IDENTIFICATION OF UROKINASE-TYPE PLASMINOGEN-ACTIVATOR RECEPTOR IN HUMAN ENDOTHELIAL-CELLS AND ITS MODULATION BY PHORBOL-MYRISTATE ACETATE

Human endothelial cells express antithrombotic properties by producing prostacyclin, heparan sulfate and plasminogen activator (PA). Using a n established cell line, TKM-33, from human umbilical vein endothelial cells, the pericellular urokinase-type PA (u-PA) activity and express ion of u-PA receptor (u-PAR) were investigated, The endothelial cells produced and secreted large amounts of u-PA and low levels of tissue-t ype PA (t-PA) and of PA inhibitor-1 (PAI-1), which were identified by immunohistochemical study and electrophoretic enzymography. Diisopropy lfluoro-phosphate-treated I-125-u-PA bound specifically to acid-treate d monolayered endothelial cells with a K-d of 3.46 +/- 1.17 nM, and B- max of (0.09 +/- 0.04) x 10(6) sites/cell, mRNA of u-PAR was detected by using Northern blot analysis. Thus, these endothelial cells express u-PAR which bounds u-PA specifically. Phorbol myristate acetate (PMA) stimulation to the endothelial cells altered the K-d value to 3.18 +/ - 0.64 nM, and B-max value to (0.19 +/- 0.10) x 10(6) sites/cell, resp ectively. PMA treatment of endothelial cells increased u-PAR mRNA. Sim ilarly, H7-treated endothelial cells showed a dose-dependent increase of u-PAR mRNA. However, PMA and H7 did not stimulate the expression of u-PA and t-PA mRNAs significantly. The expression of PAI-1 mRNA was i ncreased by both PMA and H7. These findings suggest that the establish ed endothelial cell line, TKM-33, possesses the character of endotheli al cells and expresses u-PAR on their cell surface which is occupied b y intrinsic u-PA secreted from the cells. The pericellular u-PA activi ty and the expression of u-PAR were regulated by protein kinase pathwa y.