Sorting nexin 27 interactome in T‐lymphocytes identifies zona occludens‐2 dynamic redistribution at the immune synapse

Abstract

T Lymphocyte recognition of antigens leads to the formation of a highly organized structure termed immune synapse (IS) by analogy with the neuronals synapse. Sorting nexin 27 (SNX27) controls the endosomal traffic of PSD95, Dlg1, ZO-1 (PDZ) domain-interacting proteins, and its alteration is associated with impaired synaptic function and neurological diseases. In T-lymphocytes, SNX27-positive vesicles polarize to the IS, the identity of SNX27 interactors in these conditions nonetheless remains unknown. Here we used proteomics to analyze the SNX27 interactome purified from IS-forming T cells, and confirmed the conserved nature of the SNX27/WASH/retromer association in hematopoietic cells. Furthermore, our comparative interactome analysis of SNX27 wild-type and a mutant-deficient for PDZ cargo recognition identified the epithelial cell-cell junction protein zona occludens-2 (ZO-2) as an IS component. Biochemistry and microscopy approaches in T cells confirmed SNX27/ZO-2 PDZ-dependent interaction, and demonstrated its role controlling the dynamic localization of ZO-2 at the IS. This study broadens our knowledge of SNX27 function in T lymphocytes, and suggests that pathways that delimit polarized structures in nervous and epithelial systems also participate in IS regulation.

Transcellular communication at the immunological synapse: a vesicular traffic-mediated mutual exchange

“…Remarkably, gap junctions have been described at the IS. Of note, the GJ channel-forming protein connexin 43, a protein involved in gap junction assembly, interacts with the epithelial cell-cell junction protein zona occludens-2 (ZO-2) 45 , which was recently identified as an IS component 46 . This suggests that ZO-2 could participate in gap junction formation at the IS.…”

Interplay Between SNX27 and DAG Metabolism in the Control of Trafficking and Signaling at the IS

“…The participation of SNX27-retromer in intracellular trafficking and its accumulation at the IS suggest a role in the transport of cargo to the cell-cell interface. Proteomic analysis of the SNX27 interactome from IS-forming T cells confirmed its association with DGKζ, the retromer and WASH complexes, and additional cargoes that associate to SNX27 to traffic to the IS [127]. These include the protein zonula occludens-2 (ZO-2), a constituent of tight junctions never before identified in T lymphocytes, centromere protein J (CENPJ), which is part of the centrosome, or the Rho guanine nucleotide exchange factor 7 (ARHG7, also known as β p21-activated kinase-interactive exchange factor (β-PIX)) among others.…”

“…This polarized trafficking is mediated by the binding of the PX domain to PtdIns(3)P and the FERM domain to PtdIns(4,5)P 2 -and/or PtdIns(3,4,5)P 3 -enriched membrane regions [117,126]. The SNX27 PDZ domain also influences this process, although the specific PDZ-binding motif-containing cargoes directing SNX27 recruitment to the IS still remain unknown [126,127].…”

Viral targeting of PDZ polarity proteins in the immune system as a potential evasion mechanism

“…Other PDZ polarity proteins of the MAGUK subfamily also play a role in immune response. For example, PALS1 of the Crumbs complex is required for the efficient TCR-induced activation of NF-kB and T-cell proliferation (17); ZO-1 and ZO-2 are expressed in T lymphocytes and are relocated to the IS after TCR stimulation (18). ZO-2 contains a CT PDZbm that, in epithelial cells, interacts with the PDZ domain of sorting nexin 27 (SNX27) to regulate the trafficking of ZO-2 to the tight junction (19).…”

“…The researchers propose that Tax-1 targeting of SNX27 down-regulates GLUT-1 recycling to the membrane, favoring virus release. This mechanism might contribute to T-cell unresponsiveness because SNX27 is also implicated in TCR recycling and IS stabilization (18,50,51).…”