Hypoxia and etanidazole alter radiation-induced apoptosis in HL60 cells but not in MOLT-4 cells.
OBJECTIVE
To examine how hypoxia influences ionizing irradiation-induced apoptosis in cultured mammalian cells and how a hypoxic cell radiosensitizer sensitizes apoptosis under hypoxic conditions.


METHODS
Two cell lines derived from human lymphocytes, HL60 and MOLT-4, were exposed to 15 Gy X-rays under aerobic and hypoxic conditions. Etanidazole was used as a hypoxic cell radiosensitizer. The apoptotic morphological changes of nuclei and the induction of ladder-like DNA fragmentation were assessed by fluorescence microscopy and agarose gel electrophoresis, respectively.


RESULTS
In HL60 cells, apototic cell death and the activation of caspases 8, 9 and 3 were less induced under the hypoxic conditions than under the aerobic ones. Treatment of hypoxic cells with etanidazole enhanced X-ray-induced apoptosis and caspase activation. However, in MOLT-4 cells, neither hypoxia nor etanidazole influenced X-ray-induced apoptosis and caspase activation. In both cell lines, the frequency of X-ray-induced DNA double-strand breaks (DSB) under hypoxia was significantly smaller than that in aerobic conditions. Treatment of hypoxic cells with etanidazole enhanced them.


CONCLUSIONS
These results suggested that X-ray-induced apoptosis in HL60 cells was initiated by DNA DSB and the treatment of hypoxic cells with etanidazole sensitized them through the enhancement of DSB induction, whereas X-ray-induced apoptosis in MOLT-4 cells occurred through damage other than to DNA.
Inanami
O
O
Laboratory of Radiation Biology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
Sugihara
K
K
Okui
T
T
Hayashi
M
M
Tsujitani
M
M
Kuwabara
M
M
D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects*; D001973:Bromodeoxyuridine / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology*; D002460:Cell Line; D004249:DNA Damage; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D017341:Etanidazole / Q000494:pharmacology*; D018922:HL-60 Cells; D006801:Humans; D011836:Radiation Tolerance / Q000187:drug effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
D011838:Radiation-Sensitizing Agents; D017341:Etanidazole; D020169:Caspases; D001973:Bromodeoxyuridine