Nitric oxide prevents IL-1beta and IFN-gamma-inducing factor (IL-18) release from macrophages by inhibiting caspase-1 (IL-1beta-converting enzyme).
Procytokine processing by caspase-1 is required for the maturation and release of IL-1beta and IFN-gamma-inducing factor (IGIF) (or IL-18) from activated macrophages (Mphi). Nitric oxide (NO) has emerged as a potent inhibitor of cysteine proteases. Here, we tested the hypothesis that NO regulates cytokine release by inhibiting IL-1beta-converting enzyme (ICE) or caspase-1 activity. Activated RAW264.7 cells released four to five times more IL-1beta, but not TNF-alpha, in the presence of the NO synthase inhibitor N(G)-monomethyl-L-arginine. Stimulated peritoneal Mphi from wild-type mice (inducible NO synthase (iNOS)+/+) also released more IL-1beta if exposed to N(G)-monomethyl-L-arginine, whereas Mphi from iNOS knockout mice (iNOS-/-) did not. Inhibition of NO synthesis in stimulated RAW264.7 cells also resulted in a threefold increase in intracellular caspase-1 activity. The NO donor S-nitroso-N-acetyl-DL-penicillamine inhibited caspase-1 activity in cells as well as the activity of purified recombinant caspase-1 and also prevented the cleavage of pro-IL-1beta and pro-IGIF by recombinant caspase-1. The inhibition of caspase-1 by NO was reversible by the addition of DTT, which is consistent with S-nitrosylation as the mechanism of caspase-1 inhibition. An in vivo role for the regulation of caspase-1 by NO was established in iNOS knockout animals, which exhibited significantly higher plasma levels of IL-1beta and IFN-gamma than their wild-type counterparts at 10 h following LPS injection. Taken together, these data indicate that NO suppresses IL-1beta and IGIF processing by inhibiting caspase-1 activity, providing evidence for a unique role for induced NO in regulating IL-1beta and IGIF release.
Department of Surgery, University of Pittsburgh, PA 15261, USA.
Y M
YM
Kim
R V
RV
Talanian
J
J
Li
T R
TR
Billiar
D000818:Animals; D019556:COS Cells; D020170:Caspase 1 / Q000378:metabolism*; D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007375:Interleukin-1 / Q000276:immunology / Q000378:metabolism*; D020382:Interleukin-18 / Q000276:immunology / Q000378:metabolism*; D008262:Macrophage Activation; D017737:Macrophages, Peritoneal / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000276:immunology*; D019323:omega-N-Methylarginine / Q000494:pharmacology
D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D007375:Interleukin-1; D020382:Interleukin-18; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D020170:Caspase 1