Ionizing radiation modulates the TRAIL death-inducing signaling complex, allowing bypass of the mitochondrial apoptosis pathway.
In many tumor cell types, ionizing radiation (IR) or DNA-damaging anticancer drugs enhance sensitivity to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, which is of great clinical interest. We have investigated the molecular mechanism underlying the response to combined modality treatment in p53-mutant Jurkat T leukemic cells overexpressing Bcl-2. These cells are largely resistant to individual treatment with TRAIL or IR, but sensitive to combined treatment, in vitro as well as in vivo. We demonstrate that IR and DNA-damaging anticancer drugs enable TRAIL receptor-2 and CD95/Fas to bypass the mitochondrial pathway for effector caspase activation. This was validated by RNA interference for Bax and Bak and by overexpression of dominant-negative Caspase-9. Improved effector caspase activation was neither caused by altered expression of proapoptotic components nor by impaired activity of inhibitor of apoptosis proteins or nuclear factor-kappaB signaling. Rather, we found that pretreatment of cells with IR caused quantitative and qualitative changes in death receptor signaling. It strongly improved the capacity of ligand-bound receptors to recruit FADD and activate Caspase-8 and -10 in the death-inducing signaling complex, while c-FLIP(L) levels were unaffected.
Division of Immunology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
I
I
Verbrugge
E
E
de Vries
S W G
SW
Tait
E H J
EH
Wissink
H
H
Walczak
M
M
Verheij
J
J
Borst
D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis; D020169:Caspases / Q000378:metabolism; D004249:DNA Damage; D004789:Enzyme Activation; D053200:Fas-Associated Death Domain Protein / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism; D034622:RNA Interference; D011839:Radiation, Ionizing; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D015398:Signal Transduction; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000502:physiology*; D019014:fas Receptor / Q000276:immunology
D000970:Antineoplastic Agents; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D019014:fas Receptor; D020169:Caspases