Faculty Collaboration Database

Relationships between Rap1b, affinity modulation of integrin alpha IIbbeta 3, and the actin cytoskeleton. J Biol Chem 2002 Jul 12;277(28):25715-21

Date

05/08/2002

Pubmed ID

11994301

DOI

10.1074/jbc.M202791200

Scopus ID

2-s2.0-0037067748 (requires institutional sign-in at Scopus site)   172 Citations

Abstract

The affinity of integrin alpha(IIb)beta(3) for fibrinogen is controlled by inside-out signals that are triggered by agonists like thrombin. Agonist treatment of platelets also activates Rap1b, a small GTPase known to promote integrin-dependent adhesion of other cells. Therefore, we investigated the role of Rap1b in alpha(IIb)beta(3) function by viral transduction of GFP-Rap1 chimeras into murine megakaryocytes, which exhibit inside-out signaling similar to platelets. Expression of constitutively active GFP-Rap1b (V12) had no effect on unstimulated megakaryocytes, but it greatly augmented fibrinogen binding to alpha(IIb)beta(3) induced by a PAR4 thrombin receptor agonist (p < 0.01). The Rap1b effect was cell-autonomous and was prevented by pre-treating cells with cytochalasin D or latrunculin A to inhibit actin polymerization. Rap1b-dependent fibrinogen binding to megakaryocytes was blocked by POW-2, a novel monovalent antibody Fab fragment specific for high affinity murine alpha(IIb)beta(3). In contrast to GFP-Rap1b (V12), expression of GFP-Rap1GAP, which deactivates endogenous Rap1, inhibited agonist-induced fibrinogen binding (p < 0.01), as did dominant-negative GFP-Rap1b (N17) (p < 0.05). None of these treatments affected surface expression of alpha(IIb)beta(3). These studies establish that Rap1b can augment agonist-induced ligand binding to alpha(IIb)beta(3) through effects on integrin affinity, possibly by modulating alpha(IIb)beta(3) interactions with the actin cytoskeleton.

Author List

Bertoni A, Tadokoro S, Eto K, Pampori N, Parise LV, White GC, Shattil SJ

Author

Gilbert C. White MD Professor in the Medicine department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

3T3 Cells
Actins
Amino Acid Sequence
Animals
Cricetinae
Cytoskeleton
Humans
Mice
Mice, Inbred BALB C
Platelet Glycoprotein GPIIb-IIIa Complex
Protein Binding
rap GTP-Binding Proteins