SLAT promotes TCR-mediated, Rap1-dependent LFA-1 activation and adhesion through interaction of its PH domain with Rap1

Abstract

SLAT (also known as DEF6) promotes T cell activation and differentiation by regulating NFAT-Ca 2+ signaling. However, its role in TCR-mediated inside-out signaling, which induces integrin activation and T cell adhesion, a central process in T cell immunity and inflammation, has not been explored. Here, we show that SLAT is crucial for TCR-induced adhesion to ICAM-1 and affinity maturation of LFA-1 in CD4 + T cells. Mechanistic studies revealed that SLAT interacts, through its PH domain, with a key component of inside-out signaling, namely the active form of the small GTPase Rap1 (which has two isoforms, Rap1A and Rap1B). This interaction has been further shown to facilitate the interdependent recruitment of Rap1 and SLAT to the T cell immunological synapse upon TCR engagement. Furthermore, a SLAT mutant lacking its PH domain drastically inhibited LFA-1 activation and CD4 + T cell adhesion. Finally, we established that a constitutively active form of Rap1, which is present at the plasma membrane, rescues the defective LFA-1 activation and ICAM-1 adhesion in SLAT-deficient (Def6 −/− ) T cells. These findings ascribe a new function to SLAT, and identify Rap1 as a target of SLAT function in TCR-mediated inside-out signaling.

Identification of a Novel Alternatively Spliced Form of Inflammatory Regulator SWAP-70-Like Adapter of T Cells

“…To explore the role of SLAT2 in regulating LFA-1 function following TCR engagement, we examined the effect of ectopic SLAT2 expression on the TCR-mediated adhesion to ICAM-1. SLAT-transfected Jurkat-TAg cells showed an increase in TCR-induced adhesion to ICAM-1 relative to control transfectants, as previously shown [16]. In contrast, SLAT2 had no effect on TCR-induced adhesion to ICAM-1 (Figure 4(a)).…”

“…SLAT is involved in TCR-induced adhesion through interaction of its PH domain with Rap1 GTPase, which was required for T cell adhesion to ICAM-1 [16]. Therefore, the deletion of the PH domain in SLAT2 likely explains the inability of SLAT2 to promote adhesion to ICAM-1.…”

“…The human homolog of SLAT, termed IRF-4-binding protein (IBP), was independently isolated by another group [ 8 ]. Structurally, SLAT contains, beginning at its N terminus, a Ca 2+ -binding EF-hand domain [ 15 ], an immunoreceptor tyrosine-based activation motif- (ITAM-) like sequence, a phosphatidylinositol 3,4,5-trisphosphate-binding pleckstrin homology (PH) domain [ 3 ], and a catalytic Dbl homology (DH) domain [ 9 – 14 , 16 ]. Our previous study of Def6 -deficient mice revealed SLAT to be a critical selective regulator of the TCR-coupled Ca 2+ /NFAT signaling pathway, controlling positively CD4 + Th cell activation and differentiation, as evidenced by its critical role in the development of T cell-dependent inflammatory diseases such as allergic lung inflammation [ 17 ] and experimental autoimmune encephalomyelitis [ 18 ].…”

“…SLAT2 protein was expressed in differentiated Th2 cells after two rounds of in vitro stimulation, but not in differentiated Th1, Th17, and Treg cells. Similar to SLAT, SLAT2 enhanced TCR-mediated activation of NFAT and production of IL-4, but unlike SLAT [ 16 ] it was not required for TCR-induced adhesion to intercellular adhesion molecule-1 (ICAM-1). Ectopic expression of SLAT2 or SLAT in Jurkat T cells resulted in the expression of distinct forms of filopodia, namely, short versus long ones, respectively.…”

Leukocyte arrest: Biomechanics and molecular mechanisms of β 2 integrin activation

“…RIAM deficient mice have no defect in platelet arrest [206,208], but a severe defect in neutrophil arrest [207], macrophage adhesion [207], and lymphocyte adhesion [206,207]. A recent study shows that SLAT (SWAP-70-like adaptor of T cells) can interact with Rap-1 through its PH domain and promotes TCR-mediated, Rap1-dependent LFA-1 activation and adhesion [278]. Since SLAT is activated by T cell receptor engagement, this mechanism is unlikely to be involved in triggering arrest.…”