title: Pasteurella multocida toxin- induced osteoclastogenesis requires mTOR activation.
abstract: BACKGROUND
  Pasteurella multocida toxin (PMT) is a potent inducer of osteoclast formation. Pigs suffering from an infection with toxigenic Pasteurella multocida strains develop atrophic rhinitis characterised by a loss of turbinate bones and conchae. However, on the molecular level the process of bone loss remains largely uncharacterised.
  
  
  RESULTS
  Recently it was found that PMT activates the serine/threonine kinase mammalian target of rapamycin (mTOR) in fibroblasts. Using RAW264.7 macrophages, we investigated the role of the mTOR complex 1 (mTORC1) in PMT-mediated osteoclast formation. PMT induces the differentiation of RAW264.7 macrophages into multinucleated, tartrate resistant acid phosphatase (TRAP) positive osteoclasts that are capable to resorb bone. In the presence of the mTORC1 inhibitor rapamycin, PMT was significantly less able to induce the formation of TRAP-positive osteoclasts. Accordingly, the resulting resorption of bone was strongly reduced. A major target of mTOR is the 70 kDa ribosomal protein S6 kinase 1 (p70 S6K1). Activated p70 S6K1 decreases the expression of programmed cell death protein 4 (PDCD4), a negative transcriptional regulator of osteoclastogenesis, at the protein and gene level. Ultimately this results in the activation of c-Jun, a component of the activator protein 1 (AP-1) complex, which is a major transcription factor for the induction of osteoclast-specific genes. We now demonstrate that c-Jun and its downstream target, the osteoclast-specific bone degrading protease cathepsin K, are upregulated upon PMT treatment in an mTOR-dependent manner.
  
  
  CONCLUSIONS
  Activation of mTOR signalling plays a central role in the formation of osteoclasts through the bacterial toxin PMT. On the molecular level, PMT-induced activation of mTOR leads to down regulation of PDCD4, a known repressor of AP-1 complex, culminating in the activation of c-Jun, an essential transcription factor for triggering osteoclastogenesis.
authors.affiliation: Zentrum für Infektiologie, Medizinische Mikrobiologie und Hygiene, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120, Heidelberg, Germany.
authors.forename: Bianca
authors.initials: B
authors.lastname: Kloos
authors.affiliation: Zentrum für Infektiologie, Medizinische Mikrobiologie und Hygiene, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120, Heidelberg, Germany.
authors.forename: Sushmita
authors.initials: S
authors.lastname: Chakraborty
authors.affiliation: Zentrum für Infektiologie, Medizinische Mikrobiologie und Hygiene, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120, Heidelberg, Germany.
authors.forename: Sonja G
authors.initials: SG
authors.lastname: Lindner
authors.affiliation: Center for Molecular Biomedicine (CMB), Department of Biochemistry, University of Jena, Hans Knöll Str. 2, 07745, Jena, Germany.|Integrated Research and Treatment Center, Center for Sepsis Control and Care (CSCC), Jena University Hospital, Erlanger Allee 101, 07747, Jena, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Noack
authors.affiliation: Department of Internal Medicine 3 and Institute of Clinical Immunology, University of Erlangen-Nuremberg, 91054, Erlangen, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Harre
authors.affiliation: Department of Internal Medicine 3 and Institute of Clinical Immunology, University of Erlangen-Nuremberg, 91054, Erlangen, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Schett
authors.affiliation: Institute of Toxicology, Medical Center of the University Mainz, Obere Zahlbacher Str. 67, 55131, Mainz, Germany.
authors.forename: Oliver H
authors.initials: OH
authors.lastname: Krämer
authors.affiliation: Zentrum für Infektiologie, Medizinische Mikrobiologie und Hygiene, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120, Heidelberg, Germany. kubatzky@uni-heidelberg.de.
authors.forename: Katharina F
authors.initials: KF
authors.lastname: Kubatzky
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D001427:Bacterial Toxins / Q000378:metabolism*; D001862:Bone Resorption / Q000378:metabolism / Q000382:microbiology / Q000473:pathology / Q000662:veterinary*; D056657:Cathepsin K / Q000378:metabolism; D002460:Cell Line; D008264:Macrophages / Q000378:metabolism / Q000382:microbiology* / Q000473:pathology; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D046912:Multiprotein Complexes / Q000378:metabolism*; D010010:Osteoclasts / Q000378:metabolism / Q000382:microbiology* / Q000473:pathology; D010326:Pasteurella Infections / Q000150:complications / Q000378:metabolism / Q000473:pathology / Q000662:veterinary*; D016979:Pasteurella multocida / Q000502:physiology*; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D015398:Signal Transduction; D013552:Swine; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D046912:Multiprotein Complexes; C062258:Pasteurella multocida toxin; C498443:Pdcd4 protein, mouse; D016755:Proto-Oncogene Proteins c-jun; D016601:RNA-Binding Proteins; D018808:Transcription Factor AP-1; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D056657:Cathepsin K