Role of chromosomal instability in the acquisition of cellular malignancy - Cytogenetic analysis

The aim of our work during this training period takes part of a study on the role of chromosome instability in the cellular immortalization. We have also tried ta show the chromosome specificity involved in different donors. The hypothesis is that the same chromosomes are involved for a given donor and do not depend on the way of induction (heavy ions irradiation, SV40 transfection) but these chromosomes are different and specific for each donor. For this, we have followed the morphological aberrations (to follow total instability) and karyotypical aberrations (to follow overinvolved chromosomes) in two new healthy donors. We have established cultures with fibroblasts from each of these donors. The cultures were either followed or analysed until senescence, irradiated by heavy ions (gold, oxygen and nickel), or transfected by SV40. We have showed for each passage the evolution and the chronology of events leading to cell immortalization. We have observed a strong chromosome instability a few passages after irradiation or after SV40 transfection and preceding the apparition of invasive clones. This shows that chromosome instability allows an accumulation and selection of clones having a proliferative advantage. By in situ hybridization, we have demonstrated that some chromosomes are instable first. There exists a chronology of chromosomal instability. We have also observed the predominance of some aberrations involving some chromosomes. Actually, chromosomes 3,5 and 6 were overinvolved for one don or after gold irradiation, this instability was found after transfection (for one cell line only) but not after oxygen irradiation ( either we have not yet observed an instability or the LET used was too small to induce an instability). As for the other donor, results after transfection have also shown some clones involving some chromosomes more than others, but results after irradiation were to incomplete to conclude. The former donor has shown a instability of chromosomes 13, 16 and 1 whatever the way of immortalization. According to these results, and although preliminary, we have demonstrated that the chromosomes involved are different in these 3 donors. It will be necessary to study thoroughly these results before affirming which chromosomes are involved preferentially from one donor to another. It would be interesting to understand the molecular mechanisms generating this chromosomal instability. (author)