Epithelial-mesenchymal transition (EMT) is an early step in the acquisition of invasiveness by malignant tumors. It has been clarified that the tumor microenvironment affects malignancy in a number of different carcinomas, in particular, that a hypoxic environment induces EMT. Activation of Notch signaling induces EMT, but it remains unclear how the Notch pathway is involved in oral squamous cell carcinoma (OSCC) under hypoxia. Three OSCC cell lines were cultured for examination under hypoxic (1% O2) and normoxic (21% O2) conditions. Expression of E-cadherin was investigated as a hallmark of EMT by immunohistochemical examination. Cell motility and invasion were examined by wound-healing and invasion assays, respectively. The expression of Notch pathway molecules was analyzed by qPCR. Hypoxia increased the mRNA expression of Notch receptors, ligands and target genes, and Snail. Hypoxia decreased the expression of E-cadherin, and increased the motility and invasiveness of OSCC cell lines. γ-secretase inhibitor, a Notch-specific inhibitor, prevented these effects caused by h-ypoxia. These findings suggest that hypoxia induces EMT in OSCC cell lines via activation of Notch signaling, and inhibition of the Notch signaling pathway to suppress EMT may be a useful approach for the treatment of OSCC.

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a b s t r a c tBackground: As oral neoplasm often originates from epithelium, an immortalized epithelial cell line could be useful for the research of oral carcinogenesis. Although several oral epithelial cell lines were reported, they were either derived from cancer or immortalized by human papilloma virus or simian virus 40 genes, which have the potential to induce carcinogenesis. Materials and methods: We established two immortalized cell lines from human oral epithelium by transducing mutant cyclin dependent kinase 4, cyclin D 1 , and human telomerase reverse transcriptase with or without dominant-negative p53 into primary-cultured normal oral gingival epithelial cells using recombinant lentivirus vectors and named them MOE (mouth-ordinary-epithelium) 1a and MOE1b, respectively. Results: MOE1 cells could be passaged for nine months or more, and the morphology of the cells did not change in comparison with that of fresh primary-cultured epithelial cells. MOE1 cells did not show epithelial-mesenchymal transition. MOE1b cells retain functional p53 and were considered to have less risk of genomic instabilities. Anchorage-independent growth was not observed in MOE1 cells. The expressions of cancer-associated genes including keratin-17 were not elevated in MOE1 cells, whereas oral cancer-derived HSC-2 cells showed overexpression of them. Furthermore, interleukin (IL)-1␤, IL-6, IL-8, tumor necrosis factor-␣, matrix metalloproteinase (MMP)-2, and MMP-9 were induced in response to lipopolysaccharide or heat-killed bacterium in MOE1 cells. Discussion: MOE1 cells kept the characteristics of normal epithelial cells without acquiring typical features of cancer cells and they could be useful not only for the study of oral neoplasm but also for other oral diseases.