RANK ligand (RANKL), a critical osteoclastogenic factor expressed in marrow stromal/preosteoblast cells is upregulated in Paget's disease of bone (PDB). We previously demonstrated that heat shock factor-2 (HSF-2) is a downstream target of fibroblast growth factor-2 (FGF-2) signaling to induce RANKL expression in bone marrow stromal/preosteoblast cells. In this study, we identified a 2.5-fold increase in serum FGF-2 levels in patients (n=8) with PDB compared to normal subjects (n=10). We showed that HSF-2 co-immunoprecipitates with heat shock protein-27 (HSP-27) and that FGF-2 stimulation significantly increased phospho-HSP-27 levels in marrow stromal cells. Confocal microscopy revealed HSF-2 co-localization with HSP-27 in unstimulated cells and HSF-2 nuclear translocation upon FGF-2 stimulation. We further show that FGF-2 stimulation significantly increased the levels of p-STAT-1 in these cells. Western blot analysis confirmed that siRNA suppression of STAT-1 significantly decreased (3.2-fold) RANKL expression and promoter activity in FGF-2 stimulated cells. Chromatin immunoprecipitation (ChIP) assay revealed STAT-1 binding to putative motif located far upstream (-8 kb) in the hRANKL gene promoter region. These results suggest STAT-1 is a downstream effector of FGF-2 signaling and that elevated levels of FGF-2 stimulates RANKL expression in PDB.