Gene amplification: an example of accelerated evolution in tumorigenic cells.
During selection for methotrexate resistance, tumorigenic CHEF/16 cells and derivatives from CHEF/16 tumors underwent amplification of the dihydrofolate reductase gene (DHFR) at accelerated rates compared with closely related nontumorigenic CHEF/18 cells. "Dot blot" analysis showed that the CHEF/16 cells contained many more copies of the DHFR gene than did the CHEF/18 cells, when assayed at similar elevated levels of methotrexate resistance. Chromosome analysis of cell samples taken at several time points during amplification revealed large differences between the nontumorigenic CHEF/18 cells and the two tumorigenic cell lines. The tumorigenic cells developed few chromosome rearrangements over a 4-log increase in methotrexate resistance, other than increased length of a single chromosome, which was shown by in situ hybridization to contain most or all of the amplified DHFR gene copies. In contrast, the CHEF/18 cells underwent complex, progressive changes in almost every chromosome, and in situ hybridization suggested a dispersed pattern of gene amplification. The data support the hypothesis that unregulated amplification is a pathological process, occurring readily in neoplastic but rarely in normal cells, that together with other chromosomal disturbances contributes to the rapid evolution and progression of cancer.
D000818:Animals; D005075:Biological Evolution; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D002871:Chromosome Banding; D006224:Cricetinae; D003412:Cricetulus; D004351:Drug Resistance; D004622:Embryo, Mammalian; D005784:Gene Amplification; D005796:Genes / Q000187:drug effects; D007621:Karyotyping; D008727:Methotrexate / Q000494:pharmacology; D010957:Plasmids; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics
D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate