Targeting FUNDC1 Enhances Radiosensitivity of Esophageal Squamous Cell Carcinoma by Suppressing Mitochondrial Function.

Abstract

Introduction: As one of the most important treatments of Esophageal Squamous Cell Carcinoma (ESCC), the therapeutic effect of radiotherapy is still limited. FUN14 DomainContaining 1 (FUNDC1), a key regulator of mitophagy, has been implicated in tumor progression in several malignancies. However, its role in ESCC remains unclear. This study investigated the role of FUNDC1 in mitochondrial morphology, mitophagy, and radiosensitivity in ESCC cells.

Materials and methods: We evaluated FUNDC1 expression in ESCC using bioinformatics and immunohistochemistry. The effects of FUNDC1 knockdown on malignant behavior were assessed through CCK-8, wound healing, and transwell assays. Flow cytometry analyzed cell cycle and apoptosis. Radiosensitivity was determined by colony formation assays with survival curve fitting using the Linear-Quadratic (LQ) model. DNA damage was assessed by γH2AX foci formation. Mitochondrial morphology and mitophagy were examined using live cell staining and immunofluorescence. Western blotting measured protein expression.

Results: FUNDC1 expression was elevated in multiple cancers. High FUNDC1 expression was associated with advanced tumor stage and showed an unfavorable survival trend in ESCC patients. In our clinical cohort, a significant association with overall survival was observed in the M0 subgroup. FUNDC1 knockdown inhibited proliferation, migration, and invasion, particularly after irradiation. It also enhanced IR-induced G2/M arrest, γH2AX foci formation, and apoptosis. Mechanistically, FUNDC1 knockdown attenuated IR-induced mitochondrial fission and mitophagy-related changes, accompanied by increased cytochrome c release and apoptosis. In addition, FUNDC1 knockdown was associated with reduced total HMGB1 expression, impaired HMGB1 nuclear-to-cytoplasmic translocation, and suppressed RAGE/ERK activation, and these changes were partially reversed by 14-3-3σ overexpression.

Discussion: Our findings suggest that FUNDC1 promotes malignant behavior and radioresistance in ESCC cells. FUNDC1 knockdown was accompanied by reduced mitochondrial fission, attenuated mitophagy-related changes, and enhanced apoptosis after irradiation. FUNDC1 may also modulate HMGB1/RAGE/ERK signaling through a mechanism involving 14-3-3σ, although the precise causal relationships remain to be established.

Conclusion: FUNDC1 knockdown inhibited malignant behavior and enhanced radiosensitivity in ESCC cells, associated with altered mitochondrial morphology, reduced mitophagy-related changes, and suppression of HMGB1/RAGE/ERK signaling. FUNDC1 may serve as a potential target for radiosensitization in ESCC.