A ROLE FOR APOPTOSIS IN THE TOXICITY AND MUTAGENICITY OF BLEOMYCIN INAHH-1 TK(+ -) HUMAN LYMPHOBLASTOID-CELLS/

The chromosomal mutagen, bleomycin, is also noted for its toxic proper ties, although the mechanism of cell death is not fully understood. In order to determine if cell death occurred by apoptosis or necrosis, A HH-1 tk(+/-) cells were exposed to bleomycin and the percentage of via ble, apoptotic and necrotic cells quantified by flow cytometry. Logist ic regression analysis indicated that the primary manner of cell death was through the apoptosis pathways, that apoptosis was delayed, and t hat apoptosis was accompanied by an arrest in the G(2) phase of the ce ll cycle, Once apoptosis was established as a mechanism for cell death , the efficiency with which these pathways removed damaged cells from the population was evaluated with the use of specific-locus mutation a ssays (tk and hprt) as indicators of cells with DNA damage that mainta ined viability and clonogenicity. Linear regression analysis detected a significant, concentration-dependent increase in the numbers of TFTr clones with the slow-growth phenotype. This suggests that a proportio n of cells with bleomycin-induced DNA damage did not undergo cell deat h by apoptosis and that apoptosis, a mechanism for the destruction of damaged cells, is not fully efficient in the AHH-1 tk(+/-) cell line.