The ubiquitin-like protein PLIC-1 or ubiquilin 1 inhibits TLR3-Trif signaling.

Background: The innate immune responses to virus infection are initiated by either Toll-like receptors (TLR3/7/8/9) or cytoplasmic double-stranded RNA (dsRNA)-recognizing RNA helicases RIG-I and MDA5. To avoid causing injury to the host, these signaling pathways must be switched off in time by negative regulators.

Methodology/principal Findings: Through yeast-two hybrid screening, we found that an ubiquitin-like protein named protein linking integrin-associated protein to cytoskeleton 1(PLIC-1 or Ubiquilin 1) interacted with the Toll/interleukin-1 receptor (TIR) domain of TLR4.

Ikaros stability and pericentromeric localization are regulated by protein phosphatase 1.

Ikaros encodes a zinc finger protein that is involved in gene regulation and chromatin remodeling. The majority of Ikaros localizes at pericentromeric heterochromatin (PC-HC) where it regulates expression of target genes. Ikaros function is controlled by posttranslational modification.

Recruitment of ikaros to pericentromeric heterochromatin is regulated by phosphorylation.

Ikaros encodes a zinc finger protein that is involved in heritable gene silencing. In hematopoietic cells, Ikaros localizes to pericentromeric heterochromatin (PC-HC) where it recruits its target genes, resulting in their activation or repression via chromatin remodeling. The function of Ikaros is controlled by post-translational modifications.

Flightless I homolog negatively modulates the TLR pathway.

To date, much of our knowledge about the signaling networks involved in the innate immune response has come from studies using nonphysiologic model systems rather than actual immune cells. In this study, we used a dual-tagging proteomic strategy to identify the components of the MyD88 signalosome in murine macrophages stimulated with lipid A. This systems approach revealed 16 potential MyD88-interacting partners, one of which, flightless I homolog (Fliih) was verified to interact with MyD88 and was further characterized as a negative regulator of the TLR4-MyD88 pathway.

In vivo dual-tagging proteomic approach in studying signaling pathways in immune response.

Up to date, few successes have been achieved to identify the signaling molecules directly from immune cells due to their low-abundance and dynamic nature. Here, we designed an in vivo dual-tagging quantitative approach that integrated epitope-tagging which allows single affinity purification of the natural complexes formed at real-time, and amino acid-coded mass tagging (AACT) that assists mass spectrometry-based quantitative measurement, to identify the specific components of a signaling complex formed in macrophage cells upon lipopolysaccharide (LPS) stimulation. The sensitivity and accuracy of this quantitative method are significantly higher than those of tandem affinity purification, because the multiple step of purifications are avoided to preserve weakly interacting molecules.

Common interaction surfaces of the toll-like receptor 4 cytoplasmic domain stimulate multiple nuclear targets.

Toll-like receptor 4 (TLR4) mediates the host response to lipopolysaccharide (LPS) by promoting the activation of pro- and anti-inflammatory cytokine genes. To activate each gene, numerous signal transduction pathways are required. The adaptor proteins MyD88 and TIRAP contribute to the activation of several and possibly all pathways via direct interactions with TLR4's Toll/interleukin-1 receptor (IL-1R) (TIR) domain.

A common mechanism for mitotic inactivation of C2H2 zinc finger DNA-binding domains.

Many nuclear proteins are inactivated during mitotic entry, presumably as a prerequisite to chromatin condensation and cell division. C2H2 zinc fingers define the largest transcription factor family in the human proteome. The linker separating finger motifs is highly conserved and resembles TGEKP in more than 5000 occurrences.