RESUMO
gamma-Irradiation action within a dose range of 0-20 Gy on parental djungarian hamster fiborblasts, DH-TK- cell line, and the progenies of these irradiated cells, surviving acute exposure to 20 Gy irradiation, PIC-20 cell line, was examined. The PICs were 3 times more radioresistant than the parental cells as calculated from D0. Using a method of anomalous viscosity time dependence (AVTD) it was revealed that starting (initial) level (in untreated cells) of chromatin compactness in radioresistant progenies was more than 1.4 times as high as for parental cells. The analysis of dose dependence has shown that irradiation with a dose of 5 Gy resulted in complete chromatin loop relaxation in radiosensitive DH-TK- cells and partial one in radioresistant PIC-20 cells. Besides, the beginning of DNA-membrane complexes degradation following the irradiation with doses over 15 Gy in DH-TK- cells was observed. It was shown that the increased state of relative chromatin relaxation in PIC-20 cells determines an increasing in reparation effectiveness that resulted in lower percent of residual damages in these cells. Using the Nosern hybridization method the expression level of mts 1, tag 7 and vseap 1 genes was studied. It is revealed that tag 7 and vseap 1 gene expression in radioresistant cells were correspondingly 6 and 10 times higher than in radiosensitive parental cells and the level of mts 1 gene expression was not changed. So, based on the results obtained we suggest that acquired radioresistance in progenies of irradiated cells is determined by rearrangements in chromatin structure and accompanied constitutive changes of gene expression.
