Proteolytic modulation of thrombopoietin activity: comparison of thrombin, plasmin, and urokinase.
Several observations suggest that limited proteolysis of full-length 70 kD human thrombopoietin (Tpo) may be important for Tpo biology. Recently, it was reported that thrombin cleaves full-length recombinant human Tpo (rhTpo) sequentially at two sites, Arg(195) within the glycan domain followed by Arg(117) within the cytokine domain, and that these cleavages modulate Tpo activity in vitro. We demonstrate that urokinase and plasmin also cleave rhTpo in a time-dependent manner. Urokinase cleavage is confined to the glycan domain, and generates a 35 kD N-terminal fragment that contains the intact cytokine domain, and is associated with increased Tpo activity. In contrast, plasmin cleaves Tpo sequentially at two specific sites (Arg(205) within the glycan domain followed by Lys(52) within the cytokine domain), and is associated with a marked decrease in Tpo activity. These proteolytic events have potential implications for regulation of Tpo activity in vivo.
Reiner
A P
AP
Department of Medicine, University of Washington, Seattle 98195, USA. apreiner@u.washington.edu
Aramaki
K M
KM
D001665:Binding Sites; D002455:Cell Division / Q000187:drug effects; D005341:Fibrinolysin / Q000378:metabolism / Q000494:pharmacology; D005343:Fibrinolytic Agents / Q000378:metabolism / Q000494:pharmacology; D006490:Hemostatics / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D010960:Plasminogen Activators / Q000378:metabolism / Q000494:pharmacology; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D020539:Sequence Analysis, Protein; D012697:Serine Endopeptidases / Q000378:metabolism* / Q000494:pharmacology; D013917:Thrombin / Q000378:metabolism / Q000494:pharmacology; D013926:Thrombopoietin / Q000187:drug effects / Q000378:metabolism*; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism / Q000494:pharmacology
D005343:Fibrinolytic Agents; D006490:Hemostatics; D010446:Peptide Fragments; D011994:Recombinant Proteins; D013926:Thrombopoietin; D010960:Plasminogen Activators; D012697:Serine Endopeptidases; D013917:Thrombin; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator