Ligand-activated PPARs form heterodimers with a retinoid X receptor (RXR) and bind to specific PPAR responsive elements (PPREs) to regulate target gene expression.
This lack of response may be attributed, at least in part, to the presence of nonfunctional hERα as determined by the inability of hERα to bind hormone, to recognize and bind to specific DNA-responsive elements and/or its inability to recruit other transcriptional activation factors [ 6, 11, 12].
After ligand binding, the ERs form homo- or hetero dimers that bind to specific palindromic estrogen response elements (ERE) sequences [ 5] in the promoter region of estrogen-responsive genes, resulting in recruitment of coactivators or corepressors to the promoter.
Oestrogens exert their action by binding to intracellular oestrogen receptor (ER) proteins that, on dimerisation, bind to specific DNA sequences (oestrogen-responsive elements (EREs)) in the regulatory regions of target gene promoters.
Wild type retinoic acid receptors (RARs) are known to bind to specific DNA sequences called RA responsive elements (RAREs) and are able to repress transcription by recruiting co-repressor complexes such as SMRT/NCoR/HDAC [20].
Members of the estrogen receptor family bind to specific conserved DNA recognition sequences in the DNA of their responsive genes.
Androgen effects are classically exerted through binding of the hormone to intracellular specific receptors [ 18, 19], which consequently dimerize, translocate to the nucleus and bind to specific elements of DNA, affecting thus the transcription of androgen-responsive genes [ 14].
This heterodimer binds to specific xenobiotic responsive elements found in the promoter of target genes and subsequently regulates their transcription [6].
Upon oxidative stress or infection, cytoplasmic Nrf2 is released from its inhibitor Keap-1, translocates into the nucleus, and forms a cofactor complex that binds to specific antioxidant responsive elements (ARE) found in promoters of phase II antioxidant and detoxifying enzymes.
These proteins bind to specific nucleotide motifs16, 17.
