bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Properties of Single Walled Carbon Nanotube Reinforced Polystyrene Composites
Authors: Antonucci Vincenza , Faiella Gabriella , Giordano Michele , Nicolais Luigi , Pepe Gianpiero
Published: February 2007

Composites of carbon nanotubes (CNT) in polymeric matrices have attracted considerable attention in the research communities due to their good electrical conductivity, high stiffness and high strength at relatively low CNT contents. Effective utilization of CNT in composites depends primarily on the ability to disperse them homogeneously throughout the polymer matrix, avoiding the formation of bundles due to van der Waals interactions existing between the nanotubes. In this work composites of polystyrene at various percentages of SWNT were fabricated using Latex Technology technique, a polymer type‐independent method based on using a surfactant as a dispersing agent. An electrical characterization of SWNT composites was performed both in DC and AC modes. From the analysis of DC data a percolative behavior was found for the conductivity as function of SWNT content. The innovative contribution of this work consists in the modeling of the composite material upon its electrical properties. AC measurements and the analysis of impedance as function of angular frequency lead to the formulation of an equivalent circuit able to model the composite material in correspondence of the percolative threshold.
Modelling and Experimental Characterisation of Hygrothermoelastic Stress in Polymer Matrix Composites
Authors: Gigliotti Marco , Jacquemin Frédéric , Molimard Jérôme , Vautrin Alain
Published: February 2007

Summary: The present paper is concerned with the modelling and the simulation of hygrothermal deformation of composite laminates. The temperature and moisture fields are established by employing the Fick's law for transient and cyclical environmental conditions, then the Classical Plate Theory (CLT) adapted for taking into account such conditions is applied. The hygrothermoelastic law of the composite is supposed to be constant but the diffusion coefficients depend on the temperature. The paper shows the ability of the model to handle complex environmental loading, close to service conditions. Finally, a model of plate with moderate rotations is introduced to predict the nonlinear deformations of unsymmetric plates under temperature and moisture cycling conditions.
Coupon Tests on z‐Pinned and Unpinned Composite Samples for Damage Resistant Applications
Authors: Lenzi F. , Riccio A. , Clarke A. , Creemers R.
Published: February 2007

The main objective of the work was to determine the mechanical properties of Z‐pinned and unpinned composites samples. Tensile and interlaminar fracture tests under mode I have been carried out on thermoset polymer matrix composite samples composed of CYTEC 977‐2 and carbon fibre yarn HTA‐12K/35. The presence of the Z‐pins has been found to significantly increase the interlaminar fracture toughness. The crack resistance improvement has been found to be accompanied by a small reduction of the in‐plane stiffness properties for a Z‐pins density of 2%. The results are presented in relation to the size and pinning quality and are rationalised on the basis of the location of Z‐pin block within the sample.
PMMA/PC Blends: Effect of Mixing Conditions on Compatibility
Authors: Penco Maurizio , Sartore Luciana , Sciucca Stefania Della , Di Landro Luca , D'Amore Alberto
Published: February 2007

In this work the effect of melt mixing condition and of a trans‐esterification catalyst on miscibility of poly(methyl methacrylate) (PMMA)/polycarbonate of bisphenol A (PC) blends is studied. In particular, at high temperature chemical reactions between PMMA and PC phases can take place; these strongly change the compatibility in the blend and materials having single Tg can be obtained. FT‐IR analyses, coupled with solvent extraction, suggest that a grafting reaction of PC on PMMA is involved. SEC and DSC data are consistent with spectroscopic results, and some decrement of the molar weight distribution (MWD) of PC phase is observed. On the other hand, the presence of a fraction of modified material having higher MWD of starting PMMA is also noticed. The single Tg characteristic of some materials has been confirmed by experimental data of structural relaxation performed by differential scanning calorimetry (DSC). These materials showed optical clarity and the morphological analysis performed by scanning electron microscopy (SEM) confirm the homogeneity of these materials.
Efficiency and Aging Comparison Between N,N′‐Bis (3‐methylphenyl)‐N,N′‐diphenylbenzidine (TPD) and N,N′‐Di‐[(1‐naphthalenyl)‐N,N′‐diphenyl]‐1,1′‐biphenyl‐4,4′‐diamine (NPD) Based OLED Devices
Authors: Maglione Maria Grazia , Minarini Carla , Miscioscia Riccardo , Nenna Giuseppe , Romanelli Emma , Tassini Paolo
Published: February 2007

In this paper we present and discuss experimental results to evaluate performances and aging behaviour of two Hole Transporting Material (HTM), TPD and NPD, in Organic Light Emitting Device (OLED) with structure: ITO/HTM/Alq3/Al. For each of these HTMs, devices with several thicknesses have been built, to measure and emphasize behaviours of material‐geometry combinations. Electro‐optical properties have been measured to estimate and compare brightness, power efficiency and aging decays.
A Molecular Photosensor Based on Photoswitching of Charge Carrier Mobility
Authors: Weiter Martin , Vala Martin , Zmeškal Oldřch , Nešpůrek Stanislav , Toman Petr
Published: February 2007

