Abstract: BACKGROUND ＆ AIM: To study the effect of As2O3＋tRA and As2O3 on apoptosis and differentiation of NB4 cells to evaluate the possible relation of these expressions among CD11b, Annexin Ⅴ and C/EBP ε,PML- RAR α mRNA. MATERIAL AND METHODS: As2O3＋tRA and As2O3 were added to the culture system to induce NB4 cells apoptosis and differentiation. NB4 cells were incubated and collected at 0, 4, 8, 12, 16, 20, 24, 48 and 72 hours , The expression of CD11b, AnnexinⅤ were determined by FACS，We used semi- quantitative RT- PCR.to detect mRNA expressions of C/EBP ε, PML/RAR α. RESULTS: The mRNA expression of C/EBP ε were markedly increased after NB4 cells stimulated by As2O3＋tRA and As2O3 within 0 to 72 hours,it leads to NB4 cells CD11b expression increased. The CD11b expression was more significant increased by As2O3＋tRA .As2O3＋tRA and As2O3 had the same role to degrade PML- RAR α fuse gene, As2O3＋tRA was more powerful in degradating PML- RAR α fuse gene.Apoptosis was started in the early time after NB4 cells cultured with As2O3＋tRA and As2O3 ,The expression of Annexin Ⅴ peak was occurred from 4 to 20 hours, With time prolong the expression of Annexin Ⅴ decreased. CONCLUSION: As2O3＋tRA and As2O3 could stimulate NB4 cells expression CD11b,C/EBP ε and decrease PML- RAR α fuse gene, leaded to NB4 cells apoptosis .In some given dose the effect of As2O3＋tRA was more significant to induce NB4 cells apoptosis and differentiation than that of As 2O3.

Key words: arsenic trioxide, retinoic acid, C/EBP ε, acute promyelocytic leukemia, PML- RAR α