Intracellular Trafficking of lnterleukin-1 Receptor I Requires Tollip

Interleukin-1 receptor (IL-1RI) is a master regulator of inflammation and innate Immunity. When triggered by IL-1 beta , IL-1RI aggregates with IL-1R-associated protein (IL-1RAcP) and forms a membrane proximal sig-nalosome that potently activates downstream signaling cascades. IL-1 beta also rapidly triggers endocytosis of IL-1 RI. Although internalization of IL-1RI significantly impacts signaling, very little is known about trafficking of IL-1 RI and therefore about precisely how endocytosis modulates the overall cellular response to IL-1 beta . Upon internalization, activated receptors are often sorted through endosomes and delivered to lysosomes for degradation. This is a highly regulated process that requires ubiquitination of cargo proteins as well as protein-sorting complexes that specifically recognize ubiquitinated cargo. Here, we show that IL-1 beta induces ubiquitination of IL-1RI and that via these attached ubiquitin groups, IL-1RI interacts with the ubiqultin-binding protein Tollip. By using an assay to follow trafficking of IL-1RI from the cell surface to late endosomes and lysosomes, we demonstrate that Tollip Is required for sorting of IL-1RI at late endosomes. In Tollip-deficient cells and cells expressing only mutated Tollip (incapable of binding IL-1RI and ubiquitin), IL-1RI accumulates on late endosomes and is not efficiently degraded. Furthermore, we show that IL-1RI interacts with Tom1, an ubiquitin-, clathrin-, and Tollip-binding protein, and that Tom1 knockdown also results in the accumulation of IL-1RI at late endosomes. Our findings suggest that Tollip functions as an endoso-mal adaptor linking IL-1RI, via Tom1, to the endosomal degradation machinery.