AJP - Renal Physiology, Vol 267, Issue 2 303-F310, Copyright © 1994 by American Physiological Society
Expression of plasminogen/plasmin receptors on human glomerular epithelial cells
L. Becquemont, G. Nguyen, M. N. Peraldi, C. J. He, J. D. Sraer and E. Rondeau
Institut National de la Sante et de la Recherche Medicale U 64, Hopital Tenon, Paris, France.
The aim of the present study was to display plasminogen/plasmin receptors
on human glomerular epithelial cell (HGEC) membranes and to determine the
properties of receptor-bound plasminogen at the cell surface. Using an
immortalized human glomerular epithelial cell line (E71-A1), we found a
specific, saturable, and reversible binding of 125I-labeled plasminogen and
125I-labeled plasmin to HGEC that involved the lysine binding sites of both
ligands. 125I-plasminogen and 125I-plasmin bound to the same receptors with
different affinities: Kd = 1.20 +/- 0.08 and 0.30 +/- 0.05 microM,
respectively (P < 0.001). The number of binding sites per cell was 6.00
+/- 0.56 x 10(6) for plasminogen and 2.00 +/- 0.47 x 10(6) for plasmin (P
< 0.05). Similar receptor affinities were found on isolated glomeruli,
on immortalized and nonimmortalized HGEC, and on purified HGEC membranes.
The apparent kinetic constants of plasminogen activation by receptor-bound
urokinase-type plasminogen activator (u-PA) compared with solution-phase
u-PA [Michaelis constant (Km) = 0.80 +/- 0.54 vs. 3.15 +/- 0.78 microM, P
< 0.0001; catalytic constant (kcat) = 0.39 +/- 0.17 vs. 0.50 +/- 0.29
s-1, not significant; kcat/Km = 0.57 +/- 0.35 vs. 0.16 +/- 0.11
microM-1.s-1, P < 0.05, respectively] showed a higher efficiency of
plasminogen activation at the cell surface. When measured by a chromogenic
assay using S22-51, receptor-bound plasmin activity on HGEC was partly
protected from its inhibitor, alpha-2-antiplasmin, whereas solution-phase
plasmin was not.(ABSTRACT TRUNCATED AT 250 WORDS)
