Growth hormone induces CCAAT/enhancer binding protein α (C/EBPα) in cultured rat hepatocytes

Background/Aims: The transcription factor CCAAT/enhancer binding protein α (C/EBPα) is a transactivator of several genes in the liver, which are regulated by growth hormone. Methods: Growth hormone (100 ng/ml) was added to primary rat hepatocytes cultured on a laminin-rich matrix. C/EBP mRNA and protein levels were measured by RNase protection assay and Western blotting, respectively. DNA binding activity was measured by electrophoretic mobility shift assay (EMSA). Results: Growth hormone treatment for 6 h to 3 days increased C/EBPα mRNA levels. Addition of growth hormone for 24 h and 4 days also enhanced the levels of the 42 and 30 kDa isoforms of immunoreactive C/EBPα. EMSA showed that addition of growth hormone for 24 h enhanced the abundance of a protein complex binding to a consensus C/EBP binding DNA oligonucleotide. This protein complex was supershifted by antibodies directed against C/EBPα but not against C/EBPβ. There were no consistent effects on C/EBPß mRNA or protein at any timepoint. The growth hormone effect on C/EBPα expression was not affected by simultaneous incubation with insulin or glucocorticoids, two hormones that previously have been reported to affect C/EBPs. Conclusions: Growth hormone enhances the levels of C/EBPα mRNA and protein as well as the DNA binding activity of C/EBPα in cultured rat hepatocytes.