title: Differential regulation of urokinase-type-1 inhibitor complex endocytosis by phorbol esters in different cell lines is associated with differential regulation of alpha 2-macroglobulin receptor and urokinase receptor expression.
abstract: Complex between urokinase and its type-1 inhibitor (uPA-PAI-1) may, when bound to the urokinase receptor (uPAR), be endocytosed by an ensuing binding of the complex to the multiligand receptors alpha (2)-macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2MR/LRP) and glycoprotein 330 (gp330). We have found that phorbol esters regulate endocytosis of uPA-PAI-1 differently in different cell lines. In COS-1 cells, expressing uPAR and high levels of alpha 2MR/LRP under basal conditions, phorbol esters cause a time-dependent decrease in endocytosis concomitantly with a parallel down-regulation of alpha 2MR/LRP expression. An up-regulation of uPAR expression was also observed. General endocytosis via the clathrin-coated pit pathway was not affected by PMA treatment, as judged from measurements of transferrin endocytosis. In LLC-PK1 cells, expressing alpha 2MR/LRP but not uPAR under basal conditions, phorbol esters transiently increase endocytosis in parallel with a transient induction of uPAR expression, while there was virtually no change in alpha 2MR/LRP expression. Differential regulation of endocytosis therefore seems to be caused by differential regulation of the receptors, with either the alpha 2MR/LRP-level (in COS)-1 cells) or the uPAR-level (in LLC-PK1 cells) being rate-limiting.
authors.affiliation: Department of Molecular Biology, University of Aarhus, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Kjøller
authors.forename: A C
authors.initials: AC
authors.lastname: Simonsen
authors.forename: L
authors.initials: L
authors.lastname: Ellgaard
authors.forename: P A
authors.initials: PA
authors.lastname: Andreasen
mesh_terms: D000818:Animals; D002460:Cell Line; D002461:Cell Line, Transformed; D002522:Chlorocebus aethiops; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007668:Kidney / Q000166:cytology; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D017395:Plasminogen Activator Inhibitor 1 / Q000494:pharmacology*; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000378:metabolism; D055293:Receptors, Urokinase Plasminogen Activator; D013552:Swine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014568:Urokinase-Type Plasminogen Activator / Q000037:antagonists & inhibitors*
chemical_list: D026503:Low Density Lipoprotein Receptor-Related Protein-1; C524898:PLAUR protein, human; D017395:Plasminogen Activator Inhibitor 1; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D055293:Receptors, Urokinase Plasminogen Activator; D014568:Urokinase-Type Plasminogen Activator; D013755:Tetradecanoylphorbol Acetate