Molecular cloning and expression analysis of rainbow trout (Oncorhynchus mykiss) CCAAT/enhancer binding protein genes and their responses to induction by GH in vitro and in vivo

Abstract

CCAAT/enhancer-binding proteins (C/EBPs) are transcription factors consisting of six isoforms and play diverse physiological roles in vertebrates. In rainbow trout (Oncorhynchus mykiss), in addition to the reported C/EBPβ1, we have isolated cDNA of four other isoforms, C/EBPα, C/EBPβ2, C/EBPδ1, C/EBPδ2, from the liver. Comparison of the deduced amino acid sequence of rainbow trout C/EBPs with those of other vertebrates revealed that C/EBP isoforms are highly conserved. The profiles of tissue-specific expression of individual C/EBP isoform mRNA, determined by quantitative real-time (RT)-PCR showed distinct patterns. Furthermore, injection of bovine GH into yearling rainbow trout resulted in a significant increase of mRNA levels of C/EBPβ1, C/EBPβ2, and C/EBPδ2 but not C/EBPα and C/EBPδ1 in the liver. GH-dependent increase of mRNA levels of C/EBPβ1, C/EBPβ2, C/EBPδ2, and IGF-II were also confirmed by treating rainbow trout hepatoma cells expressing a goldfish GH receptor with bGH. Together with our previous findings, the results presented in this paper strengthen our previous hypothesis that GH may regulate the expression of the IGF-II gene via mediating the expression of C/EBPβ1, C/EBPβ2, and C/EBPδ2 mRNA.