title: Itk functions to control actin polymerization at the immune synapse through localized activation of Cdc42 and WASP.
abstract: Actin polymerization at the immune synapse is required for T cell activation and effector function; however, the relevant regulatory pathways remain poorly understood. We showed previously that binding to antigen presenting cells (APCs) induces localized activation of Cdc42 and Wiskott-Aldrich Syndrome protein (WASP) at the immune synapse. Several lines of evidence suggest that Tec kinases could interact with WASP-dependent actin regulatory processes. Since T cells from Rlk-/-, Itk-/-, and Rlk-/- x Itk-/- mice have defects in signaling and development, we asked whether Itk or Rlk function in actin polymerization at the immune synapse. We find that Itk-/- and Rlk-/- x Itk-/- T cells are defective in actin polymerization and conjugate formation in response to antigen-pulsed APCs. Itk functions downstream of the TCR, since similar defects were observed upon TCR engagement alone. Using conformation-specific probes, we show that although the recruitment of WASP and Arp2/3 complex to the immune synapse proceeds normally, the localized activation of Cdc42 and WASP is defective. Finally, we find that the defect in Cdc42 activation likely stems from a requirement for Itk in the recruitment of Vav to the immune synapse. Our results identify Itk as a key element of the pathway leading to localized actin polymerization at the immune synapse.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology*; D018797:Cell Cycle Proteins; D004789:Enzyme Activation; D007109:Immunity / Q000502:physiology; D051379:Mice; D008856:Microscopy, Fluorescence; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051567:Proto-Oncogene Proteins c-vav; D013154:Spleen / Q000166:cytology; D013601:T-Lymphocytes / Q000276:immunology*; D051316:Wiskott-Aldrich Syndrome Protein; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D000199:Actins; D018797:Cell Cycle Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; C496619:Vav1 protein, mouse; C495768:Was protein, mouse; D051316:Wiskott-Aldrich Syndrome Protein; D011505:Protein-Tyrosine Kinases; C080813:emt protein-tyrosine kinase; D020764:cdc42 GTP-Binding Protein