HMGB3 promotes brain metastasis in lung adenocarcinoma by recruiting SSBP1 for nuclear translocation to remodel mitochondrial metabolism

Background: Brain metastasis, a leading cause of death in patients with lung adenocarcinoma (LUAD), arises from tumor cells adapting to the brain’s unique microenvironment of the brain through metabolic remodeling regulated by key oncogenes. Here, we aimed to determine the role of high mobility group protein B3 (HMGB3) in regulating tumor cell metabolism to promote the progression and brain metastasis in LUAD. Methods: In this study, a LUAD cell model predisposed to brain metastasis was developed in this study, and differentially expressed genes HMGB3 was identified. HMGB3 expression in LUAD was then validated through a series of in vitro and in vivo experiments, including western blotting, single-cell RNA sequencing (scRNA-seq), and immunohistochemistry (IHC). Tissue microarray (TMA) and LUAD brain metastasis clinical samples were used to explore the expression of HMGB3 and its clinical significance in LUAD. Additionally, we performed gene enrichment analysis on scRNA-seq and bulk RNA-seq, along with western blotting, to identify the pathways through which HMGB3 may cause brain metastasis. We then used coimmunoprecipitation and mass spectrometry to identify protein single-stranded DNA binding protein 1 (SSBP1), which interacts with HMGB3. Finally, gain and loss-of-function and rescue experiments were conducted to study SSBP1’s roles in LUAD cells. Results: HMGB3 upregulation in LUAD primary tumors and brain metastases associated with poor prognosis independent of metastasis. HMGB3 enhanced the migration, invasion, and epithelial-mesenchymal transition (EMT) capabilities of LUAD cells in vitro and promotes the occurrence and development of brain metastasis in vivo. Mechanistically, HMGB3 recruited SSBP1, inducing its nuclear translocation and reprogramming mitochondrial metabolism, thereby increasing cytoplasmic reactive oxygen species (ROS) levels, which activated the phosphatidylinositol 3-kinase–protein kinase B (PI3K-Akt) pathway by downregulating phosphatase and tensin homolog (PTEN), enhancing tumor cell proliferation, migration, invasion, and EMT. Conclusions: This study demonstrated that HMGB3 functions as a driver gene in the brain metastasis of LUAD, promoting metabolic adaptation of tumor cells to the brain microenvironment through the regulation of mitochondrial metabolism, thereby offering potential therapeutic targets for LUAD brain metastases.