A composite element binding the vitamin D receptor, retinoid X receptor alpha, and a member of the CTF/NF-1 family of transcription factors mediates the vitamin D responsiveness of the c-fos promoter.
The hormonal form of vitamin D, 1 alpha,25-dihydroxyvitamin D3 [1,25- (OH)2D3], transiently stimulates the transcription of the c-fos proto-oncogene in osteoblastic cells. We have identified and characterized a vitamin D response element (VDRE) in the promoter of c-fos. The 1,25-(OH)2D3-responsive region was delineated between residues -178 and -144 upstream of the c-fos transcription start site. A mutation that inhibited binding to the sequence concomitantly abolished 1,25-(OH)2D3-induced transcriptional responsiveness; similarly, cloning to the site upstream of a heterologous promoter conferred copy-number-dependent vitamin D responsiveness to a reporter gene, demonstrating that we have identified a functional response element. The structure of the c-fos VDRE was found to be unusual. Mutational analysis revealed that the c-fos VDRE does not conform to the direct repeat configuration in which hexameric core-binding sites are spaced by a few nucleotide residues. In contrast, the entire 36-bp sequence was essential for binding. We identified the vitamin D receptor and the retinoid X receptor alpha as components of the complex that bound the c-fos VDRE. However, our results also show that a putative CCAAT-binding transcription factor/nuclear factor 1 (CTF/NF-1) family member bound the response element in conjunction with the nuclear hormone receptors. The expression of this CTF/NF-1 family member appeared restricted to bone cells. These data hint at new molecular mechanisms of action for vitamin D.
Candeliere
G A
GA
Genetics Unit Shriners Hospital, Montréal, Québec, Canada.
Jurutka
P W
PW
Haussler
M R
MR
St-Arnaud
R
R
D001483:Base Sequence; D001665:Binding Sites; D001842:Bone and Bones / Q000166:cytology / Q000378:metabolism*; D022762:CCAAT-Enhancer-Binding Proteins; D002117:Calcitriol / Q000378:metabolism*; D002478:Cells, Cultured; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation; D008969:Molecular Sequence Data; D051839:NFI Transcription Factors; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics*; D018167:Receptors, Calcitriol / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D047488:Retinoid X Receptors; D015398:Signal Transduction; D014018:Tissue Distribution; D014157:Transcription Factors / Q000378:metabolism
D022762:CCAAT-Enhancer-Binding Proteins; C077305:CTF-1 transcription factor; D004268:DNA-Binding Proteins; D051839:NFI Transcription Factors; D016760:Proto-Oncogene Proteins c-fos; D018167:Receptors, Calcitriol; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; D002117:Calcitriol