Mounting evidence suggests that the position in the cell cycle of cells exposed to an oxidative stress could determine their survival or apoptotic cell death. This study aimed at determining whether nitric oxide (NO)induced cell death in colon cancer cells might depend on their position in the cell cycle, based on a clone of the cancer cell line HT29 exposed to an NO donor, in combination with the manipulation of the cell entry into the cell cycle. We show that PAPA NONOate (pNO), from 10 ؊4 M

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... o 10 ؊3 M, exerted early and reversible cytostatic effects through ribonucleotide reductase inhibition, followed by late resumption of cell growth at 5 ؋ 10 ؊4 M pNO. In contrast, 10 ؊3 M pNO led to late programmed cell death that was accounted for by the progression of cells into the cell cycle as shown by (a) the accumulation of apoptotic cells in the G 2 -M phase at 10 ؊3 M pNO treatment; and (b) the prevention of cell death by inhibiting the entry of cells into the cell cycle. The entry of pNO-treated cells into the G 2 -M phase was associated with actin depolymerization and its S-glutathionylation in the same way as in control cells. However, the pNO treatment interfered with the build-up of a high reducing power, associated in control cells with a dramatic increase in reduced glutathione biosynthesis in the G 2 -M phase. This oxidative stress prevented the exit from the G 2 -M phase, which requires a high reducing power for actin deglutathionylation and its repolymerization. Finally, our demonstration that programmed cell death occurred through a caspase-independent pathway is in line with the context of a nitrosative/oxidative stress. In conclusion, this work, which deciphers the connection between the position of colonic cancer cells in the cell cycle and their sensitivity to NOinduced stress and their programmed cell death, could help optimize anticancer protocols based on NO-donating compounds.