PI 3-Kinase p110β Regulation of Platelet Integrin αIIbβ3

Jackson, Shaun P.; Schoenwaelder, Simone M.

doi:10.1007/82_2010_61

Cited by 12 publications

(10 citation statements)

References 138 publications

(164 reference statements)

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“…This is consistent with the recent finding that knockdown of PIPKIγ reduced PIP2 levels by 40% and PIP3 to undetectable levels [36]. PI3K is known to promote integrin activation [37], but detailed elucidation of this process will require future investigations in vivo. We note that in our competition experiment ( Figure Figure 5 A mechanism of spatiotemporal regulation of talin in mediating integrin activation.…”

Section: Discussionsupporting

confidence: 90%

A novel membrane-dependent on/off switch mechanism of talin FERM domain at sites of cell adhesion

et al. 2012

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The activation of heterodimeric (α/β) integrin transmembrane receptors by cytosolic protein talin is crucial for regulating diverse cell-adhesion-dependent processes, including blood coagulation, tissue remodeling, and cancer metastasis. This process is triggered by the coincident binding of N-terminal FERM (four-point-one-protein/ezrin/radixin/moesin) domain of talin (talin-FERM) to the inner membrane surface and integrin β cytoplasmic tail, but how these binding events are spatiotemporally regulated remains obscure. Here we report the crystal structure of a dormant talin, revealing how a C-terminal talin rod segment (talin-RS) self-masks a key integrin-binding site on talin-FERM via a large interface. Unexpectedly, the structure also reveals a distinct negatively charged surface on talin-RS that electrostatically hinders the talin-FERM binding to the membrane. Such a dual inhibitory topology for talin is consistent with the biochemical and functional data, but differs significantly from a previous model. We show that upon enrichment with phosphotidylinositol-4,5-bisphosphate (PIP2) -a known talin activator, membrane strongly attracts a positively charged surface on talin-FERM and simultaneously repels the negatively charged surface on talin-RS. Such an electrostatic "pull-push" process promotes the relief of the dual inhibition of talin-FERM, which differs from the classic "steric clash" model for conventional PIP2-induced FERM domain activation. These data therefore unravel a new type of membrane-dependent FERM domain regulation and illustrate how it mediates the talin on/off switches to regulate integrin transmembrane signaling and cell adhesion.

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Section: Discussionsupporting

confidence: 90%

A novel membrane-dependent on/off switch mechanism of talin FERM domain at sites of cell adhesion

et al. 2012

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“…In platelets, Akt activation is both PI3K dependent and independent, but sustained Akt activation is PI3K dependent. 31 …”

Section: Resultsmentioning

confidence: 99%

Deubiquitinases Modulate Platelet Proteome Ubiquitination, Aggregation, and Thrombosis

Gupta

Wei

McIntyre

2015

ATVB

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Objective Platelets express a functional ubiquitin-proteasome system. Mass spectrometry shows platelets contain several deubiquitinases, but whether these are functional, modulate the proteome, or affect platelet reactivity are unknown. Approach and Results Platelet lysates contained ubiquitin-protein deubiquitinase activity hydrolyzing both Lys48 and Lys63 poly-ubiquitin conjugates that was suppressed by the chemically unrelated deubiquitinase inhibitors PYR41 and PR619. These inhibitors acutely and markedly increased mono- and poly-ubiquitination of the proteome of resting platelets. PYR41 (i.v., 15 min) significantly impaired occlusive thrombosis in FeCl3-damaged carotid arteries, and deubiquitinase inhibition reduced platelet adhesion and retention during high shear flow of whole blood through microfluidic chambers coated with collagen. Total internal reflection microscopy showed adhesion and spreading in the absence of flow was strongly curtailed by these inhibitors with failure of stable process extension, and reduced retraction of formed clots. Deubiquitinase inhibition also sharply reduced homotypic platelet aggregation in response to the incomplete agonists ADP and collagen acting through GPVI, but also to the complete agonist thrombin. Suppressed aggregation was accompanied by curtailed PAC-1 binding to activated IIb/IIIa and inhibition of P-selectin translocation to the platelet surface. Deubiquitinase inhibition abolished the agonist-induced spike in intracellular calcium, suppressed Akt phosphorylation, and reduced agonist-stimulated PTEN phosphatase phosphorylation. Platelets express the proteasome-associated deubiquitinases USP14 and UCHL5, and selective inhibition of these enzymes by b-AP15 reproduced the inhibitory effect of the general deubiquitinase inhibitors on ex vivo platelet function. Conclusions Remodeling of the ubiquitinated platelet proteome by deubiquitinases promotes agonist-stimulated intracellular signal transduction and platelet responsiveness.

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“…The PI3K - Akt signaling pathway is involved in platelet aggregation and secretion under various stimulation conditions 24-27 . Rac has been implicated in Akt activation.…”

Section: Resultsmentioning

confidence: 99%

Role for the Guanine Nucleotide Exchange Factor Phosphatidylinositol-3,4,5-Trisphosphate–Dependent Rac Exchanger 1 in Platelet Secretion and Aggregation

Qian

Breton

Chen

et al. 2012

ATVB

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Objective Recent studies have shown a role for Rac1 in regulating platelet functions, but how Rac1 is activated in platelets remains unclear. PIP3-dependent Rac exchanger 1 (P-Rex1) was originally identified in neutrophils that regulates phagocyte functions. We sought to examine whether P-Rex1 plays a role in platelet activation. Methods and Results Western blotting showed P-Rex1 expression in mouse and human platelets. Mice lacking P-Rex1 exhibited prolonged bleeding time and increased re-bleeding. When challenged with low doses of the G protein-coupled receptor (GPCR) agonists U46619 and thrombin, P-Rex1-/- platelets displayed significantly reduced secretion and aggregation compared to WT platelets. Increasing the concentration of these agonists could overcome the defect. Platelet aggregation induced by collagen, a non-GPCR agonist, was also compromised in the absence of P-Rex1. Along with these phenotypic changes were impaired Rac1 activation, reduced ATP secretion, decreased phosphorylation of Akt, JNK and p38 MAPK in P-Rex1-/- platelets upon agonist stimulation. Conclusion These results demonstrate for the first time the presence of P-Rex1 in platelets and its role in platelet secretion as well as aggregation induced by low-dose agonists for GPCR and by collagen.

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PI 3-Kinase p110β Regulation of Platelet Integrin αIIbβ3

Cited by 12 publications

References 138 publications

A novel membrane-dependent on/off switch mechanism of talin FERM domain at sites of cell adhesion

A novel membrane-dependent on/off switch mechanism of talin FERM domain at sites of cell adhesion

Deubiquitinases Modulate Platelet Proteome Ubiquitination, Aggregation, and Thrombosis

Role for the Guanine Nucleotide Exchange Factor Phosphatidylinositol-3,4,5-Trisphosphate–Dependent Rac Exchanger 1 in Platelet Secretion and Aggregation

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