SMURF1 (Ebisawa et al. 2001), SMURF2 (Kavsak et al. 2000) or NEDD4L (Kuratomi et al. 2005) ubiquitin ligases, recruited to TGF-beta receptor complex through interaction with SMAD7, ubiquitinate both SMAD7 and/or TGF-beta receptor I (TGFBR1), targeting the complex for degradation. This was inferred from experiments using a recombinant mouse Smad7 with recombinant human ubiquitin ligases and TGF-beta receptors.