BMP-2 augments FGF-induced differentiation of PC12 cells through upregulation of FGF receptor-1 expression

When exposed to various neurotrophic factors, including fibroblast growth factors (FGF)-1 and -2, rat pheochromocytoma-derived PC12 cells differentiate into sympathetic neuron-like cells possessing elongated neurites. We found that while bone morphogenetic protein-2 (BMP-2) exerted little effect by itself on the differentiation of PC12 cells, in combination with FGF it strongly induced neurite outgrowth, even at subthreshold concentrations of FGF. Analysis of gene expression revealed that FGF receptor-1 (FGFR-1) mRNA was abundantly expressed in PC12 cells and that its expression was upregulated by pretreating the cells with BMP-2. Crosslinking the receptors with (125)I-FGF-2 and then immunoprecipitating them confirmed that expression of FGFR-1, but not other FGF receptor types, was enhanced by BMP-2. Furthermore, Scatchard analyses revealed that the numbers of FGF-2 binding sites were increased by approximately 40% after BMP-2 treatment. Pretreatment with BMP-2 also enhanced peak and sustained levels of FGF-induced ERK1/2 phosphorylation in PC12 cells. Finally, the augmentation of neurotrophic activity by BMP-2 was inhibited by SU5402, an FGFR-1 inhibitor. These findings indicate that BMP-2 augments FGF-induced differentiation of PC12 cells through selective upregulation of FGFR-1 expression, and suggest that BMP-2 and FGF act in concert to regulate cell differentiation in the nervous system.