Importantly, V-ATPase-dependent acidification of endocytotic vesicles seems to be essential for the following cytotoxic effects it triggers significant conformational changes of TcdA and TcdB that lead to the formation of channels in the vesicle's membrane and allow the toxin N-termini to access the cytosol ( Barth et al., 2001 Giesemann et al., 2006 Schwan et al., 2011). The subsequent internalization includes (but is not restricted to) the clathrin-mediated endocytosis (CME) pathway ( Papatheodorou et al., 2010 Gerhard et al., 2013 Chandrasekaran et al., 2016). It is known that at least two host receptor proteins support toxin attachment to the surface membrane of attacked cells ( LaFrance et al., 2015 Yuan et al., 2015). The preceding events have been also intensively investigated. This particular step is relatively well described and represents one of the major mechanisms underlying the cytopathic effects of TcdA and TcdB. Toxin-mediated inactivation of the small GTPases leads to disorganization of the cytoskeleton and changes in cell morphology, often denoted as cell rounding ( Just et al., 1995 Nottrott et al., 2007). The activated toxin N-termini produced in the last step inactivate members of the Ras superfamily of small GTPases via glucosylation ( Pfeifer et al., 2003 Just and Gerhard, 2005 Jank et al., 2007 Pruitt et al., 2010). ( Voth and Ballard, 2005) The major cytotoxic effects of TcdA and TcdB develop through a cascade of events that can be divided into three major steps: (a) binding, (b) endocytosis, and (c) translocation and release of the toxin's N-terminus from the endosomes into the host cytosol ( Tucker and Wilkins, 1991 Jank et al., 2007 Papatheodorou et al., 2010). ![]() These toxins play a central role in the development of the bacterial pathogenicity at the cellular level and of the clinical symptoms at the whole organism level. difficile bacteria produce two main virulence proteins, the large glucosyltransferases Toxin A (TcdA) and Toxin B (TcdB). difficile infections (CDI) range from light to very severe and life-threatening antibiotic-associated diarrhea and pseudomembranous colitis. difficile) is one of the leading causes of healthcare-related infections. The spore-producing gram-positive bacterium Clostridium difficile ( C. ![]() Identifying ClC-5 as a potential specific host ion transporter hijacked by toxins produced by pathogenic bacteria widens the horizon of possibilities for novel therapies of life-threatening gastrointestinal infections. Our data shed light on the intersection between the endocytotic cascade of host epithelial cells and the internalization pathway of the large virulence C. The dispensable role of electrogenic ion transport suggests that the voltage-dependent nonlinear capacitances of mammalian CLC transporters serve important physiological functions. difficile toxins by accelerating the acidification and maturation of vesicles of the early and early-to-late endosomal system. These data suggest that ClC-5 enhances the cytotoxic action of C. In addition, the transport-incompetent mutant ClC-5 E268Q similarly enhanced both endosomal acidification and intoxication by TcdA but facilitated the internalization of the toxin to a lower extent. Impairing the cellular uptake of TcdA by deleting the toxin CROPs domain did not abolish the effects of ClC-5. In colon HT29 cells, 34% of internalized TcdA localized to ClC-5-containing vesicles defined by colocalization with Rab5, Rab4a, and Rab7 as early and early-to-late of endosomes but not as Rab11-containing recycling endosomes. In accordance with the established physiological function of ClC-5, its expression lowered the endosomal pH in HEK293T cells by approximately 0.6 units and enhanced approximately 5-fold the internalization of TcdA. Enhanced intoxication by TcdA and TcdB was observed in cells expressing ClC-5 but not ClC-4, another chloride/proton exchanger with similar function but different localization. We investigated the role of ClC-5, a chloride/proton exchanger expressed in the endosomes of gastrointestinal epithelial cells, in the activation and processing of C. ![]() difficile toxins TcdA and TcdB invade host intestinal epithelia by endocytosis and use the acidic environment of intracellular vesicles for further processing and activation.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |