TRAF4/SMURF2/HER2 complex formation was verified by co-immunoprecipitation analysis in four HER2-positive breast cancer cell lines studied (Fig. 5A and Supplementary Fig. S6A) and in transiently transfected HCC1954 cells and HEK293T cells (Supplementary Fig. S6B). Here, TRAF4 is linked to breast cancer.