Background and purpose: B cell-specific MLV integration site 1 (BMI-1) gene plays an important role in DNA damage after exposure to irradiation. The present study aimed to investigate the effect of BMI-1 on radiosensitivity of esophageal carcinoma cell after down-regulation of BMI-1 expression by silencing siRNA. Methods: Three pairs of siRNA based on the sequences of the BMI-1 mRNA were synthesized (siRNA1

siRNA2 and siRNA3) by compa-ny

and transfected into cultured TE13 cells as the BMI-1 siRNA groups

and a negative one was synthesized to be used as the negative control (NC) group. The untransfected group was named as the control group. BMI-1 mRNA and protein expression in esophageal cancer TE13 cells were detected by reverse transcription polymerase chain reaction (RT-PCR) and Western blot in different groups. This study used flow cytometry assay to analyze cell cycle of transfected cells

and examined cellular growth and radiosensitivity in vitro by MTT and clone formation assay. mRNA and protein expression of p16 and CDK4 in esophageal cancer TE13 cells were detected by RT-PCR and Western blot. Results: The results of RTPCR and Western blot showed that the expressions of BMI-1 at gene and protein levels were inhibited after silencing the BMI-1 gene. The mRNA and protein expression of BMI-1 in BMI-1 siRNA3 group were both significantly lower than that in BMI-1 siRNA1 and 2 groups. There was no significant difference in the cell proliferation among control

NC and BMI-1 siRNA3 groups. The values of D

0

D

q

and SF2 in BMI-1 siRNA3 group were 1.761

2.122 and 0.6255

respectively

obviously lower than those in control group (2.514

2.694 and 0.8268) and those in NC group (2.506

2.664 and 0.8231)

while the value of N in BMI-1 siRNA3 group (3.336) was higher than that in control group (2.92) and that in NC group (2.895)

which showed higher radiosensitivity in BMI-1 siRNA3 group. In addition

the cell cycle was arrested at G

2

/M phase after irradiation in control and NC gr

oups. The percentage of G

0

/G

1

phase in BMI-1 siRNA3 group was higher than that of control group and NC group

while the percentage of G

2

/M phase was lower than those in the latter. The up-regulation of p16 and down-regulation of CDK4 at gene and protein levels were detected after knockdown of BMI-1 expression by siRNA (P0.01). Conclusion: siRNA could inhibit BMI-1 gene expression in esophageal cancer TE13 cells and enhance radiosensitivity

followed by eliminating the cell cycle arrest at G

2

/M stage after irradiation in vitro

which is related to the regulation of the protein expression of p16 and CDK4.