The X-Linked Lymphoproliferative Disease Gene Product SAP Associates with PAK-Interacting Exchange Factor and Participates in T Cell Activation

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 103; no. 39; pp. 14447 - 14452
• Main Authors: Gu, Cuiping, Tangye, Stuart G., Sun, Xiaoqing, Luo, Ying, Lin, Zhixin, Wu, Jun
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 26.09.2006; National Acad Sciences
• Subjects: Antibodies; Antigens, CD - metabolism; Biological Sciences; Calcium; Calcium Signaling - physiology; cdc42 GTP-Binding Protein - metabolism; Cell Cycle Proteins - chemistry; Cell Cycle Proteins - metabolism; Cells; Cellular immunity; Complementary DNA; Gene Expression; Guanine Nucleotide Exchange Factors - chemistry; Guanine Nucleotide Exchange Factors - metabolism; Humans; Immune system; Intracellular Signaling Peptides and Proteins - chemistry; Intracellular Signaling Peptides and Proteins - metabolism; Lymphocyte Activation - immunology; Lymphocytes; Lymphoproliferative Disorders - metabolism; Membrane Glycoproteins - metabolism; Molecules; Mutation; Natural killer cells; NFATC Transcription Factors - metabolism; Protein Binding; Proteins; Proto-Oncogene Proteins c-fyn - metabolism; Receptors; Receptors, Immunologic - metabolism; Rho Guanine Nucleotide Exchange Factors - metabolism; Signaling Lymphocytic Activation Molecule Associated Protein; Signaling Lymphocytic Activation Molecule Family; src Homology Domains; T lymphocytes; T-Lymphocytes - immunology; Western blotting
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0606624103

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.