The IκB kinase complex regulates the stability of cytokine-encoding mRNA induced by TLR-IL-1R by controlling degradation of regnase-1

ArticleinNature Immunology 12(12):1167-75 · December 2011with53 Reads
DOI: 10.1038/ni.2137 · Source: PubMed
Abstract
Toll-like receptor (TLR) signaling activates the inhibitor of transcription factor NF-κB (IκB) kinase (IKK) complex, which governs NF-κB-mediated transcription during inflammation. The RNase regnase-1 serves a critical role in preventing autoimmunity by controlling the stability of mRNAs that encode cytokines. Here we show that the IKK complex controlled the stability of mRNA for interleukin 6 (IL-6) by phosphorylating regnase-1 in response to stimulation via the IL-1 receptor (IL-1R) or TLR. Phosphorylated regnase-1 underwent ubiquitination and degradation. Regnase-1 was reexpressed in IL-1R- or TLR-activated cells after a period of lower expression. Regnase-1 mRNA was negatively regulated by regnase-1 itself via a stem-loop region present in the regnase-1 3' untranslated region. Our data demonstrate that the IKK complex phosphorylates not only IκBα, thereby activating transcription, but also regnase-1, thereby releasing a 'brake' on IL-6 mRNA expression.
    • "They respond to exogenous signals such as LPS or cytokines produced at the site of inflammation. These stimulants induce expression of MCPIP1 (Iwasaki et al., 2011; Matsushita et al., 2009). Simultaneously MCPIP1 influences the biology of macrophages. "
    [Show abstract] [Hide abstract] ABSTRACT: MCPIP1 and IER3 are recently described proteins essential for maintenance of immune homeostasis. IER3 is involved in the regulation of apoptosis and differentiation and has been shown lately to protect activated T cells and macrophages from apoptosis. MCPIP1 is an RNase critical for controlling inflammation-related mRNAs. MCPIP1 interacts with and degrades a set of stem-loop-containing mRNAs (including IL-6). Our results demonstrate the involvement of MCPIP1 in the regulation of IER3 mRNA levels. A dual luciferase assay revealed that over-expression of MCPIP1 resulted in a decrease of luciferase activity in the samples co-transfected with constructs containing luciferase CDS attached to IER3 3'UTR. We identified a stem-loop structure similar to that described to be important for destabilization of the IL-6 mRNA by MCPIP1. Examination of IER3 3'UTR sequence, structure and evolutionary conservation revealed that the identified stem-loop is buried within a bigger element. Deletion of this fragment abolished the regulation of IER3 3'UTR-containing transcript by MCPIP1. Finally, using immunofluorescence-combined single-molecule RNA FISH we have shown that the MCPIP1 protein co-localizes with IER3 mRNA. By this method we also proved that the presence of the wild-type NYN/PIN-like domain of MCPIP1 correlated with the decreased level of IER3 mRNA. RNA immunoprecipitation further confirmed the interaction of MCPIP1 with IER3 transcripts in vivo.
    Full-text · Article · Jul 2016
    • "In addition to transcriptional control, these mediator mRNAs are post-transcriptionally regulated [58]. It has been reported that the ribonuclease regnase-1 brakes IL-6 mRNA expression in resting macrophages, and NFκB signaling would cause phosphorylation and degradation of regnase-1, thereby releasing this brake [59]. AsFig. "
    [Show abstract] [Hide abstract] ABSTRACT: The tristetraprolin (TTP) family of mRNA-binding proteins contains three major members, Ttp, Zfp36l1, and Zfp36l2. Ttp down-regulates the stability of AU-rich element-containing mRNAs and functions as an anti-inflammation regulator. To examine whether other TTP family proteins also play roles in the inflammatory response, their expression profiles and the possible mRNA targets were determined in the knockdown cells. Ttp mRNA and protein were highly induced by lipopolysaccharide (LPS), whereas Zfp36l1 and Zfp36l2 mRNAs were down-regulated and their proteins were phosphorylated during early lipopolysaccharide stimulation. Biochemical and functional analyses exhibited that the decrease of Zfp36l2 mRNA was cross-regulated by Ttp. Knockdown of Zfp36l1 and Zfp36l2 increased the basal level of Mkp-1 mRNAs by prolonging its half-life. Increasing the expression of Mkp-1 inhibited the activation of p38 MAPK under lipopolysaccharide stimulation and down-regulated Tnfα, and Ttp mRNA. In addition, hyper-phosphorylation of Zfp36l1 might stabilize Mkp-1 expression by forming a complex with the adapter protein 14-3-3 and decreasing the interaction with deadenylase Caf1a. Our findings imply that the expression and phosphorylation of Zfp36l1 and Zfp36l2 may modulate the basal level of Mkp-1 mRNA to control p38 MAPK activity during lipopolysaccharide stimulation, which would affect the inflammatory mediators production. Zfp36l1 and Zfp36l2 are important regulators of the innate immune response.
    Full-text · Article · Jul 2015
    • "Overexpression of Reg1 suppressed the luciferase activity in an RNase-activity dependent manner (Figure 1K). Consistent with a previous report (Iwasaki et al., 2011), overexpression of Reg1 suppressed Reg1 3′ UTR containing nucleotides 1-210, but not in the case where nucleotides 1-200, which contains the SL, were absent. Collectively, Reg1-bound mRNAs obtained by RIP-Seq are indeed targeted by Reg1 for degradation. "
    [Show abstract] [Hide abstract] ABSTRACT: Regnase-1 and Roquin are RNA binding proteins essential for degradation of inflammation-related mRNAs and maintenance of immune homeostasis. However, their mechanistic relationship has yet to be clarified. Here, we show that, although Regnase-1 and Roquin regulate an overlapping set of mRNAs via a common stem-loop structure, they function in distinct subcellular locations: ribosome/endoplasmic reticulum and processing-body/stress granules, respectively. Moreover, Regnase-1 specifically cleaves and degrades translationally active mRNAs and requires the helicase activity of UPF1, similar to the decay mechanisms of nonsense mRNAs. In contrast, Roquin controls translationally inactive mRNAs, independent of UPF1. Defects in both Regnase-1 and Roquin lead to large increases in their target mRNAs, although Regnase-1 tends to control the early phase of inflammation when mRNAs are more actively translated. Our findings reveal that differential regulation of mRNAs by Regnase-1 and Roquin depends on their translation status and enables elaborate control of inflammation. Copyright © 2015 Elsevier Inc. All rights reserved.
    Full-text · Article · May 2015
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