Association of hepatic nuclear factor-4 in the apolipoprotein B promoter: a preliminary report

Abstract

Previous studies have examined the arrangement of regulatory elements along the apolipoprotein B (apoB) promoter region (-3067 to +940) and a promoter fragment extending from nucleotides -150 to +124 has been demonstrated to be essential for transcriptional activation of the apoB gene in hepatic and intestinal cells. It has also been shown that transcriptional activation of apoB requires a synergistic interaction between hepatic nuclear factor-4 (HNF-4) and CCAAT/ enhancer-binding protein α (C/EBPα) transcription factors. Here, we have examined the hypothesis that HNF-4 factor binding to DNA may induce a DNA helix bend, thus facilitating the communication with a C/EBPα factor located one helix turn from this HNF-4 factor in the apoB promoter. A gel electrophoretic mobility shift assay using wild type double-stranded oligonucleotides or modified wild type duplex oligonucleotides with 10 nucleotides inserted between HNF-4 and C/ EBPα factor motifs showed similar retarded complexes, indicating that HNF-4 and C/EBPα factors interact independently of the distance between binding sites. However, when only one base, a thymidine, was inserted at the -71 position of the apoB promoter, the complex shift was completely abolished. In conclusion, these results regarding the study of the mechanisms involving the interaction between HNF-4 and C/EBPα factors in the apoB promoter suggest that the perfect 5'-CCCTTTGGA-3' motif is needed in order to facilitate the interaction between the two factors.

Predicting tissue-specific enhancers in the human genome

“…Subsequent EI optimization then correctly predicted the noncoding ECR in intron 1 as a skeletal muscle enhancer in precise agreement with the previously defined TNNC1 skeletal muscle enhancer (Christensen et al 1993;Parmacek et al 1994). In a second example, EI correctly identified the APOB promoter element as a fetal liver (and adult liver) enhancer and predicted transcription factors HNF4 and C/EBP to be activating APOB expression, in concordance with previous experimental studies (Novak et al 1998).…”

Synergistic activation of the Atlantic salmon hepatocyte nuclear factor (HNF) 1 promoter by the orphan nuclear receptors HNF4 and chicken ovalbumin upstream promoter transcription factor I (COUP-TFI)

“…These results argue against the above mechanism of synergistic activation through co-operative binding applying in this case. A similar situation is observed in the synergistic activation of the apolipoprotein A1 promoter by HNF3 and HNF4 [24] and of the apolipoprotein B promoter by C\EBPα and HNF4 [26], which are not dependent on the spatial or stereospecific relationship of the two cognate sites involved. Recent models have suggested that binding of factors to adjacent recognition sequences may be intrinsically cooperative in certain cases [29,30].…”

“…The promoters of several liver-expressed genes are synergistically activated in co-transfection experiments by the nuclear hormone receptor HNF4 in conjunction with another transcription factor [14,[24][25][26]. In most cases this synergism requires the presence of recognition sequences for both HNF4 and the second protein [24][25][26][27]. In this sense the promoter of the mammalian HNF1 gene is atypical in that COUP-TFs increase HNF4-mediated activation without actually binding to the HNF1 promoter themselves [14].…”

Study of activity transcription factors C/EBPalpha in region - 53 to - 33 of promoter apolipoprotein B gene

“…We hypothesized that despite C/EBPα bound to element V produces a weak interaction with HNF-4, this heat-stable factor also may be forming a complex with HNF-4 and C/EBPα factors bound to element III and IV, as reported by Kardassis et al (1992) and Metzger et al (1993). HNF-4 factor binds to regulatory region -86 to -62, inducing a DNA helix bend, facilitating communication with C/EBPα proteins bound to element IV and located one helix turn from this HNF-4 (Novak et al 1998).…”

“…Both transcription factor have an overlapping binding site within the region -86 to -53 from the ApoB promoter, and act synergically to activate transcription (Kardassis et al, 1992). We have shown previously that mechanisms involving the interaction between HNF-4 and C/EBPα factors in Apo B promoter require a perfect 5´-CCTTTGGA-3' motif to facilitate the interaction between these two factors (Novak et al, 1998). As shown in figure 1, C/EBPα factor binds in two locations, element IV (-72 to -53) and element V (-53 to -33).…”