Involvement of CD95-independent caspase 8 activation in arsenic trioxide-induced apoptosis.
Arsenic trioxide (As2O3)-treatment is effective in acute promyelocytic leukemia (APL) patients with t(15;17). Clinically achievable concentrations of As2O3 induce apoptosis in NB4, an APL cell line, in vitro. Here, to study the mechanism of As2O3-induced apoptosis, we established an As2O3-resistant subline, NB4/As. Growth of NB4/As was inhibited by 50% after 2 day-treatment (IC50) at 1.6 microM As2O3, whereas IC50 of NB4 was 0.3 microM. Degradation of PML-RARalpha and change of the PML-subcellular localization were similarly induced by As2O3 in NB4 and NB4/As, suggesting that their contribution to apoptosis is small. Treatment with 1 microM As2O3 induced the activation of caspase 3 as well as a loss of mitochondrial transmembrane potential (deltapsim) in NB4 but not in NB4/As. Caspase 8 and Bid were also activated by As2O3 in NB4 but not in NB4/As. In NB4, an inhibitor of caspase 8 blocked not only the activation of caspase 3 but also the loss of deltapsim. Neither cell line expressed CD95/Fas, and agonistic anti-Fas antibody (CH-11) failed to cause apoptosis. Neither antagonistic anti-CD95/Fas antibody nor anti-Fas ligand antibodies influenced the As2O3-induced apoptosis. NB4/As had a higher concentration of intracellular glutathione (GSH) than NB4 (96 vs 32 nmol/mg). Reduction of the GSH level by buthionine sulfoxide (BSO) completely restored the sensitivity to As2O3 in NB4/As. Furthermore, caspase activation and the loss of deltapsim were recovered by combination treatment with BSO. These findings suggest that the As2O3 treatment activates caspase 8 in a CD95-independent but GSH concentration-dependent manner. In combination with BSO, As2O3 might be applied to therapy of leukemia/cancers which are insensitive to the clinically achievable concentrations of As2O3.
Kitamura
K
K
Department of Infectious Diseases, Nagoya University School of Medicine, Japan.
Minami
Y
Y
Yamamoto
K
K
Akao
Y
Y
Kiyoi
H
H
Saito
H
H
Naoe
T
T
D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects*; D000077237:Arsenic Trioxide; D001152:Arsenicals / Q000494:pharmacology* / Q000627:therapeutic use; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D004789:Enzyme Activation; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000188:drug therapy / Q000473:pathology*; D010087:Oxides / Q000494:pharmacology* / Q000627:therapeutic use; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000276:immunology
D000970:Antineoplastic Agents; D001152:Arsenicals; D010087:Oxides; D019014:fas Receptor; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D005978:Glutathione; D000077237:Arsenic Trioxide