Caffeine induces S-phase apoptosis in cis-diamminedichloroplatinum-treated cells, whereas cis-diamminedichloroplatinum induces a block in G2/M.
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 upregulated 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.
Shinomiya
N
N
Department of Biology, National Defense Medical College, Tokorozawa, Japan.
Takemura
T
T
Iwamoto
K
K
Rokutanda
M
M
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D002945:Cisplatin / Q000494:pharmacology*; D016213:Cyclins / Q000378:metabolism; D003584:Cytological Techniques; D004247:DNA / Q000737:chemistry; D053938:DNA Fragmentation / Q000187:drug effects; D016195:G2 Phase / Q000187:drug effects; D007399:Interphase / Q000187:drug effects; D051379:Mice; D008938:Mitosis / Q000187:drug effects*; D015739:Nocodazole / Q000494:pharmacology; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D016196:S Phase / Q000187:drug effects; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D000697:Central Nervous System Stimulants; D016213:Cyclins; D011838:Radiation-Sensitizing Agents; D002110:Caffeine; D004247:DNA; D016203:CDC2 Protein Kinase; D002945:Cisplatin; D015739:Nocodazole