Research ArticleImmunology

Superresolution imaging of the cytoplasmic phosphatase PTPN22 links integrin-mediated T cell adhesion with autoimmunity

Sci. Signal.  04 Oct 2016:
Vol. 9, Issue 448, pp. ra99
DOI: 10.1126/scisignal.aaf2195

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T cells need to move through the circulation, attach to endothelial cells, transmigrate into tissues, and stably interact with target cells. The phosphatase PTPN22 targets phosphorylated tyrosines in Src and Syk family kinases, many of which are phosphorylated and activated in migrating T cells in response to the binding of the integrin LFA-1 to its ligand ICAM-1. Burn et al. used superresolution microscopy to show that PTPN22 formed clusters in nonmigrating T cells, which were dispersed in T cells that migrated on surfaces coated with ICAM-1. Freed from these complexes, PTPN22 interacted with its targets near the front of the migrating T cell, which inhibited LFA-1 signaling. In contrast, clusters containing the PTPN22 R620W mutant, a variant that is associated with autoimmune diseases, failed to disaggregate in migrating T cells, and thus, LFA-1 clustering and signaling were not inhibited. Together, these data suggest how a mutation associated with autoimmunity dysregulates T cell adhesion and migration.

Abstract

Integrins are heterodimeric transmembrane proteins that play a fundamental role in the migration of leukocytes to sites of infection or injury. We found that protein tyrosine phosphatase nonreceptor type 22 (PTPN22) inhibits signaling by the integrin lymphocyte function-associated antigen–1 (LFA-1) in effector T cells. PTPN22 colocalized with its substrates at the leading edge of cells migrating on surfaces coated with the LFA-1 ligand intercellular adhesion molecule–1 (ICAM-1). Knockout or knockdown of PTPN22 or expression of the autoimmune disease–associated PTPN22-R620W variant resulted in the enhanced phosphorylation of signaling molecules downstream of integrins. Superresolution imaging revealed that PTPN22-R620 (wild-type PTPN22) was present as large clusters in unstimulated T cells and that these disaggregated upon stimulation of LFA-1, enabling increased association of PTPN22 with its binding partners at the leading edge. The failure of PTPN22-R620W molecules to be retained at the leading edge led to increased LFA-1 clustering and integrin-mediated cell adhesion. Our data define a previously uncharacterized mechanism for fine-tuning integrin signaling in T cells, as well as a paradigm of autoimmunity in humans in which disease susceptibility is underpinned by inherited phosphatase mutations that perturb integrin function.

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