Protein-tyrosine phosphorylation and p72syk activation in human platelets stimulated with collagen is dependent upon glycoprotein Ia/IIa and actin polymerization.
In human platelets treated with acetylsalicylic acid, collagen induced protein-tyrosine-phosphorylation of several proteins. The major 75 kDa band included cortactin and auto-phosphorylated p72syk. p72syk activity rapidly increased upon collagen stimulation, whereas p60c-src activation was below detectable levels. A combination of inhibitors to remove the effects of extracellular and intracellular Ca2+, released ADP, and fibrinogen binding to GPIIb/IIIa delayed and attenuated the major 75 kDa band. By contrast, p72syk activation was not inhibited by these treatments. Cytochalasin D completely inhibited protein tyrosine phosphorylation and p72syk activation. It also potently inhibited aggregation and [Ca2+]i elevation. Anti-GPIa/IIa MoAb in a concentration-dependent manner partially attenuated protein tyrosine phosphorylation and p72syk activation. Its inhibitory effects on intracellular Ca2+ mobilization, release of intracellular granule contents, and aggregation also were partial. No tyrosine kinase activity was coprecipitated with GPIa/IIa. These results suggest that p72syk activation lies upstream of protein tyrosine phosphorylation, Ca2+ mobilization, ADP release, thromboxane A2 production and aggregation. GPIa/IIa plays a key role in p72syk activation induced by collagen, but other collagen receptors may work in synergy to fully activate p72syk. Actin polymerization is a prerequisite for both p72syk activation and other intracellular signal transduction pathways.
Asazuma
N
N
Department of Clinical and Laboratory Medicine, Yamanashi Medical University, Japan.
Yatomi
Y
Y
Ozaki
Y
Y
Qi
R
R
Kuroda
K
K
Satoh
K
K
Kume
S
S
D000199:Actins / Q000737:chemistry*; D000244:Adenosine Diphosphate / Q000097:blood; D000595:Amino Acid Sequence; D001704:Biopolymers; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000097:blood; D003094:Collagen / Q000494:pharmacology*; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000097:blood; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D010766:Phosphorylation; D015539:Platelet Activation; D010980:Platelet Membrane Glycoproteins / Q000276:immunology / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000097:blood*; D013268:Stimulation, Chemical; D000072377:Syk Kinase
D000199:Actins; D001704:Biopolymers; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D010980:Platelet Membrane Glycoproteins; D000244:Adenosine Diphosphate; D003094:Collagen; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D002118:Calcium