A novel protein complex that interacts with the vitamin D₃ receptor in a ligand-dependent manner and enhances VDR transactivation in a cell-free system

Abstract

Steroid, retinoid, vitamin D 3 , and thyroid hormones signal through ligand-dependent transcription factors that collectively comprise a superfamily of intracellular, soluble receptors (hereafter collectively called nuclear receptors) that reside in the nucleus or translocate there in response to hormonal signals. As the largest known family of eukaryotic transcriptional regulators, nuclear receptors are implicated via the target genes they modulate in the control of cell growth and differentiation, homeostasis, development, and several physiological processes (for review, see Freedman 1997 and references therein). Moreover, because they are regulated tightly by small lipophilic molecules, they are extremely attractive as pharmacologic targets.Nuclear receptors all share a common organization in functional domains and extensive homologies in structure. A DNA-binding domain allows the receptors to bind as homodimers, or heterodimers with a common partner, retinoid X receptor (RXR), to specific DNA response elements typically composed of two hexameric half-sites organized as direct or inverted repeats. The carboxy-terminal half of the prototype nuclear receptor includes a ligand-binding domain (LBD) with a superimposed dimerization surface, and a ligand-dependent transcriptional activation function called AF-2, located at the extreme carboxyl terminus of the receptor (Danielian et al. 1992;Barettino et al. 1994;Durand et al. 1994). Crystallographic analyses have revealed that binding of a specific ligand, all-trans retinoic acid (ATRA), to retinoic acid receptor ␥ (RAR␥) induces a conformational change in its structure that modifies the orientation of the AF-2 core motif, contained within the last of 12 ␣-helices that

An architectural perspective of vitamin D responsiveness

“…The multisubunit DRIP (VDR-Interacting Protein) complex also binds to VDR in response to the ligand vitamin D [8,9]. This interaction occurs through the LBD of VDR in the same manner as the p160/SRC coactivators, resulting in transcriptional enhancement [10].…”

The MN1 oncoprotein synergizes with coactivators RAC3 and p300 in RAR-RXR-mediated transcription

“…Binding of cellular proteins to immobilized GST fusion proteins was carried out essentially according to Rachez et al (1998). Two cDNA fragments encompassing MN1 amino acids 48-256 and 365-520 were fused in frame with the pGEX3X vector (Pharmacia).…”

Nuclear receptors coordinate the activities of chromatin remodeling complexes and coactivators to facilitate initiation of transcription

“…While the order of events occurring during this process and the mechanism by which it occurs are less well de®ned, several studies have provided information which allow us to speculate as to what may be occurring. Indeed, roles for the SWI/ SNF and SMCC (Fondell et al, 1996;Rachez et al, 1998Rachez et al, , 1999 complexes have been shown during this stage of the initiation process in vitro. Based on these studies, we suggest that the fourth step could be an exchange of coactivators at the AF-2 surface of the NR-LBD.…”