DNA binding activity of C/EBPβ and C/EBPδ for the rat α2-macroglobulin gene promoter is regulated in an acute-phase dependent manner

Turpentine-induced acute-phase (AP) response in rats is followed by transcriptional activation Of the (alpha(2)- macroglobulin (MG) gene mediated by cytokine interleukin-6 (IL-6) and glucocorticoids. Based on nucleotide sequence analysis of the alpha(2)-MG gene promoter regions responsive to IL-6, we postulated that binding of members of the liver-enriched CCAAT-enhancer-binding proteins (C/EBP) family of transcription factors to the type I IL-6 responsive element (IL-6RE) may participate in the transcriptional activation of this gene during AP response. Results of Western immunoblot and Northern-blot assays revealed coordinate changes in the pool levels of C/EBPalpha, -beta, and -delta protein isoforms and their genes expression in liver in response to turpentine. By means of an in vitro phosphorylation assay, South-Western blot, and selective proteolysis we have also found that only abilities of 35-kD C/EBPbeta and 27-kD C/EBPdelta to bind to the alpha(2)-MG gene promoter were affected by phosphorylation. Based on these data we concluded that transcriptional induction of the rat alpha(2)-MG gene during AP response correlates with both increased synthesis and phosphorylation- induced binding of 35-kD C/EBPbeta and 27-kD C/EBPdelta.