Neoplastic odontogenic epithelial cells express bone sialoprotein

Bone sialoprotein (BSP) is synthesized and secreted by bone-, dentine- and cementum-forming cells and has been implicated in de novo bone formation and mineralization. In this study, we used histological sections of odontogenic neoplasms and performed immunohistochemical and in situ hybridization analyses. In ameloblastoma, BSP mRNA signals were seen in the neoplastic epithelial cells forming nests, strips and islands. BSP deposition was also seen in the stellate reticulum of the tumour masses revealed by immunohistochemistry using human BSP antibodies. In calcifying epithelial odontogenic tumour, the calcified masses demonstrated positive immunoreactivity to the human BSP antibodies, and the hybridization signals for BSP were located in the cells near the calcified particles. In the calcifying odontogenic cyst, strong BSP signals were seen in cells surrounding the characteristic nests of ghost cells, which often calcify subsequently. BSP protein was also found in these cells by immunohistochemistry. The active expression of BSP in the epithelial elements of the odontogenic tumours of adult patients suggests the activation of this matrix protein gene in the neoplastic process, and that BSP may play an important role in tumour formation and differentiation with respect to pathological calcification.