Cleavage-Mediated Regulation of Myd88 Signaling by Inflammasome-Activated Caspase-1.

Coordination among multiple signaling pathways ensures an appropriate immune response, where a signaling pathway may impair or augment another signaling pathway. Here, we report a negative feedback regulation of signaling through the key innate immune mediator MyD88 by inflammasome-activated caspase-1. NLRP3 inflammasome activation impaired agonist- or infection-induced TLR signaling and cytokine production through the proteolytic cleavage of MyD88 by caspase-1.

Extension and refinement of the recognition motif for Toll-like receptor 5 activation by flagellin.

TLRs sense conserved and essential molecular components of microbes that invade multicellular organisms. The wide range of TLR agonists, differing in size and shape, is recognized either through a single or a pair of binding sites on the ectodomains of TLRs. TLR5 recognizes bacterial flagellin through two distinct binding sites on the ectodomain, the first facilitating primary binding of flagellin and the second guiding receptor dimerization necessary for signaling.

The role of N-terminal segment and membrane association in MyD88-mediated signaling.

MyD88 is a central signaling mediator of innate immunity, composed of the N-terminal death (DD) and C-terminal Toll/interleukin-1 receptor (TIR) domain linked by an intermediary (INT) domain. We showed that the N-terminal domain (NTD), composed of apparently unstructured 21 amino-acid residues, is involved in localization and clustering of MyD88 and is required for the efficient signaling, since the deletion mutant is unable to reconstitute MyD88-dependent signaling. Furthermore, we found that the NTD peptide interacts with phosphatidic acid, which potentiates MyD88-mediated signaling through TLRs.

Activation of lymphoma-associated MyD88 mutations via allostery-induced TIR-domain oligomerization.

Myeloid differentiation 88 (MyD88) is the key signaling adapter of Toll-like and interleukin-1 receptors. Recurrent lymphoma-associated mutations, particularly Leu265Pro (L265P), within the MyD88 Toll/interleukin-1 receptor (TIR) domain sustain lymphoma cell survival due to constitutive nuclear factor κB signaling. We found that mutated TIR domains displayed an intrinsic propensity for augmented oligomerization and spontaneous formation of cytosolic Myddosome aggregates in lymphoma cell lines, mimicking the effect of dimerized TIR domains.

β-1,3-glucanase class III promotes spread of PVY and improves protein production.

Glucanases are enzymes regulating the size exclusion limit and permeability of plasmodesmata and play a role in biotic stress. In plant genomes, they are encoded as relatively large gene families divided into four classes. Most studies of plant virus interactions have focused on glucanases from classes I and II.

Determination of the physiological 2:2 TLR5:flagellin activation stoichiometry revealed by the activity of a fusion receptor.

Toll-like receptor 5 (TLR5) recognizes flagellin of most flagellated bacteria, enabling activation of the MyD88-dependent signaling pathway. The recently published crystal structure of a truncated zebrafish TLR5 ectodomain in complex with an inactive flagellin fragment indicated binding of two flagellin molecules to a TLR5 homodimer, however this complex did not dimerize in solution. In the present study, we aimed to determine the physiological stoichiometry of TLR5:flagellin activation by the use of a chimeric protein composed of an active flagellin fragment linked to the N-terminus of human TLR5 (SF-TLR5).

MARCKS as a negative regulator of lipopolysaccharide signaling.

Myristoylated alanine-rich C kinase substrate (MARCKS) is an intrinsically unfolded protein with a conserved cationic effector domain, which mediates the cross-talk between several signal transduction pathways. Transcription of MARCKS is increased by stimulation with bacterial LPS. We determined that MARCKS and MARCKS-related protein specifically bind to LPS and that the addition of the MARCKS effector peptide inhibited LPS-induced production of TNF-α in mononuclear cells.

The ectodomain of the Toll-like receptor 4 prevents constitutive receptor activation.

Toll-like receptor 4 (TLR4) is involved in activation of the innate immune response in a large number of different diseases. Despite numerous studies, the role of separate domains of TLR4 in the regulation of receptor activation is poorly understood. Replacement of the TLR4 ectodomain with LPS-binding proteins MD-2 or CD14 resulted in a robust ligand-independent constitutive activation comparable with the maximal stimulation of the receptor with LPS.

Therapeutic applications of nucleic acids as ligands for Toll-like receptors.

Intracellular TLRs, represented by TLRs 3, 7, 8 and 9, are specialized for the recognition of different types of microbe-derived nucleic acids. However, endogenous nucleic acids can also activate these TLRs, triggering autoimmunity. Nucleic acid-sensing TLRs initiate innate immune responses upon infection, but these receptors also initiate the development of protective adaptive immune responses.