C/EBPalpha and HNF6 protein complex formation stimulates HNF6-dependent transcription by CBP coactivator recruitment in HepG2 cells.

Abstract

We previously demonstrated that formation of complexes between the DNA-binding domains of hepatocyte nuclear factor 6 (HNF6) and forkhead box a2 (Foxa2) proteins stimulated Foxa2 transcriptional activity. Here, we used HepG2 cell cotransfection assays to demonstrate that HNF6 transcriptional activity was stimulated by CCAAT/enhancer-binding protein alpha (C/EBPalpha), but not by the related C/EBPbeta or C/EBPdelta proteins. Formation of the C/EBPalpha-HNF6 protein complex required the HNF6 cut domain and the C/EBPalpha activation domain (AD) 1/AD2 sequences. This C/EBPalpha-HNF6 transcriptional synergy required both the N-terminal HNF6 polyhistidine and serine/threonine/proline box sequences, as well as the C/EBPalpha AD1/AD2 sequences, the latter of which are known to recruit the CREB binding protein (CBP) transcriptional coactivator. Consistent with these findings, adenovirus E1A-mediated inhibition of p300/CBP histone acetyltransferase activity abrogated C/EBPalpha-HNF6 transcriptional synergy in cotransfection assays. Co-immunoprecipitation assays with liver protein extracts demonstrate an association between the HNF6 and C/EBPalpha transcription factors and the CBP coactivator protein in vivo. Furthermore, chromatin immunoprecipitation assays with hepatoma cells demonstrated that increased levels of both C/EBPalpha and HNF6 proteins were required to stimulate association of these transcription factors and the CBP coactivator protein with the endogenous mouse Foxa2 promoter region. In conclusion, formation of the C/EBPalpha-HNF6 protein complex stimulates recruitment of the CBP coactivator protein for expression of Foxa2, a transcription factor critical for regulating expression of hepatic gluconeogenic genes during fasting.

• Authors: Yuichi Yoshida, Douglas E Hughes, Francisco M Rausa 3rd, Il-Man Kim, Yongjun Tan, Gretchen J Darlington, Robert H Costa
• Journal: Hepatology (Baltimore, Md.) (Hepatology) Vol. 43 Issue 2 Pg. 276-86 (Feb 2006) ISSN: 0270-9139 [Print] United States
• PMID: 16440369 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• CCAAT-Enhancer-Binding Protein-alpha
• FOXA2 protein, human
• Hepatocyte Nuclear Factor 6
• Multiprotein Complexes
• Hepatocyte Nuclear Factor 3-beta
• CREB-Binding Protein

Topics

• Amino Acid Sequence
• Animals
• CCAAT-Enhancer-Binding Protein-alpha (metabolism, physiology)
• CREB-Binding Protein (metabolism)
• Cell Line, Tumor
• Chromatin Immunoprecipitation
• Hepatocyte Nuclear Factor 3-beta (genetics)
• Hepatocyte Nuclear Factor 6 (metabolism, physiology)
• Humans
• Mice
• Multiprotein Complexes (physiology)
• Promoter Regions, Genetic
• Transcription, Genetic (physiology)
• Transfection