The CD3 ζ Subunit Contains a Phosphoinositide-Binding Motif That Is Required for the Stable Accumulation of TCR–CD3 Complex at the Immunological Synapse

Abstract

T cell activation involves a cascade of TCR-mediated signals that are regulated by three distinct intracellular signaling motifs located within the cytoplasmic tails of the CD3 chains. While all the CD3 subunits possess at least one ITAM, CD3 ε subunit also contains a proline-rich sequence (PRS) and a basic-rich stretch (BRS). The CD3 ε BRS complexes selected phosphoinositides, interactions that are required for normal cell surface expression of the TCR. The cytoplasmic domain of CD3 ζ also contains several clusters of arginine and lysine residues. Herein, we report that these basic amino acids enable CD3 ζ to complex the phosphoinositides PtdIns(3)P, PtdIns(4)P, PtdIns(5)P, PtdIns(3,5)P2, and PtdIns(3,4,5)P3 with high affinity. Early TCR signaling pathways were unaffected by the targeted loss of the phosphoinositide-binding functions of CD3 ζ. Instead, the elimination of the phosphoinositide-binding function of CD3 ζ significantly impaired the ability of this invariant chain to stably accumulate at the immunological synapse during T cell-antigen presenting cell interactions. Without its phosphoinositide-binding functions, CD3 ζ was concentrated in intracellular structures following T cell activation. Such findings demonstrate a novel functional role for CD3 ζ BRS-phosphoinositide interactions in supporting T cell activation.

A conserved αβ transmembrane interface forms the core of a compact T-cell receptor–CD3 structure within the membrane

“…A mounting pool of evidence implicates ligand-induced alterations in receptor structure (1) and/or TCR-CD3 configuration (2)(3)(4)(5)(6) as the triggering event. Changes in the structured extracellular (EC) domains are proposed to translate, through an unknown mechanism, into alterations in the CD3 and ζζ cytoplasmic tails, converting them to a conformation that is receptive to phosphorylation by Lck and binding of other proximal signaling components (7)(8)(9)(10)(11)(12). This type of signaling model implies a pathway between EC and cytoplasmic domains that may involve alterations in the subunit transmembrane (TM) domains with respect to each other and/ or the lipid bilayer (13)(14)(15)(16).…”

Basic residues in the T-cell receptor ζ cytoplasmic domain mediate membrane association and modulate signaling

“…There is one BRS motif in the membrane proximal part of CD3ε, but there are at least three in separate locations on the TCRζ (10,11). Several studies have suggested that the BRS motifs promote close association of the CD3ε and TCRζ cytoplasmic domains with membranes, through interactions with negatively charged phospholipids (6,(10)(11)(12)(13)(14).…”

T cell adhesion triggers an early signaling pole distal to the immune synapse

“…Similar unexpected distributions can be found in former reports of T-cell-APC contacts, but the presence of an antisynapse was most often neither analyzed nor discussed. (Brossard et al, 2005;Costello et al, 2002;DeFord-Watts et al, 2011Holdorf et al, 2002;Le Floc'h et al, 2013;Revy et al, 2001). A spatiotemporal analysis of the patterning of 30 signaling sensors has also been performed, identifying the distal pole as a place where several of these sensors accumulate (Singleton et al, 2009).…”