Pellino proteins are more than scaffold proteins in TLR/IL‐1R signalling: A role as novel RING E3–ubiquitin‐ligases

Abstract
Members of the Toll‐like receptor (TLR) and IL‐1 receptor (IL‐1R) family initiate signalling pathways that shape innate immunity. Pellino proteins have recently been implicated as evolutionary conserved scaffold proteins in TLR/IL‐1R signalling leading to nuclear factor‐κB and mitogen activated protein kinase‐dependent gene expression. We found that Pellino proteins contain a new RING‐like motif. Because RING motifs are a feature of a subclass of E3–ubiquitin‐ligases that target specific proteins for ubiquitination, we suggest that Pellino proteins are involved in TLR/IL‐1R signalling not only as scaffold proteins but also as RING E3–ubiquitin‐ligases. In support of this hypothesis we show that Pellino proteins induce IRAK‐1 polyubiquitination in a RING‐dependent manner. We further propose a model in which Pellino‐mediated IRAK‐1 polyubiquitination regulates TLR/IL‐1R signalling.

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