Myddosomes in Toll-like receptor signaling-one to bind and rule them all.

Abstract

Toll-like receptors (TLRs) are innate immune sensors for the presence of pathogens and endogenous danger signals. TLR activation results in conserved intracellular signaling events that orchestrate inflammation and antimicrobial defense. While the identity and interplay of key TLR signaling components are well established, how these largely cytosolic proteins are physically connected is not well understood. For the activation of conserved intracellular signaling events, most TLRs engage the adapter MyD88 (myeloid differentiation primary response 88), which assembles into higher-order protein complexes, myddosomes. In their recent publication, Fisch et al. present evidence that oligomeric myddosomes detach from initiating TLRs and evolve into larger scaffolds that dynamically assemble not only proximal but also distal cytosolic elements required to execute the entire cascade of the TLR-MyD88 signaling pathway. Coinciding with decline in TLR signaling over time, myddosomes progressively recruit autophagy machinery that mediates myddosome clearance. These findings expand the current understanding of TLR signaling by positioning myddosomes as the central structural element that physically assembles the key executors and regulators of TLR-MyD88-dependent intracellular signaling cascades.