Characterization of Interleukin-1 Receptor-associated Kinase in Normal and Endotoxin-tolerant Cells

Abstract

Interleukin-1 receptor-associated kinase (IRAK), a signal transducer for interleukin-1, has also been suggested to participate in the Toll-like receptor-mediated innate immune response to bacterial endotoxin lipopolysaccharide (LPS). Using the human promonocytic THP-1 cell line, we demonstrated that the endogenous IRAK is quickly activated in response to bacterial LPS stimulation, as measured by its in vitro kinase activity toward myelin basic protein. LPS also triggers the association of IRAK with MyD88, the adaptor protein linking IRAK to the Toll-like receptor/interleukin-1␤ receptor intracellular domain. Macrophage cells with prolonged LPS treatment become tolerant to additional dose of LPS and no longer express inflammatory cytokines. Endotoxin tolerance is a common phenomenon observed in blood from sepsis patients. We observed for the first time that the quantity of IRAK is greatly reduced in LPS-tolerant THP-1 cells, and its activity no longer responds to further LPS challenge. In addition, IRAK does not associate with MyD88 in the tolerant cells. Furthermore, application of AG126, a putative tyrosine kinase inhibitor, can substantially alleviate the LPS-induced cytokine gene expression and can also decrease IRAK level and activity. Our study indicates that IRAK is essential for LPS-mediated signaling and that cells may develop endotoxin tolerance by down-regulating IRAK.

Chronic Lymphocytic Leukemia: A Paradigm of Innate Immune Cross-Tolerance

“…This microRNA has been identified as critical for endotoxin-induced tolerance (45,(48)(49)(50)(51)(52)(53)(54). Shao et al (59) demonstrated the association between the miR-146a gene and severe sepsis in 226 septic patients.…”

“…Several investigators suggested that ET in human monocytes and mouse macrophages is associated with decreased TLR4-MyD88-IRAK complex formation, impairment of IRAK-1 activity, and TRAF6 expression (45)(46)(47)(48)(49). In this regard, miRNAs have emerged as an important regulatory mechanism for gene expression of a number of TLR4 pathway components during ET (49); in particular, miR146a is critical for ET development in human monocytes (48,(50)(51)(52)(53)(54). As shown in Fig.…”

Ligand-induced differential cross-regulation of Toll-like receptors 2, 4 and 5 in intestinal epithelial cells

“…Interestingly, the effects in these cell types are in agreement to that what we observed for intestinal mIC cl2 epithelial cells. Tolerance and cross-tolerance between TLR2 and TLR4 upon long-term (24 h) TLR activation has been attributed to changes in expression of TLRs, as well as to the function of several signaling molecules including IRAK-1, NF-B and MAP kinases (Dobrovolskaia et al, 2003;Li et al, 2000Li et al, , 2006Medvedev et al, 2000Medvedev et al, , 2002Otte et al, 2004;Wang et al, 2002). Whether differences in signalling molecules also contribute to the here observed TLR (cross)-regulation upon short-term TLR activation in mIC cl2 cells awaits detailed investigation of the cell signalling dynamics.…”

Sepsis-induced suppression of lung innate immunity is mediated by IRAK-M

“…We next examined expression of downstream regulators of the LPS/TLR4 signaling pathway. As IRAK-1 and IRAK-4 are essential components of signaling through the Toll/IL-1 receptor complex and have been shown to be downregulated in monocyte/macrophage cell lines rendered endotoxin tolerant (24,25), we first examined IRAK-1 and IRAK-4 expression in pulmonary macrophages isolated from septic and control animals. In these experiments, the total population of pulmonary macrophages (alveolar plus interstitial) was isolated from lung digests by adherence purification in order to obtain sufficient number of cells for mRNA and protein analysis.…”