title: Bacteroides fragilis toxin stimulates intestinal epithelial cell shedding and gamma-secretase-dependent E-cadherin cleavage.
abstract: Enterotoxigenic Bacteroides fragilis - organisms that live in the colon - secrete a metalloprotease toxin, B. fragilis toxin. This toxin binds to a specific intestinal epithelial cell receptor and stimulates cell proliferation, which is dependent, in part, on E-cadherin degradation and beta-catenin-T-cell-factor nuclear signaling. Gamma-secretase (or presenilin-1) is an intramembrane cleaving protease and is a positive regulator of E-cadherin cleavage and a negative regulator of beta-catenin signaling. Here we examine the mechanistic details of toxin-initiated E-cadherin cleavage. B. fragilis toxin stimulated shedding of cell membrane proteins, including the 80 kDa E-cadherin ectodomain. Shedding of this domain required biologically active toxin and was not mediated by MMP-7, ADAM10 or ADAM17. Inhibition of gamma-secretase blocked toxin-induced proteolysis of the 33 kDa intracellular E-cadherin domain causing cell membrane retention of a distinct beta-catenin pool without diminishing toxin-induced cell proliferation. Unexpectedly, gamma-secretase positively regulated basal cell proliferation dependent on the beta-catenin-T-cell-factor complex. We conclude that toxin induces step-wise cleavage of E-cadherin, which is dependent on toxin metalloprotease and gamma-secretase. Our results suggest that differentially regulated beta-catenin pools associate with the E-cadherin-gamma-secretase adherens junction complex; one pool regulated by gamma-secretase is important to intestinal epithelial cell homeostasis.
authors.affiliation: Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, 1550 Orleans St, CRB2 Bldg Suite 1M.05, Baltimore, MD 21231, USA.
authors.forename: Shaoguang
authors.initials: S
authors.lastname: Wu
authors.forename: Ki-Jong
authors.initials: KJ
authors.lastname: Rhee
authors.forename: Ming
authors.initials: M
authors.lastname: Zhang
authors.forename: Augusto
authors.initials: A
authors.lastname: Franco
authors.forename: Cynthia L
authors.initials: CL
authors.lastname: Sears
mesh_terms: D053829:Amyloid Precursor Protein Secretases / Q000378:metabolism*; D001427:Bacterial Toxins / Q000494:pharmacology*; D015820:Cadherins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D019073:HT29 Cells; D006801:Humans; D007422:Intestines / Q000166:cytology* / Q000187:drug effects; D020782:Matrix Metalloproteinases / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008666:Metalloendopeptidases / Q000494:pharmacology*; D008954:Models, Biological; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D017434:Protein Structure, Tertiary
chemical_list: D001427:Bacterial Toxins; D015820:Cadherins; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D053829:Amyloid Precursor Protein Secretases; C405031:Bacteroides fragilis toxin; D020782:Matrix Metalloproteinases; D008666:Metalloendopeptidases