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Pneumolysin activates macrophage lysosomal membrane permeabilization and executes apoptosis by distinct mechanisms without membrane pore formation

Pneumolysin activates macrophage lysosomal membrane permeabilization and executes apoptosis by distinct mechanisms without membrane pore formation
Pneumolysin activates macrophage lysosomal membrane permeabilization and executes apoptosis by distinct mechanisms without membrane pore formation

Intracellular killing of Streptococcus pneumoniae is complemented by induction of macrophage apoptosis. Here, we show that the toxin pneumolysin (PLY) contributes both to lysosomal/phagolysosomal membrane permeabilization (LMP), an upstream event programing susceptibility to apoptosis, and to apoptosis execution via a mitochondrial pathway, through distinct mechanisms. PLY is necessary but not sufficient for the maximal induction of LMP and apoptosis. PLY's ability to induce both LMP and apoptosis is independent of its ability to form cytolytic pores and requires only the first three domains of PLY. LMP involves TLR (Toll-like receptor) but not NLRP3/ASC (nucleotide-binding oligomerization domain [Nod]-like receptor family, pyrin domain-containing protein 3/apoptosis-associated speck-like protein containing a caspase recruitment domain) signaling and is part of a PLY-dependent but phagocytosis-independent host response that includes the production of cytokines, including interleukin-1 beta (IL-1β). LMP involves progressive and selective permeability to 40-kDa but not to 250-kDa fluorescein isothiocyanate (FITC)-labeled dextran, as PLY accumulates in the cytoplasm. In contrast, the PLY-dependent execution of apoptosis requires phagocytosis and is part of a host response to intracellular bacteria that also includes NO generation. In cells challenged with PLY-deficient bacteria, reconstitution of LMP using the lysomotrophic detergent LeuLeuOMe favored cell necrosis whereas PLY reconstituted apoptosis. The results suggest that PLY contributes to macrophage activation and cytokine production but also engages LMP. Following bacterial phagocytosis, PLY triggers apoptosis and prevents macrophage necrosis as a component of a broad-based antimicrobial strategy. This illustrates how a key virulence factor can become the focus of a multilayered and coordinated innate response by macrophages, optimizing pathogen clearance and limiting inflammation. Importance: Streptococcus pneumoniae, the commonest cause of bacterial pneumonia, expresses the toxin pneumolysin, which can make holes in cell surfaces, causing tissue damage. Macrophages, resident immune cells essential for responses to bacteria in tissues, activate a program of cell suicide called apoptosis, maximizing bacterial clearance and limiting harmful inflammation. We examined pneumolysin's role in activating this response. We demonstrate that pneumolysin did not directly form holes in cells to trigger apoptosis and show that pneumolysin has two distinct roles which require only part of the molecule. Pneumolysin and other bacterial factors released by bacteria that have not been eaten by macrophages activate macrophages to release inflammatory factors but also make the cell compartment containing ingested bacteria leaky. Once inside the cell, pneumolysin ensures that the bacteria activate macrophage apoptosis, rather than necrosis, enhancing bacterial killing and limiting inflammation. This dual response to pneumolysin is critical for an effective immune response to S. pneumoniae.

Animals, Apoptosis, Bacterial Proteins, Cells, Cultured, Humans, Intracellular Membranes, Lysosomes, Macrophages, Mice, Permeability, Streptococcus pneumoniae, Streptolysins, Journal Article, Research Support, Non-U.S. Gov't
2150-7511
Bewley, Martin A.
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Naughton, Michael
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Preston, Julie
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Mitchell, Andrea
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Holmes, Ashleigh
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Marriott, Helen M.
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Read, Robert C.
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Mitchell, Timothy J.
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Whyte, Moira K.B.
7c8b9870-17db-4359-ac5c-57ba9197ed82
Dockrell, David H.
a068c9bf-35b8-4c10-8f91-58639cfeca0b
Bewley, Martin A.
1412f184-67e0-4fe7-8692-db253d411471
Naughton, Michael
235a6edf-2c7c-44b7-a4c4-6180430ff514
Preston, Julie
eb55d4a3-5581-4596-b4a8-ed91c910091c
Mitchell, Andrea
565b1f82-ada5-4974-a843-7db42d9db28a
Holmes, Ashleigh
a3195eff-246d-4fd9-877c-6a432a21828c
Marriott, Helen M.
34ca8904-d637-4081-b34c-12be45ecef9f
Read, Robert C.
b5caca7b-0063-438a-b703-7ecbb6fc2b51
Mitchell, Timothy J.
56ddfd4d-d6f7-4250-8864-17f156904f95
Whyte, Moira K.B.
7c8b9870-17db-4359-ac5c-57ba9197ed82
Dockrell, David H.
a068c9bf-35b8-4c10-8f91-58639cfeca0b

