Myddosome clustering in IL-1 receptor signaling regulates the formation of an NF-kB activating signalosome
Signaling pathways can produce digital invariant outputs and analog outputs that scale with the amount of stimulation. In IL-1 receptor (IL-1R) signaling both types of outputs require the Myddosome, a multi-protein complex. The Myddosome is required for polyubiquitin chain formation and NF-kB signaling. However, the ways in which these signals are spatially and temporally regulated to drive switch-like and proportional outcomes is not understood. We find that during IL-1R signaling, Myddosomes dynamically re-organize into large, multi-Myddosome clusters at the cell membrane. Blockade of Myddosome clustering using nanoscale extracellular barriers reduces NF-kB activation. We find that Myddosomes function as a scaffold that assembles an NF-kB signalosome consisting of E3-ubiquitin ligases TRAF6 and LUBAC, K63/M1-linked polyubiquitin chains, phospho-IKK, and phospho-p65. This signalosome preferentially assembles at regions of high Myddosome density, which enhances the recruitment of TRAF6 and LUBAC. Extracellular barriers that restrict Myddosome clustering perturbed the recruitment of both ligases. We found that LUBAC was especially sensitive to clustering with a sevenfold lower recruitment to single Myddosomes than clustered Myddosomes. This data reveals that the clustering behavior of Myddosome provides the basis for digital and analog IL-1R signaling.