title: Urokinase binding and catabolism by Hep G2 cells is plasminogen activator inhibitor-1 dependent, analogous to interactions of tissue-type plasminogen activator with these cells.
abstract: The adherent human hepatoma cell line Hep G2 exhibits receptor mediated endocytosis and catabolism of tissue-type plasminogen activator.plasminogen activator inhibitor type-1 (t-PA.PAI-1) complexes formed when exogenous t-PA combines with endogenous PAI-1 in the extracellular matrix. To determine whether the other major PA, urokinase (u-PA), which also complexes with PAI-1, is metabolised via the same mechanism, 125I-labelled high (hmw) and low (lmw) molecular weight forms of u-PA were incubated with Hep G2 cells at 4 degrees C for 2 hr in the absence and presence of a 100-fold excess of unlabelled ligand in order to detect specific binding. Both hmw and lmw 125I-u-PA formed complexes with PAI-1 and these bound specifically and with high affinity (apparent Kd 3.9 and 4.1 nM, with Bmax 78 x 10(3) and 83 x 10(3) binding sites/cell respectively). Binding by each form of radiolabelled u-PA was inhibited in a dose-dependent fashion by unlabelled t-PA, hmw-u-PA, lmw-u-PA, and by monoclonal anti-PAI-1 antibody. At 37 degrees C, bound hmw and lmw 125I-u-PA.PAI-1 complexes were internalised and degraded rapidly. These findings indicate that the specificity of the previously described receptor which mediates PAI-1 dependent catabolism of t-PA by Hep G2 cells extends to complexes of u-PA with this inhibitor.
mesh_terms: D000911:Antibodies, Monoclonal; D001665:Binding Sites; D002460:Cell Line; D004705:Endocytosis; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D017395:Plasminogen Activator Inhibitor 1 / Q000276:immunology / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism; D055293:Receptors, Urokinase Plasminogen Activator; D010959:Tissue Plasminogen Activator / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014568:Urokinase-Type Plasminogen Activator / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; C524898:PLAUR protein, human; D017395:Plasminogen Activator Inhibitor 1; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D010959:Tissue Plasminogen Activator; D014568:Urokinase-Type Plasminogen Activator