title: A cytokeratin 8-like protein with plasminogen-binding activity is present on the external surfaces of hepatocytes, HepG2 cells and breast carcinoma cell lines.
abstract: Plasminogen binding to cell surfaces may be important for tumor invasion and other processes that involve cellular migration. In this investigation, the principal plasminogen-binding protein was identified in the plasma membrane fraction of rat hepatocytes. The protein had an apparent mass of 59 kDa, was insoluble in a spectrum of detergents, and was identical to cytokeratin 8 (CK 8) as determined by sequence analysis of nine amino acids at the N terminus of two cyanogen bromide fragments. The 59 kDa protein bound CK 8-specific antibody in western blot analyses. These studies demonstrate that CK 8 or a CK 8-like protein binds plasminogen. Given this newly determined and potentially important CK 8 function, immunofluorescence and immunoelectron microscopy studies were performed to determine whether CK 8 may be present on the external surfaces of unpermeabilized, viable hepatocytes. All of the cells in each preparation were immunopositive with two separate CK 8-specific antibodies. A punctate pattern of immunofluorescence was detected on the cell surface with approximately even intensity from cell to cell. By immunoelectron microscopy, CK 8 was preferentially associated with microvilli. In order to determine whether other epithelial cells express cell-surface CK 8, immunofluorescence and immunoelectron microscopy studies were performed with HepG2 hepatocellular carcinoma cells and with BT20 and MCF-7 breast carcinoma cells. The pattern of antigen expression was equivalent with each cell type and comparable to that observed with hepatocytes. These studies support the hypothesis that CK 8 is associated with the external cell surface where it may express important proteinase receptor function.
authors.affiliation: Department of Pathology, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Hembrough
authors.forename: J
authors.initials: J
authors.lastname: Vasudevan
authors.forename: M M
authors.initials: MM
authors.lastname: Allietta
authors.forename: W F
authors.initials: WF
authors.lastname: Glass
authors.forename: S L
authors.initials: SL
authors.lastname: Gonias
mesh_terms: D000595:Amino Acid Sequence; D001943:Breast Neoplasms / Q000378:metabolism* / Q000648:ultrastructure; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000648:ultrastructure; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D007633:Keratins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D008113:Liver Neoplasms / Q000378:metabolism / Q000648:ultrastructure; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010958:Plasminogen / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D007633:Keratins; D010958:Plasminogen