Supplementary Figure 3 from Role of Tumor Necrosis Factor-α and TRAIL in High-Dose Radiation–Induced Bystander Signaling in Lung Adenocarcinoma
ARTICLE ABSTRACT
In the present study, ionizing radiation (IR)–induced bystander effects were investigated in two lung cancer cell lines. A549 cells were found to be more resistant to radiation-conditioned medium (RCM) obtained from A549 cells when compared with the H460 exposed to RCM procured from H460 cells. Significant release of tumor necrosis factor-α (TNF-α) was observed in A549 cells after IR/RCM exposure, and the survival was reversed with neutralizing antibody against TNF-α. In H460 cells, significant release of TNF-related apoptosis-inducing ligand (TRAIL), but not TNF-α, was observed in response to IR, RCM exposure, or RCM + 2Gy, and neutralizing antibody against TRAIL diminished clonogenic inhibition. Mechanistically, TNF-α present in RCM of A549 was found to mediate nuclear factor-κB (NF-κB) translocation to nucleus, whereas the soluble TRAIL present in RCM of H460 cells mobilized the nuclear translocation of PAR-4 (a proapoptotic protein). Analysis of IR-inducible early growth response-1 (EGR-1) function showed that EGR-1 was functional in A549 cells but not in H460 cells. A significant decrease in RCM-mediated apoptosis was observed in both A549 cells stably expressing small interfering RNA EGR-1 and EGR-1−/− mouse embryonic fibroblast cells. Thus, the high-dose IR-induced bystander responses in A549 may be dependent on the EGR-1 function and its target gene TNF-α. These findings show that the reduced bystander response in A549 cells is due to activation of NF-κB signaling by TNF-α, whereas enhanced response to IR-induced bystander signaling in H460 cells was due to release of TRAIL associated with nuclear translocation of PAR-4. [Cancer Res 2007;67(24):11811–20]
