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Prepublished online as a Blood First Edition Paper on April 3, 2003; DOI 10.1182/blood-2002-09-2897.
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Blood, 1 August 2003, Vol. 102, No. 3, pp. 940-948
HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY
SHIP-2 forms a tetrameric complex with filamin, actin, and GPIb-IX-V: localization of SHIP-2 to the activated platelet actin cytoskeleton
Jennifer M. Dyson,
Adam D. Munday,
Anne M. Kong,
Richard D. Huysmans,
Maria Matzaris,
Meredith J. Layton,
Harshal H. Nandurkar,
Michael C. Berndt, and
Christina A. Mitchell
From the Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia; and Joint Protein Structure Laboratory, Ludwig Institute for Cancer Research and the Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
The platelet receptor for the von Willebrand factor (VWF) glycoprotein Ib-IX-V (GPIb-IX-V) complex mediates platelet adhesion at sites of vascular injury. The cytoplasmic tail of the GPIb subunit interacts with the actin-binding protein, filamin, anchoring the receptor in the cytoskeleton. In motile cells, the second messenger phosphatidylinositol 3,4,5 trisphosphate (PtdIns(3,4,5)P3) induces submembraneous actin remodeling. The inositol polyphosphate 5-phosphatase, Src homology 2 domain-containing inositol polyphosphate 5-phosphatase-2 (SHIP-2), hydrolyzes PtdIns(3,4,5)P3 forming phosphatidylinositol 3,4 bisphosphate (PtdIns(3,4)P2) and regulates membrane ruffling via complex formation with filamin. In this study we investigate the intracellular location and association of SHIP-2 with filamin, actin, and the GPIb-IX-V complex in platelets. Immunoprecipitation of SHIP-2 from the Triton-soluble fraction of unstimulated platelets demonstrated association between SHIP-2, filamin, actin, and GPIb-IX-V. SHIP-2 associated with filamin or GPIb-IX-V was active and demonstrated PtdIns(3,4,5)P3 5-phosphatase activity. Following thrombin or VWF-induced platelet activation, detection of the SHIP-2, filamin, and receptor complex decreased in the Triton-soluble fraction, although in control studies the level of SHIP-2, filamin, or GPIb-IX-V immunoprecipitated by their respective antibodies did not change following platelet activation. In activated platelets spreading on a VWF matrix, SHIP-2 localized intensely with actin at the central actin ring and colocalized with actin and filamin at filopodia and lamellipodia. In spread platelets, GPIb-IX-V localized to the center of the platelet and showed little colocalization with filamin at the plasma membrane. These studies demonstrate a functionally active complex between SHIP-2, filamin, actin, and GPIb-IX-V that may orchestrate the localized hydrolysis of PtdIns(3,4,5)P3 and thereby regulate cortical and submembraneous actin.

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