Arsenic Trioxide (As2O3) Induced Apoptosis in NB4 Cell lines

Park, Kyeong Bae; Hong, Dae Sik; Suh, Won Suk; Lee, Nam Soo; Park, Sung Gyu; Won, Jong Ho; Jung, Hee Jung; Kim, Sook Ja; Hong, Young Seon; Jin, Jong Youl; Park, Hee Sook; Shin, Sang Man

Abstract

BACKGROUND: Recently, inorganic arsenic trioxide (As2O3) was reported to induce complete remission in a high proportion of patients with refractory acute promyelocytic leukemia (APL). To illustrate cellular and molecular mechanisms of As2O3 in the treatment of APL, many experimental studies were performed on APL-derived cell lines in vitro. Previous studies showed that As2O3 inhibited proliferation and induced apoptosis in the APL-derived cell lines. This study was done to clarify the in vitro mechanisms of As2O3-induced apoptosis in APL-derived NB4 cell lines.
METHODS
To determine the effects of As2O3 in the various concentrations, NB4 cells were cultured with 0.1 to 2micro M/L of As2O3. To assay the apoptosis in NB4 cell lines, DNA fragmentation assay and TUNEL were performed. To find out the molecular change of As2O3- induced apoptotic NB4 cell lines, RT-PCR and Western blot analysis for PML-RARalpha chimeric protein expression and flow cytometry for bcl- 2/bax expression were performed. To clarify the caspase activation pathway, Western blot analysis and flow cytometry for procaspase expression were performed.
RESULTS
As2O3 induces apoptosis on NB4 cells in relatively high concentration (0.5 to 2 micro M/L) for 2 days. After 2 days of culture the PML-RARalpha chimeric protein expression decreased rapidly by Western blot and RT-PCR analysis and bcl-2 expression also decreased by flow cytometry. The expression of bax by flow cytometry showed a marked increase in high concentration (2micro M/L) but there was no change in low concentration (0.5micro M/L). In the Western blot analysis, the amount of pro`enzyme of caspase-3 was significantly decreased in the cells with high concentration (2micro M/L) compared with that in the cells with low concentration (0.5micro M/L). As2O3 induces proteolytic processing of pro-caspase 7 but not pro-caspase 9 and 8.
CONCLUSION
Apoptosis of APL-derived NB4 cell lines was induced by As2O3 and progressed rapidly in higher concentrations. During apoptosis, activation of caspase-7 pathway and degradation of PML-RARalpha chimeric protein, decrease in bcl-2 and increase in bax were shown.