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

Eur J Immunol. 2001 Oct;31(10):2885-91. doi: 10.1002/1521-4141(2001010)31:10<2885::aid-immu2885>3.0.co;2-2.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Antigens, CD*
  • CCAAT-Enhancer-Binding Protein-beta
  • Cell Line
  • Down-Regulation
  • Histocompatibility Antigens Class II / analysis
  • Humans
  • Membrane Proteins / analysis
  • Membrane Proteins / metabolism*
  • Molecular Sequence Data
  • Molecular Weight
  • Proteins / chemistry
  • Proteins / genetics
  • Proteins / isolation & purification*
  • RNA / analysis
  • Receptor-CD3 Complex, Antigen, T-Cell / antagonists & inhibitors*
  • Receptors, Platelet-Derived Growth Factor / metabolism
  • Repetitive Sequences, Amino Acid
  • Signal Transduction
  • T-Lymphocytes / chemistry

Substances

  • Antigens, CD
  • CCAAT-Enhancer-Binding Protein-beta
  • CD223 antigen
  • Histocompatibility Antigens Class II
  • Membrane Proteins
  • Proteins
  • Receptor-CD3 Complex, Antigen, T-Cell
  • RNA
  • Receptors, Platelet-Derived Growth Factor