Transforming Growth Factor β1 Helps Maintain Differentiated Functions in Mitogen-Treated Primary Rat Hepatocyte Cultures

Abstract

Mechanisms that control function and repair of the injured liver remain unclear. We hypothesized that after liver injury, elevated blood TGF-β1 levels may reflect an adaptive response to help maintain differentiated functions in surviving hepatocytes affected by excessive amounts of HGF. We thus studied the effect of HGF, EGF, TGF-β1, HGF + TGF-β1, or EGF + TGF-β1 on the expression of liver-enriched transcription factors and genes which remain under their regulatory activity. The peak [3H]thymidine uptake induced by 20 ng/ml of either HGF or EGF was seen after 72 h; however, DNA binding of C/EBP and HNF1 decreased already after 6 h (electrophoretic mobility shift assay). Addition of TGF-β1 antagonized these effects. Also at the mRNA level, TGF-β1 counteracted at one point or another the decrease in C/EBPα, C/EBPβ, HNF1β, and HNF4 expression; HNF1α and COUP-TF showed similar responses and, additionally, were downregulated by TGF-β1 at 24 h (Northern blot). Albumin and apolipoprotein B mRNA levels were decreased after 24-h treatment with HGF, whereas addition of TGF-β1 increased their levels. The same pattern was found with EGF, but not until 48 h. PEPCK mRNA was dramatically lowered with either EGF or HGF, and TGF-β1 did not counteract these effects. Id-1 was expressed only in cultures treated for 24 and 48 h with both the mitogen (EGF, HGF) and TGF-β1 and in those treated for 48 h with TGF-β1 alone.