Polymer photoelectronic device based on interaction between π‐conjugated polymer matrices and photochromic molecules was fabricated. The theoretical and experimental studies proved that the photochromic reaction in studied devices should eventuate in changes of optical and electrical properties of polymers such as luminescence and conductivity. The quantum chemical calculations showed that the presence of dipolar species in the vicinity of a polymer chain modifies the on‐chain site energies and consequently increases the width of the distribution of hopping transport states. Optical switching was studied using standard absorption and photoluminescence spectroscopy. A strong photoluminescence quenching after the photochromic conversion caused by radiative energy transfer was observed. The influence of photoswitchable charge carrier traps on charge transport were evaluated by Space Charge Limited Current (SCLC) method. It was shown that deep traps may significantly affect the energy of the transport level, and thus modulate the transport of charge carriers.
A Study on Thermal Degradation of Organic LEDs Using IR Imaging
Authors: Nenna G. , Flaminio G. , Fasolino T. , Minarini C. , Miscioscia R. , Palumbo D. , Pellegrino M.
Published: February 2007

In this paper, we present a correlation study between the working temperature of OLEDs (Organic Light Emitting Diodes) and the electroluminescence and driving voltage changes. The aim is to investigate the relationship between the operating temperature and the aging mechanisms. We have found that performances degradation of devices is strictly related to the glass transition temperature (Tg) of organic layers, and that electrical failure is reached only for temperatures higher than Tg.
Synthesis and Relaxation Properties of bis(5‐Hydroxypenthyl)Phthalate ‐ the Model Oligoester to Study the Relaxation Properties of Polyesters
Authors: Sułkowski Wiesław W. , Maślanka Sławomir , Pentak Danuta , Wolińska Agnieszka , Janeczek Henryk , Paluch Marian , Sułkowska Anna
Published: February 2007

The description of polymer relaxation proprieties is the way to characterize the influence of polymer structure on its useful proprieties of stability and resistance. To perform physicochemical profiles of polymers the synthesis and investigation of model compounds was required. The instrumental methods such as NMR, FTIR, dielectric spectroscopy were used. The results of the experiments allowed us to improve the technology of the synthesis processes and the extension of the range of their usage. Moreover the obtained polymers were more stable and more resistant to degradation. To acquire the profile of the relaxation properties of the linear, hyperbranched and dendrite unsaturated polyester resins, the synthesis of the oligoesters as the model compounds was performed. Pentane‐1,5‐diol phthalic anhydride was used as substrate of the process. The structures of the obtained model compound were confirmed by elemental analysis and 1H NMR and FTIR spectroscopy. Measurements of the relaxation processes of the model compound were also done. The determination of the α, β and β′ relaxation processes for model oligoesters allow us to describe the practical properties of commercial compounds.

The description of model relation of the relaxation process may facilitate the interpretation of the dependence between useful properties of polyesters and their molecular structure.
Modification Reactions of Methylhydrosiloxanes with Tricyclodecadiene
Authors: Mukbaniani O. , Zaikov G. , Tatrishvili T. , Mukbaniani N. , Koberidze Kh.
Published: February 2007

The reaction of hydride polyaddition of methylhydridesiloxane and methylhydridesiloxane‐dimethylsiloxane oligomers to unsaturated carbocyclic compound ‐ tricyclodecadiene, at the various ratio of initial compounds, in the presence of platinum hydrochloric acid has been investigated. It was shown that hydrosilylation reaction proceeds both to 1.2 and 9.10 positions and by intermolecular with formation of branching systems. The polyorganosiloxanes with tricyclodecenyl fragment in the side chain, completely soluble in organic solvents were synthesized. For fully characterization of hydride addition of methylhydridesiloxane to tricyclodecadiene, by quantum‐chemical half empiric AM1 method, for all initial, intermediate and final products, in modelling reaction of hydrosilylation of methyldimethoxysilane to tricyclodecadiene, the heats of formations (ΔHf), change of energy (ΔH) of the system depending on the change of distance (RC‐Si) between C‐Si bonds, also the charges values (q) on the atoms, dipole moments (µ) and bonds orders (Pij) are calculated. It was concluded, that the course of hydride addition of modelling reaction of methyldimethoxysilane to tricyclodecadiene energetically is more favourable by 9.10‐addition. The hydride polyaddition reaction order, activation energies and rate constants were found. The synthesized oligomers were characterized by 1H and 13C NMR, FTIR, thermogravimetry, gel permeation chromatography, differential scanning calorimetry and wide angle X‐ray methods.
Expression pattern of a gene for a secreted metalloproteinase during late stages of tumor progression
Authors: Ostrowski Lawrence E. , Finch Joanne , Krieg Peter , Matrisian Lynn , Patskan George , O'connell John F. , Phillips James , Slaga Thomas J. , Breathnach Richard , Bowden G. Tim
Published: February 2007

We have reported that transin RNA, a 1.9‐kb RNA coding for a novel, secreted proteinase, was overexpressed during the progression of benign mouse skin papillomas to malignant squamous cell carcinomas (SCCs) induced by a two‐stage protocol (Proc Natl Acad Sci USA 83:9413, 1986). Recently a high degree of similarity has been demonstrated between rabbit stromelysin, a secreted metalloproteinase that degrades proteoglycans found in the basement membrane and the amino acid sequence predicted in rat transin cDNA.

