Despite constant contact with the large population of commensal bacteria, the colonic mucosa is normally hyporesponsive to these potentially proinflammatory signals. Here we report that the single immunoglobulin IL-1 receptor-related molecule (SIGIRR), a negative regulator for Toll-IL-1R signaling, plays a critical role in gut homeostasis, intestinal inflammation, and colitis-associated tumorigenesis by maintaining the microbial tolerance of the colonic epithelium. SIGIRR-deficient (Sigirr(-/-)) colonic epithelial cells displayed commensal bacteria-dependent homeostatic defects, as shown by constitutive upregulation of inflammatory genes, increased inflammatory responses to dextran sulfate sodium (DSS) challenge, and increased Azoxymethane (AOM)+DSS-induced colitis-associated tumorigenesis. Gut epithelium-specific expression of the SIGIRR transgene in the SIGIRR-deficient background reduced the cell survival of the SIGIRR-deficient colon epithelium, abrogated the hypersensitivity of the Sigirr(-/-) mice to DSS-induced colitis, and reduced AOM+DSS-induced tumorigenesis. Taken together, our results indicate that epithelium-derived SIGIRR is critical in controlling the homeostasis and innate immune responses of the colon to enteric microflora.

IRAK4 is a member of IL-1 receptor (IL-1R)–associated kinase (IRAK) family and has been shown to play an essential role in Toll-like receptor (TLR)–mediated signaling. We recently generated IRAK4 kinase-inactive knock-in mice to examine the role of kinase activity of IRAK4 in TLR-mediated signaling pathways. The IRAK4 kinase–inactive knock-in mice were completely resistant to lipopolysaccharide (LPS)- and CpG-induced shock, due to impaired TLR-mediated induction of proinflammatory cytokines and chemokines. Although inactivation of IRAK4 kinase activity did not affect the levels of TLR/IL-1R–mediated nuclear factor κB activation, a reduction of LPS-, R848-, and IL-1–mediated mRNA stability contributed to the reduced cytokine and chemokine production in bone marrow–derived macrophages from IRAK4 kinase–inactive knock-in mice. Both TLR7- and TLR9-mediated type I interferon production was abolished in plasmacytoid dendritic cells isolated from IRAK4 knock-in mice. In addition, influenza virus–induced production of interferons in plasmacytoid DCs was also dependent on IRAK4 kinase activity. Collectively, our results indicate that IRAK4 kinase activity plays a critical role in TLR-dependent immune responses.

The Toll-interleukin-1 receptor (TIR) 1 superfamily, a large family of proteins defined by the presence of an intracellular TIR domain, plays crucial roles in the immune response. This superfamily can be divided into two main subgroups, based on the extracellular domains: the immunoglobulin (Ig) domaincontaining receptors (1), and the leucine-rich repeat motifcontaining receptors (2). The Ig domain subgroup includes IL-1R1, IL-18 receptor, T1/ST2, and SIGIRR. IL-1 has been demonstrated to be a key player in the immune response and inflammatory response at both local and systemic levels by activating gene expression of such genes as MIP-2, KC, and C-reactive protein. IL-18 plays important roles in promoting Th1 cell differentiation and natural killer cell activation. T1/ ST2 (3) and SIGIRR (4), also known as TIR8 (5), have been shown to function as negative regulators for Toll-IL-1R-mediated signaling. The leucine-rich repeat motif subgroup consists of at least 11 Toll-like receptors (TLRs) (2, 6 -10). These receptors have received intense attention because different TLRs were found to be activated by specific pathogen products (8,(11)(12)(13)(14)(15)(16).Due to the similarity in their intracellular domain, the Toll-IL-1 receptors employ related yet distinct signaling components and downstream pathways. Genetic and biochemical studies revealed that IL-1R mediates a very complex pathway involving a cascade of kinases organized by multiple adapter molecules into signaling complexes, leading to activation of the transcription factors NF-B, ATF, and AP-1 (17-19). Based on published studies (20 -23), a model of the IL-1 pathway is postulated. Upon IL-1 stimulation, adapter molecule MyD88 (24) is first recruited to the IL-1 receptor, followed by the recruitment of two serine-threonine kinases, IRAK4 (25,26) and IRAK (27,28), and the adapter TRAF6 (29), resulting in the formation of the receptor complex (Complex I). During the formation of Complex I, IRAK and IRAK4 are activated, leading to the hyperphosphorylation of IRAK. Pellino 1⅐IRAK4⅐IRAK⅐TRAF6 complex is then formed, releasing these signaling molecules from the receptor (20). The released components interact with the membrane bound pre-associated TAK1⅐TAB1⅐TAB2⅐TAB3 (21, 23), resulting in the formation of Complex II (IRAK⅐TRAF6⅐TAK1⅐TAB1⅐TAB2⅐TAB3), followed by the translocation of TRAF6⅐TAK1⅐TAB1⅐TAB2⅐TAB3 (Complex III) from the membrane to the cytosol. The translocated Complex III interacts with additional factors in the cytosol, leading to TAK1 activation. It has been implicated that TRAF6 functions as part of a unique E3 complex, mediating TAK1 activation through nonclassical ubiquitination catalyzed by the ubiquitination proteins Ubc13 and Uev1A (30, 31). Once activated, TAK1 can directly phosphorylate IKK␤ and mitogenactivated protein kinase kinase 6, leading to the activation of both the JNK and NF-B signaling pathways (32-35). In addition to TAK1, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase 1 and 3 have also been i...

The objective of the present study is to investigate the possibility of preparing pure protein microspheres from regenerated silk fibroin (RSF). It is found that RSF microspheres, with predictable and controllable sizes ranging from 0.2 to 1.5 mm, can be prepared via mild selfassembling of silk fibroin molecular chains. The merits of this novel method include a rather simple production apparatus and no potentially toxic agents, such as surfactants, initiators, crosslinking agents, etc. The results show that the particle size and size distribution of RSF microspheres are greatly affected by the amount of ethanol additive, the freezing temperature and the concentration of silk fibroin. Finally, the mechanism of RSF microspheres formation is also discussed based on our experimental results.

Interleukin-1 (IL-1) receptor-associated kinase (IRAK) is phosphorylated after it is recruited to the receptor, subsequently ubiquitinated, and eventually degraded upon IL-1 stimulation. Although a point mutation changing lysine 134 to arginine (K134R) in IRAK abolished IL-1-induced IRAK ubiquitination and degradation, mutations of serines and threonines adjacent to lysine 134 to alanines ((S/T)A (131-144)) reduced IL-1-induced IRAK phosphorylation and abolished IRAK ubiquitination. Through the study of these IRAK modification mutants, we uncovered two parallel IL-1-mediated signaling pathways for NFB activation, TAK1-dependent and MEKK3-dependent, respectively. These two pathways bifurcate at the level of IRAK modification.