ANTIOXIDANT ENZYMES ARE ELEVATED IN DIMETHYLBENZ[A]ANTHRACENE-INDUCEDNEOPLASTIC MURINE KERATINOCYTES CONTAINING AN ACTIVE RAS(HA) ONCOGENE

Antioxidant enzyme activities and peroxidation potential were measured in primary mouse keratinocytes and neoplastic keratinocytes containin g an active ras(Ha) oncooene. In neoplastic cell lines, SP-1 and 308, the activities of Cu, Zn-superoxide dismutase, catalase, and glutathio ne transferase were significantly elevated. The peroxidation potential was lower in cell homogenates prepared from neoplastic keratinocytes than in those prepared from normal keratinocytes Consistently, neoplas tic 308 cell line was found to be more resistant than the normal kerat inocytes to cytotoxicity induced by UV-B irradiation. The present stud y suggests that the enhanced antioxidant defense system protects the i nitiated cells from UV-B-induced oxidative stress, and that the enhanc ed enzymic antioxidant defense system is potentially a mechanism favor ing the selective growth of neoplastic keratinocytes.