DIFFERENTIAL INDUCTION OF CHROMOSOMAL INSTABILITY BY DNA STRAND-BREAKING AGENTS

To investigate the role of DNA strand breakage as the molecular lesion responsible for initiating genomic instability, five different strand -breaking agents, bleomycin, neocarzinostatin, hydrogen peroxide, rest riction endonucleases, and ionizing radiation, were examined for their capacity to induce delayed chromosomal instability, These studies use d GM10115 human-hamster hybrid cells, which contain one copy of human chromosome 4 in a background of 20-24 hamster chromosomes, Chromosomal instability was investigated using fluorescence in situ hybridization to visualize chromosomal rearrangements involving the human chromosom e, Rearrangements are detected multiple generations after treatment, i n clonal populations derived from single progenitor cells surviving tr eatment of the specified DNA-damaging agents, Clastogenic and cytotoxi c activities of all agents were tested by examining chromosome aberrat ion yields in first-division metaphases and by clonogenic survival ass ays, Analysis of over 250 individual clones representing over 50,000 m etaphases demonstrates that when compared at comparable levels of cell kill, ionizing radiation, bleomycin, and neocarzinostatin are equally effective at eliciting delayed genomic instability, These observation s document, for the first time, the persistent destabilization of chro mosomes following chemical treatment, In contrast, the analysis of nea rly 300 clones and 60,000 metaphases, involving treatment with four di fferent restriction endonucleases and/or hydrogen peroxide, did not sh ow any delayed chromosomal instability, These data indicate that DNA s trand breakage per se does not necessarily lead to chromosomal instabi lity but that the complexity or quality of DNA strand breaks are impor tant in initiating this phenotype.