LAP, a lymphocyte activation gene-3 (LAG-3)-associated protein that binds to a repeated EP motif in the intracellular region of LAG-3, may participate in the down-regulation of the CD3/TCR activation pathway.
The threshold, extent and termination of TCR activation is controlled in part by inhibitory co-receptors expressed on activated T cells. The lymphocyte activation gene product (LAG-3), a ligand for MHC class II molecules co-caps with the CD3/TCR complex and inhibits cell proliferation and cytokine secretion in response to CD3 signaling. We first investigated whether LAG-3 is localized in activated T cells in detergent-resistant membrane rafts enriched in glycosphingolipids and cholesterol. We showed that both LAG-3 and MHC class II are present in the cell fraction of glycosphingolipid-rich complexes (GSL complexes) before the assembly of the immunological synapse by CD3/TCR complex cross-linking. Using the LAG-3 intracytoplasmic region as bait in the yeast two-hybrid cloning system, we next identified a novel protein termed LAP for LAG-3-associated protein. LAP is encoded by a 1.8-kb RNA message in lymphocytes and encodes a 45-kDa protein that is expressed in most tissues. We showed that LAP binds specifically in vitro and in vivo to the Glu-Pro (EP) repeated motif present in the LAG-3 intracytoplasmic region. LAP also binds to the EP motif of another functionally important receptor, the PDGFR. Thus, LAP is a candidate molecule for a new type of signal transduction and/or coupling of clustered rafts to the microtubule networks that could explain how negative signaling of co-receptors may occur through molecules devoid of any immunoreceptor tyrosine-based inhibitory motif consensus sequence.
Iouzalen
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Laboratoire d'Immunologie des Tumeurs, Université Paris-Sud, Chatenay Malabry, France.
Andreae
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Hannier
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S
Triebel
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F
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D015703:Antigens, CD; D022782:CCAAT-Enhancer-Binding Protein-beta; D002460:Cell Line; D015536:Down-Regulation; D000949:Histocompatibility Antigens Class II / Q000032:analysis; D006801:Humans; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification*; D012313:RNA / Q000032:analysis; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000037:antagonists & inhibitors*; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000737:chemistry; D000093322:Lymphocyte Activation Gene 3 Protein
D015703:Antigens, CD; D022782:CCAAT-Enhancer-Binding Protein-beta; D000949:Histocompatibility Antigens Class II; D008565:Membrane Proteins; D011506:Proteins; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D012313:RNA; D017479:Receptors, Platelet-Derived Growth Factor; D000093322:Lymphocyte Activation Gene 3 Protein; C000720326:Lag3 protein, human