Repression of the Promoter Activity Mediated by Liver Receptor Homolog-1 through Interaction with Ku Proteins

Abstract

The mammalian nuclear receptor superfamily of evolutionarily related DNA-binding transcription factors consists of approximately 50 members, many of which mediate gene expression in a ligand-dependent manner. From their functional similarities, nuclear receptors are divided into A-F regions that include the N-terminal A/B region, the highly conserved DNA-binding domain (DBD; C region), the C-terminal ligand-binding domain (LBD; E/F region), and the D region, which serves as a hinge between the C and the E/F regions. The A/B and the E/F regions contain ligand-independent activation function (AF-1) and ligand-dependent activation function (AF-2), respectively. 1-3) Nuclear receptors regulate gene expression through interactions with coregulator complexes along with the general transcriptional machinery. 4,5) The coregulators associating with the C-terminal region that mediate AF-2 are well documented, whereas the proteins interacting with the N-terminal region that mediate AF-1 and the mechanism involved are not well defined. 6)Liver receptor homolog-1 (LRH-1; NR5A2), part of the nuclear receptor family, is a monomeric orphan receptor initially identified as mammalian homolog of Drosophila Fushi tarazu factor 1 (NR5A3).7-10) The closest mammalian homolog of LRH-1 is steroidogenic factor-1 (SF-1; NR5A1), which is essential for the development and differentiation of steroidgenic tissues and sexual differentiation.11,12) LRH-1 is highly expressed in the liver and intestine involved in enterohepatic circulation, and the ovary. 7,9,13,14) LRH-1 is also expressed in the pancreas, placenta, and pre-adipocyte. 7,15,16) To date, four isoforms of LRH-1, referred to as LRH-1 v1 (NM_205860), 10) LRH-1 (NM_003822), 9,10) fetoprotein transcription factor (FTF; U93553), 17) and LRH-1 v2 (35-323 aa, AF049102), 17) have been reported. The most abundant isoform in liver is LRH-1 (NM_003822) which lacks 46 amino acid residues corresponding to exon 2. 9) LRH-1 v2 is a truncated version of LRH-1 with a deletion in the D region that corresponds to exon5, and does not possess transactivation activity.7) FTF, the N-terminally truncated isoform, is identical to LRH-1 except for a deletion in the A/B region of LRH-1 v1.LRH-1 plays an important role in the homeostasis of bile acids and cholesterol, controlling the expression of a number of genes, including small heterodimer partner (SHP; NR0B2) 18,19) and enzymes for the conversion of cholesterol to bile acids (CYP7A1 and CYP8B1) 10,20) and for high density lipoprotein-remodeling.21) In addition, LRH-1 contributes to development and ovulation.14,22,23) Unlike most nuclear receptors, LRH-1 binds to the LRH-1 response element (LRHRE) (5Ј-YCAAGGYCR-3Ј, Y; pyrimidine, R; purine), three base-pairs longer than the consensus nuclear receptor half-site, as a monomer. 7)Nuclear receptors typically regulate transcription in a ligand-dependent fashion. The binding of a ligand causes the repositioning of helix 12 within the LBD resulting in interaction with the coactivators.1-3) However, the mechanisms...

Interactions of Thyroid Hormone Receptor with Ku Proteins and Interleukin Enhancer Binding Factor 3 Modulate the Promoter Activity of Thyroid-Stimulating Hormone Alpha

“…1,2,9) Taken together, the results from our previous and present studies show that Ku proteins bind to the DNA-binding domain (DBD) of FXR, LRH-1 and TRα, the D region of FXR and LRH-1, and the A/B region of TRα. In contrast, ILF3 associated with DBD of LRH-1 and TRα as well as the D region of LRH-1.…”

“…1,2) In addition, we found that Ku proteins associate with several nuclear receptors, including thyroid hormone receptor alpha (TRα).…”

“…After 18-to 24-h incubation, cells were subjected to a luciferase assay as described previously. 1,2,9) The results are representative of two independent sets of experiments.…”

Interleukin enhancer-binding factor 3 functions as a liver receptor homologue-1 co-activator in synergy with the nuclear receptor co-activators PRMT1 and PGC-1α

“…All plasmids expressing GST-fused proteins were as described previously [15]. The expression plasmid for c-Myc epitopetagged LRH-1 and the luciferase reporter plasmid containing the SHP promoter ( − 572 to + 10; GenBank ® accession number AF044315) were also described previously [15].…”

“…To identify LRH-1 cofactors, we previously performed a GST (glutathione transferase) pull-down assay using nuclear extracts from HeLa cells and GST fused to FTF, one of the LRH-1 isoforms. Two major protein bands specifically bound to LRH-1 were identified as Ku80 and Ku70 [15]. We also found other specific, but unidentified, bands; hence, we attempted to determine their identity using MS.…”