• Jin-Sung Chung, Ponciano D Cruz, and Kiyoshi Ariizumi.
• Department of Dermatology, The University of Texas Southwestern Medical Center and Dermatology Section (Medical Service), Dallas Veterans Affairs Medical Center, Dallas, TX, USA.
• Eur. J. Immunol. 2011 Jun 1; 41 (6): 1794-9.

AbstractMost coinhibitory receptors regulate T-cell responses through an ITIM that recruits protein tyrosine phosphatases (PTPs) to mediate inhibitory function. Because syndecan-4 (SD-4), the coinhibitor for DC-associated heparan sulfate proteoglycan integrin ligand (DC-HIL), lacks such an ITIM, we posited that SD-4 links with a PTP in an ITIM-independent manner. We show that SD-4 associates constitutively with the intracellular protein syntenin but not with the receptor-like PTP CD148 on human CD4(+) T cells. Binding to DC-HIL allowed SD-4 to assemble with CD148 through the help of syntenin as a bridge, and this process upregulated the PTP activity of CD148, which is required for SD-4 to mediate DC-HIL's inhibitory function. Using a mouse model, we found SD-4 to be located away from the immunological synapse formed between T cells and APCs during activation of T cells. These findings indicate that SD-4 is unique among known T-cell coinhibitors, in employing CD148 to inhibit T-cell activation at a site distal from the synapse.Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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