PARTICIPATION OF TWO ISOFORMS OF C/EBPβ TRANSCRIPTION FACTOR IN THE ACUTE-PHASE REGULATION OF THE RAT HAPTOGLOBIN GENE

✍ Scribed by Ilijana Grigorov; Tanja MilosavljeviIć; Ivana Cvetković; Miodrag Petrović

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 260 KB
• Volume: 22
• Category: Article
• ISSN: 1065-6995
• DOI: 10.1006/cbir.1998.0307

✦ Synopsis

Previous analyses of the mechanism of the transcriptional induction of the rat haptoglobin (Hp) gene during acute-phase (AP)-reaction have revealed the involvement of several trans-acting nucleoproteins (NPs) in controlling this process. In this study, by using antibodies against C/EBPbeta factor in Western immunoblot assay, we found that rat liver trans-acting NPs p35 and p20 are two characteristic C/EBPbeta isoforms whose expression is induced under AP-conditions. DNA-binding assays identified the binding sites for these two C/EBPbeta proteins in the functionally defined elements A and C of the rat Hp gene and also revealed that they have specific binding affinity towards these elements. Under non-induced conditions, p35 was the only C/EBPbeta binding factor; however, upon AP-conditions both, 35 kDa- and 20 kDa-C/EBPbeta binding activities were significantly induced suggesting that these interactions are necessary for the activation of the Hp gene. By in vitro phosphorylation assay and selective proteolysis, we also present evidence that p35 requires phosphorylation for its DNA binding ability. Thus, we conclude that increase in binding of C/EBPbeta isoforms during AP-reaction occurs through their upregulation and structural modification.