Autoregulation enables different pathways to control CCAAT/enhancer binding protein β (C/EBPβ) transcription

CCAAT/enhancer binding protein β (C/EBPβ) also named liver-enriched transcriptional activating protein (LAP) is a member of the C/EBP family of transcription factors and is involved in hepatocyte-specific gene expression and in the process of tissue differentiation. The activity of LAP/C/EBPβ can be regulated at the transcriptional and posttranslational level or by protein-protein interaction with other transcription factors. In this study we show that LAP/C/EBPβ can stimulate its own transcription. Deletion analysis of the rat LAP/C/EBPβ promoter in luciferase reporter gene experiments demonstrated that the region located between nucleotide −121 to −71, comprising two recently characterized cAMP responsive element (CRE)-like elements, is important for autoregulation. Gel shift experiments using oligonucleotides with overlapping point mutations identified the sequence GCAATGA (β-site) adjacent to and partially overlapping the first CRE-like site as core motif for LAP/C/EBPβ binding. Analysis of a mutated β-site in reporter gene experiments showed the functional relevance of this site for autoregulation. The composite C/EBPβ-CRE-element in the promoter enables synergistic activation of transcription by LAP/C/EBPβ and the proteinkinase A (PKA)/cAMP responsive element binding protein (CREB) pathway in a cell-type specific manner. In hepatoma cells nuclear factor kappa B (NF-κB) increased autoregulation and therefore could mediate enhanced activation during inflammatory responses. In summary, our results demonstrated that the assembly of the three binding sites in the promoter and thus the interaction between LAP/C/EBPβ and members of the CREB or NF-κB family allows the control of LAP/C/EBPβ gene transcription as a response to different stimuli in a tissue specific manner.