Inhibition of IRAK1 Ubiquitination Determines Glucocorticoid Sensitivity for TLR9-Induced Inflammation in Macrophages

Abstract

Inflammatory responses are controlled by signaling mediators that are regulated by various posttranslational modifications. Recently, transcription-independent functions for glucocorticoids (GC) in restraining inflammation have emerged, but the underlying mechanisms are unknown. In this study, we report that GC receptor (GR)–mediated actions of GC acutely suppress TLR9-induced inflammation via inhibition of IL-1R–associated kinase 1 (IRAK1) ubiquitination. β-TrCP–IRAK1 interaction is required for K48-linked ubiquitination of IRAK1 at Lys134 and subsequent membrane-to-cytoplasm trafficking of IRAK1 interacting partners TNFR-associated factor 6 and TAK1 that facilitates NF-κB and MAPK activation. Upon costimulation of macrophages with GC and TLR9-engaging ligand, GR physically interacts with IRAK1 and interferes with protein–protein interactions between β-TrCP and IRAK1. Ablation of GR in macrophages prevents GC-dependent suppression of β-TrCP–IRAK1 interactions. This GC-mediated suppression of IRAK1 activation is unique to TLR9, as GC treatment impairs TLR9 but not TLR4 ligand–induced K48-linked IRAK1 ubiquitination and trafficking of IRAK1 interacting partners. Furthermore, mutations in IRAK1 at Lys134 prevent TLR9 ligand–induced activation of inflammatory signaling mediators and synthesis of proinflammatory cytokines to an extent comparable to GC-mediated inhibition. Collectively, these findings identify a transcription-independent, rapid, and nongenomic GC suppression of TLR9 ligand–mediated IRAK1 ubiquitination as a novel mechanism for restraining acute inflammatory reactions.

Alternative MyD88 -Cyclin D1 signaling in breast cancer cells regulates TLR3 mediated cell proliferation

“…Activation of this signaling pathway further regulates IRAK1 mediated activation of TNF Receptor Associated Factor 6 (TRAF6) and Transforming growth factor beta-activated kinase 1 (TAK1) that further causes activation of TGF-Beta Activated Kinase 1 (TAB1). Thus our findings are well correlated with earlier reports for different convergent signaling pathways (Kong et al, 2017; Dong et al, 2006; Cui et al, 2012; Xiong et al, 2011, Johnsen and Whitehead 2006; Rhyasen and Starczynowski 2014, O’Neill and Bowie 2007, Conforti et al, 2010; Salaun et al, 2006; Gambara et al, 2014; Oshiumi et al, 2003; Yamamoto 2003, Ma et al, 2018, Klein and Assoian 2008, Alt et al, 2000).…”

“…But this proliferative effect has been perturbed by the addition of MyD88 inhibitor suggesting that the said effect of TLR 3 is mediated by the MyD88. In the present investigation, TLR3 activation through TLR3 ligand stimulated the expression of downstream signaling factors, including IRAK1, TRAF6, TAB1, and TAK1 and suppressed the MyD88 inhibitor that correlates with other signaling cascade (Kong et al, 2017). It has been reported that activation of other TLRs, in contrast to TLR3, can induce canonical pathway through MyD88 mediated activation of Interleukin 1 Receptor Associated Kinase 1(IRAK1).…”

“…Phosphorylation of IRAK1 helps in dissociation of TRAF6 complex from the membrane, and may facilitate formation of TRAF6, TAK1, and TAB1 complex in the cytosol. Later, the phosphorylated IRAK1 may get ubiquitinated and degraded as suggested by other research groups (Kong et al, 2017; Dong et al, 2006; Cui et al, 2012; Xiong et al, 2011). Thus, dissociation of the complex from the membrane may lead to phosphorylation of TAK1, as has been shown by research groups in other signal pathways (Cui et al, 2012).…”

Modeling Corticosteroid Pharmacogenomics and Proteomics in Rat Liver

“…To describe this pattern, model F assumed an inhibition of mRNA production by DR n in conjunction with a secondary, DR-mediated process inhibiting the rate of target protein degradation. The basis of this putative nongenomic, post-translational model of CS action is a recently identified molecular mechanism mediated by dexamethasone (Kong et al, 2017). The mRNA and protein expressions of 10 mRNA and their corresponding proteins were well described by this model.…”

“…Our understanding of the biology and mechanisms behind this observation is limited. However, recent studies in macrophages by Kong et al (2017) have provided key insights into a novel posttranslational mechanism of glucocorticoid signaling. They demonstrated that dexamethasone-activated GR acts in a rapid, transcription-independent manner to interact with an inflammation-related cytoplasmic protein IRAK1 and thus interferes with protein-protein interactions between IRAK1 and b-TrCP (an E3 ligase), and subsequently suppresses K48 linkage-specific ubiquitination of IRAK1.…”