DNA sequencing of a mouse cDNA isolated from an SCC (initiated by 7,12‐dimethylbenz[a]anthracene [DMBA] and promoted by 12‐O‐tetradecanoylphorbol‐13‐acetate (TPAJ) showed greater than 85% nucleotide similarity and 90% amino acid similarity to the rat transin‐1 cDNA nucleotide and predicted amino acid sequences. Using this mouse transin cDNA clone as a probe (labeled with 32P) we found enhanced levels of transin mRNA transcripts in SCCs induced by a protocol giving rise to metastatic tumors (repeated N‐methyl‐N‐nitroso‐N'‐nitroguanidine [MNNG] treatments) compared with the level found in SCCs induced by a protocol that had a lower probability of giving rise to metastatic tumors (MNNG initiation followed by TPA promotion). A study of primary SCCs and metastatic lesions induced by repeated benzo[a]pyrene treatment showed that the levels of transin mRNA transcripts were reduced in the metastatic lesions in comparison to the primary tumors. Southern analysis of the DNA isolated from epidermis, papillomas, and SCCs indicated that neither transin gene amplification nor rearrangement accounted for increased levels of the transin mRNA transcripts. These data suggest a role for enhanced levels of transin production in the invasion and metastasis of chemically induced SCCs.
The chemical carcinogen, chloroacetaldehyde, modifies a specific site within the regulatory sequence of human cytomegalovirus major immediate early gene in vivo
Authors: Kohwi‐Shigematsu Terumi , Nelson Jay A.
Published: February 2007

The reaction of chemical carcinogens with DNA is well documented, but whether this interaction occurs at specific sites in chromatin is unknown. We have examined in vivo the reaction of a known carcinogen, chloroacetaldehyde, with the active and inactive major immediate early gene of human cytomegalovirus. We found that during active transcription of the gene, this chemical carcinogen reacts with a unique DNA site in the 5′ flanking sequence of the major immediate early gene. However, no reaction was detected in infected nonpermissive cells in which the gene was inactive. The chloroacetaldehyde‐reactive site is located at ‐836 pmn 10 bp from the mRNA cap site in the part of the regulatory region that can both negatively and positively affect promoter activity [Nelson et al., Mol Cell Biol 7:4125–4129, 1987]. These results suggest, at least in the case of chloroacetaldehyde, the possibility that the molecular mechanism of chemical carcinogenesis involves a chemical reaction at specific sites in chromatin within the sequences responsible for regulation of gene expression. Such carcinogen‐DNA interaction occurs as a consequence of a non‐B DNA structure that contains unpaired DNA bases existing at specific sites in chromatin.
In vitro and in vivo regulation of liver epithelial cells carrying a metallothionein‐rasT24 fusion gene
Authors: Seyama Toshio , Godwin Andrew K. , Dipietro Margaret , Winokur Thomas S. , Lebovitz Russell M. , Lieberman Michael W.
Published: February 2007

We inserted a zinc‐responsive metallothionein‐rasT24 fusion gene in both orientations into a retroviral vector (SVX) and infected Fisher rat liver epithelial cells. Only the construction in which the viral long terminal repeat and the metallothionein promoters were in opposite orientations resulted in cell lines with biologically altered behavior. Two lines (MTR‐1 and MTR‐6) showed altered morphology in vitro when ZnSO4 was added to the medium. These cell lines grew in soft agarose in a dose‐dependent manner. Immunoprecipitation experiments revealed dose‐dependent increases in the rate of synthesis of the mutant p21Ha‐ras protein in these lines in response to ZnSO4. Both lines produced poorly differentiated metastatic adenocarcinomas when injected subcutaneously in Fisher rats, and tumors derived from MTR‐6 cells grew more rapidly in animals on a zinc‐supplemented diet than on a zinc‐deficient diet. Uninfected liver epithelial cells showed no change in morphology in vitro after ZnSO4 addition and did not grow in soft agarose or after subcutaneous transplantation during the 14‐wk experimental period. These results indicate that altered levels of expression of a single gene (rasT24) can have profound effects on the biologic behavior of tumor cells both in vitro and in vivo.
Characterization of DNA‐protein complexes induced in intact cells by the carcinogen chromate
Authors: A. Charles Miller , Costa Max
Published: February 2007

Potassium chromate induced the formation of DNA‐protein complexes in cultured Chinese hamster ovary cells. The DNA‐protein complexes were isolated by ultracentrifugal sedimentation in the presence of 2% sodium dodecyl sulfate (SDS) and 5 M urea. Two‐dimensional SDS‐polyacrylamide gel electrophoresis analysis of the chromate‐induced DNA‐protein complexes revealed that two acidic proteins of 53 and 45 kDa and a basic protein of 54 kDa were selectively complexed to the DNA. Numerous other proteins also became associated with the DNA to a lesser degree as the chromate concentration was increased. Nuclease digestion was not a prerequisite for the resolution of the protein component of the DNA‐protein complexes using two‐dimensional gel electrophoresis. Ultracentrifugal analysis of the DNA‐protein complexes in the presence of proteinase K, nucleases, or a chelating agent demonstrated that protein aggregation was not responsible for the increased protein recovery in chromate‐treated samples and that the complexes were disrupted by EDTA. These data suggest that the selectively complexed proteins were associated with the DNA through strong interactions that may be mediated by the trivalent form of chromium.
Differences between normal and transformed murine fibroblasts in the expression of various promoter/enhancer—chloramphenicol acetyltransferase constructs
Authors: Begemann Martin , Hsiao W.‐L. Wendy , Weinstein I. Bernard
Published: February 2007

