ONCOGENES AND CELLULAR-SENSITIVITY TO RADIOTHERAPY - A STUDY ON MURINE KERATINOCYTES TRANSFORMED BY V-H-RAS, V-MYC, V-NEU, ADENOVIRUS E1A AND MUTANT P53

Mechanisms involved in cellular radioresistance are mostly unknown and may be related to specific genetic alterations. In order to correlate the most frequent oncogenic alterations detected in tumors and ionizi ng radiation resistance, we studied the effect of irradiation on murin e keratinocytes transformed by different oncogenes. Mouse PAM 212 kera tinocytes were transformed by transfection or retroviral mediated infe ction with the oncogenes v-H-ras, v-myc, adenovirus Ela, neu and a mut ant p53 (mp53). Cells were gamma irradiated with a Co-60 source. Cell viability was evaluated by the crystal violet method and thymidine upt ake and data adjusted to the linear-quadratic model. Surviving fractio n 2Gy (SF2) and DO was calculated. Cell cycle study was assessed by in corporation of bromodeoxyridine (BrdUrd) and flow cytometry. p53 prote in was studied by Western-blot and apoptosis in DNA agarose gels. The surviving fraction for the different keratinocytes, PAM 212, 212 neo, 212 Ela, 212 v-H-ras, 212 myc, 212 neu and 212 mp53 was 0.79, 0.78, 0. 34, 0.82, 0.68, 0.74, and 0.72, respectively. Ela oncogene induced a g reat sensitivity to irradiation and v-H-ras a mild radioresistance. In flow cytometry, 212 Ela keratinocytes displayed a pronounced and prol onged arrest in G2/M phase. Apoptosis was observed after irradiation o nly in the 212 Ela keratinocytes. With these results, we conclude that some oncogene products may modulate radiosensitivity in keratinocytes . Mechanisms involved in radiosensitivity mediated by the Ela oncogene seem to be related to p53 protein level, induction of apoptosis and t o an irreversible premitotic arrest in G2/M phase, ineffective for rep air of DNA damage.