Smurf1 colocalizes with TRAF4. HeLa cells were transfected with expression constructs for TRAF4, catalytically inactive Smurf1C699A (Sf1CA), or both genes, and then examined by immunofluorescent staining. TRAF4 alone localized to clusters of unknown identity (a), whereas Smurf1 alone localized to predominantly the cell surface, including filipodia (b). Coexpression of the two proteins caused Smurf1 and TRAF4 to colocalize, in what seem to be patches at the cell surface (c–f). 4,6-Diamidino-2-phenylindole (DAPI) staining in panels a, b and f.