Inhibiting MT 2‐ TFE 3‐dependent autophagy enhances melatonin‐induced apoptosis in tongue squamous cell carcinoma

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 ‐ LC 3 puncta, and the upregulation of LC 3‐ II and downregulation of SQSTM 1/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 TFE 3 (Ser321) dephosphorylation, subsequently activated TFE 3 nuclear translocation, and increased TFE 3 reporter activity, which contributed to the expression of autophagy‐related genes and lysosomal biogenesis. Luzindole, a melatonin membrane receptor blocker, or MT 2 ‐si RNA partially blocked the ability of melatonin to promote mTORC 1/ TFE 3 signaling. Furthermore, we verified in a xenograft mouse model that melatonin with hydroxychloroquine or TFE 3 ‐si RNA exerted a synergistic antitumor effect by inhibiting autophagy. Importantly, TFE 3 expression positively correlated with TSCC development and poor prognosis in patients. Collectively, we demonstrated that the melatonin‐induced increase in TFE 3‐dependent autophagy is mediated through the melatonin membrane receptor in TSCC . These data also suggest that blocking melatonin membrane receptor‐ TFE 3‐dependent autophagy to enhance the activity of melatonin warrants further attention as a treatment strategy for TSCC .