title: Initiation of plasminogen activation on the surface of monocytes expressing the type II transmembrane serine protease matriptase.
abstract: uPA (urokinase-type plasminogen activator) activates plasminogen with high efficiency when bound to its cellular receptor uPAR, but only after a prolonged lag phase during which generated plasmin activates pro-uPA. How the activity of this proteolytic system might be rapidly initiated is unknown. We have now found that 2 monocytic cell lines display distinct patterns of plasminogen activation. U937 cells, but not THP-1 cells, displayed the expected lag phase, suggesting a constitutive initiation mechanism on the latter. This was shown to be due to the plasmin-independent activation of uPAR-bound pro-uPA by a cell surface-associated protease and to correlate with the expression of matriptase, a type II transmembrane serine protease that was highly expressed in THP-1 cells but undetectable in U937 cells. Kinetic analysis demonstrated that matriptase is a relatively poor activator of pro-uPA in solution, approximately 100-fold less efficient than plasmin (k(cat)/K(m) 1.16 x 10(5) M(-1)s(-1) cf 1.21 x 10(7) M(-1)s(-1)). However, down-regulation of matriptase expression in THP-1 cells by siRNA reduced the activation of cell-associated pro-uPA and the subsequent rapid initiation of plasminogen activation by 76% to 93%. Matriptase was also found to be expressed by peripheral blood monocytes and may therefore be a specific mechanism for the rapid initiation and regulation of plasminogen activation by these cells.
authors.affiliation: Biomedical Research Centre, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
authors.forename: Lynette M
authors.initials: LM
authors.lastname: Kilpatrick
authors.forename: Roger L
authors.initials: RL
authors.lastname: Harris
authors.forename: Kate A
authors.initials: KA
authors.lastname: Owen
authors.forename: Rosemary
authors.initials: R
authors.lastname: Bass
authors.forename: Christine
authors.initials: C
authors.lastname: Ghorayeb
authors.forename: Amit
authors.initials: A
authors.lastname: Bar-Or
authors.forename: Vincent
authors.initials: V
authors.lastname: Ellis
mesh_terms: D001483:Base Sequence; D020134:Catalytic Domain; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D018076:DNA, Complementary / Q000235:genetics; D004789:Enzyme Activation; D015870:Gene Expression; D006801:Humans; D007700:Kinetics; D009000:Monocytes / Q000201:enzymology* / Q000378:metabolism; D010958:Plasminogen / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D011956:Receptors, Cell Surface / Q000378:metabolism; D055293:Receptors, Urokinase Plasminogen Activator; D012697:Serine Endopeptidases / Q000097:blood / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020298:U937 Cells; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; C524898:PLAUR protein, human; D034741:RNA, Small Interfering; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D010958:Plasminogen; D012697:Serine Endopeptidases; C485595:matriptase; D014568:Urokinase-Type Plasminogen Activator