The Cytoplasmic Domain of the α-Subunit of Glycoprotein (GP) Ib Mediates Attachment of the Entire GP Ib-IX Complex to the Cytoskeleton and Regulates von Willebrand Factor-induced Changes in Cell Morphology

Janet G Cunningham,Sylvie C Meyer,Joan E.B Fox

doi:10.1074/jbc.271.19.11581

Janet G Cunningham, Sylvie C Meyer + Show 1 more

Open Access

https://doi.org/10.1074/jbc.271.19.11581

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Abstract

The glycoprotein (GP) Ib-IX complex is one of the major platelet membrane glycoproteins. Its extracellular domain binds von Willebrand factor at a site of injury, an interaction that leads to activation of intracellular pathways. Its intracellular domain associates tightly with the platelet cytoskeleton through actin-binding protein. The goal of the present study was to investigate the role of the cytoplasmic domain of the GP Ib-IX complex and its interaction with the cytoskeleton. Cultured cells were transfected with the cDNAs coding for GP Ib(beta), GP IX, and full-length or truncated forms of GP Ib(alpha). Western blots of detergent-insoluble fractions of Triton X-100-lysed cells showed that deletion of amino acids Trp-570 to Ser-590 from the cytoplasmic domain of GP IB(alpha) abolished the interaction of the entire GP Ib-IX complex with the cytoskeleton. Truncated GP Ib(alpha) that was unable to associate with the cytoskeleton retained its ability to associate with GP Ib(beta), to be inserted into the membrane, and to bind von Willebrand factor. Cells expressing GP Ib(alpha) changed their shape following adhesion to immobilized von Willebrand factor. Cells expressing truncated GP Ib(alpha) also changed their shape following adhesion but showed a very different morphology as compared to cells expressing full-length GP Ib(alpha). These results show that GP Ib-IX-von Willebrand factor interactions lead to cytoskeletal reorganizations, that the cytoplasmic domain of GP Ib(alpha) regulates these reorganizations, and that the cytoplasmic domain of GP Ib(alpha) is absolutely required for attachment of the GP Ib-IX complex to the cytoskeleton.

Highlights

The glycoprotein (GP)1 Ib-IX complex is one of the major platelet transmembrane complexes [1,2,3,4]
Cells expressing truncated GP Ib␣ changed their shape following adhesion but showed a very different morphology as compared to cells expressing full-length GP Ib␣. These results show that GP Ib-IX-von Willebrand factor interactions lead to cytoskeletal reorganizations, that the cytoplasmic domain of GP Ib␣ regulates these reorganizations, and that the cytoplasmic domain of GP Ib␣ is absolutely required for attachment of the GP Ib-IX complex to the cytoskeleton
Because previous work with synthetic peptides had shown that peptides based on sequences in the cytoplasmic domain of the GP Ib␣ subunit could bind to actin-binding protein in vitro [22], we focused on truncations in the cytoplasmic domain of the GP Ib␣ subunit of the complex

Summary

Introduction

The glycoprotein (GP) Ib-IX complex is one of the major platelet transmembrane complexes [1,2,3,4] It consists of two disulfide-linked subunits, GP Ib␣ (Mr ϭ 145,000) and GP Ib␤ (Mr ϭ 24,000), that are noncovalently complexed with another glycoprotein, GP IX (Mr ϭ 22,000) [5,6,7,8]. This complex binds von Willebrand factor on exposed vascular subendothelium and. It is well established that GP Ib-IX associates with the cytoskeleton, the importance of the cytoplasmic domain of this receptor in regulating ligand binding or ligand-induced transmembrane signaling has not been investigated

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