The Mammalian Target of Rapamycin-70-kDa Ribosomal Protein S6 Kinase Axis Inhibits the Biological Function of Tongue Squamous Cell Carcinoma

Purpose: Studies have shown the mammalian target of rapamycin (mTOR) and 70-kDa ribosomal protein S6 kinase (p70S6K) to be tumor suppressors in many cancers. These factors may have synergistic functions in tongue squamous cell carcinoma (TSCC), which is the most common malignant cancer in the oral region. We aimed to investigate the expression of the mTOR-p70S6K axis in TSCC patients and its biological function in TSCC cell lines.

Materials and methods: Sixty-eight TSCC patients were included in this study, and their features, including age, gender, tumor differentiation, lymphatic metastasis, and clinical stage, were recorded. The expression of mTOR and p70S6K was detected by immunohistochemistry. Small interfering RNA constructs were delivered into TSCC cells to downregulate mTOR and p70S6K expression in vitro. After transfection, cell proliferation, migration or invasion, apoptosis, and chemoresistance assays were performed to examine cellular variations of biological function.

Results: High expression of the mTOR-p70S6K axis was associated with higher tumor stage, lymph node metastasis, and poor tumor differentiation. Suppression of mTOR and p70S6K in TSCC cells resulted in the inhibition of cell proliferation, metastases, and chemoresistance. Inhibiting mTOR expression could inhibit p70S6K expression but not vice versa.

Conclusions: The high expression of mTOR and p70S6K is closely associated with malignant characterization of TSCC patients, and it could inhibit biological functions of TSCC cell lines. Taken together, the mTOR-p70S6K axis may serve as a potential therapeutic strategy for TSCC.