MITOTIC AND POST MITOTIC CONSEQUENCES OF GENOMIC INSTABILITY INDUCED BY ONCOGENIC HA-RAS

Induced expression of a mutant human Ha-ras oncogene in NIH3T3 cells l eads to the rapid production of multicentric chromosomes, acentric chr omosome fragments, double minute chromosomes, increased heteroploidy, and increased capacity to undergo gene amplification. In this study we have used fluorescent-in-situ hybridization (FISH) to demonstrate tha t induction of the Ha-ras oncogene also leads to disruption of the mit otic machinery, resulting in aberrant mitoses and abnormal daughter ce lls. Cells induced to express an oncogenic Ha-ras transgene accumulate chromosomes that lag outside of the rest of the chromosomal architect ure, chromosomes that form bridges between daughter nuclei at anaphase , and that form micronuclei. Many of these mitotic aberrations contain structurally abnormal chromosomes. These ras-induced changes were sup pressed by the introduction of a gene encoding the dominant negative e ffector of ras, raf301. Expression of raf301 in cells induced to expre ss Ha-ras reduced the level of growth in soft agar, chromosome aberrat ions, mitotic aberrations, and frequency of gene amplification. These data provide evidence for an association between Ha-ras induced transf ormation chromosome aberrations and gene amplification. Furthermore th ey offer insight into how the cell responds to the formation of aberra nt chromosomes, and how disrupting chromosomal architecture could lead to further imbalances in the distribution of genetic material between daughter cells.