Proceedings of the National Academy of Sciences of the United States of America
1091-6490
0027-8424
Mỹ
Cơ quản chủ quản: NATL ACAD SCIENCES , National Academy of Sciences
Lĩnh vực:
Multidisciplinary
Các bài báo tiêu biểu
Formation of stable adducts and absence of depurinating DNA adducts in cells and DNA treated with the potent carcinogen dibenzo[ <i>a,l</i> ]pyrene or its diol epoxides
Polycyclic aromatic hydrocarbons (PAH) are widespread environmental contaminants, and some are potent carcinogens in rodents. Carcinogenic PAH are activated in cells to metabolites that react with DNA to form stable covalent DNA adducts. It has been proposed [Cavalieri, E. L. & Roger, E. G. (1995)
Xenobiotica
25, 677–688] that unstable DNA adducts are also formed and that apurinic sites in the DNA resulting from unstable PAH adducts play a key role in the initiation of cancer. The potent carcinogen dibenzo[
a,l
]pyrene (DB[
a,l
]P) is activated in cells to (+)-
syn
- and (−)-
anti
-DB[
a,l
]P-11,12-diol-13,14-epoxide (DB[
a,l
]PDE), which have been shown to form stable adducts with DNA. To evaluate the importance of unstable PAH adducts, we compared stable adduct formation to apurinic site formation. Stable DB[
a,l
]PDE adducts were determined by
33
P-postlabeling and HPLC. To measure apurinic sites they were converted to strand breaks, and these were monitored by examining the integrity of a particular restriction fragment of the dihydrofolate reductase gene. The method easily detected apurinic sites resulting from methylation by treatment of cells or DNA with dimethyl sulfate or from reaction of DNA with DB[
a,l
]P in the presence of horseradish peroxidase. We estimate the method could detect 0.1 apurinic site in the 14-kb fragment examined. However, apurinic sites were below our limit of detection in DNA treated directly with (+)-
syn
- or (−)-
anti
-DB[
a,l
]PDE or in DNA from Chinese hamster ovary B11 cells so treated, although in these samples the frequency of stable adducts ranged from 3 to 10 per 14 kb. We also treated the human mammary carcinoma cell line MCF-7 with DB[
a,l
]P and again could not detect significant amounts of unstable adducts. These results indicate that the proportion of stable adducts formed by DB[
a,l
]P activated in cells and its diol epoxides is greater than 99% and suggest a predominant role for stable DNA adducts in the carcinogenic activity of DB[
a,l
]P.
Tập 94 Số 25 - Trang 13542-13547 - 1997
Evidence for the aldo-keto reductase pathway of polycyclic aromatic <i>trans</i> -dihydrodiol activation in human lung A549 cells
Polycyclic aromatic hydrocarbons (PAHs) are tobacco carcinogens implicated in the causation of human lung cancer. Metabolic activation is a key prerequisite for PAHs to cause their deleterious effects. Using human lung adenocarcinoma (A549) cells, we provide evidence for the metabolic activation of (±)-
trans
-7,8dihydroxy-7,8-dihydrobenzo[
a
]pyrene (B[
a
]P-7,8-
trans
-dihydrodiol) by aldo-keto reductases (AKRs) to yield benzo[
a
]pyrene-7,8-dione (B[
a
]P-7,8-dione), a redox-active
o
-quinone. We show that B[
a
]P-7,8-
trans
-dihydrodiol (AKR substrate) and B[
a
]P-7,8-dione (AKR product) lead to the production of intracellular reactive oxygen species (ROS) (measured as an increase in dichlorofluorescin diacetate fluores-cence) and that similar changes were not observed with the regioisomer (±)-
trans
-4,5-dihydroxy-4,5-dihydrobenzo[
a
]pyrene or the diol-epoxide, (±)-
anti
-7,8-dihydroxy-9α,10β-epoxy-7,8,9,10-tetrahydro-B[
a
]P. B[
a
]P-7,8-
trans
-dihydrodiol and B[
a
]P-7,8-dione also caused a decrease in glutathione levels and an increase in NADP
+
/NADPH ratios, with a concomitant increase in single-strand breaks (as measured by the comet assay) and 7,8-dihydro-8-oxo-2′-deoxyguanosine (8-oxo-dGuo). The specificity of the comet assay was validated by coupling it to human 8-oxo-guanine glycosylase (hOGG1), which excises 8-oxo-Gua to yield single-strand breaks. The levels of 8-oxo-dGuo observed were confirmed by an immunoaffinity purification stable isotope dilution ([
15
N
5
]-8-oxo-dGuo) liquid chromatography-electrospray ionization/multiple reaction monitoring/mass spectrometry (LC-ESI/MRM/MS) assay. B[
a
]P-7,8-
trans
-dihydrodiol produced DNA strand breaks in the hOGG1-coupled comet assay as well as 8-oxo-dGuo (as measured by LC-ESI/MRM/MS) and was enhanced by a catechol
O
-methyl transferase (COMT) inhibitor, suggesting that COMT protects against
o
-quinone-mediated redox cycling. We conclude that activation of PAH-
trans
-dihydrodiols by AKRs in lung cells leads to ROS-mediated genotoxicity and contributes to lung carcinogenesis.
