RELATIONSHIP BETWEEN THE ADAPTIVE RESPONSE TO OXIDANTS AND STABLE MENADIONE-RESISTANCE IN CHINESE-HAMSTER OVARY CELL-LINES

To study the genetic changes that generate resistance to oxidants in m ammalian cells, we isolated cell lines that are resistant to the napht hoquinone, menadione, from a Chinese hamster ovary cell line (CHO-K1). Cross-resistance to other oxidants (H2O2 and sodium arsenite) was obs erved, The IC50 of menadione (measured using a clonogenic assay) was 7 .8-fold greater for one menadione-resistant cell line (MRc40) than for CHO-K1, Acquisition of resistance was associated with elevations of 2 - and 3.2-fold in the low molecular weight thiols, glutathione and cys teine, respectively, Further characterization demonstrated significant changes in the expression of enzymes associated with the oxidative st ress response and with protection against oxidizing agents, The expres sions of glutathione S-transferase pi (GST pi), glutathione peroxidase (GPX) and heme oxygenase mRNAs were all increased, Accompanying these changes the enzyme activity of GST pi, GPX and gamma-glutamyl transpe ptidase (gamma-GT) were also elevated. Interestingly, in a revertant c ell line heme oxygenase overexpression approached wild-type levels, In triguingly, similar changes in gene expression seen in the menadione-r esistant cells were also observed in wild-type cells following transie nt oxidative stress, indicating that the observed changes in the resis tant line may be due to the immortalization of a normally transient ad aptive stress response.