Hypoxia-induced HIF-1α and ZEB1 are critical for the malignant transformation of ameloblastoma via TGF-β-dependent EMT

Ameloblastic carcinoma (AC) is defined as a rare primary epithelial odontogenic malignant neoplasm and the malignant counterpart of benign epithelial odontogenic tumor of ameloblastoma (AB) by the WHO classification. AC develops pulmonary metastasis in about one third of the patients and reveals a poor prognosis. However, the mechanisms of AC oncogenesis remain unclear. In this report, we aimed to clarify the mechanisms of malignant transformation of AB or AC carcinogenesis. The relatively important genes in the malignant transformation of AB were screened by DNA microarray analysis, and the expression and localization of related proteins were examined by immunohistochemistry using samples of AB and secondary AC. Two genes of hypoxia-inducible factor 1 alpha subunit (HIF1A) and zinc finger E-box-binding homeobox 1 (ZEB1) were significantly and relatively upregulated in AC than in AB. Both genes were closely related in hypoxia and epithelial-mesenchymal transition (EMT). In addition, expressions of HIF-1 alpha and ZEB1 proteins were significantly stronger in AC than in AB. In the cell assays using ameloblastoma cell line, AM-1, hypoxia condition upregulated the expression of transforming growth factor-beta (TGF-beta) and induced EMT. Furthermore, the hypoxia-induced morphological change and cell migration ability were inhibited by an antiallergic medicine tranilast. Finally, we concluded that hypoxia-induced HIF-1 alpha and ZEB1 were critical for the malignant transformation of AB via TGF-beta-dependent EMT. Then, both HIF-1 alpha and ZEB1 could be potential biomarkers to predict the malignant transformation of AB.