Enhancement of vitronectin expression in human HepG2 hepatoma cells by transforming growth factor-beta 1

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-beta 1 (TGF beta 1) in this hepatoma cell line by Northern hybridization, polypeptide and immunoprecipitation analyses and compared the response to another TGF beta-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 TGF beta 1-induced production and extracellular deposition of vitronectin. Accordingly, TGF beta 1 enhanced the expression of vitronectin mRNA at picomolar concentrations (2-20 ng/ml) as shown by Northern hybridization analysis. Comparison of the temporal TGF beta 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. TGF beta 1 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 TGF beta 1 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 alpha subunit of the receptor in response to TGF beta 1. These effects of TGF beta are probably involved in various processes of the liver where matrix induction and controlled pericellular proteolysis is needed, as in tissue repair.