title: Microvillus-specific Mr 75,000 plasma membrane protein of human choriocarcinoma cells.
abstract: We have previously purified from cultured JEG-3 choriocarcinoma cells an Mr 75,000 protein, originally detected using antibodies to a retrovirus-related synthetic peptide. Using polyclonal antibodies, we have now localized this protein immunocytochemically in JEG-3 cells at both light and electron microscopic levels. In immunofluorescence microscopy of saponin-permeabilized cells, the antigen appeared as dots and short strands at the apical cell surface. In pre-embedding immunoperoxidase electron microscopy, the Mr 75,000 protein was specifically localized to microvilli on the apical cell surface. Immunoferritin electron microscopy was used to assess more quantitatively the antigen distribution in the plane of the plasma membrane, and to define the position of the antigenic site(s) with respect to the membrane. The immunoferritin results confirmed the microvillus specificity of the Mr 75,000 protein and showed that the antigenic portion of the protein is within a few nanometers from, and on the cytoplasmic side of, the lipid bilayer. In detergent extraction experiments, the Mr 75,000 antigen was highly enriched in the soluble fractions. These results demonstrate that the Mr 75,000 protein is a membrane protein highly specific for microvilli.
authors.forename: R
authors.initials: R
authors.lastname: Pakkanen
authors.forename: K
authors.initials: K
authors.lastname: Hedman
authors.forename: O
authors.initials: O
authors.lastname: Turunen
authors.forename: T
authors.initials: T
authors.lastname: Wahlström
authors.forename: A
authors.initials: A
authors.lastname: Vaheri
mesh_terms: D002451:Cell Compartmentation; D002462:Cell Membrane / Q000032:analysis; D002822:Choriocarcinoma / Q000032:analysis*; D005260:Female; D006801:Humans; D007158:Immunologic Techniques; D008565:Membrane Proteins / Q000032:analysis*; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D008871:Microvilli / Q000032:analysis*; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000032:analysis*; D011247:Pregnancy
chemical_list: D008565:Membrane Proteins; D009363:Neoplasm Proteins