In the present study, the expression of the stress-inducible genes GADD153, c-jun, heme oxygenase-1 (HO-1), and HSP70 was compared among parental hamster diploid fibroblasts (HA-1), and cell lines isolated for resistance to either H2O2 (OC14) or O2 (O2R95). Both OC14 and O2R95 cell lines are known to have significantly augmented cellular antioxidant defenses, including increased glutathione content, as well as enhanced catalase, superoxide dismutase, and glutathione peroxidase activities. Northern analysis indicated that basal expression of HO-1 and c-jun is also elevated in these resistant cell lines. Relative to HA-1 values, basal GADD153 mRNA expression was approximately threefold higher in O2R95, but twofold lower in OC14 cells. HSP70 mRNA expression was comparable among parental and resistant cell lines. Both OC14 and O2R95 cells showed greatly enhanced survival following H2O2 exposure. The H2O2 doses that induced 50% toxicity in parental and resistant cells (3 vs. 30-60 x 10(-13) mol/cell, respectively) differed by more than an order of magnitude. Similarly, GADD153, c-jun, and HO-1 mRNA were elevated in control cells following exposure to doses of H2O2 an order of magnitude lower than is required for gene activation in resistant cell lines. Nonetheless, at equitoxic doses, the level of induction of GADD153 and HO-1 was greater in resistant than in parental cell lines. Taken together, our results suggest that alterations in the basal level of expression of certain stress-responsive genes, including HO-1, c-jun, and GADD153, may contribute to the H2O2-resistant phenotype in these fibroblast cell lines. Further, changes in the regulation of these genes in response to adverse stimuli may provide an additional mechanism for enhanced cell survival following oxidative stress.