Abstract
Full platelet activation with serotonin secretion and thromboxane A2 (TxA2) formation induced by a low dose of thrombin receptor agonist peptide (TRAP) or high
dose ADP requires platelet aggregation. This requirement can be replaced by pretreatment
of platelets with a combination of reagents including: GPIIb/IIIa inhibitors yielding
ligand-induced binding sites (LIBS), either arginine–glycine–aspartate–serine (RGDS)
peptide or Ro 43-5054, cytochalasin to disrupt actin filaments and crosslinking by
a GPIIb/IIIa mAb (pl-62). Crosslinking is required since Fab fragments of pl-62 do
not support activation. Engagement of the Fc receptor by the mAb Fc domain is not
required for pl-62 augmentation, since it is not blocked by the anti-Fc receptor mAb,
IV-3. Another GPIIb/IIIa inhibitor, Ro 44-9883, not yielding LIBS epitopes, serves
as a negative control and shows a requirement for LIBS in addition to crosslinking.
Focal adhesion kinase tyrosine phosphorylation induced by TRAP is blocked by these
GPIIb/IIIa antagonists, but restored by pl-62 crosslinking independent of LIBS induction.
Tyrosine phosphorylation of a peptide comigrating with p38 MAP kinase is also inhibited
by these antagonists and restored by pl-62 crosslinking. However, p38 MAP kinase activation
by low dose TRAP is not affected by these aggregation inhibitors. Tyrosine phosphorylation
of a 34-kDa phosphoprotein in the absence of aggregation or TxA2 formation was uniquely augmented by Ro 43-5054 but not Ro 44-9883 under the above
activation conditions.
Keywords
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Article info
Publication history
Accepted:
July 11,
2001
Received in revised form:
July 11,
2001
Received:
May 16,
2001
Identification
Copyright
© 2001 Elsevier Science Ltd. Published by Elsevier Inc. All rights reserved.