High levels of poly(A)+ RNAs homologous to certain endogenous retrovirus‐related DNA sequences are frequently seen in carcinogen‐transformed rodent cells. To explore the underlying mechanism, transient expression assays were done to determine whether carcinogen‐ or radiation‐transformed C3H 10T1/2 cell lines differ from normal 10T1/2 cells in terms of their ability to express the chloramphenicol acetyltransferase (CAT) gene when it is linked to various promoter/enhancer sequences, including two independently isolated intracisternal A particle (IAP) long terminal repeat sequences designated prcm and pMIA6. We found that with several constructs, CAT activity was always 3‐ to 10‐fold higher in the transformed 10T1/2 cell lines than in the normal 10T1/2 cells. The prcm‐CAT construct displayed the highest CAT activity in both the normal and transformed C3H 10T1/2 cells. Studies with 32P‐labeled prcm‐CAT DNA and Southern blot analyses indicated that the differences in CAT activity between normal and transformed cells were not due to greater uptake or retention of the transfected DNA by the transformed cells. Competition studies provided evidence that factors required for the expression of the prcm‐CAT construct are present in limited amounts in normal 10T1/2 cells and in excess amounts in transformed 1011/2 cells. These putative factors may play a role in the increased expression of endogenous retrovirus‐related sequences in the transformed cells.
Molecular cloning of mouse epidermal cystatin A and detection of regulated expression in differentiation and tumorigenesis
Authors: Hawley‐Nelson Pamela , Roop Dennis R. , Cheng Christina K. , Krieg Thomas M. , Yuspa Stuart H.
Published: February 2007

A Xgt 11 cDNA expression library representing mouse epidermis mRNA was screened with polyclonal rabbit antiserum directed against 10–13 kDa epidermal antigens that had previously been shown to be regulated during epidermal differentiation. A cDNA clone was detected and isolated and its identity as the coding sequence for one of the antigens was confirmed by translation of hybrid‐selected mRNA from mouse epidermis. The cDNA sequence predicted a peptide homologous to the reported sequence of rat epidermis cystatin A, a thiol proteinase inhibitor. This identification was confirmed by cross‐reactivity of the μgm clone fusion protein with authentic antiserum to rat epidermis cystatin A. Southern gel analysis showed that mouse DNA may contain several closely related genes homologous to the cystatin probe. An mRNA of about 0.6 kb from epidermis and cultured mouse epidermal cells hybridized with the cystatin probe on northern analysis. The abundance of the message was high in cultured basal cells and was selectively diminished by inducing terminal differentiation in culture with an elevated Ca2+ concentration in the medium. Cystatin message was abundant in chemically induced mouse skin papillomas but reduced in carcinomas. In epidermis, mRNA was localized to the less differentiated basal and lower spinous layers by in situ hybridization. Regulation of expression of cystatin A in epidermis and tumors suggests that it may be important in the control of normal keratinocyte proliferation and differentiation and in malignant conversion.
Mutagen activation by cDNA‐expressed P1450, P3450, and P450a
Authors: Aoyama Toshifumi , Gonzalez Frank J. , Gelboin Harry V.
Published: February 2007

cDNAs for rodent P1450, P3450, and P450a were expressed in the modified vaccinia virus‐T7 RNA polymerase system. Each P450 exhibited its appropriate molecular weight and characteristic enzyme activity. Aryl hydrocarbon hydroxylase activity was catalyzed by P1450, acetanilide hydroxylase by P3450, and testosterone 7a‐hydroxylase by P450a. Ethoxycoumarin deethylase was exhibited by both P1450 and P3450. Each expressed P450 was also analyzed for its ability to activate 19 carcinogens of diverse classes to their mutagenic forms. Most notable was the activation of several polycyclic aromatic hydrocarbons by P1 and the activation of acetylaminofluorene, 4‐aminobiphenyl, and several heterocyclic amine food pyrolysate products by P3450. P450a, in contrast, showed slight mutagen activation only toward N‐hydroxy‐2‐acetyl aminofluorene. The vaccinia virus‐T7 RNA polymerase system described here can express cDNAs for diverse forms of P450, each of which can then be characterized for substrate and product specificity and for mutagen activation.
Transformation of an established mouse mammary epithelial cell line following transfection with a human transforming growth factor alpha cDNA
Authors: Shankar Vidya , Ciardiello Fortunato , Kim Nancy , Derynck Rik , Liscia Daniel S. , Merlo Giorgio , Langton Beatrice C. , Sheer Donald , Callahan Robert , Bassin Robert H. , Lippman Marc E. , Hynes Nancy , Salomon David S.
Published: February 2007

To determine whether the enhanced expression of transforming growth factor α (TGFα) is sufficient to induce the neoplastic transformation of an immortalized population of mammary epithelial cells, we cotransfected NOG‐8 cells, a cloned mouse mammary epithelial cell line, with a simian virus 40‐human TGFα cDNA expression vector plasmid and a pSV2neo plasmid. After cotransfection, nine G418‐resistant NOG‐8 colonies were cloned and expanded. All clones were subsequently analyzed for TGFα mRNA expression by northern blot analysis, TGFα secretion, anchorage‐dependent growth in serum‐free medium, anchorage‐independent growth in soft agar, and tumorigenicity in nude mice. Three TGFα‐transfected NOG‐8 clones expressed high levels of a specific TGFα mRNA, secreted elevated levels of TGFα into the culture medium (177–595 ng/108 cells/48h), exhibited an enhanced growth rate, grew aggressively as colonies in soft agar, and formed undifferentiated, invasive carcinomas in nude mice. A neutralizing mouse monoclonal antibody generated against the low molecular weight human TGFα peptide was able to inhibit colony formation in soft agar by TGFα‐transfected NOG‐8 clones that produced high levels by TGFα This inhibition suggested that TGFα acted through an external autocrine loop. NOG‐8 cells and NOG‐8 cells transfected with a pSV2neo plasmid alone secreted very low levels of TGFα, failed to grow as colonies in soft agar and did not form tumors in nude mice. These results demonstrate that overexpression of a human TGFα cDNA in immortalized, nontransformed mouse mammary epithelial cells can induce a transformed phenotype in vitro and can facilitate tumor formation in vivo.
Molecular analysis of DNA isolated from the different stages of X‐ray‐lnduced transformation in vitro
Authors: Krolewski Bozena , Little John B.
Published: February 2007

