SMURF2 and breast cancer: Although a previous research has reported that SMURF1 can ubiquitinate HER2 when triggered by a compound JAC1 [29], SMURF1 targeted by TRAF4 has not been validated [24], whereas SMURF2 has been shown to be targeted by TRAF4 for promoting TGF-beta signaling and facilitating breast cancer metastasis [15].