Influence of caspase activity on micronuclei detection: a possible role for caspase-3 in micronucleation

Aneugenic and clastogenic agents are good inducers of both micronuclei and apoptosis. In its turn, apoptosis may modify the threshold values for the induction of micro-nuclei. This is of major concern for accurate assessment of hazard related to exposure to mutagens. In the present work we studied the influence of caspases, the key regulat-ors of the apoptotic process, on the induction of micronuclei in the cytokinesis block micronucleus assay. For this, we applied a combined approach in which both human peripheral blood mononucleated cells (PBMC) and the paired human breast carcinoma cell lines MCF-7, which is caspase-3 deficient, and the caspase-3 transfected MCF-7 (MCF-7casp-3) were used to study the influence of caspase activity on micronuclei. When nocodazole induced apop-tosis was inhibited by the use of inhibitors of the two main apical caspases-8 and-9 in PBMC, the frequencies of micronucleated binucleates (MNCB) increased with inhibi-tion of these caspases confirming that apoptosis can elimin-ate micronucleated cells. On the contrary when caspase-3 was inhibited, the frequencies of MNCB was lower, suggest-ing a role of caspase-3, also in micronuclei formation. To verify this hypothesis, we compared the induction of apoptosis and micronuclei by the aneugen nocodazole, the clastogen methyl methane sulfonate (MMS) and the non-mutagenic apoptogen staurosporin in MCF-7 and MCF-7casp-3 cells. The results showed that when caspase-3 activity was impaired, in the parental MCF-7 cell line or in the MCF-7casp-3 cells in the presence of the caspase-3 inhibitor, the frequencies of nocodazole or MMS induced micronuclei decreased. These results suggest that caspase-3, besides its function as an effector caspase in the apoptotic pathway, is also involved in the formation of micronuclei