PP090: TGF-B in jaw tumor fluids induces RANKL expression in stromal fibroblasts

Abstract

Purpose Odontogenic tumor and odontogenic cyst, arising in jaw bone, grow with resorption and destruction of jaw bones. However, the mechanisms of bone resorption by odontogenic tumor and cyst are still unclear. These odontogenic lesions consist of odontogenic epithelial cells and stromal fibroblasts. It has been demonstrated that odontogenic epithelial cells of developing tooth germ induce osteoclastogenesis to prevent tooth germ from invasion of developing bone. Thus we hypothesized that odontogenic epithelial cells in odontogenic tumor and cyst induce osteoclastogenesis, and then that would play potential roles in tumor outgrowth into the jaw bones. Purpose of this study is to examine osteoclastogenesis by cytokines, focusing on TGF-b, produced by odontogenic epithelial cells. Results Concentration of TGF-b in fluids of odontogenic tumor and cyst (ameloblastoma, keratocystic odontogenic tumor and follicular cyst) was measured by ELISA, and expression of TGF-b, were examined by immunohistochemistry. Expression of RANKL, OPG and COX-2 in stromal fibroblasts in culture was assessed by RT-PCR and/or western blotting, and PGE2 synthesis was measured by ELISA. Fluids of jaw tumor and cyst increased expression of RANKL in stromal fibroblasts isolated from odontogenic tumor, but did not change expression of OPG. Induction of RANKL expression was further enhanced by acidified fluids. The induction of RANKL by the fluids was inhibited by SB-505124, a selective inhibitor of TGF-b receptor kinase or anti TGF-b neutralizing antibody, suggesting the fluids contain TGF-b. Immunohistochemistry revealed that TGF-b was positive in epithelial cells of odontogenic tumor/cyst, and phosphorylated smad3 was localized in the nuclei of odontogenic epithelial cells and stromal fibroblasts. TGF-b induced RANKL expression in the presence of cycloheximide, a protein synthesis inhibitor. Conclusions These results suggest that TGF-b signals directly enhanced RANKL gene transcription in stromal fibroblast, and then induced-RANKL would be participate in bone resorption by the lesions.