Methional, a cellular metabolite, induces apoptosis preferentially in G2/M-synchronized BAF3 murine lymphoid cells

We have previously shown that methional, derived from 4-methylthio-2-oxobutanoate, is a cellular mediator of apoptosis in BAF3 b0 murine lymphoid cells, which are dependent on IL3 for their growth in culture. When cells synchronized in S phase by double thymidine block were treated with methional immediately after thymidine withdrawal, methional was unable to induce DNA-strand breaks, whereas it inhibited the progression of cells from S to G2/M phases. This inhibition of cell cycle progression was associated with a 53% decrease in DNA synthesis. In contrast, when BAF3 b0 cells were synchronized in G2/M phase using SK&F 96365, and treated with methional immediately after drug removal, methional induced DNA-strand breaks in 49% of cells in 4 h, compared to 12% in controls. As contact time increased from 4 to 8 h, DNA-strand breaks increased to 94% in methional-treated cells compared to 11% in controls. These observations on G2/M-synchronized cells are different from those seen in BAF3b0 cells in G1 phase, 3 h after their release from the G2/M block, in that there was no decrease in size of the G1 population even after an additional 4 h incubation in the presence of methional. These results, taken together, provide a rational basis for using combinations of methional and G2/M blockers as inducers of DNA-strand breaks and apoptosis in murine lymphoid cells.