Transmembrane adaptor proteins (TRAPs) are important organizers and regulators of immunoreceptor-mediated signaling. A bioinformatic search revealed several potential novel TRAPs, including a highly conserved protein, proline rich 7 (PRR7), previously described as a component of the PSD-95/N-methyl-d-aspartate receptor protein complex in postsynaptic densities (PSD) of rat neurons. Our data demonstrate that PRR7 is weakly expressed in other tissues but is readily up-regulated in activated human peripheral blood lymphocytes. Transient overexpression of PRR7 in Jurkat T cell line led to gradual apoptotic death dependent on the WW domain binding motif surrounding Tyr-166 in the intracellular part of PRR7. To circumvent the pro-apoptotic effect of PRR7, we generated Jurkat clones with inducible expression of PRR7 (J-iPRR7). In these cells acute induction of PRR7 expression had a dual effect. It resulted in up-regulation of the transcription factor c-Jun and the activation marker CD69 as well as enhanced production of IL-2 after phorbol 12-myristate 13-acetate (PMA) and ionomycin treatment. On the other hand, expression of PRR7 inhibited general tyrosine phosphorylation and calcium influx after T cell receptor cross-linking by antibodies. Moreover, we found PRR7 constitutively tyrosine-phosphorylated and associated with Src. Collectively, these data indicate that PRR7 is a potential regulator of signaling and apoptosis in activated T cells.

• MeSH
• Adaptor Proteins, Signal Transducing biosynthesis   genetics   immunology   MeSH
• Amino Acid Motifs MeSH
• Apoptosis drug effects   physiology   MeSH
• Caco-2 Cells MeSH
• Antigens, CD biosynthesis   genetics   immunology   MeSH
• Antigens, Differentiation, T-Lymphocyte biosynthesis   genetics   immunology   MeSH
• Phosphorylation drug effects   physiology   MeSH
• HEK293 Cells MeSH
• Interleukin-2 biosynthesis   genetics   immunology   MeSH
• Ionophores pharmacology   MeSH
• Ionomycin pharmacology   MeSH
• Jurkat Cells MeSH
• Carcinogens pharmacology   MeSH
• Rats MeSH
• Lectins, C-Type biosynthesis   genetics   immunology   MeSH
• Humans MeSH
• Proto-Oncogene Proteins c-jun genetics   immunology   metabolism   MeSH
• Receptors, Antigen, T-Cell genetics   immunology   metabolism   MeSH
• Gene Expression Regulation physiology   MeSH
• T-Lymphocytes immunology   metabolism   MeSH
• Protein Structure, Tertiary MeSH
• Tetradecanoylphorbol Acetate pharmacology   MeSH
• U937 Cells MeSH
• Calcium Signaling drug effects   physiology   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Adaptor Proteins, Signal Transducing MeSH
• Antigens, CD MeSH
• CD69 antigen MeSH Browser
• Antigens, Differentiation, T-Lymphocyte MeSH
• IL2 protein, human MeSH Browser
• Interleukin-2 MeSH
• Ionophores MeSH
• Ionomycin MeSH
• Carcinogens MeSH
• Lectins, C-Type MeSH
• Proto-Oncogene Proteins c-jun MeSH
• Receptors, Antigen, T-Cell MeSH
• Tetradecanoylphorbol Acetate MeSH

Lymphocyte membrane rafts contain molecules critical for immunoreceptor signaling. Here, we report identification of a new raft-associated adaptor protein LIME (Lck-interacting molecule) expressed predominantly in T lymphocytes. LIME becomes tyrosine phosphorylated after cross-linking of the CD4 or CD8 coreceptors. Phospho-LIME associates with the Src family kinase Lck and its negative regulator, Csk. Ectopic expression of LIME in Jurkat T cells results in an increase of Csk in lipid rafts, increased phosphorylation of Lck and higher Ca2+ response to CD3 stimulation. Thus, LIME appears to be involved in regulation of T cell activation by coreceptors.

• MeSH
• Adaptor Proteins, Vesicular Transport genetics   immunology   metabolism   MeSH
• CD4 Antigens immunology   MeSH
• CD8 Antigens immunology   MeSH
• CSK Tyrosine-Protein Kinase MeSH
• Databases, Protein MeSH
• Phosphorylation MeSH
• DNA, Complementary MeSH
• Humans MeSH
• Membrane Microdomains immunology   MeSH
• Molecular Sequence Data MeSH
• Amino Acid Sequence MeSH
• src-Family Kinases MeSH
• Lymphocyte Specific Protein Tyrosine Kinase p56(lck) metabolism   MeSH
• Protein-Tyrosine Kinases metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Adaptor Proteins, Vesicular Transport MeSH
• CD4 Antigens MeSH
• CD8 Antigens MeSH
• CSK Tyrosine-Protein Kinase MeSH
• CSK protein, human MeSH Browser
• DNA, Complementary MeSH
• Lck-interacting protein, mouse MeSH Browser
• src-Family Kinases MeSH
• Lymphocyte Specific Protein Tyrosine Kinase p56(lck) MeSH
• Protein-Tyrosine Kinases MeSH

