• Beyaert, Rudy
• Haegman, Mira
• Schotte, Peter
• Janssens, Sophie
• Magez, Stefan
• Vercammen, Elisabeth
• Maelfait, Jonathan

Abstract

The cytokine interleukin (IL)-1beta is a key mediator of the inflammatory response and has been implicated in the pathophysiology of acute and chronic inflammation.IL-1beta is synthesized in response to many stimuli as an inactive pro-IL-1B precursor protein that is further processed by caspase-1 into mature IL-1beta, which is the secreted biologically active form of the cytokine.Although stimulation of membrane-bound Toll-like receptors (TLRs) up-regulates pro-IL-1beta expression, activation of caspase-1 is believed to be mainly initiated by cytosolic Nod-like receptors.In this study, we show that polyinosinic:polycytidylic acid (poly(I:C)) and lipopolysaccharide stimulation of macrophages induces pro-IL-1beta processing via a Toll/IL-1R domain-containing adaptor-inducing interferon-beta-dependent signaling pathway that is initiated by TLR3 and TRL4, respectively.Ribonucleic acid interference (RNAi)-mediated knockdown of the intracellular receptors NALP3 or MDA5 did not affect poly (I:C)-induced pro-IL-1beta processing.Surprisingly, poly (I:C)- and LPS-induced pro-IL-1 beta processing still occurred in caspase-1-deficient cells.In contrast,pro-IL-1beta processing was inhibited by caspase-8 peptide inhibitors, crmA or vFLIP expression, and caspase-8 knockdown via RNAi, indicating an essential role for caspase-8.Moreover, recombinant caspase-8 was able to cleave pro-IL-1beta in vitro at exactly the same site as caspase-1.These results implicate a novel role for caspase-8 in the production of biologically active IL-1beta in response to TLR3 and TLR4 stimulation.

Topics

• impedance spectroscopy
• activation