Polyamine depletion partially reduces the radiation-induced cell death via cell cycle delay mediated by thioredoxin.
In previous studies, polyamine depletion by DFMO (alpha-difluoromethylornithine)-treatment reduced H(2)O(2)-induced apoptotic cell death by reduction of ferric ion uptake. In the present study, we analyzed the reduction of radiation-induced cell death by polyamine depletion. Exposure of HT29 cells to radiation induced severe cell death, but when cells were pretreated with DFMO, a specific inhibitor of polyamine biosynthesis, radiation-induced cell death was reduced to 50-60% of control. Cell cycle analysis showed that, in these cells, the time to reach the G(2)/M phase arrest was delayed for 20-24 h compared to the control cells, at which stage the fate of cells exposed to ionizing radiation is determined. DFMO-treated cells also showed a low level of thioredoxin, which is a high-level determinant of the cellular fate. To investigate the relationship between the G(2)/M phase arrest and the reduction of thioredoxin caused by polyamine depletion, we also analyzed thioredoxin-antisensed (asTRX) HT29 cells as for DFMO-treated cells. In asTRX-transfected cells, the gamma-irradiation-induced G(2)/M phase arrest was also significantly delayed and radiation-induced cell death was profoundly reduced, as in the DFMO-treated cells. Both sets of cells showed a decrease of cyclin D1 and an increment of HSP25, which are involved in radiation-induced cell cycle progress. Overall, these results suggest that polyamines are essential for normal cell death of HT29 cells triggered by gamma-radiation and that this is partially mediated by the regulation of thioredoxin expression.
Moon
M S
MS
Department of Radiation Biology, Environmental Radiation Research Group, Korea Atomic Energy Research Institute, Yuseong, Daejon, Korea.
Kim
J S
JS
Kim
T L
TL
Yum
J J
JJ
Cho
E W
EW
Kim
I G
IG
D002453:Cell Cycle; D016923:Cell Death / Q000528:radiation effects*; D056741:Cyclin D; D016213:Cyclins / Q000378:metabolism; D005720:Gamma Rays; D006801:Humans; D011073:Polyamines / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011836:Radiation Tolerance; D013879:Thioredoxins / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D056741:Cyclin D; D016213:Cyclins; D011073:Polyamines; D013879:Thioredoxins