1,721,012 research outputs found
The aryl hydrocarbon receptor signal transduction pathway : mechanism and consequence of action in human mammary epithelial cells
No full textPolycyclic aryl hydrocarbons such as benzo[a]pyrene (BP) are produced during combustion or pyrolysis of organic matter and are thus ubiquitous in the human environment. BP has been shown to induce mammary carcinomas in laboratory animals, and can accumulate in lipid stores such as the mammary fat pad. In the process of converting BP to a more water-soluble and excretable form, highly mutagenic intermediates are formed. BP can enhance expression of the metabolizing enzymes involved in this process by binding to a ligand-activated transcription factor known as the aryl hydrocarbon receptor (AhR). In its native state, cytosolic AhR is found in association with a dimer of 90 kDa heat shock proteins (HSP90) and an immunophilin-like protein. Ligand binding causes loss of accessory proteins and translocation to the nucleus where it heterodimerizes with the Arnt protein. The AhR/Arnt complex modulates gene expression by binding to cognate DNA sequences in the promoter region of Ah-responsive genes.Two approaches were utilized to determine the effects of BP on human mammary epithelial cells (HMEC). Firstly, spontaneously immortalized nontransformed HMEC were subjected to multiple rounds of BP exposure and in vitro transformed clones were isolated based on a loss of contact inhibition and altered morphology. Unlike parental cells, the BP-transformed clones were found to possess chromosomal alterations that frequently occur in human breast cancer, including an isochromosome 8q. Secondly, the mechanism of resistance was investigated in a HMEC tumor cell line selected for growth in BP. AhR mRNA expression was significantly reduced in the BP-resistant cells, which led to decreased AhR protein and DNA-binding activity. Additionally, HSP90 was investigated for its ability to regulate AhR activity in vivo in HMEC tumor cell lines
Transcriptional targeting of suicide genes in cancer gene therapy
No full textThe use of tissue or tumor selective promoters in targeted gene therapy for cancer depends on strong and selective activity. Hexokinase type II (HK II) catalyzes the first committed step of glycolysis and is overexpressed in tumors, where it is no longer responsive to normal physiological inhibitors, e.g. glucagon. I show in a reporter gene assay activation of HK II in non-small cell lung carcinomas NCI-H661 and NCI-H460 at 61% and 40% of the activation observed with a constitutive promoter respectively, while it is only 0.9% in a number of different primary normal human bronchial epithelial cell lines (NHBEC). Similar results were observed in a variety of normal and tumor cells. Moreover, treatment of the transfectants with glucagon did not inhibit promoter/activation in the transformed H661 cells, while endogenous HK II in NHBEC is suppressed by glucagon, H460 and H661 cells infected with a recombinant adenovirus carrying a HK II/LacZ expression cassette, Ad HexLacZ, demonstrated beta-galactosidase activity, which correlated with the level of HK II promoter activation in these cells. Under similar conditions, no enzyme activity was observed in NHBEC. Cells were then infected with AdHexTk and treated with GCV. Our results demonstrate selectivity in toxicity with a 10--100 fold increase in IC 50 between lung cancer cells and NHBEC. There was also a 100-fold increase in IC50 in normal human mammary epithelial cells (NHMEC) relative to breast carcinoma cells MCF-7. This represents a novel use of the hexokinase type II as a selective promoter in cancer gene therapy. Other factors important in suicide gene therapy were explored. Pharmacological modulation of the bystander effect using 8-bromo-cAMP, observed in HSVTk/GCV suicide killing, was demonstrated to enhance killing efficacy by 50% when a small proportion of a target population was gene modified. The phenomenon of cellular resistance to HSVTk/GCV was examined and in a novel finding, we demonstrated dramatic in
The environmental impact of aeronautical activities : legal aspects
No full textNote:The development of resistance of malignant tumors to the chemotherapeutic agents used in the treatment of neoplastic disease is a major factor responsible for treatment failure. Rat mammary adenocarcinoma cells (MatB) which model the human disease in their pattern of growth were studied to elucidate mechanisms of drug resistance. Cell lines that have acquired drug resistance in vitro as a result of continuous exposure to increasing concentrations of drug have been utilized to this effect. Two separate cell lines were selected for resistance to either a "natural product" (AdrR) or an alkylating (MlnR) antineoplastic drug. Each line displayed phenotypic changes that were stereotypic for the selecting agent. Adriamycin selected cells maintained the multidrug resistant phenotype in vitro and in vivo. […]Le développement de la résistance des tumeurs aux médicaments anti-cancéreux est l'une des causes majeures des échecs thérapeutiques en clinique. Afin