Initiation of plasminogen activation on the surface of monocytes expressing the type II transmembrane serine protease matriptase.
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.
Kilpatrick
Lynette M
LM
Biomedical Research Centre, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
Harris
Roger L
RL
Owen
Kate A
KA
Bass
Rosemary
R
Ghorayeb
Christine
C
Bar-Or
Amit
A
Ellis
Vincent
V
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
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