CONSTITUTIVE EXPRESSION OF THE C-H-RAS ONCOGENE INHIBITS DOXORUBICIN-INDUCED APOPTOSIS AND PROMOTES CELL-SURVIVAL IN A RHABDOMYOSARCOMA CELL-LINE

Drugs used in anti-cancer chemotherapy are thought to exert their cyto toxic action by induction of apoptosis. Genes have been identified whi ch can mediate or modulate this drug-induced apoptosis, among which ar e c-myc, p53 and bcl-2. Since expression of oncogenic ras genes is a f requent observation in human cancer, we investigated the effects of th e c-H-ras oncogene on anti-cancer drug-induced apoptosis. Apoptosis in duced by a 2 h doxorubicin exposure was measured by in situ nick trans lation and flow cytometry in a rat cell line (R2T24) stably transfecte d with the c-H-ras oncogene and in a control cell line (R2NEO) transfe cted only with the antibiotic resistance gene neo. Both cell lines (R2 T24 and R2NEO) had nearly identical growth characteristics, including cell doubling time, distribution over the cell cycle phases and platin g efficiency in soft agar. Doxorubicin exposure of the R2NEO cells led to massive induction of apoptosis. In contrast, R2T24 cells, expressi ng the c-a-ras oncogene, showed significantly less apoptosis after dox orubicin incubation. Doxorubicin induced approximately 3- to 5-fold le ss cytotoxicity in the R2T24 cells than in the R2NEO cells, as determi ned by clonogenic assay in soft agar. No difference was observed in in tracellular doxorubicin accumulation between the two cell lines, indic ating that the classical, P-glycoprotein-mediated multidrug resistance phenotype is not involved in the observed differences in drug sensiti vity. In conclusion, our data show that constitutive expression of the c-a-ras oncogene suppresses doxorubicin-induced apoptosis and promote s cell survival, suggesting that human tumours with ras oncogene expre ssion might be less susceptible to doxorubicin treatment.