title: Interaction of the Wiskott-Aldrich syndrome protein with sorting nexin 9 is required for CD28 endocytosis and cosignaling in T cells.
abstract: The Wiskott-Aldrich syndrome protein (WASp) plays a major role in coupling T cell antigen receptor (TCR) stimulation to induction of actin cytoskeletal changes required for T cell activation. Here, we report that WASp inducibly binds the sorting nexin 9 (SNX9) in T cells and that WASp, SNX9, p85, and CD28 colocalize within clathrin-containing endocytic vesicles after TCR/CD28 costimulation. SNX9, implicated in clathrin-mediated endocytosis, binds WASp via its SH3 domain and uses its PX domain to interact with the phosphoinositol 3-kinase regulatory subunit p85 and product, phosphoinositol (3,4,5)P3. The data reveal ligation-induced CD28 endocytosis to be clathrin- and phosphoinositol 3-kinase-dependent and TCR/CD28-evoked CD28 internalization and NFAT activation to be markedly enhanced by SNX9 overexpression, but severely impaired by expression of an SNX9 mutant (SNX9DeltaPX) lacking p85-binding capacity. CD28 endocytosis and CD28-evoked actin polymerization also are impaired in WASp-deficient T cells. These findings suggest that SNX9 couples WASp to p85 and CD28 so as to link CD28 engagement to its internalization and to WASp-mediated actin remodeling required for CD28 cosignaling. Thus, the WASp/SNX9/p85/CD28 complex enables a unique interface of endocytic, actin polymerizing, and signal transduction pathways required for CD28-mediated T cell costimulation.
authors.affiliation: Department of Medicine, University of Toronto, Toronto, ON, Canada M5G 1X5.
authors.forename: Karen
authors.initials: K
authors.lastname: Badour
authors.forename: Mary K H
authors.initials: MK
authors.lastname: McGavin
authors.forename: Jinyi
authors.initials: J
authors.lastname: Zhang
authors.forename: Spencer
authors.initials: S
authors.lastname: Freeman
authors.forename: Claudia
authors.initials: C
authors.lastname: Vieira
authors.forename: Dominik
authors.initials: D
authors.lastname: Filipp
authors.forename: Michael
authors.initials: M
authors.lastname: Julius
authors.forename: Gordon B
authors.initials: GB
authors.lastname: Mills
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Siminovitch
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D018106:CD28 Antigens / Q000378:metabolism*; D002966:Clathrin / Q000378:metabolism; D004705:Endocytosis; D006801:Humans; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry; D015398:Signal Transduction; D058305:Sorting Nexins; D013601:T-Lymphocytes / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000737:chemistry* / Q000378:metabolism; D051316:Wiskott-Aldrich Syndrome Protein / Q000737:chemistry* / Q000378:metabolism; D018909:src Homology Domains
chemical_list: D000199:Actins; D018106:CD28 Antigens; D002966:Clathrin; C400533:SNX9 protein, human; D058305:Sorting Nexins; D033921:Vesicular Transport Proteins; D051316:Wiskott-Aldrich Syndrome Protein; D019869:Phosphatidylinositol 3-Kinases