Enhancement of vitronectin expression in human HepG2 hepatoma cells by transforming growth factor‐β1

Liver cells are considered the principal source of plasma vitronectin. The human hepatoma cell line HepG2 produces vitronectin into its culture medium. In the current work we have analyzed the regulation of vitronectin by transforming growth factor‐β1 (TGFβ1) in this hepatoma cell line by Northern hybridization, polypeptide and immunoprecipitation analyses and compared the response to another TGFβ‐regulated gene, plasminogen activator inhibitor (PAI‐1). Rabbit antibodies raised against human plasma‐derived vitronectin were used in immunodetection. Polypeptide and immunoprecipitation analyses of the medium and cells, as well as immunoblotting analysis of the cells and their extracellular matrices, indicated enhanced TGFβ1‐induced production and extracellular deposition of vitronectin. Accordingly, TGFβ1 enhanced the expression of vitronectin mRNA at picomolar concentrations (2–20 ng/ml) as shown by Northern hybridization analysis. Comparison of the temporal TGFβ induction profiles of vitronectin and PAI‐1 mRNAs showed that vitronectin was induced more slowly but the vitronectin mRNAs persisted longer. In addition, platelet‐derived and epidermal growth factors had an effect on vitronectin expression, but it was of lower magnitude. TGFβ1 enhanced the expression of PAI‐1 but, unlike previous reports, epidermal growth factor did not have any notable effect on PAI‐1 in these cells. The results indicate that TGFβ1 is an efficient regulator of the production of vitronectin by HepG2 cells and that PAI‐1 and vitronectin are not coordinately regulated. In addition, with affinity purified antibodies to vitronectin receptor, we observed strong enhancement of the α subunit of the receptor in response to TGFβ1. These effects of TGFβ are probably involved in various processes of the liver where matrix induction and controlled pericellular proteolysis is needed, as in tissue repair.