Objective      To investigate the expression of iroquois homebox 2 (IRX2) gene and its effect on cell proliferation and cell cycle in human osteosarcoma.       Methods      RT-PCR and Western blotting were used to detect the expression of IRX2 in MG-63 osteosarcoma cell line. IRX2-siRNA was used to interfere with the expression of IRX2 gene

and the cell proliferation and cell cycle were estimated by MTT assay and flow cytometry. The activation of JAK3 and STAT5 was tested by Western blotting.       Resu

lts      The expression level of IRX2 was significantly higher in the osteosarcoma cell line than in human osteoblast cell line. IRX2-siRNA-induced IRX2 silencing could markedly inhibit the cell proliferation

significantly elevate the cell percentage in S phase [(23.93±1.92)%

]

compared with the control [(15.84±1.76)%

]

and significantly reduce the cell percentage in G

2

/M phase [(10.44±1.99)%

]

compared with the control [(23.14±3.19)%

]

. IRX2-siRNA remarkably down-regulated p-JAK3 and p-STAT5

while IRX2 overexpression  up-regulated p-JAK3 and p-STAT5 and promoted the proliferation of MG-63 cells. With the inhibitors of JAK3 and STAT5

the cell proliferation promoting effect of IRX2 was attenuated.       Conclusion      IRX2 can regulate the cell proliferation of osteosarcoma partly by JAK3/STAT5 signaling pathway.