Autoregulation enables different pathways to control CCAAT/enhancer binding protein beta (C/EBP beta) transcription

CCAAT/enhancer binding protein beta (C/EBP beta) also named liver-enriched transcriptional activating protein (LAP) is a member of the C/EB beta famil y of transcription factors and is involved in hepatocyte-specific gene expr ession and in the process of tissue differentiation. The activity of LAP/C/ EBP beta can be regulated at the transcriptional and posttranslational leve l or by protein-protein interaction with other transcription factors. In th is study we show that LAP/C/EBP beta can stimulate its own transcription. D eletion analysis of the rat LAP/C/EBP beta promoter in luciferase reporter gene experiments demonstrated that the region located between nucleotide -1 21 to -71, comprising two recently characterized cAMP responsive element (C RE)-like elements, is important for autoregulation. Gel shift experiments u sing oligonucleotides with overlapping point mutations identified the seque nce GCAATGA (beta -site) adjacent to and partially overlapping the first CR E-like site as core motif for LAP/C/EBP beta binding. Analysis of a mutated beta -site in reporter gene experiments showed the functional relevance of this site for autoregulation. The composite C/EBP beta -CRE-element in the promoter enables synergistic activation of transcription by LAP/C/EBP beta and the proteinkinase A (PKA)/cAMP responsive element binding protein (CRE B) pathway in a cell-type specific manner. In hepatoma cells nuclear factor kappa B (NF-kappaB) increased auto-regulation 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 a nd thus the interaction between LAP/C/EBP beta and members of the CREB or N F-kappaB family allows the control of LAP/C/EBP beta gene transcription as a response to different stimuli in a tissue specific manner. (C) 2001 Acade mic Press.