Selective Recognition of Vitamin D Receptor Conformations Mediates Promoter Selectivity of Vitamin D Analogs

Abstract

The transcription factor VDR is the nuclear receptor for 1alpha, 25-dihydroxyvitamin D3 (VD) and the mediator of all genomic actions of the nuclear hormone and its synthetic analogs. The sharp biological profile of the model VD analog 1(S), 3(R)-dihydroxy-20(R)-(5'-ethyl-5'-hydroxy-hepta-1'(E), 3'(E)-dien-1'-yl)-9,10-secopregna-5(Z),7(E),10(19)-triene (EB1089) (i.e., its high antiproliferative effect combined with low calcemic actions) has been correlated with the selectivity of EB1089 to activate heterodimeric complexes of VDR with its partner retinoid X receptor (RXR) on VD response elements (VDREs). These VDREs are formed by an inverted palindromic arrangement of two hexameric core binding motifs spaced by nine nucleotides (IP9) rather than VDREs that are formed by direct repeats with three intervening nucleotides (DR3). In this report, ligand-dependent gel-shift assays were used for a comparison of the ability of VD and EB1089 to stabilize VDR-RXR heterodimers on these two VDRE types. The gel-shift assays revealed EB1089 to be more sensitive for complexes on IP9-type VDREs than on DR3-type VDREs. In addition, a gel-shift clipping method was established to identify and compare complexes of ligand-stabilized VDR-RXR heterodimers on different VDREs. On each VDRE, two complexes could be discriminated that seemed to contain different functional conformations of the VDR and allowed a more differential view on DNA-complexed VDR-RXR heterodimers. The VDR-RXR conformation (which was more ligand-sensitive) gained through EB1089 a higher affinity (7-fold) for DNA binding and a more sensitive (9-fold) activation of an IP9-type VDRE than of a DR3-type VDRE, whereas with the natural hormone VD, no VDRE-type preference could be observed. This indicates that promoter selectivity of VDR ligands is based on their property to selectively increase affinity for VDREs and very sensitively stabilize VDR conformations in VDR-RXR-VDRE complexes.

Structural Determinants of the Agonist-independent Association of Human Peroxisome Proliferator-activated Receptors with Coactivators

“…The impact of an additional conformation c2 of the PPAR␥ and CAR LBD has not yet been investigated in detail, but in the case of VDR the conformation c3 represents a silent, nonagonistic state of the LBD (49). With VDR both conformations were only stabilized in the presence of agonist as reported previously (48,50), whereas with PPAR␥ at least a clearly weaker amount as in the presence of specific ligand was found. However, in the case of CAR the addition of ligand showed no significant effect on the stabilization of c1.…”

Synergistic growth inhibition of prostate cancer cells by 1α,25 Dihydroxyvitamin D3 and its 19-nor-hexafluoride analogs in combination with either sodium butyrate or trichostatin A

“…*P50.05 cancer and PC-3 and DU-145 cells display many alterations that are associated with metastatic androgen-independent cancer, including aberrant p53 function and dysregulation of normal apoptotic responses (Carrol et al, 1993;Ewing et al, 1995;Isaacs et al, 1994;Tamimi et al, 1996;Mackey et al, 1998) and furthermore do not readily undergo apotosis when exposed to 1a,25(OH) 2 D 3 Zhuang and Burnstein, 1998). Interestingly, Carlberg and co-workers have demonstrated that either di erent VDR co-repressors complexes or structurally di erent vitamin D 3 analogs demonstrate VDRE selectivity (Quack and Carlberg, 1999;Nayeri and Carlberg, 1997;Danielsson et al, 1997;Polly et al, 2000). These ®ndings would allow for di erential regulation of genes by 1a,25(OH) 2 D 3 , within the same cell line, and disruption of a speci®c co-factor, such as a co-repressor with associated HDAC activity, would consequently silence a speci®c subset of 1a,25(OH) 2 D 3 -responsive genes.…”

Altered SMRT levels disrupt vitamin D3 receptor signalling in prostate cancer cells

“…It has been proposed that a specific subset of VDRE (IP9) are more commonly associated with genes that mediate growth arrest and apoptosis (Danielsson et al, 1997;Quack and Carlberg, 1999). Furthermore, IP-9-type response elements have been shown to associate with the corepressors NCoR1 or SMRT (Polly et al, 2000).…”