C-MYC OVEREXPRESSION FACILITATES RADIATION-INDUCED DHFR GENE AMPLIFICATION

To investigate the role of myc-overexpression on radiation-induced amp lification of the dihydrofolate reductase gene (DHFR) we compared dipl oid 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 hybr idization (FISH) allowed the evaluation of an increase in DHFR gene co py number following radiation treatment without the use of a preceding selection procedure. We show that DHFR gene amplification may occur i ndependently of p53 status in cells overexpressing c-myc.