Combined multi-omics profiling and machine learning analysis reveals that Bregs and RPS2 promote bone metastasis in nasopharyngeal carcinoma.

The bone is the primary site of distant metastasis in patients with nasopharyngeal carcinoma (NPC), and bone metastasis (BM) significantly increases mortality. Deciphering the complex crosstalk between cancer cells and their tumor microenvironment (TME) is crucial for identifying therapeutic targets aimed at eliminating metastasis-initiating cells and preventing the establishment of overt metastases. Regulatory B cells (Bregs), a specialized B-cell subset endowed with potent immunosuppressive functions, play a pivotal regulatory role within the TME. However, their specific contributions, phenotypic characteristics, and underlying molecular mechanisms within the BM niche of NPC remain incompletely characterized and await full elucidation. This study aims to investigate the infiltration dynamics, functional impact, and molecular underpinnings of Bregs in the context of NPC BM. The single-cell sequencing data and RNA sequencing (RNA-seq) microarray matrices from public databases were utilized for the analysis in this study. Subsequently, three machine learning methods, least absolute shrinkage and selection operator (LASSO) regression analysis, random forest algorithm, and Boruta algorithm were combined to identify prognostic genes. The high infiltration of Bregs and high expression of RPS2 in the primary lesions of BM patients were confirmed, and relevant prognostic signatures were constructed. Flow cytometry, cell counting kit-8 (CCK-8) assay, migration assay, Transwell assay, and co-culture system were used to evaluate the effects of Bregs on cell proliferation and metastasis. An animal model of intracardiac injection-induced tumor transplantation was established, and bioluminescence imaging (BLI), digital radiography (DR), and micro computed tomography (Micro-CT) were utilized to assess the impact of Bregs on BM of tumor cells. Finally, clinical cohort analysis was conducted to determine the correlation between Bregs and BM in NPC. Bregs exhibit high infiltration in the primary lesions of NPC with BM, and the high expression of RPS2 in Bregs is highly correlated with prognosis. Mechanistically, RPS2 upregulates the secretion of interleukin-10 (IL-10) by Bregs. IL-10 then activates the PI3K/AKT pathway, which in turn upregulates the expression of the CXCR6 on the surface of tumor cells. These tumor cells, under the attraction of CXCL16 secreted by macrophages in bone, show an increased tendency to undergo BM. In the primary lesions of NPC patients, Bregs expressing RPS2 within tertiary lymphoid structures are highly associated with BM. Bregs and RPS2 can be utilized for the prognostic evaluation of BM in NPC. Pharmacological inhibition targeting Bregs or IL-10 may be a feasible approach to delay and treat BM in NPC.