Calcium Transport Protein and Amelogenin Expression in Ameloblastoma: Relationship to Normal Amelogenesis

The progressive maturation of the ameloblast epithelium, formation of enamel matrix, and the mineralization of that matrix characterize normal amelogenesis. This process is regulated, in part, by the amelogenins. The expression by ameloblasts of amelogenin proteins as well as calcium transport proteins parallels matrix formation and mineralization. Odontogenic tumors reproduce, to varying degrees, the morphological and inductive relationships found among various parts of normal tooth germ. In normal amelogenesis, amelogenin, plasma membrane Ca(superscript ++)-pump PMCA , and calbindin-28KDa calbindin proteins are minimally expressed in presecretory ameloblasts, but progressively increase in expression later as the enamel matrix forms and begins to mineralize. Ameloblastomas, however, do not form matrix or mineralize. In the present study, we demonstrate by immunohistochemistry, that amelogenin, PMCA and calbindin proteins are all expressed in the ameloblast-like palisading peripheral epithelial cells of ten cases of ameloblastoma. In serial sections processed by the von Kossa technique, we also found diffuse calcium in all tumors studied. Our study suggests that ameloblastomas recapitulate a stage of differentiation beyond the presecretory stage and that the mechanisms of extracellular matrix formation and mineralization associated with normal amelogenesis may be uncoupled in ameloblastomas.