An enhancer element 6 kb upstream of the mouse HNF4alpha1 promoter is activated by glucocorticoids and liver-enriched transcription factors

Abstract

We have characterized a 700 bp enhancer element around -6 kb relative to the HNF4alpha1 transcription start. This element increases activity and confers glucocorticoid induction to a heterologous as well as the homologous promoters in differentiated hepatoma cells and is transactivated by HNF4alpha1, HNF4alpha7, HNF1alpha and HNF1beta in dedifferentiated hepatoma cells. A 240 bp sub-region conserves basal and hormone-induced enhancer activity. It contains HNF1, HNF4, HNF3 and C/EBP binding sites as shown by DNase I footprinting and electrophoretic mobility shift assays using nuclear extracts and/or recombinant HNF1alpha and HNF4alpha1. Mutation analyses showed that the HNF1 site is essential for HNF1alpha transactivation and is required for full basal enhancer activity, as is the C/EBP site. Glucocorticoid response element consensus sites which overlap the C/EBP, HNF4 and HNF3 sites are crucial for optimal hormonal induction. We present a model that accounts for weak expression of HNF4alpha1 in the embryonic liver and strong expression in the newborn/adult liver via the binding sites identified in the enhancer.

Prenatal programming of hepatocyte nuclear factor 4α in the rat: a key mechanism in the ‘foetal origins of hyperglycaemia’?

“…Whether this effect exists at physiological concentrations of glucocorticoids remains unknown. However, the interaction of glucocorticoids and Hnf4a is further supported by the recent identification in mouse Hnf4a of an enhancer element containing a glucocorticoid response sequence [41]. These data are consistent with a mechanism in which prenatal glucocorticoid exposure alters hepatic Hnf4a isoforms with the ratio of P1-promoter-driven transcripts (Hnf4a1/2) 'fixed' at a permanently high level, which would lead to permanent overactivity of the target genes such as Pck2, and contribute to hyperglycaemia.…”

Maternal diet and aging alter the epigenetic control of a promoter–enhancer interaction at the Hnf4a gene in rat pancreatic islets

“…This less open chromatin configuration at the enhancer could explain the lower levels of Hnf4a P2 transcripts in INS-1 cells compared with adult islets (60% less). In support of this hypothesis, we found that transfecting INS-1 cells with a construct containing the enhancer region (27) cloned upstream of the P2 promoter resulted in a 60% increase in luciferase activity compared with a vector containing only the P2 promoter, whereas the enhancer alone lacked any promoter activity (Fig. S3G).…”

Identification of the Flavonoid Luteolin as a Repressor of the Transcription Factor Hepatocyte Nuclear Factor 4α

“…It has been reported that HNF4␣ expression is self-regulated both directly and indirectly. HNF4␣ directly binds to the enhancer element of the HNF4␣ gene and stimulates its own expression (20). In addi- a Luciferase assays were performed using pMTP204-Luc as described under "Experimental Procedures".…”

“…tion, the transcription factors HNF1␣ and COUP-TFII are target genes of HNF4␣; HNF1␣ and COUP-TFII stimulate HNF4␣ gene expression (20,21). These observations led us to investigate whether the suppression of HNF4␣ activity by treatment with luteolin caused a decrease in the mRNA level of HNF4␣ itself in HepG2 cells.…”