Multidomain Bcl-2 homolog Bax but not Bak mediates synergistic induction of apoptosis by TRAIL and 5-FU through the mitochondrial apoptosis pathway.
The death ligand TRAIL synergizes with DNA-damaging therapies such as chemotherapeutic drugs or ionizing irradiation. Here, we show that the synergism of TRAIL and 5-fluorouracil (5-FU) and cross-sensitization between TRAIL and 5-FU for induction of apoptosis, entirely depend on Bax proficiency in human DU145 and HCT116 carcinoma cells. DU145 prostate carcinoma cells that have lost Bax protein expression due to mutation fail to release cytochrome c and to activate caspase-3 and -9 when exposed to TRAIL and 5-FU. In contrast, TRAIL sensitized for 5-FU-induced apoptosis and vice versa upon reconstitution of Bax expression. Isobolographic analyses of ED50 doses for 5-FU at increasing TRAIL concentrations showed a clear synergism of TRAIL and 5-FU in Bax-expressing cells. In contrast, the effect was merely additive in DU145 cells lacking Bax. Notably, both DU145 and HCT116 Bax-deficient cells still express Bak. This indicates that Bak is not sufficient to mediate cross-sensitization and synergism between 5-FU and TRAIL. Stable overexpression of Bak in DU145 sensitized for epirubicin-induced apoptosis but failed to confer synergy between TRAIL and 5-FU. Moreover, we show by the use of EGFP-tagged Bax and Bak that TRAIL and 5-FU synergistically trigger oligomerization and clustering of Bax but not Bak. These data clearly establish distinct roles for Bax and Bak in linking the TRAIL death receptor pathway to the mitochondrial apoptosis signaling cascade and delineate a higher degree of specificity in signaling for cell death by multidomain Bcl-2 homologs.
Department of Hematology, Oncology and Tumor Immunology, University Medical Center Charité, Humboldt University, Berlin.
Clarissa
C
von Haefen
Bernhard
B
Gillissen
Philipp G
PG
Hemmati
Jana
J
Wendt
Dilek
D
Güner
Alicja
A
Mrozek
Claus
C
Belka
Bernd
B
Dörken
Peter T
PT
Daniel
D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation; D005472:Fluorouracil / Q000494:pharmacology*; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins / Q000502:physiology*; D008565:Membrane Proteins / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein
D051017:Apoptosis Regulatory Proteins; C494772:BAK1 protein, human; C494826:BAX protein, human; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; D020169:Caspases; D005472:Fluorouracil