Collagen-induced binding to human platelets of platelet-derived growth factor leading to inhibition of P43 and P20 phosphorylation.
Platelet-derived growth factor (PDGF) is known to inhibit collagen-induced platelet aggregation. Collagen-induced binding of 125I-PDGF to human washed platelets was therefore investigated. It was found 1) to be time-dependent, reaching a plateau at 20 degrees C after 30 min, 2) collagen concentration-dependent, 3) specifically inhibited by unlabeled PDGF, and 4) saturable. Scatchard plot analysis showed a single class of sites with 3000 +/- 450 molecules bound/cell and an apparent KD of 1.2 +/- 0.2 10(-8) M. The effects of PDGF on collagen-induced phosphoinositide breakdown and protein phosphorylation were also investigated. At 50 ng/ml PDGF, a concentration which completely inhibited collagen-induced aggregation, the breakdown of [32P]phosphatidylinositol 4,5-biphosphate (PIP2) and [32P]phosphatidylinositol 4-phosphate (PIP) was observed, but the subsequent replenishment of [32P]PIP2 was inhibited. The same PDGF concentration totally inhibited collagen-induced phosphatidic acid formation. PDGF also completely prevented phosphorylation of P43 and P20, as a result of protein kinase C activation consecutive to phosphoinositide metabolism. These results suggest that (i) a specific PDGF receptor can be induced by collagen, and (ii) PDGF can effect the early events of collagen-induced platelet activation by inhibiting PIP2 resynthesis and P43 and P20 phosphorylation. It is concluded that PDGF might be involved in a negative feed-back control of platelet activation.
Bryckaert
M C
MC
Hôpital Lariboisière, Institut National de la Santé et de la Recherche Médicale U 150, Paris, France.
Rendu
F
F
Tobelem
G
G
Wasteson
A
A
D001665:Binding Sites; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D003094:Collagen / Q000494:pharmacology*; D005480:Flurbiprofen / Q000494:pharmacology; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D010712:Phosphatidic Acids / Q000097:blood; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000097:blood; D010750:Phosphoproteins / Q000097:blood*; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism* / Q000494:pharmacology
D007457:Iodine Radioisotopes; D010712:Phosphatidic Acids; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010750:Phosphoproteins; D010982:Platelet-Derived Growth Factor; C037178:phosphatidylinositol 4-phosphate; D005480:Flurbiprofen; D003094:Collagen