Calcineurin Negatively Regulates TLR-Mediated Activation Pathways

Abstract

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-κB, 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-κB, 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 IκB-α degradation, MAPK activation, and TNF-α production by FK506 were reduced in macrophages from mice deficient in MyD88, Toll/IL-1R domain-containing adaptor-inducing IFN-β (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.

TLR4 Promotes B Cell Maturation: Independence and Cooperation with B Lymphocyte-Activating Factor

“…5C). In myeloid cells, calcineurin activation without NF-kB recruitment by ITAM-coupled receptors was shown to inhibit TLR activation (29,30). Thus, a similar mechanism could play a role in BCR-mediated control of the LPS responsiveness in developing B cells, where the acute signal from the BCR, an ITAM-associated receptor, seems to inhibit TLR4 signaling through a calcineurindependent way.…”

“…In this study, we could not distinguish whether the decrease of CD23 + B cells upon BCR ligation was mainly due to induction of (29,30). As BCR is associated with ITAM-bearing molecules, we next asked whether a similar mechanism could play a role in BCRmediated regulation of LPS responsiveness in developing B lymphocytes.…”

Toll-Like Receptor-4 Modulates Survival by Induction of Left Ventricular Remodeling after Myocardial Infarction in Mice

“…PKC␦ has been shown recently to bind to a TLR signaling complex, namely TIRAP/Mal, and thus participate in TLR signaling (44). In addition, Kang et al showed a role of the phosphatase calcineurin in regulating TLR-activated pathways (30). Interestingly, all of these mediators are also believed to be key mediators in the development of LV remodeling (14).…”

“…Interestingly, such intracellular mediators have been shown to be involved in TLR signaling and regulation (29,30). To investigate whether or not these mediators are modulated by TLR4 after MI, we measured its cardiac protein activation.…”

Calcineurin deficiency decreases inflammatory lesions in transforming growth factor β1-deficient mice

“…Recently, it was reported that FK506 activates nuclear factor (NF)-kB and tumour necrosis factor (TNF)-a expression in macrophages, and this effect was shown to be through its inhibition of CN activity [25]. This suggests that innate immune responses may be up-regulated in Cnab -/-and DKO mice leading to increased proinflammatory cytokine production such as TNF-a, which can contribute to early lethality of DKO mice.…”