Radio-sensitive murine thymoma cell line 3SB: characterization of its apoptosis-resistant variants induced by repeated X-irradiation.
3SB, a mouse thymoma cell line, is one of the most radio-sensitive cells (D0 = 0.3 Gy), and its rapid apoptosis (4 h after 5 Gy irradiation, 90% apoptosis) seems to play a decisive role in enhancing the radiosensitivity. To understand the molecular mechanisms underlying extremely high radiosensitivity and rapid apoptosis, we attempted to isolate X-ray-resistant (XR) variants from 3SBH5, a stable subclone of 3SB, by repeating exposure of the cells to 2-5 Gy X-rays. Four independent stable XR variants, R111, R223, R316 and R429, were isolated by the repeated irradiation protocols. All XR cells possessed about 3 times higher D10 values than that of their parental 3SBH5. They were also resistant to apoptosis; only 10% cells underwent apoptosis 4 h after 5 Gy irradiation. The p53 protein was induced in all the cell lines after 5 Gy X-irradiation. These variants showed a cross resistance to a chemical reagent daunorubicin (DNR) that is known to be involved in the ceramide-mediated apoptosis. DNR, as well as C2-ceramide (5 muM) induced apoptosis in parental 3SBH5 cell, but not in two XR variants, R233 and R316 cells. Present result suggests that the induction of X-ray resistance by repeated X-irradiation might be achieved, at least partly, by the enhanced resistance to the ceramide-mediated apoptosis.
Hama-Inaba
H
H
Bioregulation Research Group, National Institute of Radiological Sciences, Chiba, Japan. inabahir@nirs.go.jp
Wang
B
B
Mori
M
M
Matsushima
T
T
Saitoh
T
T
Takusagawa
M
M
Yamada
T
T
Muto
M
M
Ohyama
H
H
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects*; D003630:Daunorubicin / Q000494:pharmacology; D004351:Drug Resistance / Q000235:genetics; D014644:Genetic Variation; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D051379:Mice; D016685:Mitomycin / Q000494:pharmacology; D009153:Mutagens / Q000494:pharmacology; D011836:Radiation Tolerance / Q000235:genetics*; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism; D013945:Thymoma / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*; D013953:Thymus Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis
D000970:Antineoplastic Agents; D009153:Mutagens; C064769:N-acetylsphingosine; D016159:Tumor Suppressor Protein p53; D016685:Mitomycin; D008741:Methyl Methanesulfonate; D013110:Sphingosine; D003630:Daunorubicin