Differential use of transcription activation function 2 domain of the vitamin D receptor by 1,25-dihydroxyvitamin D3 and its A ring-modified analogs

Mol Endocrinol. 1998 Apr;12(4):525-35. doi: 10.1210/mend.12.4.0083.

Abstract

Analogs of 1,25-dihydroxyvitamin D3 (1,25D3) can be used to elucidate details of vitamin D receptor (VDR) activation. The A ring-modified analog, (TN-2) has 15-fold less affinity for VDR, but its transcriptional activity is diminished 1000-fold. Likewise, the ability of TN-2 to induce a protease-resistant conformation in VDR is 1/1000 that of 1,25D3. The stability of the VDR-TN-2 complexes is also significantly lower than VDR-1,25D3 complexes. Mapping the VDR-binding site of TN-2 showed that it had a significantly greater requirement for transcription activation function 2 (AF-2) residues than 1,25D3 did. These results suggest that the increased requirement for AF-2 residues that was induced by the A ring modifications is associated with diminished receptor activation. To determine whether restoring the potency of TN-2 by additional structural modifications would change the requirements for AF-2 residues, we synthesized hybrid analogs with 1beta-hydroxymethyl-3-epi groups and with dimethyl groups at positions 26 and 27 of the side chain, without or with a double bond between CD ring positions 16 and 17. We found that the side chain modification enhanced transcriptional activity 150-fold, increased the ability of the receptor to form a protease-resistant conformation 100-fold, and stabilized the VDR-analog complexes. The addition of the 16-ene group further reduced the analog's dissociation rate and increased its potency in the protease assays. These functional changes in the hybrid analogs were associated with a significant reduction in interaction with AF-2 residues. We conclude that there is an inverse relationship between analogs' potencies and their interaction with AF-2 residues of VDR.

Publication types

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

MeSH terms

  • Animals
  • COS Cells
  • Calcitriol / analogs & derivatives*
  • Calcitriol / genetics*
  • Calcitriol / metabolism
  • Calcitriol / pharmacology
  • Cell Line
  • Chlorocebus aethiops
  • Humans
  • Kidney / cytology
  • Macromolecular Substances
  • Protein Structure, Tertiary
  • Receptors, Calcitriol / genetics*
  • Receptors, Calcitriol / metabolism
  • Receptors, Calcitriol / physiology
  • Structure-Activity Relationship
  • Transcriptional Activation / physiology*

Substances

  • Macromolecular Substances
  • Receptors, Calcitriol
  • Calcitriol