title: Effect of cellular environment on the selective activation of the vitamin D receptor by 1alpha,25-dihydroxyvitamin D3 and its analog 1alpha-fluoro-16-ene-20-epi-23-ene-26,27-bishomo-25-hydroxyvitamin D3 (Ro-26-9228).
abstract: The vitamin D analog, 1alpha-fluoro-16-ene-20-epi-23-ene-26,27-bishomo-25-hydroxyvitamin D(3) (Ro-26-9228) is tissue selective, with a gene regulation preference for bone over duodenum in vivo. In the human osteoblast-like cells, hFOB, the vitamin D receptor (VDR)-mediated transcriptional potencies of Ro-26-9228 and 1,25-dihydroxyvitamin D(3) (1,25D(3)) were similar, but in the intestinal cells, Caco-2, transcriptional potency of Ro-26-9228 was 10-50 times lower. We hypothesized that transcriptional activation of the VDR by Ro-26-9228 in the two cell types is regulated differently, and compared VDR extracted from hFOB or Caco-2 cells for their abilities to interact with a p160 coactivator [glucocorticoid receptor-interacting protein (GRIP)] and with retinoid X receptor (RXR) by pull-down assays. 1,25D(3) had similar potencies to induce interactions of VDR from the two cell types with these partners of transcription. In contrast, Ro-26-9228 induced interaction of osteoblastic VDR with RXR and GRIP but did not induce these interactions with VDR from Caco-2 cells. Further studies revealed that in hFOB cells the unoccupied VDR was cytoplasmic and proteasome sensitive, and that ligand treatment caused a rapid accumulation of the VDR in the chromatin. Both cytoplasmic and chromatin-associated ligand-bound VDR from hFOB cells had the abilities to interact with GRIP. In contrast, in Caco-2 cells, unoccupied VDR was localized in both the cytoplasm (70%) and the chromatin (30%). In Caco-2 cells, the cytoplasmic VDR was proteasome resistant, and neither 1,25D(3) nor Ro-26-9228 induced its binding to GRIP. Only a small fraction of the chromatin-associated VDR was proteasome sensitive, and this fraction was distinguishable by a faster electrophoretic mobility. 1,25D(3) induced an accumulation of the proteasome-sensitive VDR in the chromatin of Caco-2 cells and binding to GRIP. Ro-26-9228 failed to induce accumulation of the proteasome-sensitive VDR in the chromatin or binding to GRIP, but a coincubation of Caco-2 cells with the analog and a proteasome inhibitor restored these abilities. These results suggest that Ro-26-9228 has poor ability to promote the accumulation of a proteasome-sensitive, transcriptionally active VDR isoform in Caco-2 cells, whereas it does not have this limitation in hFOB cells.
authors.affiliation: Department of Endocrine Neoplasia and Hormonal Disorders, Unit 435, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
authors.forename: Ayesha
authors.initials: A
authors.lastname: Ismail
authors.forename: Cuong V
authors.initials: CV
authors.lastname: Nguyen
authors.forename: Ago
authors.initials: A
authors.lastname: Ahene
authors.forename: James C
authors.initials: JC
authors.lastname: Fleet
authors.forename: Milan R
authors.initials: MR
authors.lastname: Uskokovic
authors.forename: Sara
authors.initials: S
authors.lastname: Peleg
mesh_terms: D018938:Caco-2 Cells; D002117:Calcitriol / Q000031:analogs & derivatives / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D008024:Ligands; D010006:Osteoblasts / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000378:metabolism*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000378:metabolism*
chemical_list: D008024:Ligands; D018167:Receptors, Calcitriol; C453744:Ro 26-9228; D014807:Vitamin D; D002117:Calcitriol