title: Anthrolysin O and other gram-positive cytolysins are toll-like receptor 4 agonists.
abstract: Exposure of bone marrow-derived macrophages (BMDMs) to low concentrations of Bacillus anthracis lethal toxin (LT), whose catalytic subunit is lethal factor (LF), results in induction of a robust apoptotic response dependent on activation of Toll-like receptor (TLR)4. A similar TLR4-dependent apoptotic response is observed when BMDMs are infected with live B. anthracis (Sterne strain). However, TLR4 is considered to be a specific signaling receptor for lipopolysaccharide (LPS), a typical product of gram-negative bacteria, whereas B. anthracis is gram-positive. To understand how B. anthracis can activate TLR4, we analyzed its culture supernatants and found them to contain a potent TLR4-stimulating activity that can also induce apoptosis in macrophages in which the antiapoptotic p38 MAP kinase (whose activation is prevented by LF) was inhibited. Purification of this activity suggested it consists of anthrolysin O (ALO), a member of the cholesterol-dependent cytolysin (CDC) family. We show that recombinant ALO can activate TLR4 in a manner independent of LPS contamination and, together with LT, can induce macrophage apoptosis. We also provide genetic evidence that ALO is required for induction of macrophage apoptosis in response to infection with live B. anthracis and that other CDC family members share the ability to activate TLR4.
authors.affiliation: Laboratory of Gene Regulation and Signal Transduction, Dept. of Pharmacology, School of Medicine, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA.
authors.forename: Jin Mo
authors.initials: JM
authors.lastname: Park
authors.forename: Vincent H
authors.initials: VH
authors.lastname: Ng
authors.forename: Shin
authors.initials: S
authors.lastname: Maeda
authors.forename: Richard F
authors.initials: RF
authors.lastname: Rest
authors.forename: Michael
authors.initials: M
authors.lastname: Karin
mesh_terms: D000818:Animals; D000881:Anthrax / Q000378:metabolism / Q000473:pathology; D000942:Antigens, Bacterial / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects*; D001408:Bacillus anthracis / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification* / Q000633:toxicity*; D001427:Bacterial Toxins / Q000633:toxicity; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000819:agonists* / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism / Q000494:pharmacology / Q000633:toxicity*; D051379:Mice; D054353:Perforin; D052899:Pore Forming Cytotoxic Proteins; D011956:Receptors, Cell Surface / Q000819:agonists* / Q000378:metabolism; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D008562:Membrane Glycoproteins; D052899:Pore Forming Cytotoxic Proteins; D011956:Receptors, Cell Surface; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; C030325:anthrax toxin; C498000:anthrolysin O, Bacillus anthracis; D054353:Perforin; D048051:p38 Mitogen-Activated Protein Kinases