Volume 46 (2000) No. 5

Carcinogenesis is associated with various epigenetic mechanisms, which can alter intra- and intercellular communication and gene expression and thus affect cytokinetics, i.e. regulation of cell proliferation, differentiation, and apoptosis. These processes lead to a loss of homeostatic control. In addition to "classical" epigenetic events such as DNA methylation and histone acetylation, the major mechanisms include changes in concentrations of signal molecules (hormones, growth factors, fatty acids etc.), modulation of cell receptors and drug-, hormone- and fatty acid-metabolizing enzymes, oxidative stress, and interference with intracellular signal transduction pathways. Multidisciplinary and multibiomarker approach is necessary for setting up a battery of specific biochemical, molecular, and cellular in vitro methods detecting the epigenetic carcinogenic potential of individual chemicals or their environmental mixtures. This approach is based on studies of modes of action of xenobiotics at various levels, including the molecular mechanisms and modulations of cytokinetics, each of them having its specific predictive value.
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The chromosome aberration or sister chromatid exchange frequency was determined in 455.7 MHz microwave-exposed human lymphocytes and in lymphocytes that were subsequently exposed to MMC or X-rays. The exposure was performed by placing the cells at 5 cm from the antenna of a car phone.
In this way the specific absorption ratio was approximatively 6.5 W/kg. The temperature and humidity was kept constant during the experiments. No statistically significant difference was found between microwave-exposed and unexposed control samples. When the microwave exposure was followed by exposure to MMC, some differences were found between the combined treatments and the MMC treatments alone. However, there was no consistency in the results. Combined treatments with X-rays did not provide
any indication of a synergistic action between the RF fields and X-rays, either. Our data therefore do not support the hypothesis that RF fields act synergistically with chemical or physical mutagens.
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Genetic and environmental factors regulate lipid metabolism and phenotypic expression of CAD.
In this study we assessed the effects of apoE gene polymorphism and apoA gene promoter polymorphism on lipid metabolism and risk for CAD. In a case-control study, 166 patients with CAD were compared with 130 healthy subjects. The apoE allele frequencies of patients vs. control group were 6.3% vs. 7.7% for e2, 84.3% vs. 84.6% for e3, and 9.4% vs. 7.7% for e4. Individuals with e4e3 and e4e4 genotypes had higher total (P = 0.023) and LDL cholesterol levels (P = 0.04) than individuals with other genotypes. There were no differences in lipid parameters between the subjects with the apoA-GG genotype and subjects with AG or AA genotypes. However, univariate analysis revealed no association between risk genotypes (e3e4 and e4e4 genotypes) of apoE and CAD risk (OR = 1.1; 95% CI 0.6-2.1, P = 0.8) as well as no association between the GG genotype and CAD risk (OR 0.7; 95% CI 0.5-1.2, P = 0.19). No evidence for a synergistic interaction between e3e4 plus e4e4 genotypes and apoA1-GG genotype on CAD risk was found (OR = 1.3, 95% CI = 0.6-2.9; P = 0.5). One individual with familial defective apolipoprotein B-100 (Arg3500Gln) was found in each group. In conclusion, the apoE gene polymorphism affected the total and LDL cholesterol levels,
whereas neither the apoE gene polymorphism nor the apoA-1 gene promoter polymorphism were shown to be independent risk factors for CAD in Slovenia.
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We present the results of the examination of prognostic markers in 40 children suffering from brain tumors. Prognostic markers such as amplification of the N-myc and c-myc, deletion of the 17p, and DNA ploidy are indispensable factors for the determination of diagnosis. An increased number of c-myc gene copies
was found in malignant brain tumors, especially embryonal, more often than reported in the literature. N-myc amplification occurs in our group seldom, but it seems to be a sign of worse prognosis in glial and embryonal brain tumors. DNA aneuploidy was not found very frequently, but in high-grade tumors only.
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We have compared the therapeutic activity of IL-12 and IL-18 in mice carrying IL-2 gene-transduced syngenic sarcoma Mc12. The IL-2 gene-transduced sarcoma has previously been utilized as an
irradiated, genetically modified tumour vaccine. Murine recombinant IL-12 was capable of suppressing growth of the IL-2 gene-modified sarcoma Mc12 in syngeneic mice more efficiently than growth of the parental Mc12 sarcoma. In contrast, murine recombinant IL-18 could neither inhibit growth of the parental Mc12 sarcoma, nor suppress growth of this IL-2 gene-modified transfectant. These results suggest that although both of these cytokines are functionally related and participate in the induction of IFN gamma production as wellas in cell-mediated immune cytotoxicity, in the murine sarcoma system only IL-12 is therapeutically active and exerts its therapeutic effect in concert with the IL-2 gene. Thus, intratumoral IL-2 gene transfer improves the therapeutic efficacy of IL-12; administration of recombinant IL-12 should therefore be considered as adjuvant in IL-2 gene therapy with irradiated, genetically modified tumour vaccines.
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Langerhans cells are dendritic antigen-presenting cells residing predominantly in the epidermis. Since endogenous galactoside-binding lectins with the jelly-roll motif (galectins) are known to trigger cellular responses, including mediator release, we investigated by lectin histochemistry the cells' capacity to bind two common members of this family, i.e. galectin-1 and -3. Actually, surrounding keratinocytes express a high level of galectin-3, and these cells can be considered as donors of this lectin to Langerhans cells. Employing biotinylated galectin-1 and -3, and concomitantly an antibody against CD1a as a second marker, to visualize the position of Langerhans cells in the human epidermis, the expression of galectin-3-reactive glycoligands in contrast to the lack of binding of galectin-1 was observed. Although
the functional consequences of this selectivity are unclear, these results reveal an example for differential cellular reactivity towards two related endogenous lectins.
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The CD43 molecule (sialophorin, leukosialin, sialoglycoprotein) is a heavily O-glycosylated and sialylated glycoprotein, consisting of 381 amino acid residues (Hořejší and Stockinger, 1997).
CD43 is a type I transmembrane protein of 95 000-115 000 Mr with an extracellular domain of 239 residues carrying an N-glycan chain and about 70-85 O-linked oligosaccharides (Pallant et al., 1989).
A soluble form of CD43, called galactoglycoprotein, was detected in human blood plasma (Schmid et al., 1992). CD43 is expressed on all human leukocytes except for the majority of resting B lymphocytes. Different cell types express CD43 forms differing in the degree of sialylation of the O-linked oligosaccharide chain. CD43 expression is tightly regulated on cells of hematopoietic origin either by increasing or decreasing surface expression, or by post-translational modification, which results in precisely controlled glycosylated isoforms. The structural characteristics of the CD43 extracellular domain indicate that this molecule has both adhesive and anti-adhesive properties (Ostberg et al., 1998; Seveau et al., 2000). The mucin-like 234 amino acid extracellular domain is extensively O-glycosylated, with 70-85 O-linked carbohydrate chains. These carbohydrate structures, such as the sialyl-Lewis (sLe*) epitope, a ligand for both P- and E-selectin, can potentiate binding to lectin-like molecules. However, the adhesion molecule function for CD43 is counteracted by the presence of over 100 negatively charged sialic acid residues on its extracellular domain.
Background.