Changes in expression of CCAAT/enhancer binding protein α (C/EBPα) and C/EBPβ in rat liver after partial hepatectomy but not after treatment with cyproterone acetate

Background/Aims: The proliferation rate of adult rat liver is normally very low. It is markedly enhanced during compensatory regeneration, e.g. after partial hepatectomy, or after administration of certain growth promoters, e.g. cyproterone acetate. These two types of liver cell proliferation appear to differ, since the expression of immediate early genes is induced during compensatory regeneration but not after cyproterone acetate treatment. The transcription factor C/EBPα, which has been associated with hepatocyte differentiation and growth arrest, is suppressed during compensatory regeneration. In contrast, C/EBPβ, associated with acute phase reaction, is increased during regeneration. We have investigated the effects of the liver growth promoter cyproterone acetate on the hepatic expression of C/EBPα and C/EBPβ. Methods: Adult male rats received after cyproterone acetate treatment or were subjected to partial hepatectomy. Livers were obtained at different time intervals for measurement of C/EBPα and C/EBPβ mRNA with solution hybridization/RNAse protection assay, and C/EBPα and C/EBPβ content with immunoblotting. Results: The levels of both C/EBPα and C/EBPβ mRNA and the corresponding immunoreactivities were unchanged 2–48 h after injection of cyproterone acetate. The levels of C/EBPα mRNA and immunoreactivity were significantly suppressed 10–18 h and 18–26 h after partial hepatectomy, respectively. The levels of C/EBPβ mRNA and immunoreactivity were enhanced during compensatory regeneration 2 h after partial hepatectomy. Conclusions: Liver cell proliferation during regeneration, but not in response to cyproterone acetate treatment, is associated with changes in C/EBPα and C/EBPβ expression. This further supports the notion that changes in expression of transcription factors during liver growth in vivo are dependent on the growth inducer.