Location: Cool and Cold Water Aquaculture ResearchTitle: CCAAT/enhancer binding protein Beta-2 is involved in growth hormone-regulated insulin-like growth factor-II gene expression in the liver of rainbow trout (Oncorhynchus mykiss) Author
Submitted to: Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2010
Publication Date: 5/5/2010
Publication URL: http://handle.nal.usda.gov/10113/55683
Citation: Lo, J.H., Chen, T.T. 2010. CCAAT/enhancer binding protein Beta-2 is involved in growth hormone-regulated insulin-like growth factor-II gene expression in the liver of rainbow trout (Oncorhynchus mykiss). Endocrinology. 151:2128-2139. Interpretive Summary: While insulin-like growth factor I and II (IGF-I and IGF-II) are important hormonal factors regulating the somatic growth, development and reproduction in fish, the mechanism that regulates the expression of these growth factors is still unknown. Previously we demonstrated that growth hormone regulates the expression of IGF-I and IGF-II genes in rainbow trout. The actual mechanism of how growth hormone modulates the expression of IGF-I and IGF-II genes remains unknown. Using whole fish and liver cell lines developed from the liver of rainbow trout as experimental models, we characterized the involvement of growth hormone-induced genes called C/EBPs in modulating the expression of IGF-I and IGF-II genes. These results will enable aquaculture researchers to develop strategies to manipulate the expression of IGF-I and IGF-II genes to increase the efficiency of fish production.
Technical Abstract: Previously, we showed that levels of different CCAAT/enhancer binding protein (C/EBP) mRNAs in the liver of rainbow trout were modulated by GH and suggested that C/EBPs might be involved in GH induced IGF-II gene expression. As a step toward further investigation, we have developed monospecific polyclonal antibodies to detect rainbow trout C/EBPa, -b1, -b2, and -d2 isoform proteins. Injection of GH into adult rainbow trout resulted in a significant increase of C/EBPb1, C/EBPb2, and C/EBPd2 proteins in the liver. Chromatin immunoprecipitation analysis revealed that C/EBPb2 binds to multiple sites at the 5' promoter/regulatory region, introns, and the 3' untranslated region of the IGF-II gene. GH treatment reduced C/EBPb2 binding to several of these regions at 6 h after injection. The decreased occupancy of C/EBPb2 coincided well with an increase of histone H4 acetylation at the proximal promoter and elevation of the IGF-II mRNA level. Immunoblotting analysis showed that C/EBPb2 existed predominately as a truncated form in the liver, and cotransfection analysis further showed that the truncated C/EBPb2 acted as a negative regulator on IGF-II proximal promoter. GH treatment caused deacetylation of C/EBPb2 in the liver. In addition,weobserved a GH-dependent interaction of C/EBPb2 with a complex involving histone H1. All together, these results suggest that C/EBPb2 was regulated at multiple levels by GH, and C/EBPb2 may play a suppressive role in mediating GH-induced IGF-II expression in the liver of rainbow trout.