Characterization of SH2D1A Missense Mutations Identified in X-linked Lymphoproliferative Disease Patients

Abstract

X-linked lymphoproliferative disease (XLP) is a primary immunodeficiency characterized by extreme susceptibility to Epstein-Barr virus. The XLP disease gene product SH2D1A (SAP) interacts via its SH2 domain with a motif (TIYXXV) present in the cytoplasmic tail of the cell-surface receptors CD150/SLAM, CD84, CD229/Ly-9, and CD244/2B4. Characteristically, the SH2D1A threepronged interaction with Tyr 281 of CD150 can occur in absence of phosphorylation. Here we analyze the effect of SH2D1A protein missense mutations identified in 10 XLP families. Two sets of mutants were found: (i) mutants with a marked decreased protein half-life (e.g. Y7C, S28R, Q99P, P101L, V102G, and X129R) and (ii) mutants with structural changes that differently affect the interaction with the four receptors. In the second group, mutations that disrupt the interaction between the SH2D1A hydrophobic cleft and Val ؉3 of its binding motif (e.g. T68I) and mutations that interfere with the SH2D1A phosphotyrosine-binding pocket (e.g. C42W) abrogated SH2D1A binding to all four receptors. Surprisingly, a mutation in SH2D1A able to interfere with Thr ؊2 of the CD150 binding motif (mutant T53I) severely impaired non-phosphotyrosine interactions while preserving unaffected the binding of SH2D1A to phosphorylated CD150. Mutant T53I, however, did not bind to CD229 and CD224, suggesting that SH2D1A controls several critical signaling pathways in T and natural killer cells. Because no correlation is present between identified types of mutations and XLP patient clinical presentation, additional unidentified genetic or environmental factors must play a strong role in XLP disease manifestations.

Dual Functional Roles for the X-linked Lymphoproliferative Syndrome Gene Product SAP/SH2D1A in Signaling through the Signaling Lymphocyte Activation Molecule (SLAM) Family of Immune Receptors

“…In the case of SLAM, SAP binds with the highest affinity among the three proteins to the Tyr-281 site, and it therefore should compete favorably against SHP-2 in binding to the same site as shown previously (8,21) as well as in the present study. However, because all four members of the SLAM family of receptors examined in this study contain multiple tyrosine phosphorylation sites, the efficiency of these SH2 domaincontaining proteins in competing against each other would depend on their relative affinities for these sites and their local concentrations.…”

“…Peptides-The finding that FynT associates with SLAM in a SAP-dependent manner (21) suggests that SAP may either indirectly or directly interact with SLAM. To explore the latter possibility, we employed a purified SAP protein, either as GST-fusion or labeled with biotin, in an attempt to pull down FynT from the lysate of HEK 293 cells that transiently overexpress FynT.…”

“…changes within the protein's SH2 domain, except that, in one case, the stop codon is mutated to an Arg, which leads to the addition of 11 extra amino acids to the C terminus of SAP (the "Tail" mutant). We previously reported that a group of ten SAP mutants associated with XLP displayed reduced affinities for SLAM and SLAM-derived peptides and that these mutants were incompetent in blocking the interaction between SHP-2 and SLAM compared with wild-type SAP (14,21). To assess the relevance of the SAP-FynT interaction to the pathogenesis of the XLP syndrome, we examined the binding of the same group of mutants to FynT in a GST pull-down assay.…”

“…The physiological significance of SAP interaction with the SLAM family of receptors was underscored in findings that disease-causing missense SAP mutants displayed markedly reduced affinities for SLAM, both in vitro and in vivo, and were deficient in blocking the interaction between SHP-2 and SLAM (14,21). Moreover, the binding of SAP to 2B4 appeared to play a pivotal role in regulating target-killing activities of NK cells (5,18,20).…”

X'e Bağli Geçi̇ş Gösteren Lenfoproli̇ferati̇f Sendrom: Kli̇ni̇k, Patogenez Ve Geneti̇kle İlgi̇li̇ Geli̇şmeler

“…(Mutasyonlarla ilgili geniş bilgi internetten, http:/www.uta.fi/imt/bioinfo/SH2D1Abase/ adresinden ücretsiz olarak edinilebilir) Mutasyonlar tüm gen boyunca görülebilir. Bunları aşağıdaki gibi sınıflamak olasıdır (7,8,13,25,26):…”