Immune induction identified by TMT proteomics analysis in Fusobacterium nucleatum autoinducer-2 treated macrophages

Background: The immune-inducing effect of the quorum sensing (QS) molecule autoinducer-2 (AI-2) on macrophages has not been previously comprehensively studied. Methods: We performed proteomic analysis on macrophages cocultured with purified Fusobacterium nucleatum (F. nucleatum) AI-2 and performed western blot analysis to verify the differential protein expression. We further used the Gene Expression Profiling Interactive Analysis and Tumor Immune Estimation Resource databases to analyze the expression of differentially expressed proteins in microbial-associated digestive tract tumors. Results: Based on proteomic analysis, we identified 46 upregulated proteins and 11 downregulated proteins. The upregulated proteins were mostly inflammatory factors such as tumor necrosis factor ligand superfamily member 9 (TNFSF9). These proteins have a range of biological functions associated with the regulation of inflammatory responses, apoptosis and tumorigenesis. TNFSF9 is highly expressed in pancreatic adenocarcinoma (PAAD) tissues and is associated with M1 polarization of macrophages. Conclusions: Our data indicated that F. nucleatum AI-2 induced inflammatory responses and activated multiple signaling pathways in macrophages. TNFSF9 is the most significantly differentially expressed protein induced by F. nucleatum AI-2 and is involved in regulating immune cell infiltration in PAAD. Thus, AI-2 may become a new focus for studying the relationship between bacteria and cancer.