Mitochondrial calcium uniporter as a biomarker in lung adenocarcinoma: regulation of the immune microenvironment, apoptosis, cell cycle and mitophagy.

The mitochondrial calcium uniporter (MCU) complex is essential for maintaining mitochondrial calcium homeostasis and regulating cellular metabolism, apoptosis, proliferation, and mitochondrial quality control. Although MCU has been implicated in multiple malignancies, its biological role and regulatory mechanisms in lung adenocarcinoma (LUAD), a major subtype of non-small cell lung cancer (NSCLC), remain insufficiently defined. In this study, MCU expression was analyzed using pan-cancer and LUAD datasets from TCGA, GEO, UALCAN, and tissue microarray cohorts. GO, KEGG, and GSEA were performed to explore MCU-associated biological pathways, while ssGSEA, CIBERSORT, and TIDE algorithms were used to evaluate immune infiltration and predicted immunotherapy response. In vitro assays, including CCK-8, EdU, colony formation, Transwell assays, flow cytometry, qRT-PCR, Western blotting, immunofluorescence staining, JC-1 staining, and reactive oxygen species (ROS) detection, were conducted to assess the effects of MCU on LUAD cell behavior, mitophagy, and mitochondrial function. MCU was significantly upregulated in LUAD tissues and cell lines compared with normal controls. High MCU expression was associated with reduced immune cell infiltration, decreased immune checkpoint and HLA gene expression, and lower predicted sensitivity to immunotherapy. Functionally, MCU knockdown markedly inhibited LUAD cell proliferation, migration, and invasion, promoted apoptosis, and induced G1-phase cell cycle arrest, accompanied by increased p21 and cleaved caspase-3 expression and decreased CDK4 and Cyclin D1 expression. Conversely, MCU overexpression enhanced malignant phenotypes and suppressed apoptosis. Mechanistically, GSEA indicated that MCU was closely associated with mitophagy-related pathways. Further validation showed that MCU knockdown reduced PINK1 and PRKN expression, decreased mitochondrial LC3B accumulation, and weakened LC3B-mitochondria co-localization, indicating impaired mitophagy. MCU depletion also caused mitochondrial membrane potential dissipation and increased intracellular ROS accumulation. Collectively, these findings suggest that MCU promotes LUAD progression by remodeling the tumor immune microenvironment, enhancing malignant cellular behaviors, inhibiting apoptosis, and maintaining mitophagy-dependent mitochondrial homeostasis, highlighting MCU as a potential prognostic biomarker and therapeutic target in LUAD.