A Novel Role for the Membrane Protein G6f in Platelet Activation Induced by Weak Stimulation

Abstract

Background: The lymphocyte antigen 6 complex locus protein (G6f) is a type I transmembrane protein of the immunoglobulin super family that is expressed on the surface of human platelets. The intracellular tail of G6f contains a single tyrosine in a single YXXI motif, which undergoes phosphorylation in response to GPVI and αIIbβ3-mediatedplatelet activation. This leads to the binding of the adaptor proteinGrb2 to G6f. G6f is currently considered to be platelet-specific, but its function remains unknown. Aims: In this study, we investigated if antibodies against this mem-brane protein can influence platelet activation and aggregation caused by various agonists. Methods: Washed platelets were stimulated with low doses of agonists: thrombin (0.03-0.05 U/ml), ADP (10 μM), IgG immune complexes (IC, 40-100 nM) and collagen related peptide (CRP, 0.25-1μg/ml) with or without anti-G6f antibodies. Platelet aggregation and dense granule release were assessed by aggregometry and the serotonin release assay, respectively. Results: Platelet aggregation and granule release induced by low dose thrombin, ADP (aggregation only) and IC were strongly inhibited(>80%) by the anti-G6f antibodies whereas CRP-induced platelet activation was inhibited by 40%. These effects were not observed with higher agonist concentrations. Conclusions: Our results suggest a novel role for G6f in platelet activation caused by a broad range of agonists. The results also indicate that anti-G6f antibody promotes an inhibitory effect against agonist-induced platelet activation and aggregation. G6f may there-fore represent a possible anti-thrombotic target. However, additional mechanistic studies are required to address this.