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Integrin αIIb-mediated PI3K/Akt activation in platelets
Haixia Niu1, Xue Chen, Ralph A Gruppo
1Department of Biochemistry and Molecular Cell Biology, Shanghai Key Laboratory of Tumor Microenvironment and Inflammation, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Plos One
|October 20, 2012
Summary
Integrin αIIbβ3 signaling activates platelets via Src family kinases (SFKs) and PI3K/Akt pathways, even with limited β3 cytoplasmic domain. This study uncovers key signaling mechanisms in thrombosis and hemostasis.
Area of Science:
- Molecular biology
- Cell signaling
- Hematology
Background:
- Integrin αIIbβ3 plays a crucial role in thrombosis and hemostasis through bidirectional signaling.
- While β3 subunit signaling is well-studied, αIIb-mediated signaling remains largely uncharacterized.
- Previous work identified β3 cytoplasmic domain residues R(724)KEFAKFEEER(734) as negative regulators of αIIb-mediated signaling.
Purpose of the Study:
- To elucidate the signaling pathway utilized by αIIb-mediated outside-in signaling.
- To investigate the role of Src family kinases (SFKs) and PI3K/Akt signaling in αIIb-mediated platelet activation.
Main Methods:
- Utilized human and gene-deficient mouse platelets, genetically modified CHO cells, and kinase inhibitors (PP2, wortmannin, U0126).
- Investigated the effects of inhibitors and a palmitoylated β3 peptide on platelet aggregation, TxA2 production, granule secretion, and Akt phosphorylation (Ser473).
- Examined Akt phosphorylation in response to specific antibody and fibrinogen treatments in CHO cells expressing different αIIbβ3 variants.
Main Results:
- αIIb-mediated outside-in signaling-induced TxA2 production and granule secretion were inhibited by PP2 (SFK inhibitor) and wortmannin (PI3K inhibitor), but not U0126 (MAPK inhibitor).
- PP2, wortmannin, and the R(724)KEFAKFEEER(734) peptide inhibited Akt phosphorylation at Ser473, TxA2 production, and granule secretion.
- Akt phosphorylation in mouse platelets stimulated by PAR4 agonist was αIIbβ3-dependent and blocked by PP2, wortmannin, and the palmitoylated peptide.
- Akt was phosphorylated in CHO cells expressing αIIbβ3-Δ724 or αIIbβ3E(724)AERKFERKFE(734) but not wild-type αIIbβ3.
Conclusions:
- Src family kinases (SFKs) and PI3K/Akt signaling are integral to αIIb-mediated outside-in signaling in platelets.
- This signaling pathway activates platelets even with a truncated β3 cytoplasmic domain (8 membrane proximal residues).
- Findings provide novel insights into the signaling mechanisms of αIIb-mediated outside-in signaling in platelet function.
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