Stimulation of Toll-like receptor 3 and 4 induces interleukin-1beta maturation by caspase-8.
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-1beta 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 TLR4, 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-1beta 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.
Maelfait
Jonathan
J
Unit of Molecular Signal Transduction in Inflammation, Department for Molecular Biomedical Research, VIB, B-9052 Ghent, Belgium.
Vercammen
Elisabeth
E
Janssens
Sophie
S
Schotte
Peter
P
Haegman
Mira
M
Magez
Stefan
S
Beyaert
Rudi
R
D000818:Animals; D053181:Caspase 8 / Q000378:metabolism*; D002460:Cell Line; D005786:Gene Expression Regulation; D006801:Humans; D007249:Inflammation; D053583:Interleukin-1beta / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D034622:RNA Interference; D015398:Signal Transduction; D051196:Toll-Like Receptor 3 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
D053583:Interleukin-1beta; C495344:TLR3 protein, human; C519703:TLR3 protein, mouse; C495345:TLR4 protein, human; C493487:Tlr4 protein, mouse; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D053181:Caspase 8