A major challenge in radiation carcinogenesis is to identify the cellular gene or genes involved in initiating the process. We examined the transforming activities of DNAs obtained from C3H10T1/2 cells during x‐ray‐induced morphological transformation. DNAs extracted from mass cultures of 10T1/2 cells at different times after irradiation with 600 rad and from type III‐transformed foci were transfected into NIH 3T3 cells. The results indicate that certain oncogenes are activated beginning 3 wk after irradiation, well before the appearance of macroscopically visible transformed foci. For DNA isolated from x‐ray‐transformed 10T1/2 cells (type III foci), the frequencies of transfection were 0.003–0.11 foci/μg of genomic DNA with NIH 3T3 cells and 0.004–0.04 foci/μg genomic DNA using 10T1/2 cells as recipients. Southern blot analysis of DNAs obtained from 23 primary transfectants and from 23 x‐ray‐transformed cell lines indicated no gross rearrangements or amplification of any of the 14 oncogenes screened (v‐Ha‐ras, v‐Ki‐ras, N‐ras, v‐myc, v‐raf, v‐src, v‐fes, v‐abl, v‐mos, v‐erbA, v‐erbB, M‐myb, v‐fos, v‐sis). This suggests that x‐irradiation may activate as yet unidentified oncogenes. The occurrence of positive transfection 3 wk after irradiation is discussed in terms of the hypothesis that transformation may not occur as a direct consequence of the exposure to x‐rays but develops as a rare event in the progeny of the irradiated cells at some later time, as a consequence of the delayed activation of certain genes.
Intracellular receptor binding and nuclear transport of nerve growth factor in intact cells and a cell‐free system
Authors: Rakowicz‐Szukzynska Ewa M. , Linnenbach Alban J. , Koprowski Hilary
Published: February 2007

Nuclear uptake of125I‐labeled nerve growth factor (NGF) by cells that either express or do not express the cell surface receptor was tested using intact cells and a cell‐free system. Intracellular and consequently nuclear uptake of NGF in intact cells was dependent on the presence of surface NGF receptor, whereas nuclear uptake in a cell‐free system did not correlate with cell surface receptor expression. In the cell‐free system, nuclear transport was inhibited when NGF receptor was being actively synthesized. Preincubation of intact cells with unlabeled NGF, cycloheximide, puromycin, or actinomycin D increased nuclear uptake up to threefold. The data suggest that, in intact cells, NGF transported into the cell via the surface receptors is also bound by the NGF receptor being synthesized in the cytoplasm. NGF taken up by the nucleus inhibited transcription of ribosomal RNA genes by 70% and, in turn, inhibited cell proliferation by 60%. A direct effect of NGF on transcription is discussed.
Effects of various chemical agents on the transformation of rat fibroblasts by an activated c‐Ha‐ras oncogene
Authors: Lopez Cecilia A. , Hsiao W.‐L. Wendy , Weinstein I. Bernard
Published: February 2007

We have previously reported that the potent tumor‐promoting agent 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) and a factor from fetal calf serum (FCS) markedly enhance the transformation of mouse C3H 10T1/2 and Rat 6 fibroblasts, when added to cultures following transfection with plasmid pT24 DNA that contains an activated c‐Ha‐ras oncogene. In the present study, we examined possible enhancing or inhibiting effects of various chemicals on the transformation of Rat 6 fitbroblasts by T24 DNA when tested in the presence of calf serum, calf serum plus TPA or FCS. We found that, like TPA, the chemicals mezerein, 1‐oleoyl‐2‐acetylglycerol, and phospholipase C increased the yield of T24‐induced foci, thus further implicating protein kinase C as a critical constituent in this process. Low concentrations (10−6–10−7M) of retinoic acid (both trans and 13‐cis) also stimulated cell transformation. Several compounds inhibited T24‐induced transformation. These included nontoxic concentrations of the calcium ionophore A23187, indomethacin, and ϵ‐amino‐n‐caproic acid. Compounds that failed to exert a significant reproducible effect included vasopressin, vitamin D3, selenium, antipain, Bowman‐Birk inhibitor, vitamin B12, epidermal growth factor, platelet‐derived growth factor, insulin, and transferrin. These findings suggest that this simple in vitro system might be useful for detecting enhancers and inhibitors of ras oncogene‐induced cell transformation and also elucidating their mechanisms of action.
Mutational specificities of environmental carcinogens in the lacl gene of Escherichia coli. II: A host‐mediated approach to N‐nitroso‐N, N‐dimethylamine and endogenous mutagenesis in vivo
Authors: Horsfall Michael J. , Zeilmaker Marco J. , Mohn Georges R. , Glickman Barry W.
Published: February 2007

