Role of CAAT-enhancer binding protein isoforms in the cytokine regulation of acute-phase plasma protein genes.
Rat hepatic cells respond to interleukin (IL) -1, IL-6, and dexamethasone treatment by increasing the transcription rate of acute-phase plasma protein genes. The same conditions lead to changes in the expression of CAAT-enhancer binding protein (C/ EBP) isoforms which are specific to the hepatic cell line. To identify the relationship between C/ EBP isoforms and acute-phase protein gene activation, the hormone-specific expression of C/ EBP alpha, beta, and delta was determined in H-35 and HTC cells and was compared to acute-phase liver. C/ EBP beta was found to be the principal isoform in hepatoma cells and to be strongly stimulated by cytokines and dexamethasone in H-35 cells. Transactivating functions were observed for all three C/ EBP isoforms by cotransfection of CAT gene reporter constructs containing cytokine and glucocorticoid response elements of acute-phase protein genes and expression plasmids for mouse C/EBP alpha, beta, and delta into rat and human hepatoma cells. The degree of C/ EBP-mediated transactivation was, however, extremely variable among the different regulatory elements. Transcription run-on reactions with nuclei from transiently transfected H-35 cells indicated that cotransfected C/ EBP beta increases basal expression of reporter gene constructs as well as the dexamethasone- mediated stimulation of constructs containing the glucocorticoid response elements of the rat alpha 1-acid glycoprotein gene, but did not accelerate or enhance hormone-dependent transcription activation of reporter gene plasmids containing the IL-6 regulatory element of the beta-fibrinogen gene. Activation of the reporter gene constructs appeared to be temporally and quantitatively correlated with the amount of nuclear C/ EBP as determined by two-dimensional Western and Southwestern blot analyses.[1]References
- Role of CAAT-enhancer binding protein isoforms in the cytokine regulation of acute-phase plasma protein genes. Baumann, H., Morella, K.K., Campos, S.P., Cao, Z., Jahreis, G.P. J. Biol. Chem. (1992) [Pubmed]
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