title: Low density lipoprotein receptor-related protein modulates the expression of tissue-type plasminogen activator in human colon fibroblasts.
abstract: Human colon fibroblasts (HCF) produce tissue-type plasminogen activator (t-PA) in culture, but after 24-48 h, t-PA ceases to accumulate in the medium. Here, we report negative feedback regulation of t-PA expression, exerted by t-PA or complexes of t-PA with its physiological inhibitor, plasminogen activator inhibitor type 1 (PAI-1). Inhibition of t-PA expression could be induced by addition of exogenous t-PA or t-PA.PAI-1 complexes and reversed by monoclonal antibody directed against the active site of t-PA. Analysis of metabolically radiolabeled protein and cellular mRNA showed that both t-PA protein and mRNA levels declined considerably after 24 h. When 125I-labeled t-PA or t-PA.PAI-1 complexes were incubated with HCF, monensin-inhibitable endocytosis and catabolism were observed. The low density lipoprotein receptor-related protein (LRP) was found to be expressed by HCF and to mediate these events. Addition of the 39-kDa receptor-associated protein (RAP), an antagonist for ligand interactions with LRP, removed the block to t-PA expression and restored its accumulation in the medium. Moreover, RAP completely prevented the degradation of exogenous 125I-labeled t-PA by HCF, suggesting that LRP is the endocytic receptor for t-PA in these cells. These results demonstrate that cellular modulation of t-PA expression in HCF involves LRP receptor-mediated clearance of t-PA. This LRP receptor-mediated event results in down-regulation of t-PA expression at the mRNA level.
authors.affiliation: Department of Cell Culture and Biochemistry, Monsanto Company, St. Louis, Missouri 63167, USA. MMHard@MONSANTO.COM
authors.forename: M M
authors.initials: MM
authors.lastname: Hardy
authors.forename: J
authors.initials: J
authors.lastname: Feder
authors.forename: R A
authors.initials: RA
authors.lastname: Wolfe
authors.forename: G
authors.initials: G
authors.lastname: Bu
mesh_terms: D002478:Cells, Cultured; D003106:Colon / Q000166:cytology / Q000201:enzymology*; D004705:Endocytosis / Q000187:drug effects; D005110:Extracellular Space / Q000201:enzymology; D005347:Fibroblasts / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic; D026541:Heymann Nephritis Antigenic Complex; D006801:Humans; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008562:Membrane Glycoproteins / Q000378:metabolism; D008985:Monensin / Q000494:pharmacology; D011971:Receptors, Immunologic / Q000378:metabolism*; D010959:Tissue Plasminogen Activator / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D026541:Heymann Nephritis Antigenic Complex; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008562:Membrane Glycoproteins; D011971:Receptors, Immunologic; D008985:Monensin; D010959:Tissue Plasminogen Activator