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