FomA‐Containing Outer Membrane Vesicles of <i>Fusobacterium Nucleatum</i> Facilitate Bladder Cancer Lymphatic Metastasis via IL‐6‐Dependent M2b Macrophage Polarization

Outer membrane vesicles (OMVs) derived from the microbiota have emerged as key modulators of tumor progression and the immune microenvironment. However, the role of urinary microbiota and their associated OMVs proteins in the metastatic processes of bladder cancer (BCa) remains insufficiently understood. In this study, we investigated the impact of urinary microbiota on BCa progression and identified potential biomarkers within the urinary microbiome. We identified Fusobacterium nucleatum (F. nucleatum) as a predominant member of the urinary microbiota. Proteomic analysis of F. nucleatum OMVs revealed the outer membrane protein FomA as the most abundant component. A FomA-deficient F. nucleatum mutant strain was generated to assess the relationship between FomA and lymph node (LN) metastasis. Mechanistically, FomA-containing OMVs directly engage Toll-like receptor 2 (TLR2), triggering the NF-κB signaling pathway and upregulating interleukin-6 (IL-6) expression. Elevated IL-6 induces M2b macrophage polarization, which subsequently promotes the release of VEGF-C to facilitate LN metastasis. Furthermore, we identified pinocembrin, a natural flavonoid, as a potent inhibitor of the FomA-TLR2 interaction, effectively suppressing BCa progression. Collectively, our findings uncover a previously unrecognized microbiota-driven mechanism by which F. nucleatum-derived OMVs reprogram the tumor immune microenvironment toward a pro-metastatic state and highlight FomA as a promising therapeutic target.