A novel association of Fc receptor γ-chain with glycoprotein VI and their co-expression as a collagen receptor in human platelets

Abstract

The mechanism by which occupancy of collagen receptors is coupled to platelet activation has been uncertain. Our group previously demonstrated that glycopro tein (GP) VI, an uncharacterized platelet membrane protein, is specifically required for collagen-platelet interaction leading to activation of protein-tyrosine kinase Syk. Since collagen stimulation of platelets has recently been found to induce tyrosine phosphorylation of Fc receptor (FcR) γ-chain, a signal-generating subunit of FcR, we further investigated the relationships between FcR γ-chain and GPVI in human platelets. Our present study revealed the following. FcR γ-chain was physically and stably associated with GPVI in human platelets; both FcR γ-chain and GPVI were proportionally absent in GPVI-deficient platelets; GPVI cross-linking or collagen stimulation of platelets resulted in tyrosine phosphorylation of GPVI-associated FcR γ-chain accompanied by Syk association and activation. These findings strongly suggest that the associated complex of GPVI and FcR γ-chain is a collagen receptor featuring the signaling through immune receptors.