Fibroblast growth factors (FGFs) are important factors regulating osteogenesis. However, the early mechanisms and signaling pathways involved in FGF actions in osteoblasts are unknown. We investigated the effects of FGF-2 on cell±cell adhesion and cadherin expression and the underlying signaling pathways in immortalized human neonatal calvaria (IHNC) cells. These cells express E-and N-cadherins, as shown by immunocytochemical and Western blot analyses. rhFGF-2 increased cell±cell adhesion at 24±72 h, as measured in a cell aggregation assay, and this effect was blocked by speci® c neutralizing anti-N-cadherin, but not anti-E-cadherin antibodies. Accordingly, ELISA and Western blot analyses showed that rhFGF-2 (10±100 ng/ml) dose dependently increased N-cadherin but not E-cadherin protein levels. RT-PCR analysis showed that rhFGF-2 transiently increased N-cadherin mRNA levels in IHNC cells. The RNA polymerase II inhibitor 5, 6-dichloro-1-b-D-ribofuranosyl benzimidazole prevented the rhFGF-2-induced upregulation of N-cadherin mRNA, suggesting that transcription is necessary for this effect. Analysis of signaling molecules showed evidence that PLCg-PKC, Src, Erk 1/2 and p38 MAPK pathways are activated by rhFGF-2 in IHNC cells. The selective PKC inhibitors calphostin C, Ro-31-8220, GoÈ6976 and GoÈ6983 abrogated the stimulatory effect of rhFGF-2 on N-cadherin mRNA levels. The src-family tyrosine kinase inhibitor PP1 also blocked rhFGF-2-promoted N-cadherin expression. In contrast, the p38 MAP kinase inhibitor SB 203580 or the MEK inhibitor PD98059 had no effect on rhFGF-2-induced N-cadherin mRNA levels. Our data indicate that FGF-2 increases N-cadherin expression and function in human calvaria osteoblasts via activation of PKC and src-kinase pathways. This study identi® es N-cadherin as a previously unrecognized target gene for FGF-2 signaling pathway that regulates cell±cell adhesion in human osteoblasts. J. Cell. Biochem. 81: 68±81, 2001.© 2001 Wiley-Liss, Inc.