Calcineurin negatively regulates TLR-mediated activation pathways.
In innate immunity, microbial components stimulate macrophages to produce antimicrobial substances, cytokines, other proinflammatory mediators, and IFNs via TLRs, which trigger signaling pathways activating NF-kappaB, MAPKs, and IFN response factors. We show in this study that, in contrast to its activating role in T cells, in macrophages the protein phosphatase calcineurin negatively regulates NF-kappaB, MAPKs, and IFN response factor activation by inhibiting the TLR-mediated signaling pathways. Evidence for this novel role for calcineurin was provided by the findings that these signaling pathways are activated when calcineurin is inhibited either by the inhibitors cyclosporin A or FK506 or by small interfering RNA-targeting calcineurin, and that activation of these pathways by TLR ligands is inhibited by the overexpression of a constitutively active form of calcineurin. We further found that IkappaB-alpha degradation, MAPK activation, and TNF-alpha production by FK506 were reduced in macrophages from mice deficient in MyD88, Toll/IL-1R domain-containing adaptor-inducing IFN-beta (TRIF), TLR2, or TLR4, whereas macrophages from TLR3-deficient or TLR9 mutant mice showed the same responses to FK506 as those of wild-type cells. Biochemical studies indicate that calcineurin interacts with MyD88, TRIF, TLR2, and TLR4, but not with TLR3 or TLR9. Collectively, these results suggest that calcineurin negatively regulates TLR-mediated activation pathways in macrophages by inhibiting the adaptor proteins MyD88 and TRIF, and a subset of TLRs.
Kang
Young Jun
YJ
Department of Biological Sciences, Stanford University, Stanford, CA 94305, USA. ykang@scripps.edu
Kusler
Brenda
B
Otsuka
Motoyuki
M
Hughes
Michael
M
Suzuki
Nobutaka
N
Suzuki
Shinobu
S
Yeh
Wen-Chen
WC
Akira
Shizuo
S
Han
Jiahuai
J
Jones
Patricia P
PP
D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D000818:Animals; D019703:Calcineurin / Q000235:genetics / Q000378:metabolism*; D065095:Calcineurin Inhibitors; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D051550:I-kappa B Kinase / Q000378:metabolism; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism; D016899:Interferon-beta / Q000378:metabolism; D051379:Mice; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D034741:RNA, Small Interfering / Q000235:genetics; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D015398:Signal Transduction; D051193:Toll-Like Receptors / Q000378:metabolism*
D033942:Adaptor Proteins, Vesicular Transport; D019703:Calcineurin; D065095:Calcineurin Inhibitors; D051550:I-kappa B Kinase; D050838:Interferon Regulatory Factor-3; D016899:Interferon-beta; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D034741:RNA, Small Interfering; D018124:Receptors, Tumor Necrosis Factor; D051193:Toll-Like Receptors; C476286:Ticam1 protein, mouse