E3 ubiquitin ligase catalyzing the covalent attachment of ubiquitin moieties onto substrate proteins (, ). Involved in the TLR and IL-1 signaling pathways via interaction with the complex containing IRAK kinases and TRAF6 . Mediates 'Lys-63'-linked polyubiquitination of IRAK1 . Can activate AP1/JUN and ELK1 . Acts as a regulator of innate immunity by mediating 'Lys-63'-linked polyubiquitination of RIPK2 downstream of NOD1 and NOD2, thereby transforming RIPK2 into a scaffolding protein for downstream effectors, ultimately leading to activation of the NF-kappa-B and MAP kinases signaling (By similarity). Catalyzes 'Lys-63'-linked polyubiquitination of RIPK2 in parallel of XIAP (By similarity).
Highly expressed in brain, heart and testis, and at lower level in kidney, liver, lung, placenta, small intestine, spleen and stomach. Isoform 1 is not expressed in lung.