d'étudier les mécanismes de la résistance, des cellules isolées d'adénocarcinome mammaire de rat (MatB) ont été utilisées comme modelé expérimental. En traitant ces cellules avec des concentrations croissantes d'agents anti-cancéreux, deux lignées cellulaires résistantes ont été sélectionnées: l'une a l'adriamycine (antibiotique naturel) et l'autre au melphalan (agent alkylant). Les cellules résistantes a l'adriamycine possèdent les caractéristiques classiques du phénotype de "résistance multiple". Les cellules résistantes au melphalan (MlnR) présentent essentiellement une surexpression des glutathione-S-transferases (GST). Cette dernière classe d'enzymes joue un rôle très important dans les mécanismes de défense (cellulaires) contre les agents cytotoxiques et cancérigènes. […
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Molecular studies on the therapeutic implications and regulation of connexin 43
No full textGap junctional intercellular communication (GJIC) allows for the transport of small signaling molecules between adjacent cells. Gap junctions and their constituents, connexins, are often impaired in cancer. Restoration of connexins and GJIC in cancer cells leads to reversal of the transformed phenotype, reduction of the rate of cell growth, and inhibition of in vivo tumorigenicity. In addition, restoration of connexin43 (Cx43), one of the most abundant connexins that is often reduced in cancer, allows for the transfer of chemotherapeutic agents among neighboring cells, a phenomenon known as the "Bystander Effect". In chapter 2, I'm reporting evidence that induction of Cx43 and GJIC with cyclic-AMP (cAMP) can enhance the cytotoxic effect of the prodrug ganciclovir following infection of breast cancer cells with an adenovirus expressing the ganciclovir-activating enzyme viral thymidine kinase (vTK). This induction may provide a therapeutic advantage in suicide gene therapy due to the bystander effect when a small proportion of the cell population is expressing vTK. In chapter 3, I'm reporting that breast tumor tissue samples from patients had low to undetectable Cx43 levels, in contrast to their matched normal tissues. In addition, Cx43 protein and RNA levels were undetectable in a panel of human breast cancer lines and in rat breast tumors induced by the carcinogen dimethylbenz[a]anthracene. Together, these observations indicate that the loss of Cx43 is a common marker of cancer cells. In chapter 4, I examined the hypothesis that Cx43 downregulation occurs primarily at the transcriptional level. To determine the mechanisms behind the transcriptional regulation of Cx43, the human Cx43 promoter was investigated. Overexpression of the H-Ras oncogene in NIH3T3 cells leads to the induction of the human Cx43 promoter activity, as well as Cx43 RNA and protein levels. This stimulation involves the MEK-ERK pathway downstream of H-Ras. The promoter sequence responsible fo
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Characterization of the glutathione transferase alpha genes : roles in drug resistance and chemoprotection
No full textThe glutathione-S-transferases (GSTs) are a multigene family of enzymes that catalyze the conjugation of glutathione (GSH) with toxic endogenous and xenobiotic compounds including anticancer drugs, as part of detoxification pathways. Our laboratory previously isolated a melphalan resistant rat mammary carcinoma cell-line (MLNr MatB). The in vitro and in vivo studies demonstrated increased GST activity, especially elevated GST alpha class in MLNr cells. At the outset of my work, I examined the nature of the increased GST form in MLNr cells. I cloned the GSTA3 cDNA which is overexpressed in MLNr cells and found that it is identical to the previously described GSTA3 mRNA, suggesting that there is no additional GST alpha gene induced by melphalan. To study the role of the rat GSTA3 gene in chemotherapy resistance, and understand the mechanism of its overexpression in drug resistant tumors, I isolated the entire rGSTA3 subunit gene, including its regulatory regions, from a genomic library and characterized it. The rGSTA3 gene is approximately 15 kb in length and consists of seven exons interrupted by introns of different lengths. The functional activity of its promoter was shown by its ability to drive the expression of a CAT reporter gene in MatB cells, and its activity was greater in melphalan resistant cells. I also presented evidence that rGSTA3 subunit evolved as a duplication of the rGSTA5 subunit gene, increasing the diversification and functional benefits. In addition to drug resistance, I have been examining the implications of GST to carcinogenesis. Epidemiological studies have shown an association between Hepatitis B Virus (HBV) infection and exposure to chemical carcinogens in the incidence of hepatocellular carcinoma (HCC). The exact mechanism of these interactions is not known, but reduced GST activity could increase cellular sensitivity to chemical carcinogens. Semiquantitative RT-PCR revealed that HBV infected cells contain a significant decrease in t
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