Comparative expression profiles of keratins and apoptosis regulating proteins in keratocystic odontogenic tumor, orthokeratinized odontogenic cyst, and dentigerous cyst

Background: In addition to keratocystic odontogenic tumor (KCOT), orthokeratinized odontogenic cyst (OOC) has recently been recognized as a different jaw cyst entity whose lining epithelia are markedly keratinized. However, the odontogenic background of OOC remains still controversial. To clarify the difference in the lining epithelial natures of KCOT and OOC, we investigated differentiation modes for keratinization and neoplastic characteristics of these two cysts by immunohistochemistry for keratin subtypes and apoptosis-related proteins. Methods: Surgical specimens of KCOT (n = 20) and OOC (n = 15), as well as dentigerous cyst (DC, n = 15), which was used as a control, were examined by immunohistochemistry and western blotting for their expressions for cytokeratin (CK) 1, CK13, Bcl-2, and Bax. Immunohistochemical reactions were evaluated separately in two epithelial layers: upper spinous and basal. Results: Most of the spinous cells in the upper layer of KCOT and DC were CK13 positive (90-100%), while they were not as conspicuous in OOC (20%). In contrast, CK1 was positive in OOC (100%), while it was not positive in KCOT and DC. Basal layer cells in KCOT were positive for Bcl-2 (100%) but not for Bax (0%). Instead, they were not positive for Bcl-2 but positive Bax in OOC and DC. These immunohistochemical profiles in the three cystic lesions were confirmed by western blot analyses showing CK13 in KCOT and DC and CK1 in OOC. Conclusions: The CK expression modes were similar between KCOT and DC, indicating their odontogenic characteristics, which were not evident in OOC. The Bcl-2 positivity in KCOT suggested its neoplastic nature, though there was no neoplastic evidence in OOC and DC.