title: Legionella pneumophila induces cathepsin B-dependent necrotic cell death with releasing high mobility group box1 in macrophages.
abstract: BACKGROUND
  Legionella pneumophila (LPN) can cause a lethal infectious disease with a marked inflammatory response in humans. However, the mechanism of this severe inflammation remains poorly understood. Since necrosis is known to induce inflammation, we investigated whether LPN induces necrosis in macrophages. We also analyzed the involvement of lysosomal cathepsin B in LPN-induced cell death.
  
  
  METHODS
  The human monocytic cell line THP-1 was infected with LPN, NUL1 strain. MG132-treated cells were used as apoptotic control cells. After infection, the type of cell death was analyzed by using microscopy, LDH release and flow cytometry. As a proinflammatory mediator, high-mobility group box 1 (HMGB-1), was measured. Cathepsin B activity was also measured and the inhibitory effects of cathepsin B on LPN-induced cell death were analyzed.
  
  
  RESULTS
  THP-1 cells after treatment with high dose of LPN showed necrotic features with releasing HMGB-1. This necrosis and the HMGB-1 release were inhibited by a specific lysosomal cathepsin B inhibitor and were characterized by a rapid and high activation of cathepsin B that was not observed in apoptotic control cells. The necrosis was also accompanied by cathepsin B-dependent poly(ADP-ribose) polymerase (PARP) cleavage.
  
  
  CONCLUSIONS
  We demonstrate here that L. pneumophila rapidly induces cathepsin B-dependent necrosis in a dose-dependent manner and releases a proinflammatory mediator, HMGB-1, from macrophages. This report describes a novel aspect of the pathogenesis of Legionnaires' disease and provides a possible therapeutic target for the regulation of inflammation.
authors.affiliation: Department of Laboratory Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan.
authors.forename: Yoshitomo
authors.initials: Y
authors.lastname: Morinaga
authors.forename: Katsunori
authors.initials: K
authors.lastname: Yanagihara
authors.forename: Shigeki
authors.initials: S
authors.lastname: Nakamura
authors.forename: Hiroo
authors.initials: H
authors.lastname: Hasegawa
authors.forename: Masafumi
authors.initials: M
authors.lastname: Seki
authors.forename: Koichi
authors.initials: K
authors.lastname: Izumikawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kakeya
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Yamada
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kohno
authors.forename: Shimeru
authors.initials: S
authors.lastname: Kamihira
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002401:Cathepsin B / Q000378:metabolism*; D002460:Cell Line; D005260:Female; D024243:HMGB1 Protein / Q000378:metabolism*; D006801:Humans; D016952:Legionella pneumophila / Q000502:physiology*; D008264:Macrophages / Q000378:metabolism* / Q000382:microbiology* / Q000473:pathology; D051379:Mice; D009336:Necrosis / Q000382:microbiology / Q000503:physiopathology
chemical_list: D024243:HMGB1 Protein; D002401:Cathepsin B; C533915:Ctsb protein, mouse