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Caffeine induces S‐phase apoptosis in cis‐diamminedichloroplatinum‐treated cells, whereas cis‐diamminedichloroplatinum induces a block in G2/M

1997; Wiley; Volume: 27; Issue: 4 Linguagem: Inglês

10.1002/(sici)1097-0320(19970401)27

1097-0320

Nariyoshi Shinomiya, Toshiya Takemura, Kazutsugu Iwamoto, Makoto Rokutanda,

Adenosine and Purinergic Signaling

Caffeine overrides checkpoints in the G2 phase of the cell cycle by inhibiting DNA repair at this phase and increases the cytotoxicity of antitumor drugs, such as cis-diamminedichloroplatinum (CDDP). The enhanced cell death induced by caffeine is characterized by apoptosis. In this paper, we demonstrate that this apoptotic event occurs in S phase of the cell cycle, whereas CDDP induces a block in G2/M. DNA histogram analysis revealed that caffeine reduced G2 arrest in CDDP-treated EL-4 cells. In a synchronous population, the ratio of cyclin B:p34cdc2 was up-regulated just before the cells went into the apoptotic pathway. A rapid increase in DNA fragmentation was detected at 12–24 h, when marked regression of G2/M phase was observed. Moreover, the degree of DNA fragmentation in CDDP + caffeine-treated cells was not reduced when the cell cycle was arrested at metaphase by exposure to the spindle-inhibitor nocodazole. It is possible that execution of the apoptotic program after treatment with caffeine did not require the EL-4 cells to reenter G1 phase. The apoptotic cell fraction in the group of CDDP + caffeine was recognized as an S population by bivariate analysis of apoptosis and DNA content. These results suggest that enhancement of the apoptotic activity of CDDP-treated cells by caffeine is not a G1-phase event but an S-phase-specific event, whereas cells were arrested in G2/M phase, and that it is regulated by G2 checkpoint-related proteins. Cytometry 27:365–373, 1997. © 1997 Wiley-Liss, Inc.