Frizzled are colonic epithelial receptors for Clostridium difficile toxin B

Clostridium difficile toxin B (TcdB) is a critical virulence factor causing diseases associated with C. difficile infection (CDI). Here we carried out CRISPR/Cas9-mediated genome-wide screens and identified the members of the Wnt receptor Frizzled (FZDs) family as TcdB receptors. TcdB binds to the conserved Wnt-binding site known as the cysteine-rich domain (CRD), with the highest affinity toward FZD1, 2, and 7. TcdB competes with Wnt for binding to FZDs, and its binding blocks Wnt signaling. FZD1/2/7 triple-knockout (KO) cells are highly resistant to TcdB, and recombinant FZD2-CRD prevented TcdB binding to the colonic epithelium. Colonic organoids cultured from FZD7 KO mice, combined with knock-down of FZD1 and 2, showed increased resistance to TcdB. The colonic epithelium in FZD7 KO mice was less susceptible to TcdB-induced tissue damage in vivo. These findings establish FZDs as physiologically relevant receptors for TcdB in the colonic epithelium.