Mechanism of Tumor Budding in Patient-Derived Metachronous Oral Primary Squamous Cell Carcinoma Cell Lines

Tumor budding (TB) occurs at the deepest site of tumor invasion and is a significant prognostic indicator of cervical metastasis in oral squamous cell carcinoma (OSCC). The mechanism of TB, however, remains unclear. This study investigated the roles of the tumor microenvironment and partial epithelial-mesenchymal transition (p-EMT) in TB expression using molecular and cellular physiological analyses. We established oral metachronous carcinoma cell lines (gingival carcinoma: 020, tongue carcinoma with high TB expression: 020G) from two cancers with pathologically different TB in the same patient and subjected them to exome analysis to detect gene mutations related to carcinogenesis and malignancy. Differences in EMT expression induced by transforming growth factor-β (TGF-β) between 020 and 020G were analyzed by Western blotting and reverse transcription polymerase chain reaction, and TGF-β-induced changes in cell morphology, proliferation, migration, and invasive ability were also examined. TGF-β expression was observed in the deepest tumor invasion microenvironment. TGF-β also induced the expression of several p-EMT markers and increased the migration and invasive abilities of 020G compared with 020 cells. In conclusion, TGF-β in the deep-tumor microenvironment can induce p-EMT in tumor cells, expressed as TB.