Growth hormone induces CCAAT/enhancer binding protein alpha (C/EBP alpha) in cultured rat hepatocytes

Background/Aims: The transcription factor CCAAT/enhancer binding protein al pha (C/EBP alpha) 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 cu ltured on a laminin-rich matrix. C/EBP mRNA and protein levels were measure d by RNase protection assay and Western blotting, respectively, DNA binding activity was measured by electrophoretic mobility (EMSA). Results: Growth hormone treatment for 6 h to 3 days increased C/EBP alpha m RNA levels. Addition of growth hormone for 24 h and 4 days also enhanced th e levels of the 42 and 30 kDa isoforms of immunoreactive C/EBP alpha, 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/EBP alpha but not against C/EBP beta. There were no consistent effects on C/EBP beta mRNA or protein at any timepoint, The growth hormone effect on C/EBP alpha expression was not affected by simultaneous incubation with insulin o r glucocorticoids, two hormones that previously have been reported to affec t C/EBPs. Conclusions: Growth hormone enhances the levels of C/EBP alpha mRNA and pro tein as well as the DNA binding activity of C/EBP alpha in cultured rat hep atocytes.