title: Clostridium difficile toxin A binds colonocyte Src causing dephosphorylation of focal adhesion kinase and paxillin.
abstract: Clostridium difficile toxin A impairs tight junction function of colonocytes by glucosylation of Rho family proteins causing actin filament disaggregation and cell rounding. We investigated the effect of toxin A on focal contact formation by assessing its action on focal adhesion kinase (FAK) and the adapter protein paxillin. Exposure of NCM460 human colonocytes to toxin A for 1 h resulted in complete dephosphorylation of FAK and paxillin, while protein tyrosine phosphatase activity was reduced. Blockage of toxin A-associated glucosyltransferase activity by co-incubation with UDP-2'3' dialdehyde did not reduce toxin A-induced FAK and paxillin dephosphorylation. GST-pull down and in vitro kinase activity experiments demonstrated toxin A binding directly to the catalytic domain of Src with suppression of its kinase activity. Direct binding of toxin A to Src, independent of any effect on protein tyrosine phosphatase or Rho glucosylation, inhibits Src kinase activity followed by FAK/paxillin inactivation. These mechanisms may contribute to toxin A inhibition of colonocyte focal adhesion that occurs in human colonic epithelium exposed to toxin A.
authors.affiliation: Department of Life Science, College of Natural Science, Daejin University, Pochen, Kyungkido, Republic of Korea.
authors.forename: Ho
authors.initials: H
authors.lastname: Kim
authors.forename: Sang Hoon
authors.initials: SH
authors.lastname: Rhee
authors.forename: Charalabos
authors.initials: C
authors.lastname: Pothoulakis
authors.forename: J Thomas
authors.initials: JT
authors.lastname: LaMont
mesh_terms: D001427:Bacterial Toxins / Q000494:pharmacology*; D002460:Cell Line; D003106:Colon / Q000166:cytology*; D004768:Enterotoxins / Q000494:pharmacology*; D004848:Epithelium; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism*; D006801:Humans; D051419:Paxillin / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D019061:src-Family Kinases / Q000037:antagonists & inhibitors*
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D051419:Paxillin; C041348:tcdA protein, Clostridium difficile; D051416:Focal Adhesion Protein-Tyrosine Kinases; D019061:src-Family Kinases