<p>The function of Transforming growth factor (TGF) -β is reported to be associated with bone formation. However, the functional role of TGF-β3 in mediating the effects of orthodontic force such as the compressive force as a mechanical stress on osteoblasts remains unclear. We investigated the expression of TGF-β3 in osteoblasts and the effect of compressive force on downstream signaling pathways consisting of inflammatory cytokines and bone-specific transcription factors. Cultured MC3T3-E1 cells were subjected to continuous compressive forces, which are 0.5, 1.0, 2.0 g/cm², for 30-min, 1-h, and 2-h. Western blot analysis was determined phosphorylation of Smad-dependent and MAPKs. Investigation of TGF-3, COX-2, IL-6, and Runx2 expression levels was done by Western blot analysis and real-time polymerase chain reaction. The expression of TGF-β3 in both cell lines was significantly increased upon application of 1.0 g/cm², but not 0.5 and 2.0 g/cm² compressive force in 1-h, relative to the respective levels in unloaded control cells. At 1.0 g/cm² compressive force increased the phosphorylation of Smad2, Smad3, ERK1/2, p-38, and the expressions of inflammatory cytokines and bone-specific transcription factors. The increased expression was attenuated by pretreatment with siRNA of TGF-β3. These results indicate that a compressive force-induced of 1.0 g/cm² induces the expression of inflammatory cytokines and bone-specific transcription factors via TGF-β3 signaling in the osteogenesis.</p>