Epidermal Growth Factor Dependent Expression of Plasminogen Activator and Plasminogen Activator Inhibitor in Rat Hepatocytes in Primary Culture

ABSTRACT

PURPOSE: In order to clarify the the role of epidermal growth factor (EGF) in the regulation of plasminogen activator (PA) and plasminogen activator inhibitor (PAI) during liver regeneration, we investigated the EGF-dependent gene expression of PA and PAI-1 in rat hepatocytes in primary culture. METHODS: Hepatocytes were isolated from rats using a two step perfusion technique and cultivated in dishes precoated with rat tail collagen. DNA synthesis of the hepatocytes by EGF treatment was measured with (3)H-thymidine incorporation. Gene expression for PAI-1, uPA and tPA was examined using Northern blot hybridization analysis. RESULTS: EGF treatment increased the (3)H-thymidine incorporation of the hepatocytes up to 36 hours and normal polygonal hepatocyte morphology was achieved simultaneously. tPA and PAI-1 mRNA were detected in the control hepatocytes. With the EGF treatment, the tPA mRNA level increased with time up to 48 hours, however the PAI-1 mRNA level rapidly increased to 1 hour and then decreased quickly to the control level. On the contrary, uPA mRNA was not detected in hepatocytes with or without treatment of EGF. The EGF-dependent induction of tPA and PAI-1 mRNA was a protein synthesis independent process. CONCLUSION: These results suggest that differential expression of tPA and PAI-1 mRNA by EGF in hepatocytes may play an important role in the regulation of liver regeneration. Among PAs, tPA seemed to be more important in EGF dependent growth or regeneration of primary hepatocytes in the rat since uPA mRNA was not induced in primary hepatocyte cultures in spite of EGF treatment.