Identification of the integrin β3 L718P mutation in a pedigree with autosomal dominant thrombocytopenia with anisocytosis

Abstract

SummaryaIIbb3 integrin mutations that result in the complete loss of expression of this molecule on the platelet surface cause Glanzmann thrombasthenia. This is usually autosomal recessive, while other mutations are known to cause dominantly inherited macrothrombocytopenia (although such cases are rare). Here, we report a 4-generation pedigree including 10 individuals affected by dominantly inherited thrombocytopenia with anisocytosis. Six individuals, whose detailed clinical and laboratory data were available, carried a non-synonymous ITGB3 gene alteration resulting in mutated integrin b3 (ITGB3)-L718P. This mutation causes partial activation of the aIIbb3 complex, which promotes the generation of abnormal pro-platelet-like protrusions through downregulating RhoA (RHOA) activity in transfected Chinese Hamster Ovary cells. These findings suggest a model whereby the integrin b3-L718P mutation contributes to thrombocytopenia through gain-of-function mechanisms.

Mutations of the integrin αIIb/β3 intracytoplasmic salt bridge cause macrothrombocytopenia and enlarged platelet α‐granules

“…This was confirmed by Hughes et al who expressed αIIbβ3 in CHO cells after modifying residues of the salt bridge through site‐directed mutagenesis. While the changes permit binding of the activation‐dependent IgM MoAb PAC‐1, only for one report has spontaneous binding of Fg been observed for this class of mutation . Such results therefore differ from the C560R mutation in the β3 cysteine‐rich β (A) extracellular domain as reported for a French patient whose platelets circulated with αIIbβ3‐bound Fg .…”

“…A feature of αIIb or β3 cytoplasmic domain mutations causal of MTP is that long‐range conformational changes extend to the functional domains of the integrin and give what is often termed a partially activated state (Supporting Information Table S1). This was confirmed by Hughes et al who expressed αIIbβ3 in CHO cells after modifying residues of the salt bridge through site‐directed mutagenesis.…”

“…Rare gain‐of‐function mutations of the ITGA2B or ITGB3 genes encoding αIIbβ3 also cause macrothrombocytopenia (MTP) with a low platelet count and platelets of increased size . Mostly heterozygous with autosomal dominant (AD) expression these include D621_E660del, L718P, L718del and D723H mutations in β3, and G991C, G993del, R995Q or W in αIIb (Supporting Information Table S1) . While D621_E660del affects the extracellular cysteine‐rich βA domain of β3, the others affect transmembrane or intracellular cytoplasmic domains and in particular the salt bridge linking the negatively charged D723 of β3 with the positively charged R995 of the much studied GFFKR sequence of αIIb .…”

An intracytoplasmic β3 Leu718 deletion in a patient with a novel platelet phenotype

“…15 Phenotypes resulting from other changes in b3 that give rise to MTP, including an extracellular b1 domain D621_E660del 16 are compared in supplemental Table 1. Introduction of a cytoplasmic tail b-turn by the b3 L718P substitution 17,18 found in families from Europe and Japan results in a bend and the pushing apart of the two amino acids engaged in the salt bridge (data not shown). This is highly relevant for our study because it represents the same amino acid that is deleted in our family.…”

Inherited disorders of platelet function: selected updates

“…Nevertheless, a full Fg-binding capacity of a IIb b 3 after platelet activation with ADP is not seen. MTP may arise through (i) altered a IIb b 3 -dependent interaction with matrix proteins, (ii) restricted MK migration in the marrow and (iii) reduced proplatelet formation linked to a down-regula-tion of RhoA and altered cytoskeleton and b-tubulin function [26][27][28]. Significantly, we have identified a French woman associating MTP with classic type I GT caused by heterozygous Pro189Ser and Cys210Ser b 3 substitutions but for whom DNA analysis on the thrombogenomics platform of Cambridge University further identified a predicted damaging Gly146Arg substitution in a conserved GTPase domain of b-tubulin.…”