A novel thromboxane A2 receptor N42S variant results in reduced surface expression and platelet dysfunction

S P Nisar, M Lordkipanidzé, M L Jones, B Dawood, S Murden, M R Cunningham, A D Mumford, J T Wilde, S P Watson, S J Mundell, G C Lowe, UK GAPP Study Group

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Abstract

A small number of thromboxane receptor variants have been described in patients with a bleeding history that result in platelet dysfunction. We have identified a patient with a history of significant bleeding, who expresses a novel heterozygous thromboxane receptor variant that predicts an asparagine to serine substitution (N42S). This asparagine is conserved across all class A GPCRs, suggesting a vital role for receptor structure and function.We investigated the functional consequences of the TP receptor heterozygous N42S substitution by performing platelet function studies on platelet-rich plasma taken from the patient and healthy controls. We investigated the N42S mutation by expressing the wild-type (WT) and mutant receptor in human embryonic kidney (HEK) cells. Aggregation studies showed an ablation of arachidonic acid responses in the patient, whilst there was right-ward shift of the U46619 concentration response curve (CRC). Thromboxane generation was unaffected. Calcium mobilisation studies in cells lines showed a rightward shift of the U46619 CRC in N42S-expressing cells compared to WT. Radioligand binding studies revealed a reduction in BMax in platelets taken from the patient and in N42S-expressing cells, whilst cell studies confirmed poor surface expression. We have identified a novel thromboxane receptor variant, N42S, which results in platelet dysfunction due to reduced surface expression. It is associated with a significant bleeding history in the patient in whom it was identified. This is the first description of a naturally occurring variant that results in the substitution of this highly conserved residue and confirms the importance of this residue for correct GPCR function.

Original languageEnglish
Pages (from-to)923-32
Number of pages10
JournalThrombosis & Haemostasis
Volume111
Issue number5
DOIs
Publication statusPublished - 5 May 2014

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    Nisar, S. P., Lordkipanidzé, M., Jones, M. L., Dawood, B., Murden, S., Cunningham, M. R., Mumford, A. D., Wilde, J. T., Watson, S. P., Mundell, S. J., Lowe, G. C., & UK GAPP Study Group (2014). A novel thromboxane A2 receptor N42S variant results in reduced surface expression and platelet dysfunction. Thrombosis & Haemostasis, 111(5), 923-32. https://doi.org/10.1160/TH13-08-0672