EXPRESSION AND REGULATION OF BASIC FIBROBLAST GROWTH-FACTOR MESSENGER-RNA LEVELS IN MOUSE OSTEOBLASTIC MC3T3-E1 CELLS

Basic fibroblast growth factor (bFGF) is a potent mitogen for bone cel ls and is a constituent of the bone matrix. We have found that osteobl astic MC3T3-E1 cells expressed bFGF mRNA transcript of 4.5 kilobases ( kb). We examined factors that regulate the expression of bFGF mRNA and protein in MC3T3-E1 cells. Treatment of MC3T3-E1 cells with bFGF (10 nM) for 4-48 h induced another 7-kb bFGF transcript at 4 h. Treatment of MC3T3-E1 cells with TGF beta (10 ng/ml) also induced the 7-kb trans cript of bFGF mRNA. In contrast, heparin, parathyroid hormone, and int erleukin-1 had no effect on bFGF mRNA. Western blot analyses revealed that MC3T3-E1 cells produced a 24-kDa bFGF protein, which was increase d by TGF beta. Immunofluorescence showed that bFGF protein was localiz ed to the cytoplasm in serum deprived MC3T3-E1 cells. Treatment of the se cultures with medium containing fetal calf serum or TGF beta caused increased cytoplasmic staining for bFGF and marked shape change. Furt hermore, in the cells treated with TGF beta there was both nuclear and cytoplasmic staining for the protein. These data demonstrate that bFG F mRNA and protein are expressed in osteoblastic cells and are regulat ed by treatment with TGF beta and bFGF. Production of bFGF may be impo rtant as an autocrine and paracrine mediator of bone cell replication, differentiation, and function.