Amplified Genes in Breast Cancer: Molecular Targets for Investigation and Therapy.

Abstract : We showed earlier that micronucleation reduces the number of double minute chromosomes (DMs) containing amplified oncogenes and correlates with reduced tumorigenicity. We investigated the mechanism of micronucleation using a novel fluorescent chromosome labeling system we developed to study the distribution of DMs in living cancer cells. Our results demonstrate that DMs often cluster and form bridges between segregating daughter chromosomes during anaphase. Time-lapse observations revealed that cytokinesis severed DM bridges, and resulted in their uneven distribution to daughter cells. Occasionally, clustered DMs lagged behind pole-ward moving chromosomes and formed separate micronuclei. To further analyze DM behavior, we specifically labeled DMs using a lactose-operator/lactose-repressor-GFP system. We found that DMs appeared randomly dispersed in interphase nuclei, but later in prophase, they attached to the periphery of condensed prophase chromosomes. DMs appear to move to the nuclear periphery during chromosome condensation, make clusters, and continue to associate with chromosome arms throughout cytokinesis. Occasionally, this association is disrupted and results in micronucleation. The DM specific labeling system will not only be useful for detailed analyses of DM dynamics but will also_greatly facilitate the screening of drugs which efficiently eliminate DMs from cancer cells.