Dual mechanisms for repression of the monomeric orphan receptor liver receptor homologous protein-1 by the orphan small heterodimer partner

J Biol Chem. 2002 Jan 25;277(4):2463-7. doi: 10.1074/jbc.M105161200. Epub 2001 Oct 19.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Binding, Competitive
  • Cell Line
  • Cholesterol 7-alpha-Hydroxylase / metabolism
  • Dimerization
  • Dose-Response Relationship, Drug
  • Gene Deletion
  • Humans
  • Liver / metabolism*
  • Mice
  • Plasmids / metabolism
  • Point Mutation
  • Protein Binding
  • Protein Structure, Tertiary
  • Receptors, Cytoplasmic and Nuclear / chemistry*
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Transcription, Genetic
  • Transcriptional Activation
  • Transfection

Substances

  • Nr5a2 protein, mouse
  • Receptors, Cytoplasmic and Nuclear
  • nuclear receptor subfamily 0, group B, member 2
  • Cholesterol 7-alpha-Hydroxylase