title: Localization of protease nexin-1 on the fibroblast extracellular matrix.
abstract: Protease nexin-1 (PN-1) is a protease inhibitor that is secreted by fibroblasts and several other cultured cells. PN-1 forms complexes with certain serine proteases in the extracellular environment including thrombin, urokinase, and plasmin. The complexes then bind to the cells and are rapidly internalized and degraded. This report demonstrates that PN-1 is present on the surface of fibroblasts, bound to the extracellular matrix. Immunofluorescent studies showed that PN-1 colocalized with fibronectin on both intact cells and in preparations of extracellular matrix made from these cells. In contrast, PN-1 did not colocalize with the epidermal growth factor receptor, a plasma membrane marker. An enzyme-lined immunosorbent assay was developed which showed that the extracellular matrix contained at least 60-80% of the cellular immunoreactive PN-1. Extraction of the matrix with 2 M NaCl removed PN-1 in a form which reacted with 125I-thrombin to form complexes which were immunoprecipitated by anti-PN-1 IgG and were of identical size as complexes made from soluble PN-1 and 125I-thrombin. These data indicate that in addition to its role as a soluble protease inhibitor, PN-1 is also a component of the extracellular matrix and might control its proteolysis.
authors.affiliation: Department of Microbiology and Molecular Genetics, College of Medicine, University of California, Irvine 92717.
authors.forename: D H
authors.initials: DH
authors.lastname: Farrell
authors.forename: S L
authors.initials: SL
authors.lastname: Wagner
authors.forename: R H
authors.initials: RH
authors.lastname: Yuan
authors.forename: D D
authors.initials: DD
authors.lastname: Cunningham
mesh_terms: D016564:Amyloid beta-Protein Precursor; D002352:Carrier Proteins / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005109:Extracellular Matrix / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D007158:Immunologic Techniques; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D058258:Serpin E2
chemical_list: D016564:Amyloid beta-Protein Precursor; D002352:Carrier Proteins; D058255:Protease Nexins; D011956:Receptors, Cell Surface; C545486:SERPINE2 protein, human; D058258:Serpin E2