Permissivity for methotrexate-induced DHFR gene amplification correlates with the metastatic potential of rat adenocarcinoma cells.

During selection for methotrexate (MTX) resistance the metastatic subclone BSp73ASML of a spontaneous rat adenocarcinoma and a metastatic transfectant containing the metastogene META-1 underwent amplification of the dihydrofolate reductase (DHFR) gene at accelerated rates in contrast to non-metastatic but closely related BSp73AS cells. A four log increase in MTX resistance was associated with a 16-fold amplification and increased expression of the DHFR gene. The capacity for gene amplification in metastatic BSp73ASML cells was correlated with a deletion in the p53 gene and enhanced expression of the oncogene c-myc due to a 10-fold amplification of the myc gene. Increased expression of Ki-ras and c-raf in the non-metastatic BSp73AS cells seems to confer tumorigenicity but not permissivity for gene amplification.