Karyotypic Changes of Apoptosis-Resistant Rat Cells HindIIIG during Prolonged Cultivation after Exposure to Ionizing Irradiation

Genome instability manifested by multiple reorganization contributes to the acquisition of new properties by tumor cells, resistance to therapy in particular. Structural rearrangements of chromosomes can be induced by damage to DNA, for example, by ionizing radiation. In this study, changes in the karyotype of the pseudodiploid cell line HindIIIG-1 obtained after irradiation of apoptosis-resistant transformed rat cells HindIIIG have been examined. The HindIIIG-1 line is a result of polyploidization associated with the cell cycle block in the G2/M phase and subsequent depolyploidization. The original HindIIIG line, before irradiation, was represented mainly by a pseudodiploid population with the normal number of 42 chromosomes, tetraploid fraction composed of 14%. The cell karyotype had two numerical and one specific structural rearrangement of chromosomes (SRCs), der(14). Irradiation induced polyploidization and multiple fragmentations of chromosomes. In the process of cultivation, a pseudodiploid population of cells with the karyotype similar to the karyotype of nonirradiated cells began to predominate, but the number of clonal and nonclonal SRCs increased. At late passages, the karyotype of HindIIIG-1 cells again became identical to the karyotype of cells before irradiation and did not contain new clonal SRCs. The role of nonclonal and clonal SRCs in the process of survival of irradiated cells and the formation of new cell populations is discussed.