Transmembrane protein 9 as a novel biomarker promotes oral squamous cell carcinoma growth via IL1RN and serves as an immune therapeutic target.

[BACKGROUND] The involvement of transmembrane protein 9 (TMEM9) in various malignancies has been documented; nonetheless, its exact function and mechanistic involvement in the development of oral squamous cell carcinoma (OSCC) are still not well understood. The objective of this study is to shed light on the clinical relevance, tumor-promoting functions, and molecular pathways of TMEM9 in OSCC development.

[METHODS] Data from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases were used to analyze TMEM9 expression and its associations with prognosis and clinicopathological features, with immunohistochemistry (IHC) used for validation. The functional roles of TMEM9 in OSCC cell lines (CAL-27 and TCA8113) were assessed via small interfering RNA (siRNA)-mediated knockdown, followed by assays including 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), colony formation, Acridine Orange/Ethidium Bromide (AO/EB) staining, and transwell assays. Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, Mendelian randomization (MR), and correlation studies were used to identify downstream targets and pathways. The infiltration of immune cells was assessed through single sample gene set enrichment analysis (ssGSEA) and the Tumor IMmune Estimation Resource (TIMER) algorithms.

[RESULTS] TMEM9 expression was significantly elevated in OSCC tissues compared to normal controls and was linked to advanced T stage, higher histologic grade, smoking habits, and reduced 5-year overall survival. The suppression of TMEM9 caused a reduction in OSCC cell proliferation, migration, and colony formation, and it also promoted apoptosis. Mechanistically, TMEM9 was found to negatively regulate interleukin-1 receptor antagonist (IL1RN), and silencing IL1RN partially mitigated the anti-tumor effects observed with TMEM9 knockdown. TMEM9 expression showed negative correlations with tumor-infiltrating immune cells (e.g., neutrophils, CD8⁺ T cells, dendritic cells) and positive correlations with programmed cell death ligand 1 (PD-L1) and chemokines (CXCR4 and CCL25).

[CONCLUSIONS] TMEM9 functions as an oncogene in OSCC by inhibiting IL1RN regulating tumor progression and fostering an immunosuppressive microenvironment. This indicates a possible prognostic biomarker and therapeutic target for OSCC.