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Membrane insertion of anthrax protective antigen and cytoplasmic delivery of lethal factor occur at different stages of the endocytic pathway.

Abrami L, Lindsay M, Parton RG, Leppla SH, van der Goot FG - J. Cell Biol. (2004)

Bottom Line: The resulting complex is then endocytosed.Via mechanisms that depend on the vacuolar ATPase and require membrane insertion of PA, LF and EF are ultimately delivered to the cytoplasm where their targets reside.Here, we show that membrane insertion of PA already occurs in early endosomes, possibly only in the multivesicular regions, but that subsequent delivery of LF to the cytoplasm occurs preferentially later in the endocytic pathway and relies on the dynamics of internal vesicles of multivesicular late endosomes.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Molecular Medicine, University of Geneva, 1 rue Michel Servet, Geneva, Switzerland 1211.

ABSTRACT
The protective antigen (PA) of anthrax toxin binds to a cell surface receptor, undergoes heptamerization, and binds the enzymatic subunits, the lethal factor (LF) and the edema factor (EF). The resulting complex is then endocytosed. Via mechanisms that depend on the vacuolar ATPase and require membrane insertion of PA, LF and EF are ultimately delivered to the cytoplasm where their targets reside. Here, we show that membrane insertion of PA already occurs in early endosomes, possibly only in the multivesicular regions, but that subsequent delivery of LF to the cytoplasm occurs preferentially later in the endocytic pathway and relies on the dynamics of internal vesicles of multivesicular late endosomes.

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Endocytic routes of anthrax and diphtheria toxins. Based on the present work and the literature, we propose the following models for the delivery of anthrax lethal toxin (A) and DT (B) to the cytoplasm. Both toxins are internalized, transported to early endosomes, and sorted into the vesicular regions. (A) Anthrax toxin would be sorted into intraluminal vesicles whereby membrane insertion of PA and translocation of LF would result in trapping of the metalloprotease in the lumen of intraluminal vesicles. Once transported to late endosomes, back fusion of intraluminal vesicles with the limiting membrane would deliver LF to the cytoplasm. (B) In contrast, in early endosomes, DT would preferentially insert into the limiting membrane allowing direct delivery to the cytoplasm.
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fig5: Endocytic routes of anthrax and diphtheria toxins. Based on the present work and the literature, we propose the following models for the delivery of anthrax lethal toxin (A) and DT (B) to the cytoplasm. Both toxins are internalized, transported to early endosomes, and sorted into the vesicular regions. (A) Anthrax toxin would be sorted into intraluminal vesicles whereby membrane insertion of PA and translocation of LF would result in trapping of the metalloprotease in the lumen of intraluminal vesicles. Once transported to late endosomes, back fusion of intraluminal vesicles with the limiting membrane would deliver LF to the cytoplasm. (B) In contrast, in early endosomes, DT would preferentially insert into the limiting membrane allowing direct delivery to the cytoplasm.

Mentions: Based on the present data, we would like to propose the following models for the modes of delivery of anthrax lethal and DTs. Both toxins are internalized via clathrin-coated pits (Moya et al., 1985; Abrami et al., 2003) and transported to early endosomes where they are preferentially sorted to the vesicular regions (Fig. 5, A and B) as suggested by the fact that neither toxin affects lflF cells (40°C), which lack vesicular regions in early endosomes due to degradation of ε-COP. From that point, the pathways of the two toxins diverge. DT remains in the limiting membrane of early endosomes. Thus, upon membrane insertion, the ADP-ribosyltransferase is directly translocated from the endosomal lumen to the cytoplasm where it can reach EF-2 (Fig. 5 B). In contrast, the LF–PAheptamer complex is sorted into nascent intraluminal vesicles. Thus, upon PAheptamer-mediated membrane translocation, LF does not reach the cytoplasm but the lumen of the intraluminal vesicles (Fig. 5 A). Upon subsequent budding of ECV/MVB from early endosomes, PAheptamer and LF containing intraluminal vesicles are transported to late endosomes. There, PAheptamer is rapidly degraded but this has no consequences because PA has already fulfilled its translocation function. LF, being in the lumen of the intraluminal vesicles is protected from degradative enzymes and awaits back fusion events with the limiting membrane to be freed into the cytoplasm.