Bewley, Martin A., Naughton, Michael, Preston, Julie, Mitchell, Andrea, Holmes, Ashleigh, Marriott, Helen M., Read, Robert C., Mitchell, Timothy J., Whyte, Moira K.B. and Dockrell, David H. (2014) Pneumolysin activates macrophage lysosomal membrane permeabilization and executes apoptosis by distinct mechanisms without membrane pore formation. mBio, 5 (5). (doi:10.1128/mBio.01710-14).

Record type: Article

Abstract

Intracellular killing of Streptococcus pneumoniae is complemented by induction of macrophage apoptosis. Here, we show that the toxin pneumolysin (PLY) contributes both to lysosomal/phagolysosomal membrane permeabilization (LMP), an upstream event programing susceptibility to apoptosis, and to apoptosis execution via a mitochondrial pathway, through distinct mechanisms. PLY is necessary but not sufficient for the maximal induction of LMP and apoptosis. PLY's ability to induce both LMP and apoptosis is independent of its ability to form cytolytic pores and requires only the first three domains of PLY. LMP involves TLR (Toll-like receptor) but not NLRP3/ASC (nucleotide-binding oligomerization domain [Nod]-like receptor family, pyrin domain-containing protein 3/apoptosis-associated speck-like protein containing a caspase recruitment domain) signaling and is part of a PLY-dependent but phagocytosis-independent host response that includes the production of cytokines, including interleukin-1 beta (IL-1β). LMP involves progressive and selective permeability to 40-kDa but not to 250-kDa fluorescein isothiocyanate (FITC)-labeled dextran, as PLY accumulates in the cytoplasm. In contrast, the PLY-dependent execution of apoptosis requires phagocytosis and is part of a host response to intracellular bacteria that also includes NO generation. In cells challenged with PLY-deficient bacteria, reconstitution of LMP using the lysomotrophic detergent LeuLeuOMe favored cell necrosis whereas PLY reconstituted apoptosis. The results suggest that PLY contributes to macrophage activation and cytokine production but also engages LMP. Following bacterial phagocytosis, PLY triggers apoptosis and prevents macrophage necrosis as a component of a broad-based antimicrobial strategy. This illustrates how a key virulence factor can become the focus of a multilayered and coordinated innate response by macrophages, optimizing pathogen clearance and limiting inflammation. Importance: Streptococcus pneumoniae, the commonest cause of bacterial pneumonia, expresses the toxin pneumolysin, which can make holes in cell surfaces, causing tissue damage. Macrophages, resident immune cells essential for responses to bacteria in tissues, activate a program of cell suicide called apoptosis, maximizing bacterial clearance and limiting harmful inflammation. We examined pneumolysin's role in activating this response. We demonstrate that pneumolysin did not directly form holes in cells to trigger apoptosis and show that pneumolysin has two distinct roles which require only part of the molecule. Pneumolysin and other bacterial factors released by bacteria that have not been eaten by macrophages activate macrophages to release inflammatory factors but also make the cell compartment containing ingested bacteria leaky. Once inside the cell, pneumolysin ensures that the bacteria activate macrophage apoptosis, rather than necrosis, enhancing bacterial killing and limiting inflammation. This dual response to pneumolysin is critical for an effective immune response to S. pneumoniae.

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More information

Accepted/In Press date: 15 September 2014
e-pub ahead of print date: 7 October 2014
Additional Information: Copyright © 2014 Bewley et al.
Keywords: Animals, Apoptosis, Bacterial Proteins, Cells, Cultured, Humans, Intracellular Membranes, Lysosomes, Macrophages, Mice, Permeability, Streptococcus pneumoniae, Streptolysins, Journal Article, Research Support, Non-U.S. Gov't

Identifiers

Local EPrints ID: 417934
URI: https://eprints.soton.ac.uk/id/eprint/417934
ISSN: 2150-7511
PURE UUID: cf600edb-8ca0-40ce-978b-8b454b5a880c
ORCID for Robert C. Read: ORCID iD orcid.org/0000-0002-4297-6728

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Date deposited: 16 Feb 2018 17:31
Last modified: 19 Nov 2019 01:38

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