SPP1 Promotes NSCLC Brain Metastasis Via Sequestration of Ubiquitin Ligase RNF114 to Facilitate P85α Ubiquitination

Brain metastasis (BM) is a significant factor contributing to the poor prognosis of patients with non-small cell lung cancer (NSCLC). Secreted phosphoprotein 1 (SPP1) is implicated in the progression and metastasis of several cancers. The role of SPP1 in NSCLC remains unclear, especially in NSCLC BM. This study aimed to identify genes associated with NSCLC BM and to investigate the involvement of SPP1 in NSCLC BM. Integrated genomic analysis was utilized to identify candidate genes in NSCLC. The expression levels of SPP1 were evaluated in NSCLC tissues and cell lines. In vitro and in vivo experiments were conducted to assess the effect of SPP1 on NSCLC cell behavior and BM. The potential mechanisms of SPP1 were demonstrated by CO-IP and liquid chromatography-mass spectrometry (LC-MS). The underlying mechanism involving the PI3K/AKT/mTOR pathway was explored. The results showed that SPP1 expression was upregulated in NSCLC tissues and cell lines. Depletion of SPP1 using shRNA inhibited cell proliferation, migration, and invasion in vitro and suppressed BM in vivo. Mechanistically, SPP1 facilitates the ubiquitination of P85 alpha by interacting with the ubiquitin ligase RNF114, thus playing a role in regulating NSCLC BM through the PI3K/AKT/mTOR signaling pathway. Moreover, immunohistochemistry staining confirmed higher expression of SPP1 in NSCLC tissues with BM compared to those without BM. In summary, elevated SPP1 expression was associated with poor clinical outcomes in NSCLC patients. This study highlights the role of SPP1 as a regulator of cell metastasis and suggests its potential as a novel therapeutic target for BM in NSCLC.