An intrasanguineous host‐mediated assay was used to determine the mutational specificity of the hepato‐carinogen N‐nitroso‐N, N‐dimethylamine metabolized in vivo. A total of 114 forward mutations in the lacl gene of Escherichia coli reisolated from the livers of treated Swiss albino mice were characterized at the DNA sequence level. Consistent with the methylating ability of this compound and the demonstrated mutagenic specificity of O6‐methylguanine, the predominant mutation was the G:C→A:T transition. These were recovered, on average, seven times more frequently at guanines flanked (5′) by a purine residue than at those preceded by a pyrimidine residue—a specificity similar to that reported for many direct‐acting SN1 alkylating agents. This nitrosamine appears to be distinguished from related N‐nitroso methylating compounds by the induction of additional mutational events. Here, the exceptions consisted of four A:T→G:C transitions, four A:T site transversions, and a single G:C→T:A transversion. In addition, the DNA sequence alterations of 34 I− mutants of E. coli reisolated from otherwise untreated mice were identified. The predominant mutation was the G:C→A:T transition, which accounted for almost half of all background mutations. The sites at which these mutations were recovered appear to indicate that some of these mutations may have arisen as a result of an accelerated rate of cytosine deamination. These data suggest that many of the additional “spontaneous” mutations observed under in vivo conditions resulted from genotoxic events occurring during the host‐defense (immune) reaction.
Cellular oncogene expression in cell lines derived from tumors produced by transformed rat tracheal epithelial cells
Authors: Walker Cheryl , Nettesheim Paul
Published: February 2007

Five tumor‐derived cell lines established from transformed rat tracheal epithelial (RTE) cells were examined for activated oncogenes using the NIH 3T3 assay, and the expression of 11 cellular oncogenes in the transformed cells was quantitated and compared with expression in normal RTE cells. DNA from the tumor‐derived cell lines lacked transforming activity, but expression of several oncogenes (fos, abl, Ki‐ras, Ha‐ras, and p53) was higher in the transformed cells than in normal RTE cells.
Characterization of env gene recombination in X‐ray‐induced thymomas of C57BL76 mice
Authors: Nairn Rodney S. , McLntyre Bradley W. , Richie Ellen R. , Allison James P.
Published: February 2007

A role for specific recombination events at the env region of endogenous murine leukemia virus (MuLV) sequences in radiation carcinogenesis in C57BL mice has been suggested by a number of studies. We characterized env‐related cell surface antigens from a primary, x‐ray‐induced, and several transplanted C57BL/6 thymomas of viral and radiation etiologies by immunoprecipitation and two‐dimensional peptide mapping. DNA from lymphoma cells was also analyzed by Southern blotting for evidence of mink cell focus‐forming (MCF) type env recombination events. Although gp70 molecules with novel structural determinants were found on all transplanted lymphomas examined, expression of novel env antigens was variable among these lymphomas, and there was a lack of correlation of characteristic MCF‐type env recombination events in endogenous retrovirus DNA sequences with novel env antigens on lymphoma cell surfaces. Neither novel gp70 antigens nor MCF‐type env provirus recombinant structures were consistent features of the C57BL/6 thymomas of radiation etiology examined in this study, even though MCF‐type env recombination events have been suggested as etiologically significant in MuLV‐mediated lymphomagenesis in both RadLV and x‐ray‐induced tumors in C57BL/6 mice.
Constitutive and phorbol‐myristate‐acetate regulated antioxidant defense of mouse epidermal JB6 cells
Authors: Crawford Dana R. , Amstad Paul A. , Foo Debra D. Yin , Cerutti Peter A.
Published: February 2007

Because oxidative processes can participate in tumor promotion, it is likely that the cellular antioxidant defense also plays a role. We have compared the levels of the three major antioxidant enzymes, Cu, Zn‐superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx), in promotable mouse epidermal JB6 cells clone 41 and nonpromotable cells, clone 30. We found that the constitutive activities of SOD and catalase were approximately twice as high in clone 41 as in clone 30 while the GPx activities were comparable. Correspondingly, catalase protein concentrations were higher in clone 41, according to immunoblots. Northern blot analysis indicated that the steady‐state mRNA concentrations for SOD and catalase, but not for GPx, were considerably higher in clone 41 than in clone 30. Southern blot analysis showed no difference between the two clones in their complements of the SOD and catalase genes. Clone 41 also contained slightly higher constitutive levels of glutathione. The higher antioxidant capacity of promotable clone 41 may protect it from excessive toxicity of oxidant promoters and allow growth stimulation.

Certain tumor promoters that lack oxidizing properties may generate a cellular prooxidant state by a variety of mechanisms (e.g., it had been reported that the phorbol ester PMA decreases the activities of catalase and SOD in mouse skin). We found for JB6 cells that this loss of enzyme activity was due to a decrease in the steady‐state concentrations of catalase and SOD mRNA. No significant changes in the rates of transcription were detected in nuclear run‐off experiments. The observed decreases in catalase and SOD can be considered as part of the complex reprogramming of gene expression that is set in motion by phorbol‐12‐myristate‐13‐acetate.
Prevalence of nucleoside diphosphate kinase autophosphorylation in human colon carcinoma versus normal colon homogenates
Authors: Francis Brian , Overmeyer Jean , John William , Marshall Ernest , Haley Boyd
Published: February 2007

