Dual mechanisms for repression of the monomeric orphan receptor liver receptor homologous protein-1 by the orphan small heterodimer partner.
The orphan nuclear hormone receptor liver receptor homologous protein-1 (LRH-1; NR5A2, also known as FTF), an unusual receptor that binds DNA as a monomer, is an essential regulator of expression of a rate-limiting enzyme in bile acid formation, cholesterol 7-alpha-hydroxylase. In a classic negative feedback loop that is a crucial component of the complex regulation of cholesterol metabolism, cholesterol 7-alpha-hydroxylase expression is decreased when bile acid levels are high. This repression is thought to be based on the bile acid-dependent induction of expression of the orphan receptor small heterodimer partner (SHP) NR0B2, which inhibits the activity of LRH-1. We have explored the molecular basis for this important regulatory effect by characterizing the mechanisms by which mouse and human SHP inhibit LRH-1-mediated transactivation. Both SHP proteins specifically interact with the AF-2 transactivation domain of LRH-1 both in vivo and in vitro. This domain is a common target for coactivator interaction, and the SHP proteins can compete with p160 coactivators for binding to LRH-1. In addition to the N-terminal receptor interaction domain, SHP includes a C-terminal domain with autonomous repression function. Neither a deletion nor a point mutation specifically affecting this domain blocked the ability to interact with LRH-1 to compete for coactivator binding or to repress LRH-1 transactivation. However, the relative ability of these mutants to inhibit LRH-1-mediated transactivation was markedly decreased. We conclude that the proposed central role of SHP in cholesterol metabolism is based on a two-step mechanism that is dependent on both coactivator competition and direct transcriptional repression.
Lee
Yoon-Kwang
YK
Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
Moore
David D
DD
D000818:Animals; D001667:Binding, Competitive; D002460:Cell Line; D002790:Cholesterol 7-alpha-Hydroxylase / Q000378:metabolism; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D017353:Gene Deletion; D006801:Humans; D008099:Liver / Q000378:metabolism*; D051379:Mice; D010957:Plasmids / Q000378:metabolism; D017354:Point Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
C431936:Nr5a2 protein, mouse; D018160:Receptors, Cytoplasmic and Nuclear; C099713:nuclear receptor subfamily 0, group B, member 2; D002790:Cholesterol 7-alpha-Hydroxylase