Tetraspanins CD9 and CD151 at the immune synapse support T‐cell integrin signaling

Abstract

Understanding how the immune response is activated and amplified requires detailed knowledge of the stages in the formation of the immunological synapse (IS) between T lymphocytes and antigen-presenting cells (APCs). We show that tetraspanins CD9 and CD151 congregate at the T-cell side of the IS. Silencing of CD9 or CD151 blunts the IL-2 secretion and expression of the activation marker CD69 by APC-conjugated T lymphocytes, but does not affect the accumulation of CD3 or actin to the IS, or the translocation of the microtubule-organizing center toward the T-B contact area. CD9 or CD151 silencing diminishes the relocalization of α4β1 integrin to the IS and reduces the accumulation of high-affinity β1 integrins at the cell-cell contact. These changes are accompanied by diminished phosphorylation of the integrin downstream targets FAK and ERK1/2. Our results suggest that CD9 and CD151 support integrin-mediated signaling at the IS.Keywords: CD9 r CD151 r Immune synapse r Integrins r T-cell activation Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionInteraction between T lymphocytes and antigen-presenting cells (APCs) is critical for antigen presentation and for the initiation of the immune response. This process is characterized by the formation of a dynamic structure called the immune synapse (IS) at the contact between T cells and APCs [1]. At the T cell side of the IS, T-cell receptors (TCRs) and Correspondence: Dr.Francisco Sánchez-Madrid e-mail: fsmadrid@salud.madrid.org associated molecules accumulate in the central area (central supramolecular activation cluster; cSMAC), while adhesion receptors and integrins reorganize in a surrounding external ring called peripheral SMAC (pSMAC) [1]. The increased IS stability enhances T-cell sensitivity, stimulates cytoskeletal processes, induces downstream signaling, and drives effective T-cell differentiation [2,3]. How integrins regulate these processes is not fully understood.Several membrane receptors and integrins concentrated at the IS -CD3, CD4, ICAM-1, lymphocyte function-associated antigen 1 (LFA-1), and very late antigen 4 (VLA-4) -are associated with tetraspanins [4,5] 1968 Rocha-Perugini Vera et al. Eur. J. Immunol. 2014. 44: 1967-1975 organize membrane macrocomplexes called tetraspanin-enriched microdomains (TEMs) [6]. Tetraspanins modulate the function of their associated partners and play important roles in immunity, inflammation, and other processes [6]. Tetraspanins that accumulate at the IS include CD81, which regulates IS architectural organization and maturation [5], and CD82, which contributes to T-cell activation through Rho GTPase-dependent regulation of the actin cytoskeleton [7]. CD82 also increases the adhesion of LFA-1 integrin to its ligand ICAM-1 expressed on APCs [4]. The tetraspanins CD81, CD82, CD53, and CD9 provide T cell costimulatory signals, and CD9 localizes together with TCR signaling molecules in lipid microdomains [4]. Moreover, the T cells of mice deficien...

CD151 Expression Is Associated with a Hyperproliferative T Cell Phenotype

“…As a marker for functionally distinct T cell populations, CD151 would have to be either expressed at different expression levels on distinct populations (high/low) or CD151 would have to be present on distinct T cell subpopulations, independent of the expression level. Given reports that CD151 expression contributes to the stability of the IS (54, 55), we had expected CD151 to be expressed on all T cells, but surprisingly, CD151 marked distinct subpopulations. CD151 was expressed in a lineage dependent manner, with a higher percentage of CD8+ T cells being CD151+ at baseline (~60%; range: 26–82%) than CD4+ T cells (~25%; range: 6–43%) (Figure 1A).…”

“…Similarly to CD151, the tetraspanin CD81 is also recruited to the IS during TCR stimulation (72), but there are no studies yet on how CD81 expression is regulated as a function of T cell lineage or memory differentiation state, such as the one we present here. The tetraspanin CD9 is another possible modulator of T cell phenotype as CD9 in complex with integrins has also a role in IS formation (54). Our findings suggest that beyond their reported role in IS formation, the tetraspanin/integrin composition on T cells likely plays a mostly unrecognized role in fine-tuning T cell responsiveness and T cell homeostasis.…”

“…In immunology, CD151 has been reported as a negative regulator of FcεRI-mediated mast cell activation (53). On T cells, CD151 has been shown to stabilize the immunological synapse following T cell activation, and silencing of CD151 blunts IL-2 secretion and expression of the activation marker CD69 (54–56). Consistent with previous reports that CD151 interacts and signals in combination with integrins, silencing of CD151 expression also diminished the relocalization of α4β1 integrin to the immunologic synapse (IS), which resulted in reduced phosphorylation of the integrin targets FAK and ERK1/2 (54).…”

CD9 Regulates Major Histocompatibility Complex Class II Trafficking in Monocyte-Derived Dendritic Cells

“…Data are means Ϯ SEM of percentages of FITC ϩ CD11c ϩ cells from two independent experiments. *, P Ͻ 0.05; **, P Ͻ 0.01; ***, P Ͻ 0.001. signaling at the IS, regulating T cell activation (58). We investigated whether CD9 could also be important for the IS organization at the APC side.…”

Contact-dependent Signaling

“…93 It should also be mentioned here that tetraspanins associate with adhesion-Gprotein-coupled receptors (adhesion-GPCRs), a large family of GPCRs with extremely long extracellular N-terminals that contain a wide variety of domains, capable of interacting with many transmembrane and matrix-associated molecules. 94 Thus, taken together, tetraspanins may be important components in the architecture of contact-dependent intercellular signaling.…”