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J. Exp. Med.,
Volume 188, Number 2, July 20, 1998 267-276
Chain
Complex on Human Platelets
By
From the Department of Hematology and Oncology, Clinical Sciences for Pathological Organs,
Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan
We have previously shown that uncharacterized glycoprotein VI (GPVI), which is constitutively associated and coexpressed with Fc receptor
chain (FcR
) in human platelets, is essential for collagen-stimulated tyrosine phosphorylation of FcR
, Syk, and phospholipase C
2
(PLC
2), leading to platelet activation. Here we investigated involvement of the Src family in
the proximal signals through the GPVI-FcR
complex, using the snake venom convulxin from Crotalus durissus terrificus, which specifically recognizes GPVI and activates platelets
through cross-linking GPVI. Convulxin-coupled beads precipitated the GPVI-FcR
complex
from platelet lysates. Collagen and convulxin induced tyrosine phosphorylation of FcR
, Syk,
and PLC
2 and recruited tyrosine-phosphorylated Syk to the GPVI-FcR
complex. Using
coprecipitation methods with convulxin-coupled beads and antibodies against FcR
and the
Src family, we showed that Fyn and Lyn, but not Yes, Src, Fgr, Hck, and Lck, were physically associated with the GPVI-FcR
complex irrespective of stimulation. Furthermore, Fyn was
rapidly activated by collagen or cross-linking GPVI. The Src family-specific inhibitor PP1
dose-dependently inhibited collagen- or convulxin-induced tyrosine phosphorylation of proteins including FcR
, Syk, and PLC
2, accompanied by a loss of aggregation and ATP release
reaction. These results indicate that the Src family plays a critical role in platelet activation via
the collagen receptor GPVI-FcR
complex.
chain;
Src family;
collagen;
platelets
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