SMURF2 and breast carcinoma: 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).