Tập 105 Số 19 - Trang 6846-6851 - 2008
Relating aromatic hydrocarbon-induced DNA adducts and c-H-ras mutations in mouse skin papillomas: the role of apurinic sites. Mouse skin tumors contain activated c-H-ras oncogenes, often caused by point mutations at codons 12 and 13 in exon 1 and codons 59 and 61 in exon 2. Mutagenesis by the noncoding apurinic sites can produce G-->T and A-->T transversions by DNA misreplication with more frequent insertion of deoxyadenosine opposite the apurinic site. Papillomas were induced in mouse skin by several aromatic hydrocarbons, and mutations in the c-H-ras gene were determined to elucidate the relationship among DNA adducts, apurinic sites, and ras oncogene mutations. Dibenzo[a,l]pyrene (DB[a,l]P), DB[a,l]P-11,12-dihydrodiol, anti-DB[a,l]P-11,12-diol-13,14-epoxide, DB[a,l]P-8,9-dihydrodiol, 7,12-dimethylbenz[a]anthracene (DMBA), and 1,2,3,4-tetrahydro-DMBA consistently induced a CAA-->CTA mutation in codon 61 of the c-H-ras oncogene. Benzo[a]pyrene induced a GGC-->GTC mutation in codon 13 in 54% of tumors and a CAA-->CTA mutation in codon 61 in 15%. The pattern of mutations induced by each hydrocarbon correlated with its profile of DNA adducts. For example, both DB[a,l]P and DMBA primarily form DNA adducts at the N-3 and/or N-7 of deoxyadenosine that are lost from the DNA by depurination, generating apurinic sites. Thus, these results support the hypothesis that misreplication of unrepaired apurinic sites generated by loss of hydrocarbon-DNA adducts is responsible for transforming mutations leading to papillomas in mouse skin.
Tập 92 Số 22 - Trang 10422-10426 - 1995
Fossilized high pressure from the Earth's deep interior: The coesite-in-diamond barometer Mineral inclusions in diamonds provide an important source of information about the composition of the continental lithosphere at depths exceeding 120–150 km, i.e., within the diamond stability field. Fossilized high pressures in coesite inclusions from a Venezuela diamond have been identified and measured by using laser Raman and synchrotron x-ray microanalytical techniques. Micro-Raman measurements on an intact inclusion of remnant vibrational band shifts give a high confining pressure of 3.62 (±0.18) GPa. Synchrotron single-crystal diffraction measurements of the volume compression are in accord with the Raman results and also revealed direct structural information on the state of the inclusion. In contrast to olivine and garnet inclusions, the thermoelasticity of coesite favors accurate identification of pressure preservation. Owing to the unique combination of physical properties of coesite and diamond, this “coesite-in-diamond” geobarometer is virtually independent of temperature, allowing an estimation of the initial pressure of Venezuela diamond formation of 5.5 (±0.5) GPa.
Tập 97 Số 22 - Trang 11875-11879 - 2000
Genomic analysis of diversity, population structure, virulence, and antimicrobial resistance in <i>Klebsiella pneumoniae</i> , an urgent threat to public health Significance
Klebsiella pneumoniae
is rapidly becoming untreatable using last-line antibiotics. It is especially problematic in hospitals, where it causes a range of acute infections. To approach controlling such a bacterium, we first must define what it is and how it varies genetically. Here we have determined the DNA sequence of
K
.
pneumoniae
isolates from around the world and present a detailed analysis of these data. We show that there is a wide spectrum of diversity, including variation within shared sequences and gain and loss of whole genes. Using this detailed blueprint, we show that there is an unrecognized association between the possession of specific gene profiles associated with virulence and antibiotic resistance and the differing disease outcomes seen for
K
.
pneumoniae
.
Tập 112 Số 27 - 2015
The role of antimicrobial peptides in animal defenses It is becoming clear that the cationic antimicrobial peptides are an important component of the innate defenses of all species of life. Such peptides can be constitutively expressed or induced by bacteria or their products. The best peptides have good activities vs. a broad range of bacterial strains, including antibiotic-resistant isolates. They kill very rapidly, do not easily select resistant mutants, are synergistic with conventional antibiotics, other peptides, and lysozyme, and are able to kill bacteria in animal models. It is known that bacterial infections, especially when treated with antibiotics, can lead to the release of bacterial products such as lipopolysaccharide (LPS) and lipoteichoic acid, resulting in potentially lethal sepsis. In contrast to antibiotics, the peptides actually prevent cytokine induction by bacterial products in tissue culture and human blood, and they block the onset of sepsis in mouse models of endotoxemia. Consistent with this, transcriptional gene array experiments using a macrophage cell line demonstrated that a model peptide, CEMA, blocks the expression of many genes whose transcription was induced by LPS. The peptides do this in part by blocking LPS interaction with the serum protein LBP. In addition, CEMA itself has a direct effect on macrophage gene expression. Because cationic antimicrobial peptides are induced by LPS and are able to dampen the septic response of animal cells to LPS, we propose that, in addition to their role in direct and lysozyme-assisted killing of microbes, they have a role in feedback regulation of cytokine responses. We are currently developing variant peptides as therapeutics against antibiotic-resistant infections.
