HDL3-mediated inhibition of thrombin-induced platelet aggregation and fibrinogen binding occurs via decreased production of phosphoinositide-derived second messengers 1,2-diacylglycerol and inositol 1,4,5-tris-phosphate.
We demonstrate that physiological concentrations of HDL3 inhibit the thrombin-induced platelet fibrinogen binding and aggregation in a time- and concentration-dependent fashion. The underlying mechanism includes HDL3-mediated inhibition of phosphatidylinositol 4,5-bis-phosphate turnover, 1,2-diacylglycerol and inositol 1,4,5-tris-phosphate formation, and intracellular calcium mobilization. The inhibitory effects of HDL3 on inositol 1,4,5-tris-phosphate formation and intracellular calcium mobilization were abolished after covalent modification of HDL3 with dimethylsuberimidate. Furthermore, they could be blocked by calphostin C and bis-indolylmaleimide, 2 highly selective and structurally unrelated protein kinase C inhibitors. However, the inhibitory effects of HDL3 were not blocked by H89, a protein kinase A inhibitor. In addition, HDL3 failed to induce cAMP formation but stimulated the phosphorylation of the protein kinase C 40- to 47-kD major protein substrate. We observed a close temporal relationship between the HDL3-mediated inhibition of thrombin-induced inositol 1,4,5-tris-phosphate formation, intracellular calcium mobilization, and fibrinogen binding and the phosphorylation of the protein kinase C 40- to 47-kD major protein substrate. Taken together, these findings indicate that the HDL3-mediated inhibition of thrombin-induced fibrinogen binding and aggregation occurs via inhibition of phosphatidylinositol 4,5-bis-phosphate turnover and formation of 1,2-diacylglycerol and inositol 1,4,5-tris-phosphate. Protein kinase C may be involved in this process.
Nofer
J R
JR
Institut für Klinische Chemie und Laboratoriumsmedizin, Zentrallaboratorium, Westfälische Wilhelms-Universität, Münster, Germany.
Walter
M
M
Kehrel
B
B
Wierwille
S
S
Tepel
M
M
Seedorf
U
U
Assmann
G
G
D000328:Adult; D015703:Antigens, CD / Q000096:biosynthesis; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003029:Coagulants / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007424:Intracellular Fluid; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008875:Middle Aged; D010712:Phosphatidic Acids / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D010766:Phosphorylation; D015539:Platelet Activation; D010974:Platelet Aggregation; D011493:Protein Kinase C / Q000378:metabolism; D015290:Second Messenger Systems; D013379:Substrate Specificity; D013917:Thrombin / Q000494:pharmacology*; D013997:Time Factors
C011439:1,2-diacylglycerol; D015703:Antigens, CD; D003029:Coagulants; D004075:Diglycerides; D008075:Lipoproteins, HDL; D010712:Phosphatidic Acids; D019269:Phosphatidylinositol 4,5-Diphosphate; D015544:Inositol 1,4,5-Trisphosphate; D005340:Fibrinogen; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D013917:Thrombin; D002118:Calcium