Phosphatidylinositol 4,5-Bisphosphate Regulates Activation-Induced Platelet Microparticle Formation
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- 作者：Daniel J. O'Connell ; Nataliya Rozenvayn ; and Robert Flaumenhaft
- 刊名：Biochemistry
- 出版年：2005
- 出版时间：April 26, 2005
- 年：2005
- 卷：44
- 期：16
- 页码：6361 - 6370
- 全文大小：860K
- 年卷期：v.44,no.16(April 26, 2005)
- ISSN：1520-4995
文摘
While the role of the cytoskeleton in microparticle formation is well-described, the role ofmembrane phospholipids in regulating this process is poorly defined. PIP2 binds many cytoskeletal proteinsand may oppose microparticle formation through associations with these proteins. To determine whetherPIP2 effects microparticle formation, PIP2 was incorporated into platelet membranes prior to activation-induced microparticle formation. Incorporation of PIP2 into platelet membranes inhibited activation-inducedmicroparticle formation by 
90%. Inhibition was dose-dependent with an IC50 of 12-18 
M. Apermeabilized platelet system was next used to assess the effect of modulation of endogenous PIP2 levelson microparticle formation. Infusion of type II
PIP kinase into permeabilized platelets inhibitedmicroparticle formation by 75 ± 8%. In contrast, incubation of permeabilized platelets with PI-specificphospholipase C augmented microparticle formation by greater than 3-fold. Evaluation of PIP kinasesfollowing platelet activation demonstrated that they were lost from platelets in a calpain-dependent mannerduring microparticle formation. Purified -calpain cleaved recombinant type II PIP kinase and inhibitedits ability to phosphorylate PI(5)P. In permeabilized platelets, incubation of purified -calpain reducedPIP2 levels, while exposure to calpeptin increased PIP2 levels. Calpain has previously been implicated inplatelet microparticle formation. These studies show that calpain may help limit PIP2 formation followingplatelet activation and that PIP2 content is an important determinant of platelet microparticle formation.
90%. Inhibition was dose-dependent with an IC50 of 12-18 M. Apermeabilized platelet system was next used to assess the effect of modulation of endogenous PIP2 levelson microparticle formation. Infusion of type II PIP kinase into permeabilized platelets inhibitedmicroparticle formation by 75 ± 8%. In contrast, incubation of permeabilized platelets with PI-specificphospholipase C augmented microparticle formation by greater than 3-fold. Evaluation of PIP kinasesfollowing platelet activation demonstrated that they were lost from platelets in a calpain-dependent mannerduring microparticle formation. Purified -calpain cleaved recombinant type II PIP kinase and inhibitedits ability to phosphorylate PI(5)P. In permeabilized platelets, incubation of purified -calpain reducedPIP2 levels, while exposure to calpeptin increased PIP2 levels. Calpain has previously been implicated inplatelet microparticle formation. These studies show that calpain may help limit PIP2 formation followingplatelet activation and that PIP2 content is an important determinant of platelet microparticle formation.