Promoter-, cell-, and ligand-specific transactivation responses of the VDRB1 isoform.
The vitamin D receptor (VDR) mediates the effects of 1,25(OH)(2)D(3), the active form of vitamin D. The human VDRB1 isoform differs from the originally described VDR by an N-terminal extension of 50 amino acids. Here we investigate cell-, promoter-, and ligand-specific transactivation by the VDRB1 isoform. Transactivation by these isoforms of the cytochrome P450 CYP24 promoter was compared in kidney (HEK293 and COS1), tumor-derived colon (Caco-2, LS174T, and HCT15), and mammary (HS578T and MCF7) cell lines. VDRB1 transactivation in response to 1,25(OH)(2)D(3) was greater in COS1 and HCT15 cells (145%), lower in HEK293 and Caco-2 cells (70-85%) and similar in other cell lines tested. By contrast, on the cytochrome P450 CYP3A4 promoter, 1,25(OH)(2)D(3)-induced VDRB1 transactivation was significantly lower than VDRA in Caco-2 (68%), but comparable to VDRA in HEK293 and COS1 cells. Ligand-dependence of VDRB1 differential transactivation was investigated using the secondary bile acid lithocholic acid (LCA). On the CYP24 promoter LCA-induced transactivation was similar for both isoforms in COS1, whereas in Caco-2 and HEK293 cells VDRB1 was less active. On the CYP3A4 promoter, LCA activation of VDRB1 was comparable to VDRA in all the cell lines tested. Mutational analysis indicated that both the 1,25(OH)(2)D(3) and LCA-regulated activities of both VDR isoforms required a functional ligand-dependent activation function (AF-2) domain. In gel shift assays VDR:DNA complex formation was stronger in the presence of 1,25(OH)(2)D(3) than with LCA. These results indicate that regulation of VDRB1 transactivation activity is dependent on cellular context, promoter, and the nature of the ligand.
Esteban
Luis M
LM
Bone and Mineral Research Program, Garvan Institute of Medical Research and St. Vincents Hospital, University of New South Wales, Sydney, NSW 2010, Australia.
Fong
Colette
C
Amr
Deama
D
Cock
Terrie-Anne
TA
Allison
Susan J
SJ
Flanagan
Judith L
JL
Liddle
Chris
C
Eisman
John A
JA
Gardiner
Edith M
EM
D002460:Cell Line; D006801:Humans; D006887:Hydroxycholecalciferols / Q000494:pharmacology; D008024:Ligands; D008095:Lithocholic Acid / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology*
D006887:Hydroxycholecalciferols; D008024:Ligands; D020033:Protein Isoforms; D018167:Receptors, Calcitriol; D008095:Lithocholic Acid; C030049:1,25,26-trihydroxyvitamin D3