TLR3 mediates release of IL-1β and cell death in keratinocytes in a caspase-4 dependent manner

• Published in: Journal of dermatological science Vol. 72; no. 1; pp. 45 - 53
• Main Authors: Grimstad, Øystein, Husebye, Harald, Espevik, Terje
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ireland Ltd 01.10.2013
• Subjects: Apoptosis - immunology; Apoptosis - physiology; Carrier Proteins - genetics; Carrier Proteins - metabolism; Caspase 1 - genetics; Caspase 1 - metabolism; Caspase-4; Caspases - metabolism; Caspases, Initiator - genetics; Caspases, Initiator - metabolism; Cells, Cultured; Dermatology; Enzyme Activation; Humans; IL-1β; Inflammasomes - immunology; Inflammasomes - metabolism; Interleukin-1beta - genetics; Interleukin-1beta - metabolism; Keratinocytes; Keratinocytes - cytology; Keratinocytes - immunology; Keratinocytes - metabolism; NLR Family, Pyrin Domain-Containing 3 Protein; Poly I-C - pharmacology; Protein Precursors - genetics; Protein Precursors - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA, Small Interfering - genetics; Signal Transduction; Toll-Like Receptor 3 - antagonists & inhibitors; Toll-Like Receptor 3 - genetics; Toll-Like Receptor 3 - metabolism; Toll-like-receptor 3; Keratinocytes; IL-1β; Caspase-4; Toll-like-receptor 3
• ISSN: 0923-1811; 1873-569X
• DOI: 10.1016/j.jdermsci.2013.05.006

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. Conclusion 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.