title: Localization of cell surface sites involved in fibronectin fibrillogenesis.
abstract: Fibronectin binding sites on cultured human fibroblasts were localized by high voltage electron microscopy using either 5- or 18-nm colloidal gold beads (Au5 or Au18) bound to intact fibronectin, the 70-kD amino-terminal fragment of fibronectin that blocks incorporation of exogenous fibronectin into extracellular matrix, or 160-180-kD fragments of fibronectin with cell adhesion and heparin-binding activities. Binding sites for Au18-fibronectin on the cell surface were localized to specific regions along the edge of the fibroblast and on retraction fibers. Au18-fibronectin complexes at these sites were initially localized in clusters that co-aligned with intracellular microfilament bundles. With longer incubations, Au18-fibronectin complexes were arranged into long fibrillar networks on the cell surface and in the extracellular space. The appearance of Au18-fibronectin in these fibrillar networks and disappearance of clusters of Au18-fibronectin suggest that Au18-fibronectin complexes are arranged into matrix at specific regions of the cell surface. Au18-70-kD fragment complexes initially had a similar distribution to Au18-fibronectin complexes. With longer incubations, Au18-70-kD fragment complexes were found in long linear arrangements on the cell surface. Double labeling experiments using Au18-70-kD fragment and Au5-160-180-kD fragments showed that the 70-kD fragment and the 160-180-kD fragments bind to different regions of the cell.
mesh_terms: D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D005109:Extracellular Matrix / Q000648:ultrastructure*; D005347:Fibroblasts / Q000648:ultrastructure; D005353:Fibronectins / Q000378:metabolism*; D006046:Gold; D006801:Humans; D008854:Microscopy, Electron; D010446:Peptide Fragments / Q000378:metabolism; D017469:Receptors, Fibronectin; D011971:Receptors, Immunologic / Q000378:metabolism*; D012867:Skin / Q000166:cytology; D013997:Time Factors
chemical_list: D005353:Fibronectins; D010446:Peptide Fragments; D017469:Receptors, Fibronectin; D011971:Receptors, Immunologic; D006046:Gold