Human Platelet PIP3 Signalosome

Platelets are small, anucleate cells that play an essential role in haemostasis, but can contribute critically to the pathogenesis of cardiovascular disease. Platelets express all four Class I Phosphoinositide 3-kinase (PI3K) isoforms, with previous work revealing important roles for these enzymes in regulating platelet priming, activation and stable thrombus formation. Despite this, detailed mechanistic understanding of how these lipid kinases orchestrate these roles in platelets is limited. Class I PI3Ks predominantly regulate cell function through their catalytic product, the signalling phospholipid phosphatidylinositol-3,4,5-trisphosphate (PIP3), which coordinates the localisation and/or activity of a diverse range of binding proteins. The complete repertoire of these Class I PI3K effectors in platelets remains unknown, hampering current understanding of Class I PI3K-mediated regulation of platelet function. We therefore conducted a global, unbiased screen for PIP3-binding proteins in human platelets using affinity capture coupled to high resolution proteomic mass spectrometry. Thus, we present the first in depth analysis of the PIP3 signalosome of human platelets, revealing an extensive PIP3 interactome, including many proteins previously uncharacterised in this cell type. This work provides important new insights into how Class I PI3K shapes human platelet function.