CCNU-dependent potentiation of TRAIL/Apo2L-induced apoptosis in human glioma cells is p53-independent but may involve enhanced cytochrome c release.
Death ligands such as CD95 ligand (CD95L) or tumor necrosis factor-related apoptosis-inducing ligand/Apo2 ligand (TRAIL/Apo2L) induce apoptosis in radiochemotherapy-resistant human malignant glioma cell lines. The death-signaling TRAIL receptors 2 (TRAIL-R2/death receptor (DR) 5) and TRAIL-R1/DR4 were expressed more abundantly than the non-death-inducing (decoy) receptors TRAIL-R3/DcR1 and TRAIL-R4/DcR2 in 12 human glioma cell lines. Four of the 12 cell lines were TRAIL/Apo2L-sensitive in the absence of a protein synthesis inhibitor, cycloheximide (CHX). Three of the 12 cell lines were still TRAIL/Apo2L-resistant in the presence of CHX. TRAIL-R2 expression predicted sensitivity to apoptosis. Coexposure to TRAIL/Apo2L and cytotoxic drugs such as topotecan, lomustine (1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, CCNU) or temozolomide resulted in synergistic killing. Synergistic killing was more often observed in cell lines retaining wild-type p53 activity (U87MG, LN-229) than in p53 mutant cell lines (LN-18, T98G, U373MG). Drug exposure resulted in enhanced TRAIL-R2 expression, but decreased TRAIL-R4 expression in U87MG cells. Ectopic expression of dominant-negative p53(V135A) abrogated the drug-induced changes in TRAIL-R2 and TRAIL-R4 expression, but had no effect on synergy. Thus, neither wild-type p53 function nor changes in TRAIL receptor expression were required for synergy. In contrast, synergy resulted possibly from drug-induced cytochrome c release from mitochondria, serving as an amplifier of the TRAIL/Apo2L-mediated cascade of caspase activation. These data provide novel insights into the role of the TRAIL/Apo2L system in malignant gliomas and illustrate that TRAIL/Apo2L-based immunochemotherapy may be an effective therapeutic strategy for these lethal neoplasms.
Röhn
T A
TA
Laboratory of Molecular Neuro-Oncology, Department of Neurology, University of Tübingen, Medical School, Tübingen, Germany.
Wagenknecht
B
B
Roth
W
W
Naumann
U
U
Gulbins
E
E
Krammer
P H
PH
Walczak
H
H
Weller
M
M
D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism*; D005434:Flow Cytometry; D005910:Glioma / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D008130:Lomustine / Q000494:pharmacology*; D008562:Membrane Glycoproteins / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*
D018906:Antineoplastic Agents, Alkylating; D051017:Apoptosis Regulatory Proteins; D003574:Cytochrome c Group; D008562:Membrane Glycoproteins; D019253:Proto-Oncogene Proteins c-bcl-2; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D016159:Tumor Suppressor Protein p53; D008130:Lomustine; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases