Objective       To investigate the differentiation of side population cells from breast cancer cell line MDA-MB231 to osteoblasts after co-cultured with osteoblastic cell line MC3T3-E1 in Transwell chamber.       Methods       Side population cells were obtained by flow cytometry from MDA-MB231 cells. And then the obtained side population cells and MC3T3-E1 cells were placed into the upper and lower chambers of Transwell co-culture system respectively at a ratio of 1 to 1. Side population cells at the same density placed in the both chambers served as control. The morphology and prolifera

tion of the side population cells was observed by phase-contrast microscopy. The expression of OPN

Runx2 and Wnt-1 was detected by immunofluorescence staining and Western blotting.       Results       The side population cells were obviously differentiated in the co-culture system. Immunofluorescence staining indicated the expression of above 3 proteins was significantly stronger than in the control. Western blotting showed the same results (OPN: 5.15±0.35 

vs 

1.00±0.15

Runx2: 6.22±0.36 vs 1.00±0.14

Wnt-1: 9.30±0.28

vs

1.00±0.13

P

0.05).       Conclusion       Our co-culture system induces side population cells from MDA-MB231 cells to obtain relative biological characteristics of osteoblasts.