Characterization of a Novel Analogue of 1α,25(OH)2-Vitamin D3 with Two Side Chains: Interaction with Its Nuclear Receptor and Cellular Actions
journal contributionposted on 21.06.2000 by Anthony W. Norman, Percy S. Manchand, Milan R. Uskokovic, William H. Okamura, Janet A. Takeuchi, June E. Bishop, Jun-Iichi Hisatake, H. Phillip Koeffler, Sara Peleg
Any type of content formally published in an academic journal, usually following a peer-review process.
The hormone 1α,25(OH)2-vitamin D3 (125D) binds to its nuclear receptor (VDR) to stimulate gene transcription activity. Inversion of configuration at C-20 of the side chain to generate 20-epi-1α,25(OH)2D3 (20E-125D) increases transcription 200−5000-fold over 125D with its 20-normal (20N) side chain. This enhancement has been attributed to the VDR ligand-binding domain (LBD) having different contact sites for 20N and 20E side chains that generate different VDR conformations. We synthesized 1α,25-dihydroxy-21-(3-hydroxy-3-methylbutyl)vitamin D3 (Gemini) with two six-carbon side chains (both 20N and 20E orientations). Energy minimization calculations indicate the Gemini side chain possesses significantly more energy minima than either 125D or 20E-125D (2346, 207, and 127 minima, respectively). We compared activities of 125D, 20E-125D, and Gemini, respectively, in several assays: binding to wild-type (100%, 147%, and 38%) and C-terminal-truncated mutant VDR; transcriptional activity (of the transfected osteopontin promoter in ROS 17/2.8 cells: ED50 10, 0.005, and 1.0 nM); mediation of conformational changes in VDR assessed by protease clipping (major trypsin-resistant fragment of 34, 34, and 28 kDa). For inhibition of cellular clonal growth of human leukemia (HL-60) and breast cancer (MCF7) cell lines, the ED50(125D)/ED50(Gem) was respectively 380 and 316. We conclude that while Gemini readily binds to the VDR and generates unique conformational changes, none of them is able to permit a superior gene transcription activity despite the presence of a 20E side chain.