Elimination of micronucleated cells by apoptosis after treatment with inhibitors of microtubules

Previous studies of our laboratory showed the existence of thresholds for the induction of chromosome non-disjunction and chromosome loss and the induction of apoptosis by microtubule inhibitors .
The aim of this study was to investigate whether below the thresholds for the induction of chromosome loss and non-disjunction, as previously defined by us, apoptosis was induced directly or indirectly as a response to an aberrant chromosome segregation. Therefore human lymphocytes were exposed in vitro to five concentrations of nocodazole and five concentrations of carbendazim representing the threshold concentrations for chromosome non-disjunction and chromosome loss, two concentrations below the lowest threshold and one concentration between the two threshold values. After 72h PHA stimulation, corresponding to 48h exposure to the aneugens, the induction of apoptosis was analysed by annexin-V. The frequencies of chromosome non-disjunction and chromosome loss were estimated in cytokinesis-blocked human lymphocytes in combination with FISH. In order to check whether aneuploid cells are preferentially driven to apoptosis, we sorted by magnetic annexin beads apoptotic and viable cells from the same cultures and measured micronucleus induction, chromosome loss or chromosome non-disjunction in the apoptotic and viable fractions. Our results suggest that elimination of micronucleated cells or cells with chromosome non-disjunction does occur. The frequencies of micronucleated cells was higher in the apoptotic fraction than in the viable fraction. Cells bearing non-disjunction seem to be a less stronger trigger for apoptosis. The obtained results suggest that the presence of micronuclei in a cell correlates with apoptosis and therefore contributes to the elimination of aneuploid cells .