Plasmin-platelet interaction involves cleavage of functional thrombin receptor.
We tested the hypothesis that the inhibition of thrombin-induced platelet activation by plasmin is mediated via the enzymatic action of plasmin on the functional thrombin receptor. We monitored the binding of the anti-thrombin receptor antibody [anti-TR-(34-46)] to platelets; this binding is sensitive to the cleavage of the thrombin receptor at amino acid residues Arg-41 to Ser-42. Plasmin inhibited anti-TR-(34-46) binding in dose- and time-dependent manners. The inactive synthetic peptide with the amino acid sequence 40-55 of the thrombin receptor (D-FPRSFLLRNPNDKYEPF) was similarly cleaved by thrombin and plasmin to an active peptide (SFLLRNPNDKYEPF) that produced robust cytosolic Ca2+ responses. At high concentrations, plasmin itself can activate platelets. We explored this effect with the use of anti-TR-(1-160). This antibody abolished the cytosolic Ca2+ responses to thrombin and to the thrombin receptor-activating peptide SFLLRN but did not attenuate the plasmin-induced cytosolic Ca2+ response. Thus plasmin inhibits thrombin-evoked platelet activation by cleaving the thrombin receptor, but the plasmin-induced cytosolic Ca2+ response is not due to the generation of the tethered peptide of the thrombin receptor.
Kimura
M
M
Hypertension Research Center, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark 07103-2714, USA.
Andersen
T T
TT
Fenton
J W
JW
Bahou
W F
WF
Aviv
A
A
D000595:Amino Acid Sequence; D000906:Antibodies / Q000276:immunology; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D005341:Fibrinolysin / Q000494:pharmacology / Q000502:physiology*; D005434:Flow Cytometry / Q000379:methods; D006801:Humans; D013058:Mass Spectrometry; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D018179:Receptors, Thrombin / Q000737:chemistry / Q000276:immunology / Q000502:physiology*; D013917:Thrombin / Q000494:pharmacology
D000906:Antibodies; D010446:Peptide Fragments; D018179:Receptors, Thrombin; D013917:Thrombin; D005341:Fibrinolysin; D002118:Calcium