Antagonistic action of a 25-carboxylic ester analogue of 1alpha, 25-dihydroxyvitamin D3 is mediated by a lack of ligand-induced vitamin D receptor interaction with coactivators.
A 25-carboxylic ester analogue of 1alpha,25-dihydroxyvitamin D(3) (1alpha,25-(OH)(2)D(3)), ZK159222, was described as a novel type of antagonist of 1alpha,25-(OH)(2)D(3) signaling. The ligand sensitivity of ZK159222, in facilitating complex formation between 1alpha,25-(OH)(2)D(3) receptor (VDR) and the retinoid X receptor (RXR) on a 1alpha,25-(OH)(2)D(3) response element (VDRE), was approximately 7-fold lower when compared with 1alpha,25-(OH)(2)D(3). However, ZK159222 was not able to promote a ligand-dependent interaction of the VDR with the coactivator proteins SRC-1, TIF2, and RAC3, neither in solution nor in a complex with RXR on DNA. Functional analysis in HeLa and COS-7 cells demonstrated a 10-100-fold lower ligand sensitivity for ZK159222 than for 1alpha, 25-(OH)(2)D(3) and, most interestingly, a potency that was drastically reduced compared with 1alpha,25-(OH)(2)D(3). A cotreatment of 1alpha,25-(OH)(2)D(3) with a 100-fold higher concentration of ZK159222 resulted in a prominent antagonistic effect both in functional in vivo and in in vitro assays. These data suggest that the antagonistic action of ZK159222 is due to a lack of ligand-induced interaction of the VDR with coactivators with a parallel ligand sensitivity, which is sufficient for competition with the natural hormone for VDR binding.
Herdick
M
M
Institut für Physiologische Chemie I and Biomedizinisches Forschungszentrum, Heinrich-Heine-Universität, D-40001 Düsseldorf, Germany.
Steinmeyer
A
A
Carlberg
C
C
D000818:Animals; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002460:Cell Line; D004952:Esters; D006801:Humans; D011487:Protein Conformation; D018167:Receptors, Calcitriol / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism
D004952:Esters; D018167:Receptors, Calcitriol; C410228:ZK159222; D002117:Calcitriol