The association between Fusobacterium nucleatum Outer Membrane Vesicles and Colonic Cancer

Abstract

Fusobacterium nucleatum, a gram-negative spindle-shaped anaerobic bacterium, is a component of the human microbiome that primarily inhabits the oral cavity and is associated with many diseases, including sinusitis, tonsillitis, urinary tract infection, and inflammatory bowel disease. Recent research demonstrates an association between the presence of this bacterium and colorectal carcinoma. This study aimed to investigate the ability of this bacterium and its outer membrane vesicles (OMV) to modulate colonic cell function. Like other gram-negative bacteria, F. nucleatum secretes OMV, but little is known about how they interact with host tissue. To investigate the potential role of these structures in the host-pathogen interaction the OMV were purified, proteomically characterised and their interaction with colonic cells investigated. In this regard, the mass spectrometry-based proteomic analysis revealed the presence of 366 proteins including several biologically active proteases which appeared to be selectively enriched in the OMV. In addition, many other proteins with documented or likely roles in F. nucleatum-mediated pathogenesis were identified. The ability of the F. nucleatum OMV to modulate several colonic epithelial cellular behaviours was investigated and compared with the intact parental bacterium. The OMV induced a potent pro-inflammatory response in colonic epithelial cells, stimulating the expression and secretion of pro-inflammatory cytokines and chemokines. OMV also impaired the barrier function of model colonic epithelial monolayers, in part by degrading the tight junctional protein E-cadherin and down regulating the expression of CDH-1. This process was accompanied by cadherin switching and the induction of a mesenchymal phenotype in the colonic cells as judged prominent morphological changes, significantly increased cellular proliferation and migration and the appearance of several markers associated with EMT, including increased nuclear translocation of the pivotal EMT transcription factor, ZEB-1. Taken together, these findings and the observation that the OMV enhanced colonic resistance to the chemotherapeutic agent 5-FU, support the hypothesis that these nanostructures likely make a significant contribution to the pathogenesis of gastrointestinal disease in susceptible individuals.