title: The X-linked lymphoproliferative disease gene product SAP associates with PAK-interacting exchange factor and participates in T cell activation.
abstract: SLAM (signaling lymphocyte activation molecule)-associated protein (SAP) is a Src homology 2 (SH2) domain-containing adaptor expressed in T cells and natural killer cells. Its essential role in immune responses is underscored by the recent finding that mutations in SAP result in a rare but fatal X-linked lymphoproliferative disease (XLP). Although SAP is known to associate with SLAM-family receptors, the exact molecular mechanism by which SAP regulates lymphocyte signaling remains elusive. We here report that in T cells, SAP associates with the PAK-interacting exchange factor (PIX), a guanine nucleotide exchange factor (GEF) specific for Rac/Cdc42 GTPases. Moreover, SAP, PIX, and an activated form of Cdc42 form a complex in mammalian cells. We demonstrate that the SAP-PIX interaction is specific and is mediated by the C-terminal region of the SAP SH2 domain and the PIX SH3 domain. We further show that SAP is required for the recruitment of PIX to the SLAM-family receptors. Interestingly, overexpression of SAP, but not its homolog EAT-2, leads to a synergistic activation of nuclear factor of activating T cells (NFAT) in combination with a calcium signal in T cells. This SAP-mediated activation appears to be receptor-dependent and can be blocked by a dominant negative form of PIX. Taken together, our data strongly suggest that, in addition to the known SAP-interacting kinase Fyn, PIX may be another key player in SAP-mediated T cell activation.
authors.affiliation: Department of Life Science and Biotechnology, Shanghai Jiaotong University, 1954 Huashan Road, Shanghai 200030, China.
authors.forename: Cuiping
authors.initials: C
authors.lastname: Gu
authors.forename: Stuart G
authors.initials: SG
authors.lastname: Tangye
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Sun
authors.forename: Ying
authors.initials: Y
authors.lastname: Luo
authors.forename: Zhixin
authors.initials: Z
authors.lastname: Lin
authors.forename: Jun
authors.initials: J
authors.lastname: Wu
mesh_terms: D015703:Antigens, CD / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism*; D015870:Gene Expression; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000378:metabolism*; D008213:Lymphocyte Activation / Q000276:immunology*; D008232:Lymphoproliferative Disorders / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000378:metabolism; D011485:Protein Binding; D051076:Proto-Oncogene Proteins c-fyn / Q000378:metabolism; D011971:Receptors, Immunologic / Q000378:metabolism; D064067:Rho Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D000071179:Signaling Lymphocytic Activation Molecule Associated Protein; D000071176:Signaling Lymphocytic Activation Molecule Family; D013601:T-Lymphocytes / Q000276:immunology*; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D018909:src Homology Domains
chemical_list: C576603:ARHGEF6 protein, human; C576606:ARHGEF7 protein, human; D015703:Antigens, CD; C084093:CD244 protein, human; D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D050778:NFATC Transcription Factors; D011971:Receptors, Immunologic; D064067:Rho Guanine Nucleotide Exchange Factors; C114953:SH2D1A protein, human; D000071179:Signaling Lymphocytic Activation Molecule Associated Protein; D000071176:Signaling Lymphocytic Activation Molecule Family; C494957:FYN protein, human; D051076:Proto-Oncogene Proteins c-fyn; D020764:cdc42 GTP-Binding Protein