Submitted to: Journal of Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2007
Publication Date: 6/8/2007
Citation: Lo, J.H., Chiou, P.P., Chen, T.T. 2007. 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. Journal of Endocrinology. 194:393-406. Interpretive Summary: In humans, growth hormone acts on the liver to produce insulin-like growth factor-I and –II via signal transduction. In fish, although insulin-I and –II are also produced in the liver, it also has been shown that the production of IGF-I in the fish liver is regulated by growth hormone; it is not clear how growth hormone modulates the production of insulin-like growth factor-II. Our laboratory previously showed that growth hormone modulated the production of insulin-II in the liver of rainbow trout likely through the mediation of C/EBP (nuclear binding protein). We have identified five isoforms of C/EBP (alpha,beta1,beta2,delta1 and delta2) in the rainbow trout liver, and showed that the production of C/EBPbeta1, C/EBPbeta2, and C/EBPdelta2 are controlled by growth hormone. This is the first piece of evidence in fish that ties the expression of growth hormone-controlled insulin-like growth factor-2 gene with C/EBPbeta1, C/EBPbeta2, and C/EBPdelta2 genes. Results provide a good opportunity for further dissection of the molecular mechanism of growth hormone-controlled insulin-like growth factor-II gene expression in fish.
Technical 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/EBPbeta1,we have isolated cDNA of four other isoforms, C/EBPalpha, C/EBPbeta2, C/EBPdelta1, C/EBPdelta2, 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 isoformmRNA, 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/EBPbeta1, C/EBPbeta2, and C/EBPdelta2 but not C/EBPalpha and C/EBPdelta1 in the liver. GH-dependent increase of mRNA levels of C/EBPbeta1, C/EBPbeta2, C/EBPdelta2, 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/EBPbeta1, C/EBPbeta2, and C/EBPdelta2 mRNA.