Immunohistochemical detection of retinoblastoma protein and E2 promoter-binding factor-1 in ameloblastomas

To clarify the roles of cell cycle regulation in oncogenesis and cytodifferentiation of odontogenic tumors, expression of retinoblastoma protein (RB) and E2 promoter-binding factor-1 (E2F-1) was analyzed in ameloblastomas as well as in tooth germs.

Tissue specimens of 10 tooth germs, 40 benign ameloblastomas, and five malignant ameloblastomas were examined immunohistochemically with the use of antibodies against RB, E2F-1, and phosphorylated RB. Ki-67 antigen immunostaining was made as a marker of cell proliferation.

Immunohistochemical reactivity for RB, E2F-1, phosphorylated RB, and Ki-67 was detected in the nuclei of odontogenic epithelial cells near the basement membrane in tooth germs and benign and malignant ameloblastomas. The number of cells positive for phosphorylated RB was nearly equal to or slightly less than the number of cells positive for RB or E2F-1. The number of Ki-67-positive cells was slightly more than the numbers of cell positive for RB, E2F-1, or phosphorylated RB. The levels of immunoreactivity for RB, E2F-1, phosphorylated RB, and Ki-67 were slightly higher in benign and malignant ameloblastomas than in tooth germs. Plexiform ameloblastomas showed significantly higher expression of RB than follicular ameloblastomas. Ki-67 immunoreactivity was significantly higher in ameloblastic carcinomas than in metastasizing ameloblastomas.

Similar immunoreactivity for RB, E2F-1, phosphorylated RB, and Ki-67 in tooth germs and ameloblastomas indicated cellular expression of phosphorylated RB and active-free E2F-1 in both normal and neoplastic odontogenic tissues. Expression of RB, E2F-1, and phosphorylated RB was considered to be involved in cell proliferation and differentiation of odontogenic epithelium via control of the cell cycle.