Involvement of Fas ligand-independent caspase8 activation in AsィイD22ィエD2OィイD23ィエD2-induced apoptosis

Arsenic trioxide (As - D22 - D2O - D23 - D2) treatment is effective in acute promyelocytic leukemia（APL） patients with t(15；. Clinically achievable concentrations of As D22 - D2O - D23 - D2 induces apoptosis of NB4，and APl cell line, and some leukemia /cancer cell lines inn vitro. Here，to study the mechanism of As D22 D2O D23 d02 -induced apoptosiswe established as as D22 D2O D23 d02 -loe sensitive sublineAs. This cell line 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 thesensitivity to As - D22 - D2O - D23 - D2. PML-modification and degradation of PMl-RARα were similarlyobserved on treatment with As D22 D2O D23 D2 in NB4 and NB4 / As，Suggesting their contribution to apoptosis is small. As D22 - D2O - D23 - D2 induced the activation ofcaspase 3 as well as a loss of mitocondrial transmembrane potential （ΔΨm） in NB4. in NB4 / as，Caspase 8和Bid activated by Caspase 8和Bid activated by Caspase 8和Bid activated by Caspase 8和Bid activated by Caspase 8和Bidthe treatment with As D22 - 2o - D23 - D2 in NB4 but not in NB4 / As. in NB4，an inhibitor of caspase 8 blocked not only the activation of caspase 3 and Bid but the loss ofΔΨm. In both the cell lines，Fas expressed little and agonistic anti-Fas antibody (CH-11) failed to cause apoptosis. Thesefindings suggest that the treatment with As D22 D2O D23 D2 activate caspase 8 in a Fas-ligand如manner,and that the As D22 D2O D23 d02 -resistance in NB4 / As is induced upstream of BSO，D22 D2O D23 D2might be applied to therapy of leukemias and cancers which are insensitive tolow concentrations of As D22 - D2O - D23 - D2。

Arsenic trioxide (AsィイD22ィエD2OィイD23ィエD2)-treatment is effective in acute promyelocytic leukemia (APL) patients with t(15;17). Clinically achievable concentrations of AsィイD22ィエD2OィイD23ィエD2 induces apoptosis of NB4, and APl cell line, and some leukemia /cancer cell lines inn vitro. Here, to study the mechanism of AsィイD22ィエD2OィイD23ィエD2-induced apoptosis, we established as AsィイD22ィエD2OィイD23ィエD2-loe sensitive subline, NB4/As. This cell line 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 AsィイD22ィエD2OィイD23ィエD2. PML-modification and degradation of PMl-RARα were similarly observed on treatment with AsィイD22ィエD2OィイD23ィエD2 in NB4 and NB4 / As, Suggesting their contribution to apoptosis is small. AsィイD22ィエD2OィイD23ィエD2 induced the activation of caspase 3 as well as a loss of mitocondrial transmembrane potential (ΔΨm) in NB4. IN NB4 / As, they were not observed but restored by pretreatment with BSO. Caspase 8 and Bid were activated by the treatment with AsィイD22ィエD2OィイD23ィエD2 in NB4 but not in NB4 / As. In NB4, an inhibitor of caspase 8 blocked not only the activation of caspase 3 and Bid but also the loss of ΔΨm. In both the cell lines, Fas expressed little and agonistic anti-Fas antibody (CH-11) failed to cause apoptosis. These findings suggest that the treatment with AsィイD22ィエD2OィイD23ィエD2 activate caspase 8 in a Fas-ligand independent manner, and that the AsィイD22ィエD2OィイD23ィエD2-resistance in NB4 / As is induced upstream of BSO, AsィイD22ィエD2OィイD23ィエD2might be applied to therapy of leukemias and cancers which are insensitive to low concentrations of AsィイD22ィエD2OィイD23ィエD2.