Membrane insertion of anthrax protective antigen and cytoplasmic delivery of lethal factor occur at different stages of the endocytic pathway.

Abrami L, Lindsay M, Parton RG, Leppla SH, van der Goot FG - J. Cell Biol. (2004)

Endocytic routes of anthrax and diphtheria toxins. Based on the present work and the literature, we propose the following models for the delivery of anthrax lethal toxin (A) and DT (B) to the cytoplasm. Both toxins are internalized, transported to early endosomes, and sorted into the vesicular regions. (A) Anthrax toxin would be sorted into intraluminal vesicles whereby membrane insertion of PA and translocation of LF would result in trapping of the metalloprotease in the lumen of intraluminal vesicles. Once transported to late endosomes, back fusion of intraluminal vesicles with the limiting membrane would deliver LF to the cytoplasm. (B) In contrast, in early endosomes, DT would preferentially insert into the limiting membrane allowing direct delivery to the cytoplasm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2172425&req=5

fig5: Endocytic routes of anthrax and diphtheria toxins. Based on the present work and the literature, we propose the following models for the delivery of anthrax lethal toxin (A) and DT (B) to the cytoplasm. Both toxins are internalized, transported to early endosomes, and sorted into the vesicular regions. (A) Anthrax toxin would be sorted into intraluminal vesicles whereby membrane insertion of PA and translocation of LF would result in trapping of the metalloprotease in the lumen of intraluminal vesicles. Once transported to late endosomes, back fusion of intraluminal vesicles with the limiting membrane would deliver LF to the cytoplasm. (B) In contrast, in early endosomes, DT would preferentially insert into the limiting membrane allowing direct delivery to the cytoplasm.
Mentions: Based on the present data, we would like to propose the following models for the modes of delivery of anthrax lethal and DTs. Both toxins are internalized via clathrin-coated pits (Moya et al., 1985; Abrami et al., 2003) and transported to early endosomes where they are preferentially sorted to the vesicular regions (Fig. 5, A and B) as suggested by the fact that neither toxin affects lflF cells (40°C), which lack vesicular regions in early endosomes due to degradation of ε-COP. From that point, the pathways of the two toxins diverge. DT remains in the limiting membrane of early endosomes. Thus, upon membrane insertion, the ADP-ribosyltransferase is directly translocated from the endosomal lumen to the cytoplasm where it can reach EF-2 (Fig. 5 B). In contrast, the LF–PAheptamer complex is sorted into nascent intraluminal vesicles. Thus, upon PAheptamer-mediated membrane translocation, LF does not reach the cytoplasm but the lumen of the intraluminal vesicles (Fig. 5 A). Upon subsequent budding of ECV/MVB from early endosomes, PAheptamer and LF containing intraluminal vesicles are transported to late endosomes. There, PAheptamer is rapidly degraded but this has no consequences because PA has already fulfilled its translocation function. LF, being in the lumen of the intraluminal vesicles is protected from degradative enzymes and awaits back fusion events with the limiting membrane to be freed into the cytoplasm.

Bottom Line: The resulting complex is then endocytosed.Via mechanisms that depend on the vacuolar ATPase and require membrane insertion of PA, LF and EF are ultimately delivered to the cytoplasm where their targets reside.Here, we show that membrane insertion of PA already occurs in early endosomes, possibly only in the multivesicular regions, but that subsequent delivery of LF to the cytoplasm occurs preferentially later in the endocytic pathway and relies on the dynamics of internal vesicles of multivesicular late endosomes.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Molecular Medicine, University of Geneva, 1 rue Michel Servet, Geneva, Switzerland 1211.

ABSTRACT
The protective antigen (PA) of anthrax toxin binds to a cell surface receptor, undergoes heptamerization, and binds the enzymatic subunits, the lethal factor (LF) and the edema factor (EF). The resulting complex is then endocytosed. Via mechanisms that depend on the vacuolar ATPase and require membrane insertion of PA, LF and EF are ultimately delivered to the cytoplasm where their targets reside. Here, we show that membrane insertion of PA already occurs in early endosomes, possibly only in the multivesicular regions, but that subsequent delivery of LF to the cytoplasm occurs preferentially later in the endocytic pathway and relies on the dynamics of internal vesicles of multivesicular late endosomes.

Show MeSH
Related in: MedlinePlus