receptors, two different TcdB bindsto Nature ReviewsMicrobiology NATURE REVIEWS manner dependent cell type- FZD, ina CSPG4 and |

MICROBIOLOGY

| Publishedonline12Oct2016;doi: repeat (CROP) domains that bind to combined repetitive oligopeptide receptor-binding domains, including colonicthe epithelium. relevantically receptors for TcdB in family (FZD)as physiolog members of WNTreceptor the screen,wide Tao established.be Here, using agenome- lines, but its role (CSPG4) is aTcdB receptor incell chondroitin sulfate proteoglycan 4 understood. well not TcdB targets colonic the epithelium is receptor-mediated how endocytosis, known to enter host cells through death.cell Although toxins these are rounding and intestinal epithelial cytoskeleton actin the and initiate cell inactivate RHO GTPases to disrupt and toxin B(TcdB), of both which toxin A(TcdA; known also as ToxA) ficile The major factors virulence of ciated death indeveloped countries. leading cause of gastroenteritis-asso lowing antibiotic treatment and is the inindividuals disease foldiarrhoeal bacterium The opportunistic Gram-positive TcdB aimsforFrizzled toxin, but similar sensitivity to the enhanced resistance to full-length the cells; CSPG4-deficient cells showed ing result by generating knockout The authors screen their confirmed plasma membrane FZD2. version of TcdB, identified the they previous reports. For truncated the TcdB, which is inagreement with from screen with the full-length TcdB activity. identified They CSPG4 host factors cell that are involved in CROP domain, respectively, to find truncated version that lacked the screens TcdB with full-length or a out two CRISPR–Cas9 mediated carbohydrates. The authors carried

TcdB contains potential several Previous reports implied that BACTERIAL TOXINS are exotoxins the Clostridium difficile Clostridium ©

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L i m cells were less sensitive to trun the truncated version, whereas Fzd7 organoids that were cultured from colonic epithelium. Indeed, colonic dominant TcdB receptors inthe FZD receptors are likely the to be subepithelial myofibroblasts. Thus, whereas to CSPG4 is localized and mouse colonic epithelium, FZD7 are expressed human inthe analysis showedistry that FZD2and independent of CSPG4. mediate of TcdB entry the into cells which indicates that FZDreceptors length TcdB into ofFZD2–CRD blocked full- entry demonstrated that recombinant length TcdB. The authors further TcdB and less sensitive also to full- were resistant highly to truncated that lacked FZD1,FZD2and FZD7 cells knockout triple Consistently, nanomolar levels of binding affinity. of FZD1and FZD7,with similar but to homologous the also CRDs cysteine-richthe domain (CRD)), cellular domain of FZD2(known as TcdB binds not only to extra the receptors for TcdB, respectively. dependent and CROP-independent that CSPG4 and FZD2are CROP- domain. findings These suggest truncated toxin that lacks CROP the toxinby full-length the both and the toxin, whereas FZD2is recognized is only by recognized full-length the cated version. Consistently, CSPG4 i t e Importantly, immunohistochem Importantly, The authors went on to show that d ,

–/– p a mice were more resistant to r t o f

S p r i n g e r CSPG4

N RESEARCH HIGHLIGHTS a t u r e .

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cells, r FZD2 i g h t s

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- r v e d . associated with treatment that of diseases are provide for therapeutic benefit the modulating may WNTsignalling C. difficile TcdB binding to FZDreceptors in role of inhibiting by WNTsignalling studies are required to elucidate the type-dependent manner. Further receptors, CSPG4 and FZD, inacell that TcdB binds to two different challengedwhen with TcdB. compared litter with wild-type mates significantly reduced in age colonic inthe epithelium was accumulationfluid and tissue dam abolished TcdB binding. In addition, TcdB with recombinant FZD2–CRD epithelium, whereas co-injection of binding to and entering colonic the segments in mice and showed TcdB TcdB directly into lumen the of colon in TcdB binding, authors the injected into role the of FZDreceptors organoid death. stream and WNTsignalling to led receptors, which blocked down with WNTfor binding to FZD down. Moreover, TcdB competed noids, and was enhanced effect this TcdB colonic than wild-type orga Fzd1 in nature19799 toxin B. are colonicepithelialreceptors for ORIGINAL ARTICLE Fzd7 In summary, findings the suggest Finally, to gain and and Nature –/– colonic Fzd2 pathogenesis and whether and whether pathogenesis (2016)

http://dx.doi.org/10.1038/

www.nature.com/nrmicro were knocked also C. difficile Tao, L.

organoids inwhich in vivo in et al . Frizzled Fzd7 Andrea Toit Du insights C. difficile infection. NPG –/–

mice mice

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