Anthrax toxins cooperatively inhibit endocytic recycling by the Rab11/Sec15 exocyst

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Abstract

Bacillus anthracis is the causative agent of anthrax in humans and other mammals1,2. In lethal systemic anthrax, proliferating bacilli secrete large quantities of the toxins lethal factor (LF) and oedema factor (EF), leading to widespread vascular leakage and shock. Whereas host targets of LF (mitogen-activated protein-kinase kinases) and EF (cAMP-dependent processes)3 have been implicated in the initial phase of anthrax1,2, less is understood about toxin action during the final stage of infection. Here we use Drosophila melanogaster to identify the Rab11/Sec15 exocyst, which acts at the last step of endocytic recycling, as a novel target of both EF and LF. EF reduces levels of apically localized Rab11 and indirectly blocks vesicle formation by its binding partner and effector Sec15 (Sec15–GFP), whereas LF acts more directly to reduce Sec15–GFP vesicles. Convergent effects of EF and LF on Rab11/Sec15 inhibit expression of and signalling by the Notch ligand Delta and reduce DE-cadherin levels at adherens junctions. In human endothelial cells, the two toxins act in a conserved fashion to block formation of Sec15 vesicles, inhibit Notch signalling, and reduce cadherin expression at adherens junctions. This coordinated disruption of the Rab11/Sec15 exocyst by anthrax toxins may contribute to toxin-dependent barrier disruption and vascular dysfunction during B. anthracis infection.

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Figure 1: LF and EF synergistically inhibit Notch signalling.
Figure 2: LF and EF inhibit Rab11/Sec15-dependent recycling.
Figure 3: Conserved activity of anthrax toxins in mammals.

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Acknowledgements

We thank A. Kurciyan for help in analysing the effects of expressing wild-type and dominant-negative forms of Rab in Drosophila, A. Cooper and members of the E.B. and V.N. laboratories and H. Bellen for comments on the manuscript and suggestions. We thank S. Leppla for providing purified preparations of LF, EF and PA, S. Stibitz for B. anthracis mutants, and the following investigators for providing antibodies: R. Cohen (anti-Rab11), A. Parks (anti-Dl), K. Irvine (anti-Serrate) and J. Collier (anti-LF). Support for these studies was provided by National Institutes of Health (NIH) R01 grants AI070654 and NS29870 (E.B.), AI077780 (V.N.), an IRACDA NIH postdoctoral fellowship GM068524 (S.M.M.) and a Biomedical Research Fellowship from The Hartwell Foundation (S.M.M.).

Author information

All authors participated in designing the experiments. A.G. and B.C.-M. carried out the Drosophila experiments. S.M.M. and N.M.v.S. carried out the experiments with vertebrate cells and mice. E.B. wrote the manuscript with all other authors providing significant input.

Correspondence to Ethan Bier.

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The authors declare no competing financial interests.

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This file contains Supplementary Figures 1-12 with legends, Supplementary Tables 1-2, Supplementary Results, an additional reference and a list of Supplementary Microscopy Settings. (PDF 23277 kb)

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Guichard, A., McGillivray, S., Cruz-Moreno, B. et al. Anthrax toxins cooperatively inhibit endocytic recycling by the Rab11/Sec15 exocyst. Nature 467, 854–858 (2010) doi:10.1038/nature09446

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