Multiple fractions of gamma rays do not induce overexpression of c-myc or c-Ki-ras oncogenes in human cervical carcinoma cells.

Multiple fractions of gamma rays (0.5 Gy daily, 30 fractions) had previously been found to change the sensitivity of human cervical carcinoma HeLa cells to anticancer drugs. Preirradiated cells became resistant to cisplatin, methotrexate and vincristine, but retained the same sensitivity to gamma rays and ultraviolet light. Some mechanisms involved in resistance of preirradiated cells to cisplatin and vincristine were determined, i.e. the increased levels of metallothioneins and increased expression of plasma membrane P glycoprotein. As recent reports indicated that the resistance to cisplatin and ionizing radiation may involve expression of oncogenes, we examined whether multiple fractions of gamma rays can change the expression of c-myc and c-Ki-ras oncogenes in HeLa cells and determined whether there is a correlation between expression of these oncogenes and sensitivity of preirradiated cells to cisplatin and gamma rays. The expression of c-myc and c-Ki-ras oncogenes were examined by the use of DNA dot blot, RNA dot blot and Northern blot analyses. The results show that preirradiation did not induce either amplification or elevated expression of c-myc or c-Ki-ras oncogenes. Further, there is no correlation between expression of c-myc and c-Ki-ras oncogenes and the acquired resistance to cisplatin.