Jl. Daniel et al., EVIDENCE FOR A ROLE FOR TYROSINE PHOSPHORYLATION OF PHOSPHOLIPASE C-GAMMA-2 IN COLLAGEN-INDUCED PLATELET CYTOSOLIC CALCIUM MOBILIZATION, Biochemical journal, 302, 1994, pp. 617-622
(1) The non-specific protein kinase C inhibitor, staurosporine, inhibi
ted collagen-induced increases in cytosolic free Ca2+ while having no
effect on Ca2+ mobilization by other platelet agonists. A more specifi
c inhibitor of protein kinase C, Ro 31-8220, did not inhibit collagen-
induced Ca2+ mobilization. Neither drug had an effect on platelet adhe
sion to collagen. (2) Staurosporine inhibited collagen-stimulated tyro
sine phosphorylation, while Ro 31-8220 had no effect. (3) It also inhi
bited collagen-induced phosphatidic acid formation, inositol trisphosp
hate formation and arachidonic acid liberation. (4) Ro 31-8220 did not
inhibit collagen-stimulated arachidonic acid formation, but it enhanc
ed collagen-stimulated phosphatidic acid and inositol trisphosphate fo
rmation. (5) Immunoprecipitation of phospholipase C gamma 2 (PLC gamma
2) with a specific antibody demonstrated that PLC gamma 2 was phospho
rylated on tyrosine after stimulation by collagen. (6) The phosphoryla
tion of PLC gamma 2 was inhibited by staurosporine but not by Ro 31-82
20. These results provide additional evidence that the mechanism of si
gnal transduction for collagen is different from other platelet agonis
ts and indicate that it involves activation of PLC gamma through a tyr
osine kinase-dependent mechanism.