The G‐regulatory proteins of adenylate cyclase, tubulin, and the ras oncogene protein product require the production of GTP from ATP in order to exert their effects within the cell. This implies that the activity of nucleoside diphosphate kinase (NDPK) plays a major role in the regulation of cellular events requiring GTP and that the level of activity of this enzyme is critical. This report presents a simple method for trapping a specific isozyme of NDPK in its high‐energy phosphorylated form (NDPK∼P) using EDTA and demonstrates that this NDPK∼P is tenfold higher in malignant colon tumor tissue than in normal colon tissue. This autophosphorylation of the 21,000 and 24,000 Mr subunits of NDPK occurs rapidly at Oß, will use either [γ32P]ATP, [γ32P]GTP, or the corresponding 8‐azidopurine photoprobes, is intramolecular, displays saturation effects, and is prevented from forming if GTPγS is added. Dephosphorylation in the homogenate occurs rapidly upon addition of Mg2+ or any nucleoside‐5′‐diphosphate. The subunits autophosphorylated in the homogenates are mostly in the soluble phase, and they comigrate with the subunits of pure NDPK from human erythrocytes. Cross‐addition of normal and malignant homogenates does not decrease the level of autophosphorylation of NDPK, which indicates that the level of NDPK∼P may be a quantitative measure of the level of this specific NDPK isozyme form. Assays for NDPK activity show correspondingly elevated levels in the malignant homogenates. Using western blot and photoaffinity labeling techniques, we distinguished the NDPK∼P subunits from two closely migrating GTP‐binding proteins. These were identified as the ras gene protein product and a 20,000 Mr protein, which comigrates identically with ADP‐ribosylating factor (ARF). The ARF also comigrates in a tight band that is phosphorylated by [γ32P]ATP or [γ32P]GTP when Mg2+ is present.
Enhanced Deoxyribonuclease Activity in Human Transformed Cells and in Bloom's Syndrome Cells
Authors: Mezzina Mauro , Nocentini Silvano , Nardelli Jeannette , Renault Georges , Moustacchi Ethel , Sarasin Alain
Published: February 2007

Human hereditary diseases such as xeroderma pigmentosum, Fanconi's anemia, ataxia telangiectasia, and Bloom's syndrome are characterized by a proneness for developing cancer associated with abnormalities in the processing of DNA damage. The molecular defects responsible for predisposing human tissues to cancer are still not well understood, despite the fact that a considerable amount of work has already been done on this problem. In this paper, we show that in human tumor cell lines, in cells transformed by DNA tumor viruses, and in cells derived from certain cancer‐prone disorders, the level of activity of a 42‐kDa deoxyribonuclease is many times higher than in diploid untransformed control cells. This suggests that this activity is linked to, or may play a role in, malignant transformation.
Denaturing Gradient Gel Analysis of Single‐Base Substitutions at a Mouse Adenine Phosphoribosyltransferase Splice Acceptor Site
Authors: Dlouhy Stephen R. , Schaff Dennis A. , Trofatter James A. , Liu Hsiao‐Sheng , Stambrook Peter J. , Tischfield Jay A.
Published: February 2007

Denaturing gradient gel electrophoresis (DGGE) can detect single‐base changes in DNA. We used site‐directed mutagenesis to produce all six possible single‐base substitutions at a splice acceptor consensus AG dinucleotide within the mouse adenine phosphoribosyltransferase (aprt) gene. Studies of mouse and Chinese hamster cell aprt indicate a high level of both spontaneous and induced mutations in this region. We systematically evaluated each of the six mutations by DGGE. Five of the six mutant sequences could be distinguished from wild‐type by DGGE analysis of a 560‐bp fragment containing the mutation. However, one mutant could not be distinguished from wild‐type, and some of the mutant constructs could not be distinguished from each other. Analysis of DNA heteroduplexes consisting of wild‐type and mutant strands or two different mutant strands enabled all mutant constructs to be distinguished from wild‐type and from each other. The pairwise mixtures resulted in 24 different heteroduplexes, all of which were less stable than the parental homoduplexes. End labeling of DNA prior to heteroduplex formation and subsequent DGGE analysis enabled us to determine the relative destabilization caused by different types of single‐base mismatches.
Interleukin‐1 Beta Gene Deregulation Associated With Chromosomal Rearrangement: A Candidate Initiating Event for Murine Radiation‐Myeloid Leukemogenesis?
Authors: Silver Andrew , Boultwood Jacqueline , Breckon George , Masson Walter , Adam Julie , Shaw Alan R. , Cox Roger
Published: February 2007

The incidence of acute myeloid leukemia (AML) in CBA/H mice following exposure to single acute doses of ionizing radiation has previously been determined. A high proportion of these AMLs are characterized by rearrangement of murine chromosome 2 in the C2 and/or E5‐F regions, and there is evidence that these events are a direct consequence of radiation damage to multipotential hemopoietic cells. Using a combination of in situ chromosome hybridization and mRNA analyses, we show that the cytokine gene interleukin‐1β (IL‐1β) is encoded in the chromosome 2 F region and is translocated in a chromosome 2 ‐> 2 rearrangement in an x‐ray‐induced AML (N36). Also, IL‐1β is specifically deregulated in N36and in two other chromosome 2‐rearranged AMLs but not in a fourth, which has two cytogenetically normal chromosome 2 copies. We suggest that radiation‐induced specific chromosome 2 rearrangement associated with IL‐1β deregulation may initiate murine leukemogenesis through the uncoupling of normal proliferative control mechanisms in multipotential hemopoietic cells.
The Role of Methylation in Regulating the Expression of the Alpha‐Fetoprotein Gene in Developing Rat Liver and Hepatoma Cell Lines
Authors: Smith Catharine L. , Nordloh Peter W. , Chiu Jen‐Fu
Published: February 2007

