Human spreading factor: Synthesis and response by HepG2 hepatoma cells in culture

Abstract

Human serum spreading factor (SF) is a cell adhesion and spreading-promoting glycoprotein purified from serum or plasma that mediates effects in a wide variety of animal cell culture systems. HepG2 human hepatoma cells were found to synthesize and secrete SF into culture medium. Quantitative immunoassay of the protein indicated a concentration of about 1 microgram/ml in 48 hr-conditioned medium from confluent cultures. Although fibronectin also was synthesized and secreted into the culture medium, HepG2 cell spreading was observed in response to human serum SF, but not in response to human plasma fibronectin. Immunoprecipitation of SF from culture medium of cells metabolically-labeled with leucine, fucose or glucosamine identified a single form of the molecule of approximately 70,000 daltons. Treatment of cultures with tunicamycin inhibited incorporation of fucose and glucosamine into immunoprecipitated SF, but did not prevent synthesis and secretion of the protein. Electrophoretic analysis and cell spreading assays showed that SF secreted by tunicamycin-treated HepG2 cells was of molecular weight (mw) approximately 60,000, and was biologically active.

Detection of vitronectin mRNA in tissues and cells of the mouse.

“…Limited information is available on the tissues that produce Vn in vivo. The liver has been implicated since Vn cDNAs have been isolated from liver cDNA libraries (7,8,22), and two primary hepatocarcinoma cell lines (HepG2 and Hep3B) have been shown to synthesize Vn in vitro (20,23). Moreover, plasma Vn levels are reduced upon liver failure (46).…”

Kinetic Analysis of the Interaction between Vitronectin and the Urokinase Receptor

“…It circulates in blood in a monomeric ("closed," "native") form, but is converted into a multimeric ("extended," "opened," "denatured") form when incorporated into the extracellular matrix or treated with urea (1,2). The extended form of VN binds to specific receptors on cells (3,4) and to various other molecules such as the C5b-9 complement complex (5), the thrombin-antithrombin III complex (6,7), plasminogen activator inhibitor 1 (PAI-1) (8 -10), uPAR (11), heparin (1,2,12,13), collagen (14 -16), plasminogen (13,17), and ␤-endorphin (18). These interactions not only promote the attachment, spreading, and growth of cells (19 -21) but also influence the coagulation, fibrinolytic, and complement systems (22,23).…”

The Glycosaminoglycan Binding Site Governs Ligand Binding to the Somatomedin B Domain of Vitronectin

“…A number of ligands were identified that interact preferentially with the conformationally altered, denatured form of Vn. These ligands include collagen (11), GAGs (12)(13)(14), ␤-endorphin (15), PAI-1 (16), urokinase receptor-urokinase complex (17), and cells (18). In contrast, thrombin-antithrombin III complexes appear to preferentially interact with native Vn (19), and PAI-1 appears to bind to both forms of Vn (20).…”