TCR activation eliminates glutamate receptor GluR3 from the cell surface of normal human T cells, via an autocrine/paracrine granzyme B-mediated proteolytic cleavage.
The majority of resting normal human T cells, like neuronal cells, express functional receptors for glutamate (the major excitatory neurotransmitter in the CNS) of the ionotropic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-receptor subtype 3 (GluR3). Glutamate by itself ( approximately 10 nM) activates key T cell functions, including adhesion to fibronectin and laminin and chemotactic migration toward CXCL12/stromal cell-derived factor 1. In this study, we found by GluR3-specific immunostaining, flow cytometry, and Western blots that GluR3 cell surface expression decreases dramatically following TCR activation of human T cells. CXCR4, VLA-4, and VLA-6 also decrease substantially, whereas CD147 increases as expected, after TCR activation. Media of TCR-activated cells "eliminates" intact GluR3 (but not CXCR4 and VLA-6) from the cell surface of resting T cells, suggesting GluR3 cleavage by a soluble factor. We found that this factor is granzyme B (GB), a serine protease released by TCR-activated cells, because the extent of GluR3 elimination correlated with the active GB levels, and because three highly specific GB inhibitors blocked GluR3 down-regulation. Media of TCR-activated cells, presumably containing cleaved GluR3B peptide (GluR3 aa 372-388), inhibited the specific binding of anti-GluR3B mAb to synthetic GluR3B peptide. In parallel to losing intact GluR3, TCR-activated cells lost glutamate-induced adhesion to laminin. Taken together, our study shows that "classical immunological" TCR activation, via autocrine/paracrine GB, down-regulates substantially the expression of specific neurotransmitter receptors. Accordingly, glutamate T cell neuroimmune interactions are influenced by the T cell activation state, and glutamate, via AMPA-GluR3, may activate only resting, but not TCR-activated, T cells. Finally, the cleavage and release to the extracellular milieu of the GluR3B peptide may in principle increase its antigenicity, and thus the production, of anti-self GluR3B autoantibodies, which activate and kill neurons, found in patients with various types of epilepsy.
Ganor
Yonatan
Y
Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel.
Teichberg
Vivian I
VI
Levite
Mia
M
D000911:Antibodies, Monoclonal / Q000276:immunology; D019898:Autocrine Communication; D002448:Cell Adhesion / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D018698:Glutamic Acid / Q000494:pharmacology; D053804:Granzymes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D007797:Laminin / Q000378:metabolism; D019899:Paracrine Communication; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding; D018091:Receptors, AMPA / Q000276:immunology* / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000276:immunology*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D012995:Solubility; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism*; D013997:Time Factors
D000911:Antibodies, Monoclonal; D007797:Laminin; D010446:Peptide Fragments; D018091:Receptors, AMPA; D011948:Receptors, Antigen, T-Cell; D015842:Serine Proteinase Inhibitors; C104723:glutamate receptor ionotropic, AMPA 3; D018698:Glutamic Acid; D053804:Granzymes