title: Identification of a novel 33-kDa Ser/Thr kinase that phosphorylates the cytoplasmic tail of protease-activated receptor 1 (thrombin receptor) in human platelets.
abstract: Stimulation of human platelets with thrombin or thrombin receptor agonist peptide (TRAP/ Ser-Phe-Leu-Leu-Arg-Asn) resulted in phosphorylation of the protease-activated receptor 1 (PAR1). However, protein kinase(s), capable of phosphorylating PAR1 upon activation of this receptor, has not been as yet identified in human platelets. The present study was undertaken to assess the presence of protein kinase(s) that may interact with PAR1 using a procedure based on the ability of protein kinase to undergo renaturation and phosphorylate a protein substrate fixed in a gel. We employed a fusion protein that was prepared using a glutathione S-transferase (GST) and the cytoplasmic tail of PARI (Pro368-Thr425)(GST-PAR1) or a reverse sequenced peptide of this domain (GST-rPAR1). The results showed that treatment of platelets with thrombin induced about 10-fold increase in the activity of the 33-kDa Ser/Thr protein kinase, which was also activated by TRAP, but not by hirudin-treated thrombin or diisopropylfluorophosphate-inactivated thrombin, suggesting that it is activated through PAR1. Furthermore, treatment of platelets with thromboxane A1 analog, STA2, led to an activation of this protein kinase and phosphorylation of PAR1. In conclusion, the present study provides evidence of homologous and heterologous activation of a novel 33-kDa Ser/Thr kinase that phosphorylates the cytoplasmic tail of PAR1.
authors.affiliation: Department of Molecular Pathobiology, Mie University School of Medicine, Tsu-city, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Ido
authors.forename: T
authors.initials: T
authors.lastname: Hayashi
authors.forename: E C
authors.initials: EC
authors.lastname: Gabazza
authors.forename: K
authors.initials: K
authors.lastname: Suzuki
mesh_terms: D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism; D006629:Hirudins / Q000494:pharmacology; D006801:Humans; D007531:Isoflurophate / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000302:isolation & purification* / Q000502:physiology; D017434:Protein Structure, Tertiary; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000494:pharmacology; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D006629:Hirudins; D010446:Peptide Fragments; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin; D011993:Recombinant Fusion Proteins; C082835:thrombin receptor peptide (42-47); D007531:Isoflurophate; D013928:Thromboxane A2; C037866:STA 2; D005982:Glutathione Transferase; D017346:Protein Serine-Threonine Kinases; D013917:Thrombin