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 I D22 II D2O II D23 II D2)-treatment is effective in acute promyelocytic leukemia(APL)patients with t(15；17)。Clinically achievable concentrations of As Ii D22 IED2O I D23 IED2 induces apoptosis of NB4，and APl cell line，and some leukemia/cancer cell lines inn vitro.Here，to study the mechanism of As-D 22-D 2 O I D 23 D 2-induced apoptosis，we established as As D 22 I D 2 O I D 23 D 2-loe sensitive subline，NB4/As.This cell line had a higher concentration of intracellular glutathione(GSH)than NB4(96vs.32nmol/mg)。Reduction of the GSH level by buthionine sulfoxide(BSO)completely restored the sensitivity to As I D 22 I D 2 O I D 23 I D 2.PML-modification and degradation of PMl-RARαwere similarly observed on treatment with As I D 22个D 2 O I D 23个D 2 in NB4 and NB4/As，Suggesting their contribution to apoptosis small.As D 22 I D 2 O I D 23 D 2 induced the activation of caspase 3 as well as a loss of mitocondrial transmembrane potential(ΔΨm)in NB 4.IN NB4/As，they were not observed but restored by pretreatment with BSO。Caspase 8 and Bid were activated by the treatment with As I D 22 I D 2 O I D 23 I D 2 in NB 4 but not in NB 4/As.In NB4，an inhibitor of caspase8blocked not only the activation of caspase3 and Bid but also the loss ofΔΨm.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 I D 22 I D 2 O I D 23 I D 2 activate caspase 8 in a Fas-ligand independent manner，and that the As I D 22 I D 2 O I D 23 I D 2-resistance in NB4/As is induced upstream of BSO，As I D 22 I D 2 O I D 23 D 2 might be applied to therapy of leukemias and cancers which are insensitive to low conentrations of As D 22 D 2 O I D 2.

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.