title: TLR3 mediates release of IL-1β and cell death in keratinocytes in a caspase-4 dependent manner.
abstract: BACKGROUND
  Inflammation and timely cell death are important elements in host defence and healing processes. Keratinocytes express high levels of Toll-like receptor 3 (TLR3), and stimulation of the receptor with its ligand polyinosinic-polycytidylic acid (polyI:C) is a powerful signal for release of a variety of proinflammatory cytokines. Caspase-4 is required for maturation of pro-IL-1β through activation of caspase-1 in keratinocytes.
  
  
  METHODS
  TLR3 in keratinocytes was stimulated with polyI:C. Induction of messenger RNA of pro-IL-1β and inflammasomal components was measured using quantitative polymerase chain reaction methodology. Protein expression of IL-1β was analysed with ELISA and Western blot techniques. Activation of apoptotic caspases was measured with flow cytometry, and cytotoxicity was determined.
  
  
  RESULTS
  TLR3 induced release of substantial amounts of pro-IL-1β in keratinocytes. NLRP3 or ASC dependent processing of IL-1β into its cleaved bioactive form was found to be minimal. The release of IL-1β was due to polyI:C induced cell death that occurred through a caspase-4 dependent manner. Caspase-1 did not seem to be involved in the polyI:C induced cytotoxicity despite that TLR3 stimulation induced activation of caspase-1. In addition, the apoptotic caspases -8, -9 and -3/7 were activated by polyI:C.
  
  
  CONCLUSIONS
  TLR3 stimulation in keratinocytes induces a caspase-4 dependent release of pro-IL-1β, but further processing to active IL-1β is limited. Furthermore, TLR3 stimulation results in pyroptotic- and apoptotic cell death.
authors.affiliation: Centre of Molecular Inflammation Research, Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway; Department of Dermatology, St. Olavs Hospital HF, Trondheim University Hospital, Trondheim, Norway. Electronic address: oystein.grimstad@unn.no.
authors.forename: Øystein
authors.initials: Ø
authors.lastname: Grimstad
authors.forename: Harald
authors.initials: H
authors.lastname: Husebye
authors.forename: Terje
authors.initials: T
authors.lastname: Espevik
mesh_terms: D017209:Apoptosis / Q000276:immunology / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D020170:Caspase 1 / Q000235:genetics / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D053471:Caspases, Initiator / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004789:Enzyme Activation; D006801:Humans; D058847:Inflammasomes / Q000276:immunology / Q000378:metabolism; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D011070:Poly I-C / Q000494:pharmacology; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction; D051196:Toll-Like Receptor 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D058847:Inflammasomes; D053583:Interleukin-1beta; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C453881:NLRP3 protein, human; D011498:Protein Precursors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C495344:TLR3 protein, human; D051196:Toll-Like Receptor 3; C093516:CASP4 protein, human; D020169:Caspases; D053471:Caspases, Initiator; D020170:Caspase 1; D011070:Poly I-C
keywords: Caspase-4; IL-1β; Keratinocytes; Toll-like-receptor 3