<i>Fusobacterium nucleatum</i> Lipopolysaccharides Disrupt the Interaction of Siglec-7 to Sialoglycans Expressed on Mammalian Cells

Sialic acid-binding immunoglobulin-like lectins (Siglecs) are key immune receptors that bind to cell surface sialic acids, leading to modulation of the immune system. Interrupting the Siglec-sialoglycan binding in cancer has been proposed as a potential antitumor response strategy. We previously showed that colon-cancer-associated <i>Fusobacterium nucleatum</i> (Fn) ATCC 51191 interacts with Siglec-7 via its lipopolysaccharide (LPS), revealing Fn LPS as a new ligand for Siglec-7. Here, we used glycoengineered cells carrying sialic acid variants to investigate the capacity of LPS isolated from <i>F. nucleatum</i> strains to disrupt the interaction between sialic acid expressed on mammalian cells and Siglec-7. We first showed that LPS extracted from <i>Fusobacterium polymorphum</i> ATCC 10953, <i>F. nucleatum</i> ssp. <i>animalis</i> ATCC 51191, and <i>F. nucleatum</i> ssp. <i>nucleatum</i> ATCC 25586 strains bound to recombinant Siglec-7 in vitro, while no binding was observed with the Siglec-7R124A mutant, suggesting that the binding occurred through the carbohydrate binding V-set domain. Using glycoengineered Jurkat cells and HEK293T cells carrying modified sialic acid forms, we demonstrated that <i>F. nucleatum</i> LPS could significantly disrupt the binding of Siglec-7 to these cells and that this inhibition was decreased following neuraminidase treatment, confirming that the interaction between Fn LPS and Siglec-7 is carbohydrate-mediated. We further validated these data using Jurkat cells and HEK293T cells expressing high-affinity sialic acid ligands. We showed that <i>F. nucleatum</i> LPS significantly disrupted the binding of Siglec-7 to these cells in a specific manner. These findings offer novel insights into the development of glycomimetic approaches for limiting colon cancer progression.