Endocytosis of urokinase-plasminogen activator inhibitor type 1 complexes bound to a chimeric transmembrane urokinase receptor.
The urokinase receptor (uPAR) is linked to plasma membranes through a glycosylphosphatidylinositol (GPI) anchor. It has been posited that the GPI anchor facilitates clearance of uPAR-bound complexes between two chain urokinase (tcuPA) and plasminogen activator inhibitor type 1 (PAI-1) by the alpha 2-macroglobulin receptor (alpha 2MR) which permits re-expression of unoccupied uPA receptors on the cell surface. To test this hypothesis we compared internalization and degradation of 125I-labeled tcuPA-PAI-1 by COS cells expressing either transfected wild-type, GPI-linked uPAR (uPAR/GPI), or a chimeric receptor composed of the extracellular domains of uPAR linked to the transmembrane and cytosolic domains of the alpha chain (p55 subunit) of the interleukin-2 receptor (uPAR/IL-2R alpha). The kinetics of binding, internalization and degradation of tcuPA-PAI-1 by COS cells expressing each form of uPAR were virtually identical. However, internalization of complexes by uPAR/IL-2R alpha was more susceptible to inhibition by recombinant soluble 39-kDa alpha 2MR-associated protein (RAP) which competes for binding of tcuPA-PAI-1 complexes to alpha 2MR (p < 0.001), and the internalization was accompanied by a greater reduction in the number of surface uPAR/IL-2R alpha, than uPAR/GPI (p < 0.05). These studies indicate that the rate of internalization of tcuPA-PAI-1 is governed primarily by the extracellular domains of uPAR, whereas the GPI anchor may facilitate internalization of complexes and re-expression of uPAR when binding sites on alpha 2MR are limiting.
Li
H
H
Department of Pathology, Hospital of the University of Pennsylvania, Philadelphia 19104.
Kuo
A
A
Kochan
J
J
Strickland
D
D
Kariko
K
K
Barnathan
E S
ES
Cines
D B
DB
D000818:Animals; D002460:Cell Line; D004705:Endocytosis; D005347:Fibroblasts / Q000378:metabolism; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D007739:L Cells; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D051379:Mice; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000096:biosynthesis / Q000378:metabolism*; D055293:Receptors, Urokinase Plasminogen Activator; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000378:metabolism
D017261:Glycosylphosphatidylinositols; D026503:Low Density Lipoprotein Receptor-Related Protein-1; C524898:PLAUR protein, human; D017395:Plasminogen Activator Inhibitor 1; C524899:Plaur protein, mouse; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D055293:Receptors, Urokinase Plasminogen Activator; D011993:Recombinant Fusion Proteins; D000511:alpha-Macroglobulins; D014568:Urokinase-Type Plasminogen Activator