Abstract
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.
Highlights
Ceramide is a key signal-transducing lipid with a role in various regulatory pathways including differentiation, cell cycle arrest, and apoptosis (Cuvillier et al, 2000; Sawada et al, 2000), and induced by signals via cell-surface receptors for tumor necrosis factor (TNF) or Fas ligand (CD95/Fas/APO-1), and various stress stimuli such as radiation, heat shock, the depletion of growth factors, and chemotherapeutic agents
The mechanisms that convey activation signals to the enzymes responsible for ceramide production are poorly defined, and the pivotal executioner of ceramide to the apoptotic response still remains arguable (Chmura et al, 1997; Susin et al, 1997; Edsall et al, 1997, 1998; Cuvillier et al, 1998; Kleuser et al, 1998; Kolesnick et al, 1998)
We explored in detail the radiosensitizing activity of ceramide/DMS treatment and the cellular mechanism of radiation-induced apoptosis in Lewis lung carcinom a (LLC) cell, involving caspase-dependent pathways
Summary
Ceramide is a key signal-transducing lipid with a role in various regulatory pathways including differentiation, cell cycle arrest, and apoptosis (Cuvillier et al, 2000; Sawada et al, 2000), and induced by signals via cell-surface receptors for tumor necrosis factor (TNF) or Fas ligand (CD95/Fas/APO-1), and various stress stimuli such as radiation, heat shock, the depletion of growth factors, and chemotherapeutic agents. As an important treatment modality for lung cancer as well as many other cancers, the dose of radiation needed to efficiently remove tumor cells was very different (Zhivotovsky et al, 1999; Chinnaiyan et al, 2000). This vast difference of radiosensitivity is influenced by a complex interaction of several factors such as level of oxygen consumption, dividing rate of uncontrolled tumor cells, and ability of cells to repair the radiation-induced DNA damage. We explored in detail the radiosensitizing activity of ceramide/DMS treatment and the cellular mechanism of radiation-induced apoptosis in LLC cell, involving caspase-dependent pathways
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
