Objective    To study the effect of RNA interference inhibiting apurinic/apyrimidinic endonuclease 1 (APE1) expression in bone marrow stromal cells (BMSCs) and myeloma cell line U266 on the proliferation and apoptosis of co-cultured U266 cells.     Methods    Constructed APE1 siRNA expression vector Ad5v-APE1 siRNA was used to transfect BMSCs and U266 cells. A co-culture system of BMSCs and U266 cells was established with Transwell insert culture dish. The co-culture system of BMSCs and U266 cells were divided into four groups: a control group (untransfected BMSCs and U266 cells)

a first single treatment group (transfected BMSCs and untransfected U266 cells)

a second single treatment group (untransfected BMSCs and transfected U266 cells)

and a dual treatment group (transfected BMSCs and U266 cells). The expression levels of APE1 were detected by Western blotting. The proliferation

apoptosis

and mRNA expression levels of interleukin-6 (IL-6) and interleukin-8 (IL-8) of co-cultured U266 cells were examined by MTT assay

flow cytometry with annexin V-PE/7-AAD double staining

and RT-PCR

respectively.     Results    BMSCs and U266 cells transfected with APE1 siRNA had significantly lower protein expression of APE1 than untransfected cells (P0.01). Compared with the two single treatment groups and the control group

the proliferation inhibition and apoptosis degrees of U266 cells in the dual treatment group significantly increased (P0.01). Compared with the control group

the mRNA expression levels of IL-6 and IL-8 in U266 cells significantly decreased in the two single treatment groups (P0.01) and the dual treatment group (P0.01)

showing greater decrease in the dual treatment group (P0.01).     Conclusion    Inhibiting APE1 expression in BMSCs and/or U266 cells in a co-culture system suppresses the proliferation and promotes the apoptosis of U266 cells.