A novel thromboxane A2 receptor N42S variant results in reduced surface expression and platelet dysfunction.
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.
Shaista P
SP
Nisar
Marie
M
Lordkipanidzé
Matthew L
ML
Jones
Ban
B
Dawood
Sherina
S
Murden
Margaret R
MR
Cunningham
Andrew D
AD
Mumford
Jonathan T
JT
Wilde
Steve P
SP
Watson
S. J. Mundell, School of Physiology and Pharmacology, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK, Tel: +44 (0) 117 3311440, E-mail: s.j.mundell@bristol.ac.uk.
Stuart J
SJ
Mundell
Gillian C
GC
Lowe
D001216:Asparagine / Q000235:genetics; D001792:Blood Platelets / Q000502:physiology*; D017124:Conserved Sequence / Q000235:genetics; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D014644:Genetic Variation; D057809:HEK293 Cells; D006470:Hemorrhage / Q000097:blood / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D008875:Middle Aged; D009154:Mutation / Q000235:genetics; D015539:Platelet Activation / Q000235:genetics; D010979:Platelet Function Tests; D011869:Radioligand Assay; D043562:Receptors, G-Protein-Coupled / Q000235:genetics; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000235:genetics / Q000378:metabolism*
D043562:Receptors, G-Protein-Coupled; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D001216:Asparagine
Inherited / acquired platelet disorders; acquired; gene mutations; platelet pathology / inherited; platelet pharmacology; receptors