We have examined four possible sites of methylation in the 5′ flanking region of the alpha‐fetoprotein (AFP) gene during liver development in the rat, paying particular attention to the neonatal period, in which AFP gene transcription changes rapidly. These sites are found in Mspl/Hpall sites located at ‐ 4197, ‐ 3038, ‐ 2431, and + 3 bp relative to the transcription start site. Three of these sites are associated with sequence regions important for the regulation of AFP gene transcription. We found that, in general, the 5′ flanking region of the gene was methylated more in the adult liver than in the livers of fetal and neonatal rats. In addition, the degree of methylation of all four sites examined was increased in the adult liver. One of these sites showed increased methylation as AFP gene activity decreased, whereas the others became more methylated only after transcriptional activity of the gene had ceased. In particular, the site ( + 3 bp) just adjacent to the transcriptional initiation site of the gene was fully methylated in the adult liver In various rat hepatoma and liver cell lines methylation of this same site showed a particularly close correlation with the amount of transcriptional activity of the AFP promoter in these cell lines. Treatment of the hepatoma and liver cell lines with dexamethasone, which influences AFP gene expression, did not result in any changes in methylation of these sites in the 5′ flanking region.
Efficient Immortalization by SV40 T DNA of Skin Fibroblasts From Patients With Wilms' Tumor Associated With Chromosome 11p Deletion
Authors: Kano Yoshio , Little John B.
Published: February 2007

We report that transfection with a plasmid containing the SV40 early region (T) leads to a very high frequency of immortalization in two different strains of human diploid fibroblasts, each with a partial deletion of the short arm of chromosome 11. Immortalization often occurred without a recognizable “crisis” phase. Preimmortal cells showed a high frequency of spontaneous mutations and chromosomal aberrations. These results suggest that a gene involved in the control of senescence of human cells in vitro may be associated with this chromosome.
Major Urinary Protein as a Negative Tumor Marker in Mouse Hepatocarcinogenesis
Authors: Dragani Tommaso A. , Manenti Giacomo , Sacchi Marina R. M. , Colombo Bruno M. , Porta Giuseppe Della
Published: February 2007

A cDNA clone isolated by differential screening of a mouse liver cDNA library using RNA probes from normal adult liver and from hepatocellular tumors showed, on northern blot analysis, a single transcript of 1 kb present at high levels in normal adult mouse liver but at 15‐ to 100‐fold reduced levels in spontaneous and p‐dimethylaminoazobenzene‐ or urethan‐induced liver tumors. The transcript, which was absent in two‐wk‐old mouse liver, is coded by a developmentally regulated gene. Nucleotide sequence analysis demonstrated that the isolated clone encoded a major urinary protein (MUP). Immunocytochemistry analysis, using a goat antibody to MUP on histologic liver sections containing diethylnitrosamine‐induced liver nodules, showed that the decrease in MUP levels also occurred in microscopic nodules. Therefore, MUP decrease represents an early event in the development of mouse liver tumors, and it may be used as a tumor marker in mouse hepatocarcinogenesis.
Detection of epstein‐barr viral genomes in lymph nodes of Hodgkin's disease patients
Authors: Bignon Yves‐Jean , Bernard Dominique , Curé Hervé , Fonck Yvette , Pauchard Jacques , Travade Philippe , Legros Michel , Dastugue Bernard , Plagne Robert
Published: February 2007

Previous studies using Southern blot analysis or in situ hybridization have shown that approximately 20% of patients with Hodgkin's disease have Epstein‐Barr virus (EBV) in involved tissues. We used the more sensitive polymerase chain reaction (PCR) technique to determine if a higher percentage of EBV could be detected. Of the 16 Hodgkin's disease patients studied, the PCR technique detected EBV in eight (50%). No prognostic significance was associated with the presence of EBV in the eight EBV‐positive patients, and the presence of EBV was not associated with B cell monoclonality.
N‐methyl‐N‐nitrosourea‐lnduced mutations in a shuttle plasmid replicated in human cells
Authors: Sikpi Matthew O. , Waters Larry C. , Kraemer Kenneth H. , Preston R. Julian , Mitra Sankar
Published: February 2007

The supF gene of the recombinant shuttle plasmid pZ190 (modified pZ189) was used as a target to study the nature of mutations induced by N‐methyl‐N‐nitrosourea (MNU) in human cells. Treatment of the intact plasmid with MNU followed by its replication in human lymphoblastoid cells led to extensive inactivation and no detectable mutations of the plasmid. However, exposure of the supF DNA fragment alone, followed by its ligation into the vector, caused a ten‐fold increase in mutant frequency when replicated in O6‐methylguanine‐DNA methyltransferase‐deficient cells (from 0.54 × 10−3to5.8 × 10−3) and an 80‐fold increase when replicated in cells containing normal levels of the enzyme (from 0.047 × 10−3to3.8 × 10−3). About 45% of the mutant plasmid molecules recovered from human cells contained deletions and insertions. Sixty to 70% of the mutant molecules of wild‐type size contained a single‐base substitution. Most of these changes were of the G.C ‐A.T type, consistent with the hypothesis that O6‐methylguanine is the primary mutagenic adduct induced by MNU. However, the distribution of mutation sites was highly nonrandom; more than half of all mutations were localized at the G.C position 123, and the rest were distributed in about a dozen sites. The high yield of mutations induced in the supF DNA in a host cell whose capacity for the removal of O6‐methylguanine far exceeded the amount present in the supF suggests that the repair of damages in extrachromosomal DNA may be inefficient. This is supported by the observation that the yield of mutations in supF transfected into lymphoblastoid cells devoid of repair activity for O6‐methylguanine was comparable to that observed with repair‐proficient host cells. The present data, together with results of mutations induced in pZ189 by other agents, strongly suggest that one major determinant of mutational hot spots is the structure of the target DNA itself.