AbstractProstaglandin F2α (PGF2α) regulates fibroblast growth factor‐2 (FGF‐2) and fibroblast growth factor receptor (FGFR) expression in osteoblasts. Here, the role of FGF‐2 in PGF2α‐induced proliferation and the signaling pathway involved, were determined in calvarial osteoblasts (COBs) from Fgf2+/+ and Fgf2−/− mice. The involvement of the exported FGF‐2 isoform, was determined using the FGF‐2 neutralizing antibody to alter its binding to FGFR1. PGF2α increased activity of Ras, and MAP‐kinase cascade as well as Bcl‐2 and c‐Myc levels in Fgf2+/+ but not in Fgf2−/− COBs. Moreover, in Fgf2+/+ COBs, PGF2α‐enhanced nuclear accumulation and co‐localization of Bcl‐2/c‐Myc. Although up‐regulation of multiple proliferative and survival signals were induced by PGF2α in Fgf2+/+ COBs, phospho‐p53 was unmodified while p53 was increased. Increased phospho‐p53 was, instead, found in Fgf2−/− COBs without up‐regulation of oncogenic proteins. The lack of p53 activation in wild type osteoblasts could be due in part to the overexpression of MDM2 caused by PGF2α via FGF‐2. PGF2α, also, increased cyclins D and E in Fgf2+/+ COBs and induced an expansion of Fgf2+/+ osteoblasts in G2/M phase. These data clearly show that PGF2α induces proliferation via endogenous FGF‐2 and the exported isoform mediates PGF2α effects by acting in autocrine manner. Furthermore, silencing of FGFR1 in Fgf2+/+ COBs blocked PGF2α induced increase of phospho‐MDM2 and cyclins. J. Cell. Physiol. 224: 465–474, 2010. © 2010 Wiley‐Liss, Inc.