Objective       To determine the effects of CD133-downregulation on the radiosensitivity of CD133

+

HepG2 cancer stem cells (CSCs) in hepatocellular carcinoma.       Methods       Magnetic-activated cell sorting (MACS) was used to isolate CD133

+

and CD133

-

cells from HepG2 cells. Flow cytometry was used to detect the expression of CD133 before and after cells isolation.

The NOD/SCID mice transplantation tumor experiments were performed to validate the cancer stem-like properties of sorted CD133

+

cells. Targeted silencing towards CD133 gene was performed

and the cells were divided into blank control group

negative-transfection group and positive-transfection group. RT-PCR and Western blotting were used to detect the mRNA and protein expression of CD133. Colony formation assay was applied to detect colony formation efficiency and survival rate after irradiation at different doses. Survival curve was drawn and radiobiology parameters D

0

Dq

N and SER (sensitive enhancement ratio) were counted. Flow cytometry was used to test cell cycle and apoptosis.       Results       Flow cytometry indicated that the expression rate of CD133 was (1.36±0.20)% and (87.62±1.92)% respectively before and after MACS isolation. When the obtained CD133

+

cells at a dose of 1×10

3

/ml

subcutaneous tumor was found in the NOD/SCID mice after implantation. The expression levels of CD133 at mRNA and protein level were significantly decreased in positive-transfection group. After CD133-downregulation

the cells at G1 and S phase were decreased whereas those at G2 phase and apoptotic rate were increased significantly. Colony formation results showed that D

0

Dq

N and SF

2

were decreased while and SER was increased significantly in positive-transfection group (P0.05).       Conclusion       CD133

as a marker of CSCs in liver cancer

could be a target for radiosensitization in liver CSCs treatment.