Abstract
Toxins can invade cells by using a direct endosome-to-Golgi endocytic pathway that bypasses late endosomes/prelysosomes. This is also a route used by endogenous proteins, including GPP130, which is an integral membrane protein retrieved via the bypass pathway from endosomes to its steady-state location in the cis-Golgi. An RNA interference-based test revealed that GPP130 was required for efficient exit of Shiga toxin B-fragment from endosomes en route to the Golgi apparatus. Furthermore, two proteins whose Golgi targeting depends on endosome-to-Golgi retrieval in the bypass pathway accumulated in early/recycling endosomes in the absence of GPP130. GPP130 activity seemed specific to bypass pathway trafficking because the targeting of other tested proteins, including those retrieved to the Golgi via the more conventional late endosome route, was unaltered. Thus, a distally cycling Golgi protein mediates exit from endosomes and thereby underlies Shiga toxin invasion and retrieval-based targeting of other cycling Golgi proteins.
Highlights
Plant and bacterial toxins with enzymatic activity toward intracellular targets enter cells by endocytosis and in some cases, traffic to the Golgi apparatus and the endoplasmic reticulum (ER) before translocating into the cytosol where they exert their toxic effect
As determined by measuring Golgiassociated GPP130 staining intensity across the population of transfected cells, an average of 91 Ϯ 2% of cells had no detectable GPP130 staining, 7 Ϯ 2% showed faint GPP130 staining, and 4 Ϯ 1% had GPP130 staining comparable with control cells (n ϭ 5, Ͼ70 cells analyzed per experiment)
As an internal specificity control, the Golgi localization of a stably expressed protein, N-acetylglucosamine transferase T2 tagged with green fluorescent protein (NAGT2), whose targeting does not depend on the bypass pathway, was tested in the same cells
Summary
Plant and bacterial toxins with enzymatic activity toward intracellular targets enter cells by endocytosis and in some cases, traffic to the Golgi apparatus and the endoplasmic reticulum (ER) before translocating into the cytosol where they exert their toxic effect. Studies of toxin trafficking reveal novel aspects of membrane transport, offer possibilities for treatment of infectious diseases where toxins are involved, and offer new modes for drug delivery to the cytosolic compartment (Sandvig and van Deurs, 2000). Studies of Shiga toxin revealed, for the first time, retrograde trafficking from the plasma membrane to the ER (Sandvig et al, 1994), and in addition, exposed a novel endocytic pathway that bypasses late endosomes/prelysosomes en route from the cell surface to the Golgi (Johannes et al, 1997; Mallard et al, 1998). The bypass pathway is advantageous to toxins in that it allows trafficking to the Golgi apparatus along a route that prevents contact with degradative activities present in late endosomes/prelysosomes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
