Enhancement of radiosensitivity by combined ceramide and dimethylsphingosine treatment in lung cancer cells.
Ceramide generated from sphingomyelin in response to ionizing radiation has been implicated as a second messenger to induce cellular proapoptotic signals. Both ceramide and its metabolic inhibitor, N, N-dimethyl-D-erythro-sphingosine (DMS), might lead to sustained ceramide accumulation in cells more efficiently, thereby sensitizing them to gamma-radiation-induced cell death. To delineate this problem, the clonogenic survival of Lewis lung carcinoma (LLC) cells was evaluated following exposure to radiation together with or without C2-ceramide, DMS, or both. The treatment of ceramide/DMS synergistically decreased the survival of the irradiated cells compared with treatment with ceramide or DMS alone. Ceramide/DMS-treated cells displayed several apoptotic features after gamma-irradiation, including increased sub G(1) population, TUNEL-positive fraction, and poly-(ADP-ribose) polymerase (PARP) cleavage. We also observed ceramide/ DMS induced disruption of mitochondrial membrane potential (MMP) and activation of caspase- 9 and -3 in a radiation-dose-dependent manner. Furthermore, pretreatment of LLC cells with ceramide/DMS not only increased the protein expression level of Bax, but also decreased Bcl-2 after gamma-irradiation. Taken together, the present study indicates that the radiosensitizing activity of ceramide/DMS on LLC cells most likely reflects the dominance of pro-apoptotic signals related to the mitochondria-dependent pathway.
Park
Hye-Won
HW
Laboratory of Immunology, Korea Institute of Radiological and Medical Sciences, KAERI 215-4 Gongneung-dong, Nowon-gu, Seoul 139-706, Korea.
Song
Jie-Young
JY
Kim
Ki-Sung
KS
Han
Youngsoo
Y
Kim
Chan-Wha
CW
Yi
Seh-Yoon
SY
Yun
Yeon-Sook
YS
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D018827:Carcinoma, Lewis Lung / Q000378:metabolism / Q000532:radiotherapy*; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D015870:Gene Expression; D008175:Lung Neoplasms / Q000378:metabolism / Q000532:radiotherapy*; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D011836:Radiation Tolerance; D011838:Radiation-Sensitizing Agents; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use*; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
C494827:Bax protein, mouse; C494812:Bcl2l1 protein, mouse; C064769:N-acetylsphingosine; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011838:Radiation-Sensitizing Agents; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; C052617:Bcl2 protein, mouse; D020169:Caspases; C061800:N,N-dimethylsphingosine; D013110:Sphingosine