Platelet endothelial cell adhesion molecule-1 regulates collagen-stimulated platelet function by modulating the association of phosphatidylinositol 3-kinase with Grb-2-associated binding protein-1 and linker for activation of T cells.
BACKGROUND
Platelet activation by collagen depends on signals transduced by the glycoprotein (GP)VI-Fc receptor (FcR)γ-chain collagen receptor complex, which involves recruitment of phosphatidylinositol 3-kinase (PI3K) to phosphorylated tyrosines in the linker for activation of T cells (LAT). An interaction between the p85 regulatory subunit of PI3K and the scaffolding molecule Grb-2-associated binding protein-1 (Gab1), which is regulated by binding of the Src homology 2 domain-containing protein tyrosine phosphatase-2 (SHP-2) to Gab1, has been shown in other cell types to sustain PI3K activity to elicit cellular responses. Platelet endothelial cell adhesion molecule-1 (PECAM-1) functions as a negative regulator of platelet reactivity and thrombosis, at least in part by inhibiting GPVI-FcRγ-chain signaling via recruitment of SHP-2 to phosphorylated immunoreceptor tyrosine-based inhibitory motifs in PECAM-1.


OBJECTIVE
To investigate the possibility that PECAM-1 regulates the formation of the Gab1-p85 signaling complexes, and the potential effect of such interactions on GPVI-mediated platelet activation in platelets.


METHODS
The ability of PECAM-1 signaling to modulate the LAT signalosome was investigated with immunoblotting assays on human platelets and knockout mouse platelets.


RESULTS
PECAM-1-associated SHP-2 in collagen-stimulated platelets binds to p85, which results in diminished levels of association with both Gab1 and LAT and reduced collagen-stimulated PI3K signaling. We therefore propose that PECAM-1-mediated inhibition of GPVI-dependent platelet responses result, at least in part, from recruitment of SHP-2-p85 complexes to tyrosine-phosphorylated PECAM-1, which diminishes the association of PI3K with activatory signaling molecules, such as Gab1 and LAT.
Moraes
L A
LA
Institute for Cardiovascular & Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK. l.a.moraes@reading.ac.uk
Barrett
N E
NE
Jones
C I
CI
Holbrook
L M
LM
Spyridon
M
M
Sage
T
T
Newman
D K
DK
Gibbins
J M
JM
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D058543:Class Ia Phosphatidylinositol 3-Kinase / Q000378:metabolism; D003094:Collagen / Q000378:metabolism*; D051380:GRB2 Adaptor Protein / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D015539:Platelet Activation; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11 / Q000378:metabolism; D015398:Signal Transduction; D014443:Tyrosine / Q000737:chemistry
D048868:Adaptor Proteins, Signal Transducing; C098587:GAB1 protein, human; D051380:GRB2 Adaptor Protein; C490897:Gab1 protein, mouse; C110810:LAT protein, human; C491734:Lat protein, mouse; D008565:Membrane Proteins; D010750:Phosphoproteins; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D014443:Tyrosine; D003094:Collagen; D019869:Phosphatidylinositol 3-Kinases; D058543:Class Ia Phosphatidylinositol 3-Kinase; C516724:PTPN11 protein, human; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; C516725:Ptpn11 protein, mouse