title: The retromer component sorting nexin-1 is required for efficient retrograde transport of Shiga toxin from early endosome to the trans Golgi network.
abstract: The mammalian retromer complex is a multi-protein complex that regulates retrograde transport of the cation-independent mannose 6-phosphate receptor (CI-MPR) from early endosomes to the trans Golgi network (TGN). It consists of two subcomplexes: a membrane-bound coat comprising sorting nexin-1 (SNX1) and possibly sorting nexin-2 (SNX2), and a cargo-selective subcomplex, composed of VPS26, VPS29 and VPS35. In addition to the retromer, a variety of other protein complexes has been suggested to regulate endosome-to-TGN transport of not only the CI-MPR but a wide range of other cargo proteins. Here, we have examined the role of SNX1 and SNX2 in endosomal sorting of Shiga and cholera toxins, two toxins that undergo endosome-to-TGN transport en route to their cellular targets located within the cytosol. By using small interfering RNA (siRNA)-mediated silencing combined with single-cell fluorescent-toxin-uptake assays and well-established biochemical assays to analyze toxin delivery to the TGN, we have established that suppression of SNX1 leads to a significant reduction in the efficiency of endosome-to-TGN transport of the Shiga toxin B-subunit. Furthermore, we show that for the B subunit of cholera toxin, retrograde endosome-to-TGN transport is less reliant upon SNX1. Overall, our data establish a role for SNX1 in the endosome-to-TGN transport of Shiga toxin and are indicative for a fundamental difference between endosomal sorting of Shiga and cholera toxins into endosome-to-TGN retrograde transport pathways.
authors.affiliation: The Henry Wellcome Integrated Signalling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, BS8 1TD, UK.
authors.forename: Miriam V
authors.initials: MV
authors.lastname: Bujny
authors.forename: Vincent
authors.initials: V
authors.lastname: Popoff
authors.forename: Ludger
authors.initials: L
authors.lastname: Johannes
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Cullen
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002772:Cholera Toxin / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D046912:Multiprotein Complexes; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D022621:Shiga Toxin / Q000378:metabolism*; D058305:Sorting Nexins; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D046912:Multiprotein Complexes; D020033:Protein Isoforms; D058305:Sorting Nexins; D033921:Vesicular Transport Proteins; D022621:Shiga Toxin; D002772:Cholera Toxin