A key molecule necessary for activation of T lymphocytes through their antigen-specific T cell receptor (TCR) is the transmembrane adaptor protein LAT (linker for activation of T cells). Upon TCR engagement, LAT becomes rapidly tyrosine phosphorylated and then serves as a scaffold organizing a multicomponent complex that is indispensable for induction of further downstream steps of the signaling cascade. Here we describe the identification and preliminary characterization of a novel transmembrane adaptor protein that is structurally and evolutionarily related to LAT and is expressed in B lymphocytes, natural killer (NK) cells, monocytes, and mast cells but not in resting T lymphocytes. This novel transmembrane adaptor protein, termed NTAL (non-T cell activation linker) is the product of a previously identified WBSCR5 gene of so far unknown function. NTAL becomes rapidly tyrosine-phosphorylated upon cross-linking of the B cell receptor (BCR) or of high-affinity Fcgamma- and Fc epsilon -receptors of myeloid cells and then associates with the cytoplasmic signaling molecules Grb2, Sos1, Gab1, and c-Cbl. NTAL expressed in the LAT-deficient T cell line J.CaM2.5 becomes tyrosine phosphorylated and rescues activation of Erk1/2 and minimal transient elevation of cytoplasmic calcium level upon TCR/CD3 cross-linking. Thus, NTAL appears to be a structural and possibly also functional homologue of LAT in non-T cells.

• MeSH
• Adaptor Proteins, Signal Transducing * MeSH
• Lymphocyte Activation MeSH
• B-Lymphocytes immunology   metabolism   MeSH
• Cell Line MeSH
• Killer Cells, Natural immunology   metabolism   MeSH
• Phosphoproteins chemistry   genetics   isolation & purification   metabolism   MeSH
• Phosphorylation MeSH
• Humans MeSH
• Lymphoid Tissue cytology   metabolism   MeSH
• Membrane Microdomains chemistry   metabolism   MeSH
• Membrane Proteins chemistry   genetics   isolation & purification   metabolism   MeSH
• Molecular Sequence Data MeSH
• Monocytes immunology   metabolism   MeSH
• Mice, Inbred C57BL MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Proteins * MeSH
• Receptors, Antigen, B-Cell metabolism   MeSH
• Receptors, Fc metabolism   MeSH
• Receptors, IgE metabolism   MeSH
• Receptors, IgG metabolism   MeSH
• Amino Acid Sequence MeSH
• Signal Transduction * MeSH
• T-Lymphocytes immunology   metabolism   MeSH
• Carrier Proteins chemistry   genetics   isolation & purification   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Adaptor Proteins, Signal Transducing * MeSH
• Phosphoproteins MeSH
• LAT protein, human MeSH Browser
• Lat protein, mouse MeSH Browser
• LAT2 protein, human MeSH Browser
• LAT2 protein, mouse MeSH Browser
• Membrane Proteins MeSH
• Proteins * MeSH
• Receptors, Antigen, B-Cell MeSH
• Receptors, Fc MeSH
• Receptors, IgE MeSH
• Receptors, IgG MeSH
• Carrier Proteins MeSH

According to a recently proposed hypothesis, initiation of signal transduction via immunoreceptors depends on interactions of the engaged immunoreceptor with glycosphingolipid-enriched membrane microdomains (GEMs). In this study, we describe a novel GEM-associated transmembrane adaptor protein, termed phosphoprotein associated with GEMs (PAG). PAG comprises a short extracellular domain of 16 amino acids and a 397-amino acid cytoplasmic tail containing ten tyrosine residues that are likely phosphorylated by Src family kinases. In lymphoid cell lines and in resting peripheral blood alpha/beta T cells, PAG is expressed as a constitutively tyrosine-phosphorylated protein and binds the major negative regulator of Src kinases, the tyrosine kinase Csk. After activation of peripheral blood alpha/beta T cells, PAG becomes rapidly dephosphorylated and dissociates from Csk. Expression of PAG in COS cells results in recruitment of endogenous Csk, altered Src kinase activity, and impaired phosphorylation of Src-specific substrates. Moreover, overexpression of PAG in Jurkat cells downregulates T cell receptor-mediated activation of the transcription factor nuclear factor of activated T cells. These findings collectively suggest that in the absence of external stimuli, the PAG-Csk complex transmits negative regulatory signals and thus may help to keep resting T cells in a quiescent state.

• MeSH
• Adaptor Proteins, Signal Transducing MeSH
• Lymphocyte Activation * MeSH
• CD3 Complex metabolism   MeSH
• CSK Tyrosine-Protein Kinase MeSH
• Phosphoproteins genetics   metabolism   MeSH
• Glycosphingolipids metabolism   MeSH
• Cloning, Molecular MeSH
• DNA, Complementary genetics   MeSH
• Humans MeSH
• Membrane Proteins genetics   metabolism   MeSH
• Molecular Sequence Data MeSH
• Receptors, Antigen, T-Cell metabolism   MeSH
• Amino Acid Sequence MeSH
• Signal Transduction MeSH
• src-Family Kinases MeSH
• T-Lymphocytes immunology   MeSH
• Protein-Tyrosine Kinases metabolism   MeSH
• Protein Binding MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Adaptor Proteins, Signal Transducing MeSH
• CD3 Complex MeSH
• CSK Tyrosine-Protein Kinase MeSH
• CSK protein, human MeSH Browser
• Phosphoproteins MeSH
• Glycosphingolipids MeSH
• DNA, Complementary MeSH
• Membrane Proteins MeSH
• PAG1 protein, human MeSH Browser
• Receptors, Antigen, T-Cell MeSH
• src-Family Kinases MeSH
• Protein-Tyrosine Kinases MeSH