A β3 Asp217→Val substitution in a patient with variant Glanzmann Thrombasthenia severely affects integrin αIIBβ3 functions

Abstract

A dysfunctional Glanzmann Thrombasthenia (variant) is a rare bleeding disorder due to qualitative abnormalities of platelets alphaIIBbeta3 heterodimers. Dynamically conformational change of alphaIIBbeta3 is a complex mechanism that is not fully understood. For these reasons, genotyping and functional analysis of variant Glanzmann Thrombasthenia is important to elucidate the molecular basis of alphaIIBbeta3 receptor functions. In this report, we have analyzed the molecular effects of an A>T substitution leading to an amino acid change, D217>V, in the beta3 integrin gene identified in patients with variant Glanzmann Thrombasthenia. As the D217 residue is highly conserved among all seven beta integrin subunits and among beta3 integrins of different species, we tested the effect on the phenotype of the D217V mutation by cotransfecting the beta3 mutant (V217) or wild-type beta3 (D217) construct with the wild-type alphaIIb into eukaryotic Chinese hamster ovary cells. Levels of mutant alphaIIBbeta3 heterodimers on Chinese hamster ovary cell surface were lightly reduced as compared with the wild type. Functional investigation of alphaIIBbeta3 V217 on Chinese hamster ovary cell surface was carried out, as fibrinogen binding, adhesion and aggregation tests showed a substantial reduction in respect to the control sample. Our results confirm ex-vivo data and suggest that the D217 amino acid is required for alphaIIBbeta3 receptor interactions with fibrinogen.