Immunohistochemical detection of phosphorylated JNK, p38 MAPK, and ERK5 in ameloblastic tumors

BACKGROUND: To evaluate roles of mitogen-activated protein kinases (MAPKs) in oncogenesis and cytodifferentiation of odontogenic tumors, expression of phosphorylated JNK (p-JNK), p38 MAPK (p-p38 MAPK), and ERK5 (p-ERK5) was analyzed in ameloblastic tumors as well as in tooth germs. METHODS: Ten tooth germs, 47 ameloblastomas, and 5 malignant ameloblastic tumors were examined immunohistochemically with the antibodies against p-JNK, p-p38 MAPK, and p-ERK5. RESULTS: Immunoreactivity for p-JNK was detected in epithelial or neoplastic cells detached from the basement membrane in 7 tooth germs and 7 ameloblastomas, and the expression levels of p-JNK in ameloblastic tumors were significantly lower than that in tooth germs. Expression of p-p38 MAPK was found in epithelial or neoplastic cells in tooth germs and ameloblastic tumors except for two ameloblastomas, and increased expression was found in keratinizing cells of acanthomatous ameloblastomas. The expression level of p-p38 MAPK in ameloblastomas was significantly higher than the levels in tooth germs and malignant ameloblastic tumors. Immunoreactivity for p-ERK5 was found predominantly in epithelial or neoplastic cells near the basement membrane in tooth germs and ameloblastic tumors. The expression levels of p-ERK5 in ameloblastic tumors were slightly higher than that in tooth germs, and plexiform ameloblastomas showed significantly higher p-ERK5 expression than follicular ameloblastomas. CONCLUSION: Expression of p-JNK, p-p38 MAPK, and p-ERK5 in tooth germs and ameloblastic tumors suggests that these MAPK signaling pathways contribute to cell proliferation, differentiation, or apoptosis in both normal and neoplastic odontogenic tissues. Altered expression of these phosphorylated MAPKs in ameloblastic tumors may be involved in oncogenesis and tumor cell differentiation.