Inhibiting MT2-TFE3-dependent autophagy enhances melatonin-induced apoptosis in tongue squamous cell carcinoma
Tengfei Fan1, Huifeng Pi2,3, Min Li2
1Department of Oral and Maxillofacial Surgery, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China.
Abstract:
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.
Insights
Melatonin induces autophagy, which protects tongue squamous cell carcinoma (TSCC) cells from cell death. Blocking this autophagy enhances melatonin
Area of Science:
- Oncology
- Cell Biology
- Molecular Medicine
Background:
- Autophagy modulation is a promising therapeutic avenue for tongue squamous cell carcinoma (TSCC).
- Melatonin exhibits known anticarcinogenic properties, but its specific effects on autophagy in TSCC remain largely uncharacterized.
Purpose of the Study:
- To investigate whether melatonin induces autophagy in TSCC.
- To elucidate the role of melatonin-induced autophagy in cell death pathways within TSCC.
- To explore the underlying molecular mechanisms and therapeutic potential of targeting this pathway.
Main Methods:
- Utilized the Cal27 TSCC cell line to assess apoptosis and autophagic flux markers (GFP-LC3 puncta, LC3-II, SQSTM1/P62).
- Employed pharmacological and genetic inhibition of autophagy to evaluate its impact on melatonin-induced apoptosis.
- Investigated the role of TFE3 phosphorylation, nuclear translocation, and signaling pathways (mTORC1) using western blotting and reporter assays.
- Validated findings in a xenograft mouse model with melatonin combined with autophagy inhibitors (hydroxychloroquine) or TFE3 knockdown.
- Analyzed TFE3 expression correlation with patient prognosis.
Main Results:
- Melatonin significantly induced apoptosis and autophagic flux in Cal27 cells.
- Inhibition of autophagy potentiated melatonin-induced apoptosis, revealing a cytoprotective role for autophagy.
- Melatonin promoted TFE3 dephosphorylation and nuclear translocation, activating autophagy-related gene expression and lysosomal biogenesis.
- Melatonin receptor blockade partially inhibited mTORC1/TFE3 signaling.
- Combination therapy of melatonin with hydroxychloroquine or TFE3-siRNA showed synergistic antitumor effects in vivo.
- Elevated TFE3 expression correlated with TSCC progression and poor patient prognosis.
Conclusions:
- Melatonin-induced TFE3-dependent autophagy in TSCC is mediated via melatonin membrane receptors.
- Autophagy acts protectively in melatonin-treated TSCC cells.
- Targeting the melatonin membrane receptor-TFE3-autophagy axis presents a potential therapeutic strategy to enhance melatonin's efficacy in TSCC treatment.
