title: High molecular mass kininogen inhibits cathepsin G-induced platelet activation by forming a complex with cathepsin G.
abstract: BACKGROUND
  Preliminary studies have shown that high molecular mass kininogen (HK) inhibits cathepsin G-induced platelet activation. However, the potential mechanism underlying this inhibitory effect remains to be elucidated.
  
  
  METHODS
  Suspensions of washed and gel-filtered platelets were used in radioligand binding and aggregation studies. The amidolytic activity of cathepsin G was measured using specific chromogenic substrate. Western blot technique was utilised to explore the potential complex formation between cathepsin G and HK. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to analyse the cleavage products of HK.
  
  
  RESULTS
  At a concentration of 1 microM, HK completely blocked cathepsin G-induced platelet shape change and secretion of ATP. HK inhibited cathepsin G-induced platelet aggregation in a concentration-dependent manner with an IC(50) of 0.48 microM. Moreover, HK was found to inhibit binding of (125)I-cathepsin G to gel-filtered platelets. (125)I-cathepsin G forms a complex with HK. The complex formation did not affect the amidolytic activity of cathepsin G. HK was proteolysed upon interaction with cathepsin G.
  
  
  CONCLUSIONS
  Our results show that high molecular mass kininogen down-regulates cathepsin G-induced platelet activation by forming a complex with cathepsin G and thus prevents binding of cathepsin G to platelets. These kininogen-cathepsin G interactions may be potential targets for pharmacological intervention.
authors.affiliation: Hematology Unit, Clinical Pathology Department, Al-Mansoura Faculty of Medicine, Al-Mansoura, Egypt.
authors.forename: T E
authors.initials: TE
authors.lastname: Selim
authors.forename: H R
authors.initials: HR
authors.lastname: Ghoneim
authors.forename: H A
authors.initials: HA
authors.lastname: Abdel Ghaffar
authors.forename: R W
authors.initials: RW
authors.lastname: Colman
authors.forename: R A
authors.initials: RA
authors.lastname: Dela Cadena
mesh_terms: D001792:Blood Platelets / Q000378:metabolism; D056649:Cathepsin G; D002403:Cathepsins / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D006801:Humans; D020128:Inhibitory Concentration 50; D007700:Kinetics; D019679:Kininogen, High-Molecular-Weight / Q000378:metabolism / Q000494:pharmacology*; D010446:Peptide Fragments / Q000032:analysis; D015539:Platelet Activation / Q000187:drug effects*; D011485:Protein Binding; D012697:Serine Endopeptidases
chemical_list: D019679:Kininogen, High-Molecular-Weight; D010446:Peptide Fragments; D002403:Cathepsins; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G