C-myc overexpression facilitates radiation-induced DHFR gene amplification

To investigate the role of myc-overexpression on radiation-induced amplification of the dihydrofolate reductase gene (DHFR) we compared diploid Chinese hamster ovary cells (CHO-9) to cells of the same line that had been stably transfected with a dexamethasone-inducible c-myc cDNA. The application of flow-cytofluorometry and fluorescent in situ hybridization (FISH) allowed the evaluation of an increase in DHFR gene copy number following radiation treatment without the use of a preceding selection procedure. We show that DHFR gene amplification may occur independently of p53 status in cells overexpressing c-myc.