Molecular Mechanism for the Potentiation of the Transcriptional Activity of Human Liver Receptor Homolog 1 by Steroid Receptor Coactivator-1

Abstract

The liver receptor homolog 1 (LRH-1) belongs to the Fushi tarazu factor 1 nuclear receptor subfamily, and its biological functions are just being unveiled. The molecular mechanism for the transcriptional regulation by LRH-1 is not clear yet. In this report, we use mutagenesis and reporter gene assays to carry out a detailed analysis on the hinge region and the proximal ligand binding domain (LBD) of human (h) LRH-1 that possess important regulatory functions. Our results indicate that helix 1 of the LBD is essential for the activity of hLRH-1 and that the steroid receptor coactivator (SRC)-1 interacts directly with the LBD of hLRH-1 and significantly potentiates the transcriptional activity of hLRH-1. Cotransfection assays demonstrate that overexpressed SRC-1 potentiates hLRH-1 mediated activation of the cholesterol 7-alpha-hydroxylase promoter and increases the transcription of the endogenous cholesterol 7-alpha-hydroxylase in Huh7 cells. The interaction between SRC-1 and hLRH-1 assumes a unique pattern that involves primarily a region containing the glutamine-rich domain of SRC-1, and helix 1 and activation function-2 of hLRH-1 LBD. Mutagenesis and molecular modeling studies indicate that, similar to mouse LRH-1, the coactivator-binding cleft of hLRH-1 LBD is not optimized. An interaction between helix 1 of hLRH-1 LBD and a region containing the glutamine-rich domain of SRC-1 can provide an additional stabilizing force and enhances the recruitment of SRC-1. Similar interaction is observed between hLRH-1 and SRC-2/transcriptional intermediary factor 2 or SRC-3/acetyltransferase. Moreover, transcriptional intermediary factor 2 and acetyltransferase also potentiate the transcriptional activity of hLRH-1, suggesting a functional redundancy among SRC family members. These findings collectively demonstrate an important functional role of helix 1 in cofactor recruitment and reveal a novel molecular mechanism of transcriptional regulation and cofactor recruitment mediated by hLRH-1.

Nuclear receptor co-activators and HER-2/neu are upregulated in breast cancer patients during neo-adjuvant treatment with aromatase inhibitors

“…We observed no changes of LRH-1 mRNA during treatment, which would suggest that local aromatase upregulation by this transcriptional activator may not be a response to oestrogen deprivation. On the other hand, it is well known that the transcriptional activity of LRH-1 is stimulated through interaction with the SRCs (Xu et al, 2004). Thus, even though the LRH-1 mRNA expression is unaffected during oestrogen deprivation, this does not rule out that the transcriptional activity of LRH-1 is increased.…”

The orphan nuclear receptor LRH-1 promotes breast cancer motility and invasion

“…It is thought that LRH-1 activity is regulated primarily by the recruitment of co-activator (Xu et al 2004) or co-repressor (Sablin et al 2008) protein partners. Recently, we have described a series of short peptides, identified by phage display, that bind to the LRH-1 LBD and inhibit recruitment of co-activators .…”

“…Hence, its activity is modulated by the interaction with other co-activators and co-repressors (Goodwin et al 2000, Lee & Moore 2002, Xu et al 2004, Ortlund et al 2005. Additionally, the identification of phospholipids (Krylova et al 2005, Ortlund et al 2005, Wang et al 2005b) and sphingosine-1-phosphate (Hadizadeh et al 2008) as LRH-1 agonists suggests that the degree of receptor activation may be further regulated with endogenous ligands.…”

The nuclear hormone receptor family member NR5A2 controls aspects of multipotent progenitor cell formation and acinar differentiation during pancreatic organogenesis

“…The presence of a functional ligand-binding pocket suggests the potential to derive drugs that alter pathological, physiological or developmental processes affected by NR5A2 (Lazarus et al, 2012). NR5A2 activity is modulated by phosphorylation and sumoylation (Lee et al, 2006;Venteclef et al, 2010) and through interaction with co-activators (Xu et al, 2004;Sakai et al, 2006) and co-repressors (Goodwin et al, 2000;Suzuki et al, 2003). NR5A2 controls cell type-specific programs through direct transcriptional regulation of discrete subsets of target genes (Chen et al, 2008;Holmstrom et al, 2011;Chong et al, 2012).…”