title: The pore-forming α-toxin from clostridium septicum activates the MAPK pathway in a Ras-c-Raf-dependent and independent manner.
abstract: Clostridium septicum is the causative agent of atraumatic gas gangrene, with α-toxin, an extracellular pore-forming toxin, essential for disease. How C. septicum modulates the host's innate immune response is poorly defined, although α-toxin-intoxicated muscle cells undergo cellular oncosis, characterised by mitochondrial dysfunction and release of reactive oxygen species. Nonetheless, the signalling events that occur prior to the initiation of oncosis are poorly characterised. Our aims were to characterise the ability of α-toxin to activate the host mitogen activated protein kinase (MAPK) signalling pathway both in vitro and in vivo. Treatment of Vero cells with purified α-toxin activated the extracellular-signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 arms of the MAPK pathway and stimulated the release of TNF-α in a dose-dependent manner. Studies using inhibitors of all three MAPK components suggested that activation of ERK occurred in a Ras-c-Raf dependent manner, whereas activation of JNK and p38 occurred by a Ras-independent mechanism. Toxin-mediated activation was dependent on efficient receptor binding and pore formation and on an influx of extracellular calcium ions. In the mouse myonecrosis model we showed that the MAPK pathway was activated in tissues of infected mice, implying that it has an important role in the disease process.
authors: Department of Microbiology, Monash University, Clayton, VIC 3800, Australia. achak27@gmail.com.
authors: Anjana
authors: A
authors: Chakravorty
authors: Department of Microbiology, Monash University, Clayton, VIC 3800, Australia. milena.awad@monash.edu.
authors: Milena M
authors: MM
authors: Awad
authors: Department of Microbiology, Monash University, Clayton, VIC 3800, Australia. jackie.k.cheung@monash.edu.
authors: Jackie K
authors: JK
authors: Cheung
authors: Department of Microbiology, Monash University, Clayton, VIC 3800, Australia. thomas.hiscox@monash.edu.
authors: Thomas J
authors: TJ
authors: Hiscox
authors: Department of Microbiology, Monash University, Clayton, VIC 3800, Australia. dena.lyras@monash.edu.
authors: Dena
authors: D
authors: Lyras
authors: Department of Microbiology, Monash University, Clayton, VIC 3800, Australia. julian.rood@monash.edu.
authors: Julian I
authors: JI
authors: Rood
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000235:genetics / Q000633:toxicity*; D002470:Cell Survival / Q000187:drug effects; D002522:Chlorocebus aethiops; D052557:Clostridium septicum / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D051379:Mice; D018482:Muscle, Skeletal / Q000201:enzymology; D052899:Pore Forming Cytotoxic Proteins / Q000235:genetics / Q000633:toxicity*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D018805:Sepsis / Q000201:enzymology / Q000382:microbiology; D013154:Spleen / Q000201:enzymology; D014709:Vero Cells
chemical_list: D001427:Bacterial Toxins; D052899:Pore Forming Cytotoxic Proteins; C064270:hemolytic toxin, Clostridium septicum; D019908:Proto-Oncogene Proteins c-raf; D048049:Extracellular Signal-Regulated MAP Kinases; D020930:MAP Kinase Kinase Kinases; C089319:Ras-dependent mitogen-activated protein kinase kinase kinase