Tập 97 Số 16 - Trang 8856-8861 - 2000
Nisin-induced changes in<i>Bacillus</i>morphology suggest a paradigm of antibiotic action Nisin is a small cationic lanthionine antibiotic produced byLactococcus lactis . During its antimicrobial action, it targets intermediates in the bacterial cell-wall biosynthesis, lipid II, and undecaprenyl pyrophosphate. Here, we report results from electron microscopic investigations of the effects of lethal nisin doses onBacillus subtilis cell morphology. Bacterial membranes were permeabilized shortly afterB. subtilis was incubated with nisin, but this did not lead to immediate cell death. Cell division, as well as other life functions, persisted over at least half an hour after nisin was added. Slower bacterial elongation, consistent with cell envelope inhibition and accelerated division, resulted in cell-length reduction. Abnormal morphogenesis near the division site suggests this to be the primary site of nisin action. Morphological changes are characteristic of deregulation of a filamentous cell envelope protein, Mbl, and the division-inhibiting Min system. We propose a previously undescribed model, in which the lethal action of nisin againstB. subtilis starts with membrane permeabilization and is followed by accelerated cell division, cell envelope inhibition, and aberrant cell morphogenesis.
Tập 103 Số 52 - Trang 19896-19901 - 2006
Why fisheries collapse and what to do about it. With the collapse of fisheries in many parts of the world causing widespread economic harm, attention is focused on a possible cause and remedy of fishery collapse. Economic theory for managing a renewable resource, such as a fishery, leads to an ecologically unstable equilibrium as difficult to maintain as balancing a marble on top of a dome. A fishery should be managed for ecological stability instead--in the analogy, as easy to maintain as keeping a marble near the base of a bowl. The goal of ecological stability is achieved if the target stock is above that producing maximum sustainable yield and harvested at less than the maximum sustainable yield. The cost of managing for ecological stability, termed "natural insurance," is low if the fishery is sufficiently productive. This cost is shown to pay for itself over the long term in a variable and uncertain environment. An ecologically stable target stock may be attained either with annually variable quotas following current practice or, preferably, through a market mechanism whereby fish are taxed at dockside if caught when the stock was below target and are untaxed otherwise. In this regulatory environment, the goal of maximizing short-term revenue coincides with the goal of ecological stability, thereby also maximizing long-term revenue. This new approach to fishery management is illustrated with the recently collapsed Newfoundland fishing industry. The Newfoundland cod fishery is expected to rebuild to an ecologically stable level in about 9 years and thereafter support an annual harvest of about 75% of the 1981-1990 average.
Tập 93 Số 10 - Trang 5078-5083 - 1996
The neural code between neocortical pyramidal neurons depends on neurotransmitter release probability Although signaling between neurons is central to the functioning of the brain, we still do not understand how the code used in signaling depends on the properties of synaptic transmission. Theoretical analysis combined with patch clamp recordings from pairs of neocortical pyramidal neurons revealed that the rate of synaptic depression, which depends on the probability of neurotransmitter release, dictates the extent to which firing rate and temporal coherence of action potentials within a presynaptic population are signaled to the postsynaptic neuron. The postsynaptic response primarily reflects rates of firing when depression is slow and temporal coherence when depression is fast. A wide range of rates of synaptic depression between different pairs of pyramidal neurons was found, suggesting that the relative contribution of rate and temporal signals varies along a continuum. We conclude that by setting the rate of synaptic depression, release probability is an important factor in determining the neural code.
Tập 94 Số 2 - Trang 719-723 - 1997
Different transmitter transients underlie presynaptic cell type specificity of GABA <sub>A,slow</sub> and GABA <sub>A,fast</sub>
Phasic (synaptic) and tonic (extrasynaptic) inhibition represent the two most fundamental forms of GABA
A
receptor-mediated transmission. Inhibitory postsynaptic currents (IPSCs) generated by GABA
A
receptors are typically extremely rapid synaptic events that do not last beyond a few milliseconds. Although unusually slow GABA
A
IPSCs, lasting for tens of milliseconds, have been observed in recordings of spontaneous events, their origin and mechanisms are not known. We show that neocortical GABA
A,slow
IPSCs originate from a specialized interneuron called neurogliaform cells. Compared with classical GABA
A,fast
IPSCs evoked by basket cells, single spikes in neurogliaform cells evoke extraordinarily prolonged GABA
A
responses that display tight regulation by transporters, low peak GABA concentration, unusual benzodiazepine modulation, and spillover. These results reveal a form of GABA
A
receptor mediated communication by a dedicated cell type that produces slow ionotropic responses with properties intermediate between phasic and tonic inhibition.
Tập 104 Số 37 - Trang 14831-14836 - 2007