BACKGROUNDFibroblast growth factor 9 (FGF9), expressed in brain, kidney and developing skeletal tissues, can physiologically inhibit endochondral ossification; but little is known about how FGF9 affects osteoblasts and its detailed regulatory mechanism. Here we examined the effect of FGF9 on the activity of the murine Runt-related transcription factor 2 (Runx2) gene promoter in preosteoblast MC3T3-E1 and premyoblast C2C12 cells.

METHODSPlasmids containing the Runx2 promoter region were transfected into MC3T3-E1 and C2C12 cells and stably transfected cell lines were established. The method of luciferase reporter gene activation was used to examine the effects of FGF9 on the promoter activity.

RESULTSFGF9 (10 ng/ml) increased Runx2 promoter activity in MC3T3-E1 cells. When MC3T3-E1 cells were treated with FGF9 plus the various inhibitors or activator of the intracellular signaling transducation pathways, including 10 micromol/L U0126 (the inhibitor of mitogen-activated protein kinase kinase), 10 micromol/L SB203580 (the inhibitor of p38/mitogen activated protein kinase), or 1 micromol/L C6 ceramide (an activator of mitogen activated protein kinase), the luciferase expression did not change significantly compared with that of the cells treated with FGF9 only. However, when C2C12 cells were treated with 10 ng/ml FGF9, Runx2 gene promoter activity first decreased and then increased over a period of 1 to 5 days. Among the above inhibitors, only U0126 (10 micromol/L) completely blocked the effects of FGF9 on Runx2 gene promoter activity.

CONCLUSIONSOur data showed that FGF9 can affect Runx2 gene promoter activity in MC3T3-E1 and C2C12 cells. The action of FGF9 appears to depend partly on the mitogen-activated protein kinase kinase/mitogen-activated protein kinase pathways in C2C12 cells.