Autophagy modulation is a potential therapeutic strategy for tongue squamous cell carcinoma (TSCC). Melatonin possesses significant anticarcinogenic activity. However, whether melatonin induces autophagy and its roles in cell death in TSCC are unclear. Herein, we show that melatonin induced significant apoptosis in the TSCC cell line Cal27. Apart from the induction of apoptosis, we demonstrated that melatonin‐induced autophagic flux in Cal27 cells as evidenced by the formation of GFP‐LC3 puncta, and the upregulation of LC3‐II and downregulation of SQSTM1/P62. Moreover, pharmacological or genetic blockage of autophagy enhanced melatonin‐induced apoptosis, indicating a cytoprotective role of autophagy in melatonin‐treated Cal27 cells. Mechanistically, melatonin induced TFE3^(Ser321) dephosphorylation, subsequently activated TFE3 nuclear translocation, and increased TFE3 reporter activity, which contributed to the expression of autophagy‐related genes and lysosomal biogenesis. Luzindole, a melatonin membrane receptor blocker, or MT2‐siRNA partially blocked the ability of melatonin to promote mTORC1/TFE3 signaling. Furthermore, we verified in a xenograft mouse model that melatonin with hydroxychloroquine or TFE3‐siRNA exerted a synergistic antitumor effect by inhibiting autophagy. Importantly, TFE3 expression positively correlated with TSCC development and poor prognosis in patients. Collectively, we demonstrated that the melatonin‐induced increase in TFE3‐dependent autophagy is mediated through the melatonin membrane receptor in TSCC. These data also suggest that blocking melatonin membrane receptor‐TFE3‐dependent autophagy to enhance the activity of melatonin warrants further attention as a treatment strategy for TSCC.

中文翻译：

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抑制MT2-TFE3依赖性自噬可增强褪黑素诱导的舌鳞癌细胞凋亡

自噬调节是舌鳞状细胞癌（TSCC）的潜在治疗策略。褪黑素具有显着的抗癌活性。但是，尚不清楚褪黑激素是否诱导自噬及其在TSCC细胞死亡中的作用。在这里，我们表明褪黑激素诱导TSCC细胞系Cal27中的显着凋亡。除了诱导细胞凋亡外，我们还证明了褪黑素诱导的Cal27细胞自噬通量由GFP-LC3突点的形成，LC3-II的上调和SQSTM1 / P62的下调来证明。此外，自噬的药理或遗传阻滞增强了褪黑素诱导的细胞凋亡，表明自噬在褪黑素处理的Cal27细胞中具有细胞保护作用。从机理^上讲，褪黑激素诱导了TFE3 ^（Ser321）去磷酸化，随后激活TFE3核易位，并增加TFE3报告基因活性，这有助于自噬相关基因的表达和溶酶体生物发生。褪黑激素膜受体阻滞剂Luzindole或MT2- siRNA可以部分阻断褪黑激素促进mTORC1 / TFE3信号传导的能力。此外，我们在异种移植小鼠模型中验证了褪黑素与羟氯喹或TFE3siRNA通过抑制自噬发挥协同抗肿瘤作用。重要的是，TFE3表达与患者TSCC的发展和预后不良呈正相关。总的来说，我们证明了褪黑激素诱导的TFE3依赖性自噬的增加是通过TSCC中的褪黑激素膜受体介导的。这些数据还表明，阻断褪黑激素膜受体TFE3依赖性自噬以增强褪黑激素的活性作为TSCC的治疗策略值得进一步关注。