FP23-6 Allosteric Effects of a Nuclear Receptor A/B Domain on DNA Binding and Transactivation

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: FP23-Metabolic & Stress Receptors in Energy Homeostasis
Basic
Sunday, June 16, 2013: 10:45 AM-11:15 AM
Presentation Start Time: 11:10 AM
Room 256 (Moscone Center)

Poster Board SUN-338
Jonathan Deans*1, Jane Evans2, Nina V. Titova1, Joseph Dhabi3, Bin Fang1, Kristin Eckel-Mahan4, Nadege Braincon5, Mary C Weiss5 and Frances M. Sladek1
1University of California, Riverside, CA, 2University of California Riverside, CA, 3University of California Riverside, 4University of California Irvine, 5Pasteur Institute, Paris, France
Many human genes, including those encoding nuclear receptors, are driven by alternative promoters, which can yield distinct N-termini. Differences in temporal and spatial expression of alternative promoters is an active area of investigation but mechanistic consequences of the alternatively spliced proteins that are expressed from the promoters have not been well studied. The nuclear receptor HNF4A gene contains two highly conserved promoters (P1 and P2) that drive the expression of splice variants that differ by 16-30 amino acids in the very N-terminus in the AB domain. The promoters are under temporal and tissue-specific signals: the P1 promoter is the predominant one in the fetal and adult liver while the P2 promoter is expressed only in the fetal liver. While it has recently been established that P1-HNF4α acts as a tumor suppressor in the liver, the role of P2-HNF4α, which is up regulated in certain cases of liver cancer (hepatocellular carcinoma, HCC), is not known. Likewise, there are numerous reports of the hepatic target genes of P1-HNF4α, but very little is known about any targets unique to P2-HNF4α nor why its expression is excluded from the normal adult liver. To address these issues we employed two powerful systems – one in vivo and one in vitro. We used previously generated exon swap mice that express a single variant in the tissues where the P1 and P2 promoters are active. RNAseq from the livers of those adult mice, which express either P2-HNF4α (α7 HMZ) or P1-HNF4α (WT), revealed hundreds of dysregulated genes. To investigate the mechanism responsible for the dysregulation we used a high throughput DNA binding assay, termed Protein Binding Microarrays (PBMs), to explore differences in DNA binding specificity of the HNF4α variants. Cross referencing the PBM results with the RNAseq results and expression profiling arrays from mice in which all forms of HNF4α are knocked out allows us to identify unique, direct targets of P2- and P1-HNF4α. Since the DNA binding domains of P1- and P2-driven HNF4α are identical, these results provide one of the first examples of an allosteric effect of a nuclear receptor A/B domain on DNA binding and a subsequent functional effect in vivo.

Nothing to Disclose: JD, JE, NVT, JD, BF, KE, NB, MCW, FMS

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: NIH R01 Grants DK053892 and DK094707 awarded to FMS
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