Novel transcription factor BTNL9 enhances tumor suppression and drug sensitivity in non-small cell lung cancer through cell cycle regulation

BackgroundButyrophilins (BTNs) are immunoglobulin superfamily proteins involved in immune regulation. Among them, BTNL9 has unique structural features, including a bZIP-like domain, suggesting a potential transcriptional role. While BTNL9 is known to suppress T cell activation, its function in cancer remains largely unexplored. Recent studies suggest it may inhibit tumor progression and correlate with improved prognosis in multiple cancers. However, its molecular mechanisms and regulatory impact on lung cancer remain unclear. This study investigates the role of BTNL9 as a transcription factor and its implications for tumor progression and therapy. MethodsChIP-seq identified BTNL9-binding sites, followed by RNA-seq to assess transcriptomic profiles and validated by western blot. Drug sensitivity was evaluated through cytotoxicity assays. A xenograft model was applied to assess the effect of BTNL9 on tumor growth. TCGA data analysis examined correlations with survival, cell cycle regulators, and immune infiltration. ResultsChIP-seq identified 26,610 BTNL9 binding peaks, mapping to 9,707 genes near transcription start sites. RNA-seq and western blotting showed BTNL9 regulates cell cycle (E2F1, CDKN1A, CDK1, CDC25C, FOXM1), DNA replication (MCM2/3/7, ORC6), and p53-related transcription (BBC3, GADD45A). Integrative analysis found that 74.8% of differentially expressed genes were directly regulated by BTNL9. Functionally, BTNL9 overexpression induced cell cycle arrest, reduced proliferation, and suppressed tumor growth in vivo. BTNL9 enhanced bortezomib sensitivity in both A549 and NCI-H460 cells, with etoposide effects being more pronounced in A549. Higher BTNL9 levels strongly suppressed the expression of FOXM1, CDC25C, CDK1, CDK2, CCNA2 and CCNB1 and negatively correlated with these markers in LUAD TCGA data. Elevated BTNL9 expression was associated with improved survival, complete remission, and increased immune infiltration, including macrophages, CD8+ T cells, NK cells, and B cells in cancer tissues. ConclusionsBTNL9 functions as a transcription factor, suppresses tumor growth, and enhances drug sensitivity. Its correlation with survival and immune infiltration suggests potential role as a tumor suppressor and predictive biomarker for chemotherapy response.