Cell death and cell-cycle arrest induced by incorporation of [ 3 H]thymidine into human haemopoietic cell lines

PURPOSE: To investigate the influence of [methyl-3H]thymidine ([3H]Tdr) incorporated into human haemopoietic cell lines. MATERIALS AND METHODS: HL-60, Molt-4, Jurkat, Raji and SKW6-CL4 cells were incubated in the presence of [3H]Tdr. Cell proliferation, cell viability, DNA fragmentation and expression of caspase-3 and Bcl-2 families were examined. The cell-cycle of HL-60 was analysed using flow cytometry. RESULTS: In HL-60, Molt-4 and Jurkat, cell death was accompanied by DNA nucleosomal fragmentation and activation of caspase-3. In Raji and SKW6-CL4, it was accompanied by neither. Protein levels of Bcl-2 and Bad in HL-60 and Molt-4 did not significantly change, and that of Bax was decreased after a 3-day incubation. HL-60 incubated in the presence of 74 or 185 kBq/ml [3H]Tdr arrested at G2/M phase, and then underwent apoptosis. In 7.4 kBq/ml, the cell-cycle progressed after the delay in S-phase. CONCLUSIONS: Two different modes of cell death were observed when [3H]Tdr was incorporated into the human haemopoietic cell lines. Incorporation into HL-60 cells resulted in delay of S-phase progression, arrest at G2/M and apoptosis.