Membrane glycoprotein IV (CD36) is physically associated with the Fyn, Lyn, and Yes protein-tyrosine kinases in human platelets.

TLDR

Platelet activation by thrombin and other agonists rapidly increases tyrosine phosphorylation of multiple proteins. The study aimed to identify protein‑tyrosine kinases responsible for these phosphorylation events. The authors analyzed expression of seven Src-family PTKs and examined their association with platelet membrane glycoproteins. Five Src-related kinases were detected in platelets, with pp60SRC most abundant, and glycoprotein IV (CD36) was found in complexes with Fyn, Yes, and Lyn, indicating that GPIV engagement may trigger tyrosine‑phosphorylation signaling pathways.

Abstract

Activation of platelets with thrombin and other agonists causes a rapid increase in the phosphorylation of multiple proteins on tyrosine. To identify candidate protein-tyrosine kinases (PTKs; EC 2.7.1.112) that may be responsible for these phosphorylation events, we analyzed the expression of seven Src-family PTKs and examined the association of these kinases with known platelet membrane glycoproteins. Five Src-related PTKs were detected in platelets: pp60SRC, pp60FYN, pp62YES, pp61HCK, and two LYN products of Mr 54,000 and 58,000. The Fgr and Lck PTKs were not detected. Although strict comparative quantification of protein levels was not possible, pp60SRC was detected at higher levels than any of the other kinases. In addition, glycoprotein IV (GPIV, CD36), one of the major platelet membrane glycoproteins, was associated in a complex with the Fyn, Yes, and Lyn proteins in platelet lysates. Similar complexes were also found in two GPIV-expressing cell lines, C32 melanoma cells and HEL cells. Since PTKs appear to be involved in stimulus-response coupling at the plasma membrane, these results suggest that ligand interaction with GPIV may activate signaling pathways that are triggered by tyrosine phosphorylation.