Regulation of CYP1A induction in hepatoma 27 depending on the site of transplantation

Appearance of differentiation characteristics (induction of Ah-receptor-dependent genes) during cultivation of transformed cell clone K8 from embryonic rat fibroblasts

The differentiation status of fibroblasts can be characterized by their ability to induce Ah-receptor-dependent genes. The ability to induce Ah-receptor-dependent genes encoding cytochrome P450 isoforms, Ah-receptor repressor, and NADPH-quinine oxidoreductase were studied in the transformed cell clone K8 obtained from immortalized embryonic rat fibroblasts by treatment with benzo(a)pyrene and in the parental clone F27. Treatment with benz(a)anthracene did not induce the genes in the transformed clone K8 on passages 4-14, but the induction was recorded in the transformed clone beginning from the 16th passage and later, whereas in F27 cells the induction was observed throughout the experiment. Induction levels of mRNA of the induction-regulating genes encoding the Ah-receptor and Ah receptor nuclear translocator were similar in F27 cells and in the transformed cell clone K8 in both early and late passages. Electrophoretic mobility shift assay showed that in clone K8 transmission of the induction signal was disturbed in the early passages before interaction of the activated Ah-receptor with the recognizing region of DNA. Possible mechanisms responsible for the absence of induction in the early passages in the transformed cells are discussed.

Activity of detoxication enzymes in rat hepatoma 27 transplanted in different organs

Activities of enzymes of active oxygen forms detoxication and phase II xenobiotic metabolism were measured in rat hepatoma 27 cells transplanted to different organs. Activity of phase II xenobiotic metabolizing enzymes was higher in hepatoma cells growing subcutaneously than in those transplanted into the liver, while activity of active oxygen forms detoxication enzymes (except catalase) was higher in cells transplanted into the liver. Benz(a)pyrene induced the enzyme activities in hepatoma growing both subcutaneously and in the liver.