Structural and functional dissection of the cytoplasmic domain of the transmembrane adaptor protein SIT (SHP2‐interacting transmembrane adaptor protein)

• Published in: European journal of immunology Vol. 31; no. 6; pp. 1825 - 1836
• Main Authors: Pfrepper, Klaus‐Ingmar, Marie‐Cardine, Anne, Simeoni, Luca, Kuramitsu, Yasuhiro, Leo, Albrecht, Spicka, Jiri, Hilgert, Ivan, Scherer, Jeanette, Schraven, Burkhart
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag GmbH 01.06.2001
• Subjects: Adaptor Proteins, Signal Transducing; Amino Acid Sequence; Binding Sites; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cytoplasm - metabolism; GRB2 Adaptor Protein; Humans; Intracellular Signaling Peptides and Proteins; Jurkat Cells; Lymphocyte Activation; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Membrane Proteins - genetics; Membrane Proteins - metabolism; Molecular Sequence Data; Phosphorylation; Protein Phosphatase 2; Protein Structure, Tertiary; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Protein Tyrosine Phosphatase, Non-Receptor Type 6; Protein Tyrosine Phosphatases - chemistry; Protein Tyrosine Phosphatases - metabolism; Proteins - metabolism; SH2 Domain-Containing Protein Tyrosine Phosphatases; Signaling; SIT protein; T cell; T-Lymphocytes - immunology; T-Lymphocytes - metabolism; Transmembrane adaptor protein; tyrosine; Tyrosine - metabolism
• ISSN: 0014-2980; 1521-4141
• DOI: 10.1002/1521-4141(200106)31:6<1825::AID-IMMU1825>3.0.CO;2-V

SIT (SHP2‐interacting transmembrane adaptor protein) is a recently identified transmembrane adaptor protein, which is expressed in lymphocytes. Its structural properties, in particular the presence of five potential tyrosine phosphorylation sites, suggest involvement of SIT in TCR‐mediated recruitment of SH2 domain‐containing intracellular signaling molecules to the plasma membrane. Indeed, it has recently been demonstrated that SIT inducibly interacts with the SH2‐containing protein tyrosine phosphatase 2 (SHP2) via an immunoreceptor tyrosine‐based inhibition motif (ITIM). Moreover, SIT is capable to inhibit TCR‐mediated signals proximal of activation of protein kinase C. However, inhibition of T cell activation by SIT occurs independently of SHP2 binding. The present study was performed to further characterize the molecular interaction between SIT and intracellular effector molecules and to identify the protein(s) mediating its inhibitory function. We demonstrate that SIT not only interacts with SHP2 but also with the adaptor protein Grb2 via two consensus YxN motifs. However, mutation of both Grb2‐binding sites also does not influence the inhibitory function of SIT. In contrast, mutation of the tyrosine‐based signaling motif Y168 ASV completely abrogates the ability of SIT to inhibit T cell activation. Co‐precipitation experiments revealed that the tyrosine kinase p50csk could represent the negative regulatory effector molecule that binds to this motif.