Increased cytokine production in interleukin-18 receptor alpha-deficient cells is associated with dysregulation of suppressors of cytokine signaling.
Since interleukin (IL)-18 is a proinflammatory cytokine, mice lacking IL-18 or its ligand-binding receptor (IL-18R) should exhibit decreased cytokine and chemokine production. Indeed, production of IL-1alpha, IL-6, and MIP-1alpha was reduced in IL-18 knock-out (ko) mouse embryonic fibroblast (MEF)-like cells. Unexpectedly, we observed a paradoxical 10-fold increase in IL-1beta-induced IL-6 production in MEF cells from mice deficient in the IL-18R alpha-chain (IL-18Ralpha) compared with wild type MEF. Similar increases were observed for IL-1alpha, MIP-1alpha, and prostaglandin E2. Likewise, coincubation with a specific IL-18Ralpha-blocking antibody augmented IL-1beta-induced cytokines in wild type and IL-18 ko MEF. Stable lines of IL-18Ralpha-depleted human A549 cells were generated using shRNA, resulting in an increase of IL-1beta-induced IL-1alpha, IL-6, and IL-8 compared to scrambled small hairpin RNA. In addition, we silenced IL-18Ralpha with small interfering RNA in primary human blood cells and observed up to 4-fold increases in the secretion of lipopolysaccharide- and IL-12/IL-18-induced IL-1beta, IL-6, interferon-gamma, and CD40L. Mechanistically, despite increases in Stat1 and IL-6, induction of SOCS1 and -3 (suppressor of cytokine signaling 1 and 3) was markedly reduced in the absence of IL-18Ralpha. Consistent with these observations, activation of the p38alpha/beta and ERK1/2 MAPKs and of protein kinase B/Akt increased in IL-18Ralpha ko MEF, whereas the negative feedback kinase MSK2 was more active in IL-18 ko cells. These data reveal a role for SOCS1 and -3 in the seemingly paradoxical hyperresponsive state in cells deficient in IL-18Ralpha, supporting the concept that IL-18Ralpha participates in both pro- and anti-inflammatory responses and that an endogenous ligand engages IL-18Ralpha to deliver an inhibitory signal.
Nold-Petry
Claudia A
CA
Department of Medicine, University of Colorado Denver, Aurora, Colorado 80045, USA.
Nold
Marcel F
MF
Nielsen
Jason W
JW
Bustamante
Alex
A
Zepp
Jarod A
JA
Storm
Kathleen A
KA
Hong
Jae-Woo
JW
Kim
Soo-Hyun
SH
Dinarello
Charles A
CA
D000818:Animals; D045744:Cell Line, Tumor; D016207:Cytokines / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D020382:Interleukin-18 / Q000235:genetics / Q000378:metabolism; D053727:Interleukin-18 Receptor alpha Subunit / Q000235:genetics / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics / Q000378:metabolism*
D016207:Cytokines; C508572:IL18R1 protein, human; C508573:Il18r1 protein, mouse; D020382:Interleukin-18; D053727:Interleukin-18 Receptor alpha Subunit; C108944:SOCS1 protein, human; C106644:SOCS3 protein, human; C491590:Socs1 protein, mouse; C491411:Socs3 protein, mouse; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D011494:Protein Kinases