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Characterization of the Functional Significance of PPAR/LXR Heterodimers via a Novel Response Element
Author(s) -
Klingler Andrea M,
Rider S. Dean,
Hostetler Heather
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.630.3
Subject(s) - liver x receptor , retinoid x receptor , nuclear receptor , transactivation , peroxisome proliferator activated receptor , sterol regulatory element binding protein , biology , response element , microbiology and biotechnology , biochemistry , chemistry , transcription factor , promoter , receptor , gene , gene expression
Peroxisome proliferator‐activated receptor alpha (PPARα) and liver X receptor alpha (LXRα) are nuclear receptors known to regulate opposing processes in energy homeostasis through heterodimerization with the retinoid X receptor alpha (RXRα). Dysregulation of these proteins has been linked to such metabolic disorders as atherosclerosis, hypercholesterolemia, and hypertriglyceridemia. Among the more intriguing recent discoveries in the field is that PPARα and LXRα are also able to interact directly with each other and bind DNA as a heterodimer. Although this interaction is widely thought to be inhibitory or otherwise non‐functional, we hypothesize that PPARα‐LXRα heterodimers are indeed capable of carrying out regulatory function via previously uncharacterized response elements. Gel shift analysis of several designed direct repeat sequences revealed that PPARα‐LXRα heterodimers bind preferentially to a DR4 motif, and supershift assays confirmed both PPARα and LXRα were bound to the oligonucleotide probes. Similarly, intrinsic fluorescence quenching assays determined that PPARα‐LXRα binds to these DR4 sequences with high affinity. The sequence bound with the highest affinity was found to occur naturally in the human genome, including near the promoter regions of known PPARα and/or LXRα target genes, such as apolipoprotein A‐1 (APOA1), cytosolic sulfotransferase 2A1 (SULT2A1), and the sterol regulatory element binding protein 1‐c (SREBP‐1c). Dual luciferase reporter assays showed that overexpressing PPARα and LXRα in COS‐7 cells leads to transactivation of the endogenous APOA1 and SULT2A1 genes, but not of SREBP‐1c. These findings illuminate the complex regulatory mechanisms modulated by PPARα and LXRα, and provide a potential new avenue for targeting these receptors for treatment of metabolic disorders. Support or Funding Information This work was supported by USPHS NIH grant DK77573 and the Emerging Science Seed Grant provided by the Boonshoft School of Medicine and Wright State University.