Numb mediated degradation of Notch1 depends on the presence of an Itch-interacting domain of Numb (McGill et al. 2009). This was shown by expressing exogenous recombinant mouse Notch1, Numb and Itch in human embryonic kidney cell line HEK293 and mouse myogenic cell line C2C12. In support of this, recombinant human ITCH was shown to associate with recombinant mouse Notch1 indirectly and ubiquitinate it, in the absence of ligand, targeting it for degradation (Chastagner et al. 2008).