Abstract
We found that levels of miR-491-3p were decreased in multidrug-resistant tongue cancer (TC) cells. Induction of miR-491-3p expression sensitized TC cells to chemotherapy. In agreement, functional inhibition of miR-491-3p enhanced resistance of TC cells to chemotherapy. We found that miR-491-3p directly targeted mTORC2 component Rictor and inhibited mTORC2 activity, which was increased in resistant TC cells with high p-Akt(Ser473), p-SGK1(Ser422) and p-FOXO1(Thr24) levels. Inhibition of mTORC2 activity via either Rictor knockdown or mTOR inhibitor in turn sensitized TC cells to chemotherapy. In agreement, overexpression of Rictor increased the mTORC2 activity and induced resistance of TC cells to chemotherapy. As a feedback loop, mTORC2 downregulated miR-491-3p expression by inactivating FOXO1, which otherwise would transcriptionally induce miR-491-3p expression. Levels of miR-491-3 and Rictor or mTORC2 activity negatively correlated in TC tissues. Finally, low levels of miR-491-3p and highly expressed Rictor were associated with poor prognosis in tongue cancer patients. These data provide a rationale for targeted intervention on miR-491-3p/mTORC2 axis to enhance the efficacy of chemotherapy against tongue cancer.
Highlights
Tongue cancer is the most common oral cancer
MiR-491-3p was found to be downregulated in PYMinduced multidrug resistant tongue cancer cells termed as Tca8113/PYM
Restored expression of miR-491-3p sensitized Tca8113/PYM cells to chemotherapy, whereas functional inhibition of miR-491-3p led to enhanced resistance of tongue cancer cells to chemotherapy
Summary
Tongue cancer is the most common oral cancer. Tongue cancer frequently metastasizes and has a poorer prognosis than carcinoma of other sites in the oral cavity. Tongue cancer usually leads to malfunction of mastication, speech and deglutition. A large proportion of chemo-resistant tongue cancers show more aggressive tumor behavior and an even worse clinical outcome [3, 4]. While multiple mechanisms, such as insensitivity to drug-induced apoptosis, increased DNA repair and induction of drug-detoxifying mechanisms, have been proposed to play an important role in the development of cancer drug resistance [5], the precise causes of chemotherapy resistance in tong cancer remain elusive
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