<i>Desulfovibrio vulgaris</i> flagellin exacerbates colorectal cancer through activating LRRC19/TRAF6/TAK1 pathway

The initiation and progression of colorectal cancer (CRC) are intimately associated with genetic, environmental and biological factors. <i>Desulfovibrio vulgaris</i> (DSV), a sulfate-reducing bacterium, has been found excessive growth in CRC patients, suggesting a potential role in carcinogenesis. However, the precise mechanisms underlying this association remain incompletely understood. We have found <i>Desulfovibrio</i> was abundant in high-fat diet-induced <i>Apc</i>^<i>min/+</i> mice, and DSV, a member of <i>Desulfovibrio</i>, triggered colonocyte proliferation of germ-free mice. Furthermore, the level of DSV progressively rose from healthy individuals to CRC patients. Flagella are important accessory structures of bacteria, which can help them colonize and enhance their invasive ability. We found that <i>D. vulgaris</i> flagellin (DVF) drove the proliferation, migration, and invasion of CRC cells and fostered the growth of CRC xenografts. DVF enriched the epithelial-mesenchymal transition (EMT)-associated genes and characterized the facilitation of DVF on EMT. Mechanistically, DVF induced EMT through a functional transmembrane receptor called leucine-rich repeat containing 19 (LRRC19). DVF interacted with LRRC19 to modulate the ubiquitination of tumor necrosis factor receptor-associated factor (TRAF)6, rather than TRAF2. This interaction drove the ubiquitination of pivotal molecule TAK1, further enhancing its autophosphorylation and ultimately contributing to EMT. Collectively, DVF interacts with LRRC19 to activate the TRAF6/TAK1 signaling pathway, thereby promoting the EMT of CRC. These data shed new light on the role of gut microbiota in CRC and establish a potential clinical therapeutic target.