such terminator nucleosides may be useful in the preparative enzymatic synthesis of RNA and DNA, rendering purification simpler and lowering the cost of synthesis by preventing the uptake of potentially costly nucleotides into unwanted products.

Emodin inhibits the mutagenicity and DNA adducts induced by 1-nitropyrene

Polygonum cuspidatum S. (PC) is frequently used as a laxative and an anticancer drug in Chinese medicine. The inhibitory effect of this herb and its component, emodin, on the direct-acting mutagenicity of 1-nitropyrene (1-NP) was examined using the Ames/microsomal test with Salmonella typhimurium TA98 and the genotoxicity of 1-NP was evaluated using the SOS chromotest with E. coli PQ37. Emodin and water extracts of PC markedly decreased the mutagenicity of 1-NP in a dose-dependent manner in both assay systems. Furthermore, emodin and the extracts of PC significantly inhibited the formation of 1-NP DNA adducts in S. typhimurium TA98 in the 32P-postlabeling study. The results suggest that PC extracts and emodin act as blocking and/or suppressing agents to reduce the direct-acting mutagenicity of 1-NP.

Novel cytotoxic DNA sequence and minor groove targeted photosensitizers: conjugates of pyrene and netropsin analogues

The design, syntheses, photochemical and biological properties of conjugates of pyrene with pyrrole- (1) and imidazole-containing (2) analogues of netropsin are reported. The results of an ethidium displacement assay and circular dichroism (CD) titration studies show both compounds bind with a higher affinity to poly(dA-dT) than to poly(dG-dC). In addition they bind as strongly to T4 coliphage DNA as to calf thymus DNA suggesting the binding occurs in the minor groove. The quenching rate constants of the singlet excited states of agents 1 and 2 by molecular oxygen were found to be 8.5 x 10(9) M-1S-1 and 7.7 x 10(9) M-1S-1, suggesting the involvement of singlet oxygen. Both compounds showed some cytotoxicity to human chronic myeloid leukemia K562 cells in the dark. Upon irradiation the activities were significantly enhanced resulting in photoinduced dose modifications of 8 and 14 for 1 and 2, respectively under the conditions employed. Both agents were markedly more phototoxic than 1-pyrenebutyric acid 8. To address the mechanism of action of compounds 1 and 2 their photoactivated abilities to produce DNA strand breaks were measured. Both agents caused increased single strand breakage with increasing UV exposure. The concentrations (EC50) of 1 and 2 needed to cause 50% single-strand cleavage of pBR322 DNA upon UV-A activation were found to be 40 microM and 45 microM, respectively. In contrast, no DNA strand breaks were observed in the dark with either conjugate or with 8 following irradiation. DNA strand breaks were measured in drug treated K562 cells using alkaline elution.(ABSTRACT TRUNCATED AT 250 WORDS)

Moderate inhibition of mutagenicity and carcinogenicity of benzo[a]pyrene, 1,6-dinitropyrene and 3,9-dinitrofluoranthene by Chinese medicinal herbs

The activity of six Chinese medicinal herbs against the environmental mutagens and carcinogens benzo[a]pyrene (B[a]P), 1,6-dinitropyrene (1,6-diNP) and 3,9-dinitrofluoranthene (3,9-diNF) was determined. Samples of Prunella spica, Rheum palmatum, Polygonum multiflorum, Agrimonia pilosa, Ephedra sinica and Teitoutou were tested in an in vitro system. Antimutagenic activity against B[a]P was marked in the presence of extracts (boiled for 2 h in a water bath) whereas that against 1,6-diNP and 3,9-diNF varied from 20 to 86%. The differences in inhibition might be due to inactivation of metabolic enzymes. An extract of P. multiflorum was divided into ether, ethyl acetate and water soluble fractions, which were tested for antimutagenic activity against B[a]P. The antimutagenic action of the ethyl acetate soluble fraction was substantial and dose-dependent. Tannins and related compounds were the major components of the extract, of which epigallocatechin, epigallocatechin gallate, epicatechin gallate and tannic acid strongly inhibited the mutagenicity of B[a]P (2.5 micrograms/plate) in Salmonella typhimurium TA98 with S9 mix. To confirm the results of the in vitro test system, F344/DuCrj male rats were given a subcutaneous injection of B[a]P. Thereafter, they received water extracts of the six Chinese medicinal herbs for 50 weeks and were examined for tumors. The P. multiflorum extract significantly reduced the tumor incidence.