IL1 induces the poly-ubiquitination and degradation of IRAK1.
Pellino1-3 possess E3 ligase activity and are believed to directly catalyse polyubiquitylation of IRAK1 (Xiao et al. 2008; Butler et al. 2007; Ordureau et al. 2008). They are capable of catalysing the formation of K63- and K48-linked polyubiquitin chains; the type of linkage is controlled by the collaborating E2 enzyme. All the Pellino proteins can combine with the E2 heterodimer UBE2N:UBE2V1 (Ubc13:Uev1a) to catalyze K63-linked ubiquitylation (Ordureau et al. 2008).
IRAK1 polyubiquitination was originally thought to tag IRAK1 for proteolysis by the proteasome, but more recently has been shown to involve K63-linked, not K48-linked polyubiquitination (Windheim et al. 2008; Conze et al. 2008), which is believed to have a scaffoling function. IRAK1 is ubiquitinated on K134 and K180; mutation of these sites impairs IL1R-mediated ubiquitination of IRAK1 (Conze et al. 2008). Some authors have proposed a role for TRAF6 as the E3 ubiquitin ligase that catalyzes polyubiquitination of IRAK1 (Conze et al. 2008) but this view has been refuted (Windheim et al. 2008, Xiao et al. 2008). The current consensus is that Pellino proteins are the physiologically-relevant IRAK1 E3 ubiquitin ligases.