Relationship between changes in ploidy and stable cellular resistance to hydrogen peroxide

Abstract

Stable hydrogen peroxide (H₂O₂)‐resistant variants of the Chinese hamster ovary HA‐1 line have been isolated by culturing cells in progressively increasing concentrations of H₂O₂ (>200 days, in 50–800 μM H₂O₂). Increases in catalase activity in these variant cell lines were shown to correlate with increased H₂O₂ resistance. Stable (>240 days) H₂O₂‐resistant cell lines, seven quasidiploid (21–22 chromosomes/cell) and six quasitetraploid (40–44 chromosomes/cell) were clonally isolated from the 800 μM adapted H₂O₂‐resistant variants which were heterogeneous with respect to ploidy. The H₂O₂ dose‐modifying factors (DMFs) were 3, 5, 8, 13, 15, 26, and 27 for the seven quasidiploid cell lines, and 21, 32, 38, 40, 42, and 49 for the six quasitetraploid cell lines. The mean DMF was 14±10 for the former and 37±10 for the latter. Our data show that on the average the quasitetraploid cell lines were significantly more resistant to H₂O₂‐mediated cell killing than the quasidiploid cell lines derived from the same mixed population of 800 μM H₂O₂‐adapted cells. When catalase activities (k units/cell) of the HA‐1 cells and three of the clonally derived cell lines (two quasidiploid and one quasitetraploid) were determined and plotted vs. H₂O₂–DMF, a positive linear correlation was obtained (correlation coefficient = 0.99). This result was further confirmed when immunoreactive catalase protein/cell was detected by Western blots. Our data show that chronic exposure of cells to H₂O₂ stress (800 μM) was accompanied by increases in quasitetraploid cells within the population. Quasitetraploid cell lines derived from this population demonstrated increased stable H₂O₂‐resistance which may be related to stable increases in the expression of catalase.