Identification and functional analysis of a novel human CYP2E1 far upstream enhancer

Clinical Pharmacology, Pharmacogenetics & Teratology, Department of Pediatrics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226-4801, USA.
Molecular Pharmacology (Impact Factor: 4.12). 07/2007; 71(6):1630-9. DOI: 10.1124/mol.106.031302
Source: PubMed

ABSTRACT Both transcriptional and post-transcriptional CYP2E1 regulatory mechanisms are known, resulting in 20-fold or greater variation in CYP2E1 expression. To evaluate functional regulatory elements controlling transcription, CYP2E1 promoter constructs were used to make adenovirus vectors containing CYP2E1 promoter-driven luciferase reporters for analyses in both primary human hepatocytes and HepG2 cells. A 1.2-kilobase pair portion of the CYP2E1 promoter was associated with 5- to 10-fold greater luciferase activity. This upstream region contained five direct repeats of 59 base pairs (bp) that increased thymidine kinase-driven luciferase reporter activity in HepG2 cells more than 5-fold, regardless of orientation. Electrophoretic mobility shift assays (EMSAs) identified sequence-specific nuclear protein binding to the 59-bp repeats that was dependent on a 17-bp sequence containing a canonical GATA binding site (WGATAR). Competitive and supershift EMSA identified the participation of GATA4, another GATA family member or GATA-like factor, and a third factor unrelated to the GATA family. Involvement of the tricho-rhino-phalangeal syndrome-1 factor, which also binds a GATA sequence, was eliminated. Rather, competitive EMSA using known binding sequences for the orphan nuclear receptors, steroidogenic factor-1 (or NR5A1), and fetoprotein transcription factor (or NR5A2) implicated an NR5A member in binding a sequence overlapping the canonical GATA. Chromatin immunoprecipitation assay demonstrated in vivo binding of NR5A2 to the enhancer sequence in human hepatocytes. The enhancer sequence is conserved within the human population but seems species-specific. The identification of this novel enhancer and its putative mechanism adds to the complexities of human CYP2E1 regulation.

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    • "Multiple 853-bp repeats, ;100 kb upstream, are required for high b1 expression (Stam et al., 2002a). The presence of repeated sequences in enhancers and other regulatory elements appears to influence transcription in other systems as well (Chandler et al., 2002; Greene et al., 2007; Shadley et al., 2007; Romney et al., 2008; Espley et al., 2009). Intriguingly, two of the newly identified b1 regions that seem to have regulatory activity contain repeated sequences as well (Figure 4), in a direct (;43 kb upstream) and an inverted orientation (;15 kb upstream). "
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