Wiskott-Aldrich Syndrome Protein IsAssociated with theAdapter Protein Grb2andtheEpidermal Growth Factor Receptor inLiving Cells

Srchomology domains [i.e., Srchomology domain2(SH2) andSrchomology domain3 (SH3)] play acritical role inlinking receptor tyrosine kinases todownstream signaling networks. A well-defined function oftheSH3-SH2-SH3 adapter Grb2istolink receptor tyrosine kinases, suchastheepidermal growth factor receptor (EGFR), tothep2lrassignaling pathway. Grb2hasalsobeenimplicated toplaya roleingrowth factorregulated actin assembly andreceptor endocytosis, although theunderlying mechanisms remain unclear. Inthis study, weshowthat Grb2interacts through itsSH3domains with thehumanWiskott-Aldrich syndrome protein (WASp), whichplays arole inregulation oftheactin cytoskeleton. We findthat WASpisexpressed inavariety ofcell types and isexclusively cytoplasmic. Although theN-terminal SH3domainofGrb2bindssignificantly stronger thantheC-terminal SH3domaintoWASp,full-length Grb2showsthe strongest binding. Bothphosphorylation ofWASpanditsinteraction withGrb2, aswell aswithanother adapter protein Nck,remain constitutive inserum-starved orepidermal growth factor-stimulated